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29th General Assembly Thessaloniki, Greece 18-28 August 1997

The 29th General Assembly was held at the University of Macedonia and the nearby Congress Center of HELEXPO, Thessaloniki, Greece, from 18-28 August 1997.

The Assembly was attended by 1050 scientific participants and 70 accompanying members from 62 countries, making this the largest IASPEI General Assembly ever held. There were 716 oral papers and 695 posters scheduled in 23 symposia and 23 workshops.

Opening Ceremony

18 August 1997

The Opening Ceremony took place at 1900 on 18 August 1997, with speakers being introduced by Assoc. Prof. Anastasia Kiratzi on behalf of the Local Organizing Committee.

Prof. Basil Papazachos, Chairman of the Local Organizing Committee, welcomed the participants to the city of Thessaloniki and gave a short description of the profile of the Geophysical Laboratory of the University of Thessaloniki that hosted the meeting.

Expressing the warmest thanks of IASPEI to the local, regional and national authorities for their strong support, Prof. Claude Froidevaux the President of IASPEI gave some insight about the scientific program of the meeting. For this the landscape of the Aegean region was described for 2 distinct periods of the geological past. Going back 20 to 50 million years ago, a continuous mountain chain joins the Hellenids and the Taurids from Europe to Asia - there is no Aegean sea! The onset of subduction beneath the southern margin allows this high topography to collapse. The process is still ongoing and seismology and space geodesy are used nowadays to quantify this extension of the crust and to image the subducting African lithosphere. Closer to historic time, some 20 thousand years ago, the Aegean basin did exist, but it had lost its top 125 meter layer of sea water - this was the time of the climax of the last glaciation and a great quantity of the Earth's sea water was trapped as ice in the polar regions. The gradual melting of these ice caps replenished the Mediterranean Sea with water, so that the shorelines which had moved seaward by several tens of kilometers in the Aegean retreated landward, leaving isolated islands where neolithic men had explored large emerged land masses. Some 3500 years ago historic men were terrified by a more sudden catastrophe - the eruption of Thira, today's Santorini. All these natural phenomena with these various time scales, earthquakes included of course, form the background of our scientific program explained IASPEI's President, while thanking the local organizing team for its great efficiency in setting up the meeting.

The Rector of the University of Macedonia, Prof. I. Tsekouras, and the Rector of the University of Thessaloniki, Prof. A. Mantis, gave warm greetings to the participants and wished them every success in their scientific meetings.

The president of the Organization of Earthquake Planning and Protection of Greece, Prof. D. Papanikolaou, gave a brief report on the profile of this organization and the tasks that it has undertaken towards earthquake loss prevention in Greece.

On behalf of the local authorities of the city of Thessaloniki, the Prefect of the city Mr. K. Papadopoulos, the Mayor Mr. K. Kosmopoulos, and the General Secretary of the region of Macedonia - Thrace Mr. Ch. Sofianos, gave short greetings to the participants, wishing them a pleasant stay in Thessaloniki. They all noted the importance of scientific research related to the seismotectonic's of an area such as Greece where the seismic hazard is high and there is social demand for some progress, especially in the field of short-term earthquake prediction.

The General Assembly was opened by the Secretary-General of the Ministry of Internal Affairs, Mr. D. Lavrentakis. He noted the wide interest in Greece in earth sciences and especially in seismology. He wished to all delegates an interesting and enjoyable meeting.

Opening Plenary Session

19 August 1997

Present: Prof. C. Froidevaux (President) in the Chair and about 300 delegates and guests.

The President opened the meeting at 0830 and welcomed participants.

The President introduced the Secretary-General.

Dr. E.R. Engdahl (Secretary-General) read aloud the following list of colleagues who had died since the last IASPEI General Assembly in 1995 and asked those present to take a few moments of silence in their memory.

  • Dr. Ramon R. Cabre (Bolivia)
  • Prof. Charles L. Drake (USA)
  • Dr. Vit Karnik (Czech Republic)
  • Prof. Mark Landisman (USA)
  • Prof. Drummond H. Matthews (UK)
  • Prof. Robert P. Meyer (USA)
  • Prof. Stephan Mueller (Switzerland)
  • Prof. John E. Nafe (Canada)
  • Mr. George W. Patraw (USA)
  • Dr. Jose Pinto Peixoto (Portugal)
  • Dr. Lautaro Ponce (Chile)
  • Prof. Albert G. Prozorov (Russia)
  • Dr. Cornelius Radu (Romania)
  • Prof. Nikolai V. Shebalin (Russia)
  • Dr. Eugene M. Shoemaker (USA)
  • Prof. Laurence L. Sloss (USA)
  • Prof. Dr. Albert Stein (Germany)
  • Prof. Ziro Suzuki (Japan)
  • Dr. Ludvik Waniek (Czech Republic)

The Secretary-General announced that most of the lectures, all poster sessions, and the Technical Exhibition will be held in the halls and amphitheaters of Macedonia University (indicated by the prefix MAC in the program), whereas there as some sessions scheduled at the nearby Building No 8, Congress Center of HELEXPO (indicated by prefix HAL).

The Secretary-General announced that the major items of business at this Assembly were:

  • To develop the IASPEI scientific program for the 22nd General Assembly of IUGG and the 30th General Assembly of IASPEI, to be held in Birmingham, England, 19-30 July 1999.
  • To select a venue for the 31st General Assembly of IASPEI in 2001, which will be held jointly with IAGA. The candidate host location is Hanoi (Vietnam).

Prof. B.L.N. Kennett (First Vice-President) announced the composition of the Resolutions Committee and the guidelines for submission of resolutions:

  • Prof. B.L.N. Kennett (Australia), Chairman
  • Prof. Xie Li-Li (China)
  • Prof. A. Kiratzi (Greece)

The deadline for submission of draft resolutions was set at 1800, Tuesday, August 26.

The President closed the meeting and introduced Dr C. Papazachos, who delivered the Association Lecture òDeep Structure and Active Tectonics in the Aegean and Surrounding Areaó.

Scientific Program

Association Lectures

19 Aug, Deep Structure and Active Tectonics in the Aegean and Surrounding Area (L1), Lecturer: C. Papazachos (Greece)

26 Aug, The Global Seismic Hazard Assessment: Program: 1992-1997 (L2), Lecturer: D. Giardini (Italy)


19-20 Aug, Earthquake Scenario, Seismic Risk and Loss Assessment (S1)

Conveners: Chen, Yong (China), A. Kappos (UK), A. Shapira (Israel), K. Pitilakis (Greece)

S1 received a total of 27 papers. Thirteen papers were presented in two oral sessions and the rest in one poster session. Both oral and poster sessions were well attended - 50 to 60 people attended the oral presentations. It reflected that earthquake scenario and loss estimation are still foremost concerns in seismology and engineering.

The invited lecture given by M. Erdik, and the New Methodology of Seismic Risk and Loss Estimation in Russia, Israel, and China, attracted much interest. The contents of papers covered by speakers and poster displays included both methodology aspects and applied aspects. The advances in estimation of losses caused by earthquake scenarios in different scales (global, regional, national, and local) were presented and discussed. The Activities of the Working Group on Seismic Hazard Assessment Techniques were reported. In particular, risk assessments in Eilat (Israel) and in Central America were discussed.

Chen, Yong

19-20 Aug, Are the Oceanic Plates Rigid? (S2)

Conveners: D. Sandwell (USA), L. Fleitout (France), K. Katsambalos (Greece)

The scope of the session was to assess the importance of oceanic intraplate deformation for the formation of features such as linear volcanic chains, folds, and rift/boudinage structures. Fifteen papers (10-oral, 5-poster) were submitted from a wide range of disciplines. Of course, there was not a consensus on the importance of oceanic intraplate deformation except in two instances. First, intraplate deformation of the Indo-Australian plate has been well documented over the past 17 years. Second, several speakers showed evidence for intraplate deformation within a few hundred kilometers of the major plate boundaries.

Okal, Neumann and Langenhorst provided evidence for tearing of the young lithosphere between the Udintsev and Eltanin Fracture Zones along the recently discovered 400-km long Hollister ridge. Their paper also discussed new evidence for a deficit in seismic moment along the Eltanin System as well as a test of the rigidity of the Pacific Plate based on the NUVEL-1 model; the NUVEL-1 model suggests that the Pacific plate is rigid at the mm/yr level.

Das provided evidence for large intraplate earthquakes nearby the Macquarie Transform boundary and the Aleutian Trench. She concluded that perhaps large oceanic intraplate earthquakes are a common feature but they occur on a 100-year or more time scale so they are not commonly observed during the 30-years of seismic recording. The conclusion are that the oceanic plates are not entirely rigid.

Chapola discussed the intraplate seismicity in the African plate along the East African Rift Zone and showed that the stress field is dominated by the normal faulting stress regime. However, the seismically determined stress field is oblique to the stress inferred from the orientations of the major rift zones. This was attributed to regional stress field from the ridge- push forces surrounding the African Plate.

Kotake and Kato showed new GPS results demonstrating large non-rigid plate behavior in the back-arc regions of the Western Pacific but no evidence for intraplate deformation in the old Pacific plate itself.

The final talk of the morning session [Rohr and Furlong] showed convincing evidence for a recent reorganization of the Juan de Fuca Plate at the Pacific, North American, and Juan de Fuca triple junction. High resolution bathymetry and multi-channel seismic imaging of the thick terrigenous sediments provided documentation for the formation of a new plate boundary.

In the afternoon session Fleitout and Voisin presented a new model for buckling and boudinage instabilities of the compressing and extending oceanic lithosphere, respectively. Their model relies on the concept that the uppermost part of the fractured brittle plate is weaker than unfractured homogenous plate. Upper lithosphere fracturing of pristine lithosphere will occur when the applied stress exceeds about 1/2 of the total integrated yield force. When yielding occurs, a bending moment is created and the wavelength of the instability is related to the overall thickness of the unstressed elastic layer. The two important conclusions are: 1) The instability occurs for a very small amount of overall strain so it will dominate previously published mechanisms. 2) Pre-stress will reduce the effective elastic thickness of the lithosphere when it is subjected to vertical loads such as seamounts; this could explain the anomalously low effective elastic thicknesses of the Superswell region.

Buchanan, Pearse and Scrutton provided additional evidence for intraplate deformation in the Indian Ocean. Seismic reflection data show evidence for high-angle reverse faulting in the upper crust and sedimentary layer. Relocation of earthquake hypocenters using broadband data shows focal depths between 16 and 37 km beneath the seafloor but within the strong part of the lithosphere.

Srivastra discussed epicentral distribution beneath the Bengal fan and northern Andeman Islands suggesting deformation of the Indian Plate north of 10N. Additional ocean bottom seismic stations as well as land GPS receivers should be deployed to monitor intraplate deformations in this active area.

Vogel provided a global overview of the relationship between mantle convection and seismicity.

Sandwell suggested that slab pull is the major cause of intraplate deformation, especially in young oceanic lithosphere which is weaker than old oceanic lithosphere. He speculated that slab pull from opposing trenches is responsible for rifting along the Cocos ridge and incipient rifting along the Sala y Gomez Chain. In addition he speculated that the gravity rolls in the young/weak portions south-central Pacific are caused by stretching of the entire Pacific by the surrounding distant subduction zones.

David Sandwell

19-20 Aug, Geodynamics of the Alpine-Mediterranean Collision Zone (S3, Co-Sponsored by ICL/ILP)

Conveners: W. Spakman (The Netherlands), B.A.C. Ambrosius (The Netherlands), E. Kissling (Switzerland), D. Mountrakis (Greece), G. Veis (Greece)

This session was devoted to the Geodynamics of the Alpine-Mediterranean collision zone. Fifty-two papers were presented, of which 21 were presented orally and 31 as posters. This session attracted the attention of a lot of people and the sessions were attended by at least 100 scientists.

One of the main subjects of the session was crustal and upper mantle structure based on surface wave observations, on data obtained from seismic arrays deployed in certain areas, as well as from inversion techniques.

Apart from the tomography results, papers presented dealt with the seismotectonic's of the Alpine-Mediterranean area, and especially the Aegean and the surrounding area. Fault plane solutions of large recent earthquakes, as well as focal mechanisms from past events, determined by waveform modeling were presented and discussed in conjunction with other geological and geophysical observations. The subduction areas of the Hellenic arc, the Calabrian arc and the Vrancea area in Romania, were also studied in view of new techniques concerning the modeling of the subduction process. Certain areas were studied in detail and there many papers presented, like Albanian seismotectonic's, the Hellenic arc, and the Ionian islands strike-slip zones.

This session proved to be a major contribution towards our understanding of the structure and the deformational process along the Alpine- Mediterranean zone.

Anastasia Kiratzi

20 Aug, Strong Ground Motion in Different Tectonic Regions (S4)

Conveners: Xie, Li-li (China), N. Ambraseys (UK), N. Theodulidis (Greece)

The Symposium 4 received totally 42 papers and 39 papers were presented in two oral presentation sessions and one poster session with 3 other papers delivered to other symposium and workshop. Both oral and poster session were well attended. As a rough estimate, the oral presentations were attended by 65-85 people. It reflected that the theme of Symposium 4 is still a hot point of concern by both the seismological and engineering communities.

The areas covered by speakers and poster displays included both theoretical and applied aspects of these subjects. Interesting advancements in estimation of strong ground motion were presented and discussed. Also a number of case histories relating to recent earthquakes were analyzed, both for inter- and intraplate regions. There were also summary progress reports on the operation of strong-motion networks. Practical applications of intensity-peak acceleration a function of the height of buildings were discussed.

Li-li Xie

20-21 Aug, Continental Crustal and Lithospheric Models From Seismic and Non-Seismic Data: Frontier Regions and Revisions to Accepted Models (S5)

Conveners: W. D. Mooney (USA), G. Musacchio (Italy), Wang, Chunyong (China)

Session S5 attracted many scientific participants from the international geophysical community. About 60 abstracts were accepted, yielding two days of talks and posters. Scientists from more than twenty countries submitted abstracts, and both the oral and poster sessions were heavily attended. Oral presentations generated enthusiastic discussion and debate, and crowds of attendees gathered around posters to argue fine points, and both applaud and contradict the results being presented.

In view of venue of the 1997 IASPEI General Assembly, it was highly appropriate that the first oral presentations focused on the Aegean Sea. These talks, by French and Turkish authors, presented new and exciting results concerning the extensional tectonics of the region based on recently acquired marine multichannel seismic data. The new observations were used to constrain a revised model for the evolution of the Aegean that featured a complex interaction between extensional and strike-slip faulting. Several other oral presentations dealt with extensional tectonics elsewhere, including in Northern Europe, China, and North America.

These presentations on extensional tectonics were complimented by several important talks on compressional tectonics. Highlights include (1) a 3D seismic model of the Alps, and new deep crustal images of (2) the Brooks Range, Alaska; (3) South Island, New Zealand; (4) Central Nonshu, Japan; and (5) the Andes of South America. A key aspect of several of these presentations was the evidence for thick crustal roots and delamination of the lowermost crust in these convergent orogens.

Continent-scale presentations that synthesized multiple studies were presented for Australia and Eurasia by Australian, Russian, Indian and American speakers. These talks emphasized the strong heterogeneities of the crust and uppermost mantle, and illustrated a positive correlation between crustal age and lithospheric thickness and crustal age and intrinsic Q of the crust and lithosphere. A new global crustal model at five by five degrees was presented as well.

Overall, new results from all continents, including Antarctica, were presented during this Session. The improved quality of data and methods of interpretation, as compared with several years ago, was quite apparent. Notable as well were exciting recent collaborations between Western and Eastern European institutions.

Some ideas that arose from session S5 include emerging evidence for lower crustal delamination, the clear evidence for correlations between crustal age, heat flow, seismic attenuation and lithospheric thickness, and improved models of lithospheric stretching based on high resolution seismic reflection profiling. The session demonstrated the scientific benefits of combining the results obtained from regional seismic surveys with global tomographic studies of upper mantle structure. Taken together, such integrated data hold great promise for solving the key issues in lithospheric dynamics.

W.D. Mooney

19-20 Aug, Stochastic Seismology: Waves in Complex Media (S6)

Conveners: Wu, Ru-Shan (USA/China), K. Holliger (Switzerland), H. Sato (Japan)

S6 had 3 oral and 1 poster sessions on Tuesday and Wednesday of the first week. There were 22 oral and 29 posters, totaling 51 presentations. There was one oral presentation canceled due to illness and 3 absences due to unspecified reasons.

In general ,the Symposium was very successful. Roughly speaking, there are three types of contributions: observational, theoretical studies and numerical simulations. Observational study has a broad scope of presentations, from coda wave study, shear wave attenuation, seismic emission, to the topographic influence on seismic data. Theoretical study covers the energy transfer approach, effective medium approach and other hybrid methods. Numerical methods for simulating waves in random media includes finite difference, finite element, and the newly developed GSP (generalized screen propagators) methods.

Some notable trends have emerged in the works presented in this symposium. One is the consideration of the depth-dependence of the stochastic properties in both the observational and numerical studies. Due to the complexity in formulation, theoretical study has not been catching up with this trend. This trend is an important factor for future development. The other trend is to combine the study of heterogeneity with that of the anisotropy, which will probably continue to the future.

Based on the presentations, we will contact the publisher Elsevier for the publication of a special issue of PEPI. 12 authors have committed to submit their manuscripts within 3 months. 4 or more are considering to submit but with uncertainty.

We believe that this symposium served well for information exchange, brainstorming of concepts and ideas, and will promote the study in this field by an internationally joint effort.

Ru-Shan Wu

21 Aug, Time and Non-Time Dependent Seismicity Models and Their Application in Seismic Hazard Assessment (S7)

Conveners: B. Papazachos (Greece), J. Bonnin (France), F. Mulargia (Italy), G. Purcaru (Germany), J. Rundle (USA), I. Papoulia (Greece)

Emphasis on time-dependent seismicity was given in this symposium. Several time-dependent seismicity models were presented and discussed. The models were: (1) the "regional time and magnitude predictable model", which has been tested by data from mainshocks in Greece, China, and in subduction zones of the Circum-Pacific belt; (2) the "coupled stress release model", which has been tested by synthetic data and by data from earthquakes in Northern China; and (3) the "model of arbitrary oriented ruptures interaction", which has been studied theoretically.

Variation of seismicity parameters before large earthquakes such as b-value, number of weak earthquakes, released seismic energy, foreshock activation and seismic quiescence have been investigated in seismically dangerous zones of Kamchatka and Greece for the purpose of using the results for intermediate-term prediction.

Some interesting results on the fractal analysis problem were also presented.

B.C. Papazachos

21 Aug, Mantle Rheology and Geodynamics: Inverse Problems and Geophysical Phenomenology (S8, Co-Sponsored by CMG and SEDI)

Conveners: W.R. Peltier (Canada) and K. Lambeck (Australia), B. Hager (USA), R. Sabadini (Italy), S. Singh (UK)

This Symposium, jointly sponsored by the IUGG Committee on Mathematical Geophysics (CMG) and SEDI, attracted a nice set of papers that were presented in a one day event co-chaired by Kurt Lambeck on behalf of SEDI and Dick Peltier on behalf of CMG. A wide range of issues were discussed, ranging from the interpretation of a variety of signatures of the glacial isostatic adjustment process ( in papers by Detlef Wolf, Roberto Sabadini, Volker Klemann, Kurt Lambeck and Dick Peltier ) to problems involving the influence of mantle rheology on the mantle convection process ( papers by O. Cadek, Uli Christiansen, Luce Fleitout, Giovanni Pari and Shao-Xian Zang). Of special interest, particularly given the location of the meeting, was the paper by Kurt Lanbeck on the importance of detailed predictions of Holocene relative sea level history in the Aegean to the interpretation of a variety of archaeological issues. Also of special interest was the excellent paper by David Sandwell on seafloor topography. There was considerable useful discussion following the paper by Uli Christiansen concerning the dynamical significance that should be attached to seafloor topography. Although it has become conventional in the geodynamics literature to interpret as " dynamic " only the component of seafloor topography that is residual to that due to lithospheric cooling, there are good reasons to insist that all of the topography evident on the seafloor is in fact dynamically controlled. This topic is one that deserves to be much more fully aired.

Dick Peltier

20-21 Aug, Heat Flow, Seismic Structure and Seismicity in Active Tectonic Regimes (S9, Co-Sponsored by IHFC)

Conveners: L. Rybach (Switzerland), S.B. Smithson (USA), M. Fytikas (Greece)

Symposium S9 highlighted the state of the art in elucidating the interdependence of seismicity distribution, material properties, and crustal/lithospheric geothermal features in many parts of the world characterized by active tectonism. Contributions from a wide range of settings in North and South America, Africa, Eurasia as well as New Zealand revealed some striking similarities.

According to seismic profiling and tomography, earthquake hypocenters are preferentially located in high velocity domains and, occasionally, in transition zones between high and low velocity crustal/lithospheric realms. Distinctly different seismicity is related to the various tectonic deformation styles like delamination, indentation, and escape. From the thermal point of view, seismicity is definitely absent beyond the 800 degrees C isotherm; the threshold temperature can vary significantly and depends also on factors like local strain, deformation style, pore fluid pressure, fault rock composition, although their exact role is far from being clarified. Strictly brittle/ductile rheology considerations are oversimplifying; in some tectonic settings the depth of the seismic/aseismic boundary in a given area can vary in time. So there is ample need for further research, e.g. to shed light on the role of progressive fault evolution with increasing displacement.

L. Rybach

21-22 Aug, Earthquakes, Paleoseismology and Active Tectonics (S10, Co-Sponsored by ICL/ILP)

Conveners: Zhang, Peizhen (China), S. Pavlides (Greece)

Symposium S10 had three distinguished and related subjects: (1) Recent global developments in active tectonics, especially in the field of paleoseismology, fault segmentation, earthquake recurrence models, and advanced methods of Quaternary dating; (2) Methodology for the integration of geological information into comprehensive models of seismic hazard; and (3) Practice of seismic hazard assessment with special emphasis on geological input. The goal of this symposium was to provide a forum for both geophysicists and geologists to exchange their views on these important subjects.

The symposium received 62 abstracts, among which 20 were presented by oral and 21 were presented by poster during the assembly. An estimated 45 to 65 people attended each session of the symposium.

Presentations and discussions were focused but not restricted to the following problems:

  • New studies of paleoseismology along major active faults, especially along the faults that have been previously viewed as inactive such as the cases in Belgium and Greece. These kind of studies significantly lengthened seismic history in the regions with low recent seismic activity.
  • How the paleoseismological results are used for assessing seismic hazard. For example, how to estimate maximum magnitudes for future earthquakes, how to assess earthquake recurrence intervals along the major active faults, and how to use paleoseismological information for determining fault segmentation.
  • How the paleoseismological data can be used for studies of fault behavior and earthquake recurrence models. Paleoseismological studies provide important information to extend our limited view on earthquake activity offered by historical and instrumental records, and to help us understand the behavior of seismogenic faults. New earthquake recurrence models either along an active fault or in a region have been established and presented in the symposium.
  • New technology has been used in the studies of active tectonics and paleoseismology. The symposium has presentations on how to use georadar, shallow seismic reflection, RS, and GPS technology to study active tectonics and paleoseismology.

In summary, modern trends in Earth science have been toward the direction of multi-discipline, integration, and comprehensive. Symposium S10 tended to integrate geology to study a common problem of earthquake behavior. It was suggested that this kind of multi-disciplinary forum should be provided by IASPEI in the coming years.

Zhang, Peizhen

In this symposium 62 papers were submitted and are included in the Abstract volume, while 37 papers were presented in 2 days sessions; 22 of them oral and 15 as posters. The audience ranged between 30 and 60 persons.

After IASPEI agreement with Elsevier, we are thinking to publish the proceedings of this Symposium in a Special Issue of Tectonophysics, with selected papers and Scientific Editors: S. Pavlides, D. Pantosti. P. Zhang.

Spyros Pavlides

21-22 Aug, Structure in the Lithosphere, Geodynamic Processes and Anisotropy (S11, Co-Sponsored by ICL/ILP)

Conveners: J-P. Montagner (France), L. Vinnik (Russia), M. Warner (UK), G. Drakatos (Greece), P. Papadimitriou (Greece)

The structure of the lithosphere is still the subject of a vigorous debate. The issues related to its thickness below continents and oceans, its large-scale deformation, its relationship with mountain building, its interaction e the underlying mantle convection are some examples of puzzling questions which were addressed during the symposium. It was also demonstrated by several talks that the observations of seismic anisotropy either from surface waves or body waves are providing very important and new information on the active processes involved in lithospheric geodynamics, and can be critically compared with geological and petrological data.

This symposium falls within the scope of ICL/ILP project "Dynamics of the subcontinental Mantle: from seismic anisotropy to mountain building", and benefited from contributions of different fields in Earth sciences (Seismology, tectonics, geodynamics, mineral physics...).

Different scales of heterogeneities were investigated (from global scale down to local scale) and progress was reported on the determination of seismic anisotropy in different depth ranges of the mantle, on the comparison of anisotropic results derived from surface waves and body waves, and its relationship with geodynamics.

The symposium was well attended with an average of about of 70 scientists and the discussions were quite lively. A special issue was proposed to be published in the journal of "Physics of the Earth and Planetary Interiors". A symposium devoted to the relationship between seismic anisotropy and geodynamics should be welcome during the next IASPEI and IUGG meetings.

Jean-Paul Montagner

22 Aug, Achievements and Future Perspectives After 30 Years of Global Travel Time Data on the Bulletins of the International Seismological Centre (S12)

Conveners: A. Morelli (Italy), A. Hughes (UK), B. Karacostas (Greece)

The symposium was well attended, particularly the second half. The facilities in the meeting room HAL102 were good, but perhaps the room was too small with delegates standing on occasions.

The retiring Director of the International Seismological Centre, A.A. Hughes, opened the symposium with an historical survey of changes at ISC, culminating with the announcement of the availability of the complete published ISC database on five CD-ROM's. The following two speakers, H.R. Srivastava and J.B. Young, highlighted the use of the ISC database in seismicity studies by the Indian Government and in the detection threshold of stations by the British Government with relevance to global monitoring.

M. Rezapour followed these speakers with his analysis of Ms as computed by ISC. This provoked discussion on magnitude determination in different frequency ranges. R.G. Pearce, UK, called for the noise levels to be reported as well as the amplitude and period measurements.

The following two papers by E.A. Bergman - presented by E.R. Engdahl and G. Pegler - presented by S. Das, showed how the refinement of the ISC data lead to better solutions of hypocenters on oceanic ridges and in the Hindu Kush, areas of contrasting depth of focus. D.A. Storchak presented an inside view of earthquakes mislocated by the ISC and their causes - partly inadequate data and partly misinterpretation of the observations and derived hypocenters. The first half of the symposium was concluded by a presentation by N.V. Kondorskaya comparing ISC data with that compiled in Moscow and highlighted by differences in magnitude determinations.

The first three papers in the second half of the symposium were invited. The first paper by A.M. Dziewonski gave an historical overview of the use of ISC data in seismic tomography in the form provided directly by ISC. The second presentation by J.H. Woodhouse used the ratio of the relative S to P heterogeneity to show that this ratio increases linearly with depth to about 2000 km into the mantle, with the ratio being derived from ISC data. There was much discussion as to whether the correlation continued below 2000 km. The last invited paper by E.R. Engdahl concentrated on Earth models, tomography, and tectonic studies using refined data from ISC. It showed how a choice of well-constrained events giving reliable depth determination can improve the definition of subducting slabs and high- velocity material at and below the core-mantle boundary. The following paper by B.L.N. Kennett gave indications on how color representation of seismicity could give alternative and a wider visual picture of earthquake occurrence. The next presentation from A.H.E. Rohm concentrated on the advantages of using the ISC refined data set of Engdahl et al. in discriminating between noise and tomographic images in the mantle. Finally, a paper by J. Plomerova was presented using ISC data to determine anisotropy in the lithosphere structure in parts of the world where the lithosphere is well sampled by ISC data.

The symposium was concluded by A.M. Dziewonski wishing the ISC Director well on his retirement at the end of 1997 after 33 years of service with the ISC.

Anthony Hughes

25-26 Aug, Earthquake Prediction (S13)

Conveners: K. Hamada (Japan), Chen, Yong (China), E. Papadimitriou (Greece)

Eighty-seven papers were submitted and accepted for S13. Thirty out of 87 were presented in the oral session and the rest in the poster session. Major contributions (60 papers) were presented by people from Russia, China, Armenia, Japan and Germany.

The oral session started with general introduction of the programs including the prediction research in Iceland, Armenia, Japan and China, including special efforts by the Japanese government after the disastrous "Kobe earthquake". There were a variety of research papers. Some papers dealt with patterns of seismic activities, such as foreshocks, swarms, seismic quiescence, seismicity synchronization. Some papers dealt with groundwater related phenomena, monitoring of crustal strain by GPS dense array, particular methodologies such as "the seismolap method", "RTL prognostic parameters", the method "SVO" and the "VAN" method. Some papers dealt with regional/local problems in terms of earthquake forecasting/evaluation of earthquake potential, such as in the south Kanto District, central Japan, northern part of the Indian plate boundary region and the Indian shield, and Greece. It was also proposed "a way to monitor crustal stress changes by using stress tensor inversion of microearthquake fault plane solutions", "log- periodic modulation of experimental AE data during rock fracture" was also presented among many others.

There was a steady state progress of the methodologies in predicting/ forecasting earthquakes, although we do not have any established methodology. Some methodologies seem to be useful in some cases but not in other cases because of the complex nature of precursory phenomena to earthquakes, depending upon the time, location and surrounding circumstances.

We can see a trend of research regarding the methodology in predicting/ forecasting earthquakes. That is, quantitative and objective evaluation of precursory anomalies by using seismic data. This trend is seen particularly in China and Russia.

K. Hamada

25 Aug, Structure and Evolution of the Earth: Geophysical Observations, Laboratory Constraints, and Modeling (S14, Joint with SEDI)

Conveners: T. Shankland (USA), A. Chopelas (Germany), S. Honda (Japan), H. Paulssen (The Netherlands), J.-P. Poirier (France), D. Kondopoulou (Greece).

In the spirit of SEDI the purpose of this session combined a variety of geophysical approaches to understanding Earth's physical properties and internal dynamics. Paper topics progressed from the core to the crust.

One core paper was aimed at using laboratory measurements of iron melting under shock-wave conditions as a means to estimate temperatures at the inner-outer core boundary (<5700 K). Others concerned core motions: a stagnant boundary layer at the top of the outer core and translational vibrations of the inner core.

There were a number of papers on D". Perhaps the largest efforts were directed at determining its elastic anisotropy. It appears that there is no way to explain arrivals of scattered waves such as SH and SV without anisotropy even though diffraction and velocity heterogeneities add their own complications.

Anisotropy was also a theme of studies concerned with the lower mantle where surface waves and the SKS body wave phase were separately used to map this feature of the transition zone, ~410 - 660 km depth range. Topographies of transitions at these depths and of that at 520 km (discovered to be a global feature) were mapped and found to vary by 10s of km. Other results interpreted these features in terms of transitions from olivine structure mineralogies. Tomographic models of bulk and shear velocities were used to indicate that the most probable causes of elastic heterogeneity ( of order +/- 1%) were caused by temperature variation in the upper mantle and chemical inhomogeneity below.

Laboratory results defined wave velocities in olivine at high temperature and pressure and constrained mantle melting temperatures to be less than 4300 K. Crustal rocks were also examined, including samples from deep boreholes. Theoretical studies of elasticity brought out the difficulty of spatial averaging to reduce high orders of anisotropy to lower ones. Other results defined equations of state and thermal expansion coefficient of several oxides believed to exist in lower mantle compositions.

Finally, a substantial number of papers dealt with crustal phenomena, in particular the tectonics of plate collisions with emphasis on structure and petrology of Balkan and eastern Mediterranean regions.

T.J. Shankland

25 Aug, Volcano Seismology (S15)

Conveners: H. Benz (USA), B. Chouet (USA), Y. Ida (Japan), M. Martini (Italy), Ph. Voidomatis (Greece)

The symposium consisted of two oral sessions with presentation of 15 papers and a poster session with 9 papers. The papers covering a wide range of seismological studies of volcanoes. Attendance at the sessions averaged about 30. Roughly half of the studies were concerned primarily with volcanic earthquakes and with the seismic velocity structure of volcanoes; the others used a wide variety of techniques to investigate different aspects of volcanic activity.

Earthquake source characteristics were related to volcanic activity in Kamchatka and volcanic pulsations were used to infer intermittent magma movement at depth beneath Iwate, Japan. Volcanic tremors were studied at Deception Island and analyses of tremor data for a number of volcanoes were interpreted in terms of the kinetic energy of magma flow. Borehole strainmeter data were used to determine details of an eruption of Izu- Oshima, and to propose that a moderate earthquake in Iceland was triggered my magma injection. Multiple techniques (seismicity, water level, self- potential) were used to investigate hydothermal dynamics in the Taupo area, New Zealand. Capability for short-term warnings of volcanic activity was demonstrated by using tremor amplitude (Iceland) and strain changes (Japan).

Unfortunately absent (this was a seismology meeting!) were studies based on geodetic measurements. Nevertheless the range and quality of the papers rendered this a valuable symposium.

Alan Linde

26-27 Aug, Earthquake Nucleation, Dynamic Rupture, and its Arrest: Observations and Physical Modeling (S16)

Conveners: M. Ohnaka (Japan), G.C. Beroza (USA), M. Campillo (France), S. Das (UK), W.L. Ellsworth (USA), G. Stavrakakis (Greece)

It is of crucial importance to understand the entire earthquake cycle including rupture nucleation, arrest, and fault-restrengthening in terms of the underlying physics. An understanding of the physical conditions under which earthquake rupture nucleates in seismogenic environments, and what factors determine the nucleation zone size and the time to instability for major earthquakes, is particularly important, because it provides a physical basis for the short-term (or immediate) earthquake prediction. However, this will require interdisciplinary research of the complex physical process, and there is a clear need for enhanced communication between researchers in the different sub-disciplines to build a more comprehensive and integrated picture of the basic processes at the shallow earthquake source. The aim of this symposium was to provide a forum for this, and hence contributions were invited from a wide variety of disciplines, including seismology, geodesy, geology and rock physics.

Response to the Symposium was very high and well received (55 abstracts accepted), and oral session for the Symposium was extended from one day and a half (initial plan) to full two days. 33 papers were allocated for oral presentation, of which 5 papers were canceled. 22 papers were allocated for poster presentation. The topics presented and discussed in the Symposium were widely ranged from the constitutive law for earthquake rupture, fault zone properties, to rupture nucleation, initial seismic motion, slip in dynamic rupture, and its arrest. The highlights are briefly given below.

The session on the constitutive law for shear rupture and fault- restrengthening, fault zone properties and inhomogeneities, and rupture nucleation: M. Matsu'ura proposed a slip- and time-dependent constitutive law for the fault failure and its restrengthening, which explains the slip- weakening property in the dynamic regime, the slip-rate-weakening property in the quasistatic regime, and the time-dependent property in the static regime. The proposed law reconciles the slip-weakening law and the rate- and state-dependent law, and it has a property that the critical slip displacement increases with the duration of stationary contact. Based on their 3D fluid-controlled earthquake model, S. Miller discussed the effect of fluid pressures within fault zones on the fault zone heterogeneity and statistics of earthquakes. Self-organization of regional earthquakes was discussed by V. Lyakhovsky, who simulated long histories of crustal deformation, using a deformation and time-dependent damage rheology model for the brittle seismogenic crust. M. Ohnaka showed how consistently scale-dependent physical quantities related to shear rupture, including the size and time scales of the nucleation, are scaled by one of the constitutive law parameters Dc (critical slip displacement), and that Dc is intrinsically size scale dependent. He then presented a model explaining observations that the larger nucleation zone size results in the larger size of the pending mainshock earthquake rupture. The model predicts that the mainshock seismic moment is proportional to the 3rd power of the nucleation zone size, and this well explains Ellsworth and Beroza's data. J. McGuire studied earthquakes on oceanic transform faults using broadband methods, and found that the majority of large (Mw > 6.5) transform-fault earthquakes are slow in the sense that they radiate an anomalously large amount of low-frequency energy. He speculates that these slow phase are associated with slip in serpentinized mantle peridotites below the seismogenic zone. A. Linde discussed a connection between the size of the slow slip and associated stress redistribution and the magnitude of the associated earthquakes, and he suggests that leveling changes and changes in water wells before the great earthquakes of 1944 Tonankai and 1946 Nankaido were due to slow deformation below the seismogenic zone. J. Park, using kinetic data for the dehydration of serpentine, developed a coupled heat-fluid-reaction model in which repeated cycles of dehydration- induced seismicity are plausible at mid-crustal depths, and discussed the influence of pore fluid pressure on the earthquake process in the 15-20 km depth range where many continental earthquakes nucleate. Nucleation, breakout and stable propagating slip pulses were discussed by M Heimpel based on his discretized numerical models into which constitutive laws are incorporated. A heterogeneous cellular automaton was used to propose that the characteristics of the development of the instability is mainly controlled by fault heterogeneity (S. Steacey). A new experimental approach was presented to monitor the nucleation process from the state of frictional contact, which can be detected from the transmission properties of ultrasonic waves (N. Yoshioka).

The session on observational and theoretical studies of the rupture initiation process: Papers presented by W. Ellsworth, M. Kikuchi, Y. Iio and N. Deichmann covered a wide range of observations of nucleation and initial growth of earthquakes. Both Iio and Deichmann reported on very careful observations of microearthquakes at short range and in very high Q material. Each author concluded that the slow initial rise of the P-wave is not a source effect. Deichmann also showed that his seismograms from a 2000 m deep borehole are well-matched by a model with a variable rupture velocity, such as the one proposed by T. Sato. In his talk, Kikuchi examined the slope of the seismic moment rate function over a wide magnitude range, and concluded that in many earthquakes the steepness of the initial slope is directly related to the eventual magnitude of the earthquake. In his remarks, Ellsworth emphasized the irregular nature of the initial portion of the moment rate function which distinguishes it from simple crack models for earthquakes. The source of the irregularity appears to reflect heterogeneity surrounding the nucleation point, be it due to aseismic deformation processes (pre-slip model) or a heterogeneous earth (cascade model). Theoretical investigations of rupture were presented by T. Mikumo, M. Campillo, K. Olsen, S. Sacks and S. Singh. These papers displayed a growing sophistication in the ability to incorporate the physics of friction in computer simulations of earthquakes. Dynamic calculations presented by Mikumo used kinematically determined rupture models to estimate the stresses acting during faulting and to examine the mechanics of slip pulses. Campillo explored the influence of the shape of the slip weakening law on spontaneous nucleation, and found that laws with steep initial slopes for the loss of fault strength with displacement. He emphasized that such systems were extremely sensitive to external perturbations, so that the time to failure could be accelerated by even very small external disturbances. Olsen also investigated the influence of assumed frictional laws for rupture nucleation and propagation. He reported that supershear rupture velocities appear in model that neglect slip rate weakening effects. Sacks studied a quantized fault model to study the development of heterogeneity in the earthquake process. In the final paper of the session, Singh explored the problem of apparent simplicity of waveforms for small earthquakes, as contrast to complex waveforms for larger earthquakes. Using a composite, heterogeneous source model, he showed that the difference may be explained by attenuation alone. He concluded that if Iio's estimates of Q are correct, then it is likely that Iio's microearthquakes are truly simple sources and not compound events.

The session on observational studies of the earthquake source process: In the first 2 presentations, S. Das and A. Sarao discussed the problems of seismograms to obtain details of the earthquake rupturing process, and presented insight into how to position stations around an active fault. Perez talked about the recent (July 9, 1997) Venezuela event of size Mw = 6.9 and he showed that a strong possibility of the gap on the El Pilar fault to be filled in the not too distant future. A. Cisternas presented a study of the Mw = 8.0 earthquake which occurred in Chile on 30 July 1995 and suggested that this may be a precursor to the 1877 gap. The final three paper examined some of the tectonic features of recent large earthquakes. S. Wdowinski discussed the influence of the tectonic setting on the initiation and propagation of the 1995 Gulf of Eliat earthquake. One implication of this study is the importance of dilatational basins for segmentation of the Dead Sea fault. Y. Gao presented a study of recent strong earthquakes in the Chinese mainland, and waveform modeling results on their source mechanisms. M. Gheitanchi summarized observational studies on recent strong earthquakes in Iran. He emphasized the pervasive complexity of rupture over multiple fault segments in each of these earthquakes.

Miti Ohnaka

25-27 Aug, Subduction Zones: Structure, Dynamics and Magmatism (S17)

Conveners: D. Zhao (USA), A. Hasegawa (Japan), M. Reyners (New Zealand), Zang, Shao-Xian (China), S. Dimitriadis (Greece)

The structure, dynamics and magmatism of subduction zones are still the subjects of extensive seismological and geophysical studies. Various seismological approaches have been applied to new data sets acquired from the permanent seismic networks and temporal array observations to address the issues such as accurate hypocentral locations in the crust and the subducting slab, 2-D and 3-D velocity and attenuation structures, anisotropy, large earthquake rupture processes, detailed structure of volcanoes and the subducting slab, and focal mechanisms and stress fields in various subduction zone regions.

Several studies addressed the issues concerning the existence of metastable olivine wedge in the subducting slabs and its implications for the generation of deep earthquakes. However, there is still no sufficient and convincing evidence to achieve a definite conclusion on this topic. A number of studies have used thermal and dynamic modeling approaches to address the issues such as the corner flow in the mantle wedge and its implications for the generation of arc magmatism and volcanism, factors controlling the degree of mechanical coupling between the subducting oceanic plate and the overlying continental plate in the forearc region and the generation of large earthquakes in the main thrust zone, and also the topic on the condition (slab/mantle temperature, subduction rate, etc.) of the generation of metastable olivine wedge in the subducting slabs. Interesting and important results have been obtained by the modeling work, but the assumed structure in the modeling seems still too simple, and the complex structural features revealed by the seismological studies have not been taken into account. Incorporating the seismological results in the thermal and dynamic modeling would be an important subject of future modeling studies. To better contribute to the assessment and mitigation of seismic and volcanic hazards is an important and challenging subject to seismologists and geophysicists in the subduction zone studies.

The symposium was well attended with an average of about 100 scientists and the discussions were quite lively. A special issue was proposed to be published in the journal of "Physics of the Earth and Planetary Interiors". A symposium devoted to the controversial and challenging issues as mentioned above should be welcome during the next IASPEI and IUGG meetings.

Dapeng Zhao

26 Aug, Seismic Waves in the Elastically Nonlinear Energy-Saturated Earth (S18)

Conveners: I. Beresnev (Canada/Russia), A.V. Nikolaev (Russia), K-L. Wen (Taiwan), P. Dimitriu (Greece)

Two of the conveners (I. Beresnev and A.V. Nikolaev) couldn't make it to IASPEI, the first because of family reasons, the second owing to a delay in issuing a new passport. A total of 19 papers were presented at the oral (8) and poster (11) sessions. Geographically, 4 continents were represented: Africa, Asia, Europe and North America. More specifically, there were papers from Armenia (1), Azerbaijan (1), Greece (1), Iran (1), Israel (2), Nigeria (1), Romania (1), Russia (8), and U.S.A. (1). There was also one paper that resulted from international (Greek-Russian-German) cooperation. This wide geographical representation is very encouraging, as it is known that only several years ago research in this field was carried out almost exclusively in Russia.

Papers presented can be divided into three groups: (1) those reporting results of analytical and numerical investigations, (2) those concerning field and laboratory experiments and (3) those interpreting (unprovoked) observations.

(1) 6 papers belong to this group. In the first, Liakhovsky and Hamiel (Israel) derive a nonlinear theoretical model that describes the differing properties of the solid under tension and compression and the variation of effective elastic moduli with type of loading. Model results are confronted with laboratory and field test results, with good agreement. Hamiel (Israel) presents a novel analysis of granular media to harmonic excitation, in agreement with field experiments on soil. He also observes "string-" and "finger"-like patterns on a thin layer of mud, resembling phenomena known in fluid mechanics (Faraday instability) and suggesting soliton-like structures. Olowofela (Nigeria) derives the equation governing thermo-magneto-elastically nonlinear Rayleigh waves in an initially stressed medium and discusses their generation and propagation. Dubrovsky (Russia) proposes new equations to describe the vortex component of the seismic-wave field, corresponding to the antisymmetric terms of the strain tensor. Hovhannisian (Armenia) discusses the response of a linear harmonic oscillator in relation to the evidence provided by the Spitak earthquake. Kuliev et al. (Azerbaijan) present a 3D non-classic linearized model that, as they claim, can be applied to study nonlinear phenomena.

(2) 7 papers belong to this category. Ten Cate et al. (U.S.A.) discuss nonlinearity and memory effects observed in resonance experiments on Berea sandstone. Marmureanu et al. (Romania) test several rock and soil types in Hardin-Drnevich resonant columns and find a strong dependence of the Q-factor on shear strain and frequency. Nikolaev (Russia) maintains, with basis on observational and experimental evidence, that seismic and acoustic emission is a manifestation of the nonlinearity of the geologic medium, and that the study of the space-time evolution of emission can provide additional information on the geodynamic processes and help to monitor earthquake-prone regions. Gushchin and Pavlenko (Russia) propose new methods to evaluate the parameter of nonlinearity of the geologic medium by bi-spectral analysis of seismic noise. The methods were applied to recordings from the Dobrushka (Czech Republic) station. Buloshnikov (Russia) measured the electric field during a series of 10-100 ton explosions. He observed two significant changes in the electric field, one sharp jump immediately after the explosion, observed mainly in the near field, and another appearing 1-2 min after the explosion and lasting several minutes. Measurements of seismo- acoustic emission were found to correlate well with the electric-field changes. Finally, Yushin et al. (Russia) and Yushin (Russia) present results of experiments with ultra-high-weight (UHW) vibrators. They discuss the dynamic changes of the elastic and dissipation parameters of the ground under excitation and the physical causes of the seismic effect of UHV vibrators.

(3) 7 papers fall into this category. Dimitriu et al. (Greece, Russia and Germany) and Nikolaev (Russia) consider earthquakes, microtremors, seismic/acoustic emission (for which they propose the unifying term "seismic flow") to be manifestations of nonlinear processes-phenomena taking place in the geologic medium. According to their view, the seismic flow, combined with the aseismic flow (creep), is the medium's reaction to various excitations (e.g., tidal forces, changes in atmospheric pressure, seismic waves from earthquakes and explosions, etc.). Statistically significant evidence is presented of triggering of earthquakes by other earthquakes, nuclear explosions and earth tides. Dimitriu et al. (Greece) display multi-fractal patterns in Greek seismicity and relate them to a percolation process and critical rupture propagation. They observe that seismicity's multi-fractality suggests that the driving processes are nonlinear. Gusev et al. (Russia) present the results of long-time observation, by means of a long-base laser interferometer, and analysis of the Earth strain in Northern Caucasus. Two frequency channels were used: low- frequency (0-0.1 Hz) and high-frequency (around 1.62 KHz). Some correlation is found between various parameters of the signals from the two channels and this is interpreted as indicative of the nonlinear and active character of the geophysical medium. Chernov (Russia) reports observation of phase instability in accelerogram signals recorded on the ground surface. It is proposed that in some cases phase differences can be attributed to changes in atmospheric pressure, whereas in other cases these differences may be due to the gravitational influence of the Moon and the Sun. Finally, two papers deal with the estimation of Q values. Cheitanci and Alahyarkhani (Iran) use data from the Iranian Long-Period Array to estimate Q values for south-west Tehran. The method applied permits explanation of the properties of Coda waves near the hypocenter and determination of heterogeneities in the crust/lithosphere. Pusculcu and Turkelli (Turkey) evaluate the Q(f) dependence in Eastern Turkey by studying the attenuation of the Lg phase. Q was found to increase with frequency between 1 and 7 Hz, in agreement with other tectonically active areas in the world.

Final remarks. The conveners of S18 propose that, in order to expand the audience and trigger a fruitful exchange of ideas, during the next IASPEI Assembly our Session should be combined with the Nonlinear Site Effects Group Session (e.g., Workshop W7 on Earthquake Site Effects).

Petros Dimitriu

27-28 Aug, Slab Structure and Dynamics of Deep Subduction (S19)

Conveners: R. van der Hilst (USA), M. Gurnis (USA), C. Lithgow- Bertelloni (USA), D. Rubie (Germany), M. Weber (Germany), N. Delibassis (Greece)

The session on 'Slab Structure and Dynamics of Deep Subduction' was very well attended and offered a large variety of seismological and geodynamical presentations covering mantle discontinuities near slabs and the structure of slabs in the upper mantle as well as their fate in the lower mantle.

C. Wicks and M. Weber (U. Gottingen), Y. LeStunff (Ecole Norm. Sup., Lyon), and B. Romanowicz (U.C. Berkeley) presented intriguing evidence for a steeply dipping reflector near a depth of 400 km in the mantle just west of the Mariana slab from observations of an anomalous phase arriving between P and pP. Modeling of the impedance contrast and slowness of this phase leads to its interpretation as a steep angle reflection off the top of a thin slab of oceanic lithosphere subducted during a previous episode of subduction at the Mariana trench.

Two talks were given regarding seismicity and slabs. E. Buforn, A. Udias, and P. Coca (U. Complutense, Madrid) produced focal mechanisms for 10 earthquakes between 60 and 150 km depth by waveform modeling of direct P waves. These events are located along a narrow band in the Alboran Sea to North-South orientation from the southern Spain to northern Morocco and are interpreted as a slab produced by lithospheric delamination under this wide region. J. Berrocal and C. Fernandes (U. de San Paulo) addressed controversies about the seismotectonic's of the Andean region. Both the time distribution and flat horizontal mechanism of deep South American earthquakes indicates the slab is being twisted relatively to the south, provoked by a northward component of presumable slab translation. Correlation of the well delineated deep segments to the north and south of this central region with the shallower activity supports a hypothesis of a twisted slab, continuous at depth, at least in the central Andean region.

Geodynamic modeling results of the geoid and of mantle flow were addressed by the following two talks. R. Hofstetter (Geophy. Inst. of Israel) presented a model explaining the geoid pattern over trenches. By including dynamic support, the model minimizes topographic differences between those observed and the lower than expected heights predicted by models having simple cold descending lithosphere. B. M. Steinberger (U. Frankfurt) made mantle flow calculations to model slabs in the lower mantle by using the locations and amounts of past subduction as calculated from recent tomographic images. Results indicate that horizontal motion of slabs between 670 and 2500 km depth is only about 500 km on average, which explains the good correlation between the calculated slab locations from the flow model and fast seismic anomalies seen in mid-mantle tomographic images.

J. M. Kendall (U. of Leeds) presented evidence of a slab graveyard in the lowermost mantle based on observations of the D" discontinuity and anisotropy beneath it which are correlated with high-velocity anomalies in recent tomographic images as well as predictions of the sites of past subduction. The region exhibits transverse anisotropy which suggests compositional layering and can be explained by the simple scenario that the anisotropy is due to a layering of cold subducted material entrained within D".

J. H. Woodhouse and H. J. van Heijst (Oxford U.) used Love and Rayleigh surface waves to produce phase velocity maps of upper mantle structure. They developed a branch stripping technique which enables them to measure dispersion properties of about 30,000 fundamental modes and up to 4000 for the 4th overtone. They produced high-resolution (up to l=20), three-dimensional phase velocity maps which show good agreement with maps predicted from existing mantle models. Combining the surface wave data with body-wave and mantle-wave data enhanced the resolution of several structures, in particular fast, slab related features around the transition zone.

H. Bijwaard, W. Spakman (Utrecht U.), and E. R. Engdahl (USGS) made an invited presentation of new, high-resolution images of global mantle velocity structure produced from P wave travel times. Their model parameterization, with variable sized cells, allows imaging of upper mantle structure on scales of 60-100 km enabling previously studied regions to now be investigated with unprecedented detail. Striking features include slabs either flattening out in the transition zone or descending to mid-mantle depths, a deep cratonic root under Australia, rift zones under Africa and Iceland, and much structure near the CMB all in good agreement with other global models and several regional upper-mantle models.

The next three talks dealt with mantle discontinuities near slabs. S. X. Zang and Y. Chen (Peking U., Beijing) examined topography on the 660 km discontinuity beneath China using P-to-S converted waves recorded at CDSN stations. The discontinuity appears to be at 660 km depth beneath southern China and becomes deeper than 670 km and more complex in structure toward the north at the western edge of the Japan slab. M. P. Flanagan and P. M. Shearer (U.C. San Diego) mapped small-scale topography on the 410-km discontinuity near several deep slabs by stacking precursors to the depth phases sS, pP, and sP. Results show that '410' depths about 200-300 km away from slabs are similar to the depth estimates made from global studies using SS precursors, indicating that any uplift of the 410 discontinuity must be in a narrow zone quite near the slab. Topography of the '410' within the Peru-Chile and Tonga subduction zones indicates an elevation of the discontinuity of up to 30 km in and near the cold slab, consistent with thermodynamic predictions of the olivine phase boundary. E. G. Roth, D. A. Wiens, and P. J. Shore (Washington U., St. Louis) imaged the 410-, 520-, and 670-km discontinuities in the Tonga subduction zones using ScS reverberations. Records from several deep events are stacked together and modeled at long periods using ray theory synthetics. Modeling of the depth and impedance contrast of each discontinuity indicates a 5 km uplift of the '410' with little topography, a variable '520' uplifted as much as 20 km, and a '670' which appears generally uplifted about 15 to 25 km.

U. Christensen (U. Goettingen) discussed numerical modeling of plate subduction to investigate the effects of chemical buoyancy on slab penetration into the lower mantle; subduction rate, trench roll-back, viscosity, phase boundary deflection, mineralogy, and plate age are all variables. For older plates the compositional effect is very small, but for younger plates it may cause the slab to stagnate in the transition zone when the trench velocity is slow. This presentation set the tone for the remaining two talks in the session which addressed olivine transformations in deep slabs. L. Kerschhofer and D. C. Rubie (U. Beyreuth), M. Liu (MIT), and T. G. Sharp (ASU, Tempe) quantitatively tested olivine metastability by performing multi-anvil experiments on single crystals and extrapolating these kinetic data to pressure-temperature conditions in slabs by including factors such as water fugacity, grain size, and stress. Their observations of intracrystalline nucleation and variable rates of transformation suggest a re- evaluation of current models, which are based upon nucleation only on grain boundaries and constant growth rates. M.R. Riedel (GFZ Potsdam) and S. Karato (U. Minnesota), in an invited talk, investigated rheological weakening of subducting slabs due to the olivine-spinel transformation. They find that slab strength will have unusual temperature dependence due to the temperature dependence of the grain size, and slabs may have a complicated rheological structure containing a weak region below the tip of a metastable olivine wedge. They postulate that deep earthquakes may result from faulting of a strong spinel layer at the bottom of the slab and not from transformational faulting of a cold metastable olivine wedge in the center.

Poster presentations were given by two groups. H. Igel (U. Cambridge) and J. Ita (Carnegie Inst. Washington) used finite-difference simulations to study wave propagation through slabs. C. Dupas, L. Kerschhofer and D. C. Rubie (U. Beyreuth), T. G. Sharp (ASU, Tempe), and W. B. Durham (U.C./LLNL) presented new experimental results regarding the mechanisms by which non-hydrostatic stress enhances olivine transformation kinetics; the results indicate that non-hydrostatic stress creates nucleation sites, thus enhancing transformation kinetics and promoting intracrystalline transformation mechanisms. Although listed in the abstract volume the following presentations were withdrawn: G. Helffrich and S. Kaneshima; L. Vinnik, G.L. Kosarev, and N.V. Petersen; and G. Helffrich and J. Collier.

Megan P. Flanagan

26-27 Aug, Seismological Data and Practice - Beyond Year 2000, (S20)

Conveners: E.S. Husebye (Norway), E. Bergman (USA), F. Dowla (USA), E. Hjortenberg (Denmark), M. Joswig (Germany), H. Kawakatsu (Japan), A. Tselentis (Greece)

Despite a total of 7 conveners most of the organizational work fell on the Principal Convener E S Husebye. The efforts here amounted essentially to writing letter of invitations calling for contributions to the Symposium plus asking co-conveners to contact potential contributors within their own territories like WUS, EUS, Central Europe etc. I take the blame for not contacting co-conveners H. Kawakatsu and A. Tselentis whose addresses initially were not known to me.

The IASPEI intention was that S20 should include 'microseisms' contributions and this task was left to co-convener E. Hjortenberg. He was very enthusiastic about this but failed to find any colleague who would a talk on this topic. My I suggest that IASPEI drop this subject as qualifying for an individual symposium or related extent for attention.

The combined IASPEI and Conveners efforts proved successful as more than 40 talks/posters were announced via abstracts sent the LOC in Thessaloniki. Most of these appeared to be of good quality and hence accepted. To avoid excessive S20 program changes at a later stage we carefully checked 'attendance probabilities' for hopefuls in E. Europe and development countries; without very positive confirmations such contributions were given poster status. The final S20 program listed 21 oral presentations (2 withdrawn + 1 replacement) and 13 posters. The S20 attendance was good; the lecture room was always full and occasionally crowded.

Although the scope of S20 included all aspects of seismic network operations many contributions (14) dealt with event location and focal depth estimation. These problems have come much in focus since the recent, UN approved (Sep. 1996) comprehensive nuclear test ban treaty (CTBT) requires that the epicenter error ellipse should not exceed 1000 sq. km. Even for local events location errors occasionally exceed 30 km so high accuracy in epicenter determinations remains a problem. Few of the presentations on this topic dealt with location algorithms per se but instead on retrieving more reliable seismic phase information partly through envelope transforms of the original, complex high-frequency recordings. Novel and interesting approaches dealt with learning computer to recognize repeated shooting at known explosion sites presuming envelope waveform stationarity. Efficient algorithms for handling this kind of problems are important for seismicity studies in low-seismicity countries where often local quarry and mining explosions account for more than 90% of local event recordings.

The classical CTBT problem of source identification (earthquake or nuclear explosion) are still a research topic albeit explosion recordings are mostly confined to past nuclear tests in the Semipalatinsk area. Frequently used discriminants are spectral ratio, semblance and complexity within an advanced statistical framework.

Detailed descriptions of global (IMS, Geoscope), regional (ORFEUS) and local (Iceland) were also presented. Some of the latter ones apparently had reached a high level of sophistication with automatic handling of occasionally more than 700 micro-earthquakes on a daily basis (SIL of Iceland). Regrettably, many local/national networks are still operated in a mostly manual manner and as a consequence contribute little even to local seismicity studies. However, the potential for improvement is large with commercially available digital instrumentation and most important robust and efficient analysis software partly tied to smooth, envelope transformed waveform recordings. These aspect of local network operations were demonstrated in several presentations - both in talks and in posters.

To summarize, the IASPEI S20 symposium must be rated a success with 34 contributions and strong attendance. Obviously, the many aspects of observational seismology appear to fascinate and intrigue many seismologist at present and most likely far beyond Year 2000. Also, in an attempt to preserve the 'spirit' of S20 we have (conveners Husebye and Dowla) invited contributors to join us in publishing Proceedings from the S20 Symposium in PEPI. To ensure expedient handling we would also ask for contributions from scientists not attending S20 - this would enable us to enforce more strict deadlines as we foresee an abundance of manuscripts.

Eystein S. Husebye

28 Aug, Hotspots and Plumes: Origin, Ascent, and Interaction With the Lithosphere (S21)

Conveners: H-C. Nataf (France), U. Achauer (France), U. Christensen (Germany), J. Phipps-Morgan (USA), J. VanDecar (USA), A. Vafidis (Greece)

This one-day Symposium took place on the last day of the IASPEI meeting. It had received 19 abstracts, and was well attended by an audience of more than 50 despite the late venue and an unfortunate overlap with the end of the "Deep slabs" Symposium. The leading idea was to set a forum where seismologists could ask geodynamicists all they wanted to know about plumes and vice-versa. And this worked very well. To my surprise, they were more contributions from seismologists than from geodynamicists. This is an interesting evolution: after the great progress brought by seismic tomography to the slab problem, it seems that both communities have now recognized the need for a better understanding of hotspots.

I started the Symposium with a partial review of the attempts of seismologists to detect mantle plumes beneath hotspots, a hunt that started in the seventies, soon after Morgan proposed his model. A slow material has now been imaged in the upper mantle beneath several hotspots using regional seismic tomography. Despite recent promising results based on diffraction tomography (Ji and Nataf), firm evidence for hotspot roots in the lower mantle is still missing. Steinberger and O'Connell presented their predictions of where plumes should be at depth if they are advected in the "mantle wind" driven by large-scale density heterogeneities.

Jordan (and Katzman) reported on the puzzling results of a detailed study of a mantle profile running from Tonga to Hawaii. An almost periodic pattern is found in the upper mantle, with slow velocities beneath Tonga and high velocities beneath Hawaii, and two other high velocity zones in between, which correlate with regions of high geoid and topography attributed to the Marquesas and Society hotspots. Jordan's explanation for these rather counter-intuitive findings is that we are seeing upper mantle thermal convection combined with basalt-depletion of hotspot residual mantle. Using a completely different technique (receiver functions), Vinnik, Chevrot and Montagner find that the 660-km discontinuity is strongly smeared beneath several Pacific hotspots. They suggest that this could be due to hot plume material being trapped at the phase transition. Stutzmann, Capdeville and Montagner explored how plumes scatter surface waves. They show that sizable effects are expected, and a poster extends this to normal modes, using a mode coupling formalism. A thorough search around the Hawaiian hotspot shows no indication of such scattering.

Another puzzling observation was presented by Kennett and Widiyantoro. A detailed analysis of a recent high-resolution tomographic model reveals a cylindrical zone of slow velocities in the lithosphere, spreading into a cushion beneath it. The location is just north of the Dekkan trap, where the Reunion hotspot was situated 65 million years ago. Is this fossil evidence of the plume head, which would have preserved some of its thermal signature? The more modern and shallow structure of La Reunion was investigated by Gallart et al, using a variety of exploration seismic's techniques. They found that there is some hotspot material at the base of the crust, but much less than studies of other hotspots and the observed flexure would have suggested. Burke emphasized how peculiar the African plate is with its large number of swells. Could hot material rising from the 660 km discontinuity explain some of these features ?

Jacoby (with Smilde and Liu) provided an analysis of the most recent topographic and gravimetric data over Iceland. He showed that these data are compatible with the presence of a low-density plume beneath it, which would correlate nicely with the results of seismic tomography (Tryggvason et al., 1983; Wolfe et al., 1997). He emphasised the non-uniqueness of the gravimetric inversion and the need for better constraints on a crustal structure. Gusev (Alexandrov et al.) proposed a review of several geophysical investigations of the Volga-Kama region that shows manifestations of upper mantle convection.

Richardson and Okal gave the first account of a seismic campaign aimed at determining the structure of the Ontong-Java large igneous province. Using surface-wave dispersion, they confirm a crustal thickness of 34 km, and find a pronounced low-velocity zone at a depth of about 80 km. Ulgade (Canas et al.) inverted the codas of local earthquakes recorded by a seismic network on the Canaries islands. They find low scattering and high intrinsic attenuation, which seems to be compatible with plume activity. Abeslon (and Agnon) noticed that the morphology of ridge segments is different near a hotspot. They propose to use these differences to investigate the zone of influence of plumes in various locations, and back in time.

Finally, Laske (and Phipps-Morgan and Orcutt) presented a recently launched seismic campaign on the Hawaiian swell. The idea is to study the crust and upper mantle, using a hexagonal set-up of 7 ocean-bottom long- period seismographs (some 200 km apart) that will be moved around the swell over a 5 years-period. Laske emphasized the need for such an investigation, showing that currently available tomographic models don't agree even on the sign of seismic anomalies beneath Hawaii.

This lively Symposium was quite successful in achieving its goal, and it is clear that there is a need for further exchanges of this kind in future meetings. Everything ran smoothly, thanks to the efficiency of the IASPEI organizing committees and of our Greek colleagues.

Henri-Claude Nataf

28 Aug, Geophysical Features of the Urals and Other Mountain Belts (S22, Co-Sponsored by ICL/ILP)

Conveners: C. Juhlin (Sweden), S. Kashubin (Russia), A. Perez-Estuan (Spain), F. Wenzel (Germany), D. Papanikolaou (Greece)

The Uralian orogen of central Russia marks the Late Paleozoic collision of the East European craton with the Siberian craton and intervening terranes of oceanic, island-arc, and microcontinental origin. Unlike the other major orogens of Paleozoic age (Appalachians, Variscides, and Caledonides) the Uralides remain an intact example of a Paleozoic collisional orogen, and for this reason, constitute a unique case in which to study processes of continental evolution. The Urals are characterized by a pronounced crustal root, high P-wave velocities below the root, a broad magnetic and gravity low, and reportedly low heat flow. They are also remarkable for their preservation of ophiolites, high pressure metamorphic rocks and their great mineral wealth. During Soviet times, extensive geophysical data were collected on the Urals and new initiatives through EUROPROBE, sponsored by ICL/ILP, have resulted in major campaigns for acquisition of new high resolution seismic reflection data. Of the two remaining superdeep boreholes still being drilled in Russia, one is in the Urals, SG-4, targeted for 15000 m and presently at 5355 m depth.

A total of 7 oral and 8 poster presentations were made. Oral presentations on the Urals included papers on integration of reflection seismic and geological studies in the southern Urals to unravel the continental evolution of the orogen, magnetic and gravity modeling across the mountain belt, alternative explanations to the observed geophysical signature than that provided by the plate tectonic paradigm, and studies on heat flow. The heat flow studies show that the previous interpretation of the Urals as having extremely low heat flow needs to re-evaluated when the climatic influence is taken into account. Oral presentations on tomographic imaging of the Qinling Dabie Orogenic Belt in China and on orogenic growth in relation to seismic reflectivity were also presented. The posters presented included results from the wide-angle reflection and refraction experiments along the URSEIS profile in the southern Urals, results from the ESRU seismic reflection profiles in the middle Urals, vertical seismic profiling results in the deep SG-4 borehole, a comparison of Moho depths in the Urals from normal incidence and wide-angle reflection data, and analyses of changes in heat flow with depth in the SG-4 borehole. These analyses show the heat flow to increase with depth indicating that reliable data may only be obtained from very deep boreholes.

Chris Juhlin

28 Aug, New Approaches to the Estimation of Earthquake Size (S23)

Conveners: J. Nabelek (USA), N. Kondorskaya (Russia), A. Kiratzi (Greece)

The Symposium S23 received 49 papers in total. Sixteen papers were presented in two oral presentation sessions and 33 in one poster presentation.

Emphasis in this session was given on the Empirical Green's functions deconvolution. Various methods have been presented and compared.

Another important part of the session dealt with moment tensor inversions at regional and at teleseismic distances. Papers were presented for inversions concerning waveform modeling of earthquakes and of explosions as well.

The third part of this session was devoted to the calculation of magnitudes and especially to the moment magnitudes and to the energy magnitudes.

Anastasia Kiratzi

Brief report on the poster session in S23 devoted to empirical Green's function deconvolution:

In the context of estimating earthquake size, empirical Green's function deconvolution has become an increasingly popular procedure for retrieving the source-time function of earthquakes. The method uses the smaller of two co-located events as an empirical Green's function with which to deconvolve the source- time function from the larger event. Although in theory the method is straightforward, in practice it runs into several problems. The source of the smaller event is never a perfect delta-function and in general the rays do not leave the source in a direction perpendicular to the fault. Therefore, at best, the deconvolution gives a relative apparent source-time function of the larger event. Moreover, differences in focal mechanism and hypocentral location, as well as windowing effects, numerical instabilities and additive noise significantly degrade the signal-to- noise ratio of the results. To overcome some of these difficulties, a variety of techniques, both in the time and frequency domain, have been proposed to perform the actual deconvolution.

In an effort to assess the performance of different techniques, a group of people agreed before the conference to apply their method to a common data set and perform a blind test on a sequence of synthetic seismograms (Abstract 1836). The synthetic P-wave seismograms were generated by convolving a set of realistic source-time functions with a Q-operator, a site operator, and an instrument response and by adding actually recorded ground noise (Abstract 1837). The results of this experiment were shown in individual contributions to the poster session of S23 (Abstracts 1302, 1586, 1763, 1838, 2009, 2360, 2755) and, in a subsequent informal meeting of the participating authors, they were compared to the original source-time functions used to generate the synthetics. Although all the techniques managed to reproduce some of the features of the original source- time functions, the individual results differed significantly from each other and none of them succeeded in matching the input perfectly. The participants agreed that the meeting had been very instructive, but that additional tests on a new version of the synthetics will be needed to clarify the reasons for the strengths and limitations of each method.

N. Deichmann


19 Aug, Earthquake Early Warning Systems (W1)

Conveners: W. Lee (USA), J.M. Espinosa-Aranda (Mexico), E. Scordilis (Greece)

In accordance with the programmed W1 schedule, Oral presentations started at 10:30 with 'The Seismic Alert System of Mexico City' presented by J. M. Espinosa-Aranda, showing recent results and the general description of this development, which started operating since August 1993, also commenting the Mexico City societal response observed during the issuing of recent alert signals triggered by the Sas because of the new Guerrero earthquakes, after the September 14, 1995, 'Copala' event.

Y. Nakamura, presented the 'Seismic Measures against seismic Hazard' (SHaSH), as a new approach to mitigate the seismic effects, he proposed to estimate the present anti-seismic durability of existing structures and to prepare back-up measures to avoid an unexpected hazardous situation.

G. Papadimitriou, presented the 'Optimization of the Seismic Early Warning System for the Tohoku Shinkansen', indicating ways in which this SEWS, which started operating in 1978, can be more efficient, reducing the rate of earthquake-induced derailments and/or the rate of false alarms which generates unnecessary delays or train cancellations.

'Toward a 30 seconds Rapid Response Earthquake Information System in Taiwan' lecture, was presented by Y. M. Wu, explain how they are disseminating earthquake information by electronic media and how they will reach lower time analysis in his 48 accelerograph telemetric network using faster PCs and processing algorithms. Additionally, with the propose to push the Taiwan system into the realm of early warning Y. B. Tsai, show how to obtain better magnitude estimations presenting the lecture 'Quick Determination of Magnitude and Intensity for Seismic Early Warning'.

More, efforts to better and quick magnitude determinations for early warning systems has been developed by Greksch 1997, using historical accelerograms from North and Central America registered between 1940 and 1986. He presents the 'Earthquake Early Warning System: Real-Time Magnitude Determination From Analysis of Strong-Motion-Accelerogram'.

Unfortunately, G. Patraw passed away but Zimakov, present by him a synthesis of the 'Processing Times for an Experimental Rapid Response Dial Network'. With this lecture the W1 Oral presentation finished, because the 'Project of Early Warning System for Armenia' by G. Arzoumanian, and the 'Remote Warning System of Nuclear Power Plants (NPP) for Seismic Impacts' by O. Arakelian were not presented.

The W1 Poster presentation was attended between 12:00 to 14:00 just by J. M. Espinosa-Aranda, Y. Nakamura, Y. B. Tsai, M. Wu. Additionally R. Hofstetter presents information over his 'Household Earthquake Warning Device', explaining his technical specifications.

W. Lee

19-20 Aug, Elaboration of Historical Earthquake Data With Emphasis on the Aegean and Surrounding Area (W2)

Conveners: G. Karakaisis (Greece), M. Stucchi (Italy), V. Kouskouna (Greece)

During the W2 session, several cases of elaboration of seismic data concerning historical earthquakes were discussed. The papers presented dealt with the use of macroseismic and other information for estimating the focal parameters of historical earthquakes which occurred in the broader Aegean area as well as in some other parts of the world. The papers concerned earthquakes which occurred in Greece and surrounding areas in the 4th and 12th Centuries, in 1717, 1845, 1851, 1867, and in 1926. There were also papers on historical seismicity in Crimea, Iberian Peninsula, Algeria, Arabian Plate, and Costa Rica.

Discussion was focused on the need for careful elaboration of all available data in order to estimate focal parameters of historical events as accurately as possible. For example, an earthquake which occurred in northwestern Greece was dated around 1720, but evidence was presented that it might have occurred about 20 years earlier. For another earthquake which occurred in 1926 at southeastern Greece (close to Rhodos Island), it was reported that on the basis of instrumental data obtained at relatively distant seismic stations its magnitude should be equal to 7.4. It was revealed that there exists a long period seismogram obtained at relatively close epicentral distance. On the basis of this seismogram, the earthquake magnitude estimated to be equal to 8.0. Geochemical, satellite, and historical data were used to study the fault of the 1867 Lesbos earthquake. An unusual wave of church repairs restricted to the SE coast of Rhodos and other nearby islands is probably related to an earthquake with magnitude comparable to the 1303 and 1926 events.

Regression analysis was performed to derive relations between seismic moment and the isoseismal area of earthquakes that occurred in Greece (Lesbos, Aeghio) for different levels of macroseismic intensities. A new catalogue of strong earthquakes for the Crimea region was presented. Historical data and archaeological excavation used to study an earthquake cluster observed in 1851 in Albania and two other shocks in the 4th and the 12th Centuries. The focal parameters of the 1904 Costa Rica earthquake were reevaluated. Certain features of the macroseismic fields of the 1802 and 1838 Vrancea earthquakes were presented. The seismicity and seismotectonics of the Gulf of Aqaba, the Arabian plate, and Algeria on the basis of historical and instrumental data were presented. The use of macroseismic data banks for historical earthquakes in Greece and the Iberian Peninsula were discussed

George F. Karakaisis

19-20 Aug, Towards Reference Earth Models (W3, Co-Sponsored by SEDI)

Conveners: G. Masters (USA), B.L.N. Kennett (Australia), Y. Ricard (France)

Since the publication of the Preliminary Reference Earth Model (PREM) in 1981, there has been a dramatic increase in the quantity and quality of seismic data as well as an appreciation and understanding of the effects of 3-D structure. Furthermore, there is now a sense that a model unifying several aspects of global geophysics and geochemistry is a possibility in the foreseeable future. At the workshop, 11 presentations covered several aspects of the production of a new REM.

After an introduction summarizing progress to date by Dziewonski, most talks concentrated on seismological data sets for use in REM modeling. Engdahl and coworkers presented their reprocessed ISC data set which includes the separation of pP picks from P picks using a statistical algorithm. This data set has already seen use in global tomographic studies. Free oscillation splitting data were discussed by Resovsky and Ritzwoller, and bias in free oscillation and surface wave attenuation measurements was addressed by Masters and Laske. Finally, Schweitzer presented a compilation of P4KP measurements which give strong constraints on the P velocity in the outer core. He found that PREMs outermost core is slightly too fast but that AK135 is slightly too slow.

Two papers considered the construction of detailed near-surface models for testing against seismological data sets. A model of European crust and mantle down to 600 km at a resolution of 1x1 degree was presented by Du and co-workers and tested against surface wave data. Ricard and Nataf discussed their global "a priori" 3SMAC model which has a resolution of 2x2 degrees and has also been tested against a variety of data sets. It is likely that something like 3SMAC will form one component of a new REM. A talk by Kennett considered the question of how density should be parameterized. His results indicate that a PREM-type parameterization may be too constraining in certain parts of the Earth. Finally, Peltier presented a 1-D viscosity structure which goes a long way to explaining a variety of data sets with different intrinsic time scales. Including viscosity in a REM allows an integration of several non-seismological data sets into the modeling and is therefore very attractive. Further expansion of the REM modeling to include mineral physics data, geochemistry, etc, is also a desirable long-term goal.

Guy Masters

20-21 Aug, Lithospheric Structure: A Key for Understanding Seismotectonics and Seismic Hazard of the Carpatho-Balkan Region (W4, Co-Sponsored by ICL/ILP)

Conveners: I. Kuznetzov (Russia), M. Radulian (Romania), G.F. Panza (Italy), C. Papazachos (Greece)

A relevant part of the presentations described the most important results of the international cooperation among several key institutions in Europe made possible recently by EU, ILP, INTAS, NATO, and UNESCO funding. Papers presented covered an area limited by Slovenia and Hungary (to the north), the Black Sea (to the east), Greece (to the south), and the Adriatic Sea (to the west).

The presentations supplied an important contribution to a better resolution of the structural and geodynamical complexities of the region that were responsible for the large seismic hazard. One important outcome of the workshop was the real necessity of strengthening and broadening the international cooperation that has allowed reaching standardized results otherwise impossible when the activity is limited to national projects. The main topics treated during the workshop were seismotectonics, inverse problems for sources and structures, block-structure dynamics, and realistic modeling of complete ground motion for the definition of seismic hazards.

The main practical result presented at the workshop concerned an innovative way of defining the seismic hazard, combining the most advanced models about seismic sources, structures, and seismotectonics with the few available reliable observations about ground motion. The seismic zoning obtained in this was is particularly important for the assessment of the safety of the existing Nuclear Power Plants, lifelines, and large reservoirs in the region, and will be used as new background for the next generation of design and safety measures. The huge data bank available for the regions studied has been used to model, in a very realistic way, the seismic input for some capital cities. The case of Bucharest, described in detail, represents a paradigm to be followed in future studies.

A relevant part of the success of the workshop was due to the generosity of Greek host program and IASPEI that allowed the participation of many high level scientists from Eastern Europe and Russia. Each section of the 2- day workshop was attended by about 40 to 50 people. There were 23 oral presentations and 26 posters. The poster session was well attended and supplied the proper forum for the exchange of ideas and the establishment of new links among scientists dealing with the problem of supplying seismological knowledge to be immediately used in anti-seismic design.

I.V. Kuznetzov

20 Aug, New Concepts and Procedures in Earthquake Hazard Assessment (W5)

Conveners: V. Schenk (Czech Republic), D. Mayer-Rosa (Switzerland), R. McGuire (USA), C. Papaioannou (Greece)

From the 46 contributions prepared for the W5, 19 were presented orally, 20 as posters, and 7 were not delivered. The new approaches and modifications of the earthquake hazard and seismic risk assessments showed that these topics are still very hot problems of seismology. Special attention was paid to: (1) a compilation and verification of input hazard data using geological, seismotectonic, and other geophysical information; and (2) implementation of new statistical and/or probabilistic aspects to the hazard and risk calculations. In many contributions, the hazard and risk outputs were devoted to various world regions, i.e., the participants of the W5 could compare an effectiveness of the recent calculation methods in different seismo-geological conditions.

Vladimir Schenk

Conveners: S. Park (USA), J. Zschau (Germany), P. Varotsos (Greece)

The question of whether em signals are generated prior to earthquakes is a controversial one, and presentations in this workshop did not resolve the issue. Focus in this workshop was split equally between the seismo-electric signals reported in Greece (the VAN experiment) and observations of em signals associated with the 1995 M7.2 Kobe earthquake in Japan. Many of the presentations on the VAN experiment addressed the site selectivity phenomenon in which distant sites record SES precursors to earthquakes but closer sites do not.

The hypothesis that a conductive channel exists between the site and earthquake hypocenter was advanced again, but other presentations and workshop attendees questioned it. Regardless, it is clear that multiple channels must exist at each site because the "predicted" earthquakes are in many locations. It was also proposed that the site selectivity may be due to the type of earthquake; some sites see SES associated with strike-slip earthquakes while others see SES with thrusts. There was a lively debate about whether SES were simply artifacts of cultural noise, but neither proponents nor critics could present conclusive evidence supporting their views. Lack of progress in understanding the SES in Greece is due partially to the lack of recent seismic activity and reported SES.

More promising results were presented from Japan. Co-seismic and post- seismic changes in self potential and VLF signal propagation were reported. The change in VLF signal propagation was especially intriguing as it appears to have begun prior to the earthquake. Further, the mechanism proposed (changes in the height of the ionosphere) is simple and plausible. The connection between the earthquake and the ionospheric height is still speculative, however.

Stephen Park

21-22 Aug, Earthquake Site Effects and Models for Assessing the Site Response (W7)

Conveners: K. Kudo (Japan), P-Y. Bard (France), W.D Iwan (USA), B. Tucker (USA), G. Gazetas (Greece)

The workshop was held on Thursday, August 21, and Friday, August 22, at MAC02 (oral) and Balcony (poster) in the University of Macedonia. Twenty- seven papers were presented orally (including three invited lectures) and 23 were presented by poster (three oral and six posters were canceled). There were an average of 70 attendees with the maximum being 120.

In the first oral session on Thursday, the presentations and discussions focused on the site evaluation methods or results by mainly observational approaches. The recent developments of numerical/computational research works for assessing the site responses, especially in a sedimentary basin, were major issues in the morning session on Friday. It is especially noted that site effect studies from various (at least 10) countries as well as specific sites were displayed in the poster session on Friday. Major topics at the last oral session on Friday afternoon were individual and associate issues in evaluating site effects. In the closing discussion, a strong caution on the applicability of the H/V method for assessing site effects was presented, and the individual ideas of attendees were exchanged.

The meeting of IASPEI/IAEE Working Group on Effects of Surface Geology (ESG) on Seismic Motion was held on Thursday evening (18:00 - 19:45). Discussions were made on the possibility for special issues as a proceedings of the session W7, the Second Symposium on ESG to be held in 1998 at Yokohama, Japan, new test site for ESG study and the Workshop in the next IUGG. We decided to propose a joint session in the next IUGG to the Sub- Commission on Strong Motion Seismology, because of its close proximity with the XII WCEE in Wellington, New Zealand.

It was noted that the session time for both oral and poster presentations was too short taking into account the number of presented papers.

K. Kudo and P-Y. Bard

21 Aug, Recent Strong Earthquakes in European-Mediterranean Region (W8)

Conveners: K. Makropoulos (Greece), D. Hatzfeld (France), D. Papastamatiou (Greece)

Through the workshop's Oral and Poster presentations the ongoing efforts for understanding the physical process of the earthquake phenomenon and the application of new methods and techniques in interpreting field co- seismic and post-seismic data gathered from recent strong earthquakes were well demonstrated.

Thus, data collected from the: 1992 Erzincan (Turkey), 1993 Patras (Greece), 1995 Aigion (Greece), 1995 Kozani-Grevena (Greece), 1995 Dinar (Turkey), 1996 Cyprus, and 1997 Antakya, (Turkey) earthquakes were analyzed using body-wave inversion techniques, coupled by satellite images, GPS and InSAR data, for obtaining the source parameters and model characteristics. From the strong motion data obtained in most of the above cases, their rupture process and complexity was examined by applying modeling techniques like the Discrete Wave-Number and/or Empirical Green's Function methods. The contribution of directivity effects, site-soil conditions and related factors to the observed damage distribution, was also well addressed in a number of studies. The need for intensifying the efforts towards the collection of high quality co-seismic and post- seismic data was repeatedly addressed.

The workshop was well attended with an average of about 70 scientists who participated in a fruitful discussion. Because of the, as expected, wide spectrum of the issues addressed concerning recent earthquakes ,it has been decided not to propose special issue to be published, but rather to joint other issues according to the specific target of each contribution.

Kostas C. Makropoulos.

21 Aug, Educating the Public About Earthquake Hazards and Risk (W9)

Conveners: J. Andrews (USA), Gu, Jian-hua (China), K. Ioannides (Greece)

The session opened with an open forum discussion. Approximately 30 participants, representing countries such as Canada, India, Japan, China, Turkey, Norway, France, Nepal, Peru, Greece, and the United States, referred to a list of earthquake education and information related topics: What is the need in your country? Are the needs treated as a priority by stakeholders in the communities? What are some of the obstacles encountered in answering these needs? Some responses included:

  • There is a need for broader training of Earth scientists - traditional science curricula focus exclusively on research, but there is a growing need to develop undergraduate programs that educate scientists who choose outreach/education as a profession (U.S.).
  • There is a need for economic support for programs and materials (developing countries).
  • There is a need to develop support materials, education programs, and to initiate direct contact with scientists for representatives of the media; participants acknowledged the lack of accurate reporting, especially in the immediate post-earthquake environment. There is a need for scientists and engineers to be available to the media to promote consistency in the messages and to quell rumors based on misinformation.
  • There is a need to develop 'grass roots' programs that encourage systemic change, i.e., education of school children is of primary importance (South America, U.S.).
  • There is a need to develop participatory partnerships among scientists, government officials, and stakeholders, coupled with measurement indicators of accountability (developing countries, U.S.).

The Oral Session consisted of 11 presentations to about 75 to 80 people. Speakers' topics covered a broad range of issues that echoed the open discussion in the previous hour. Participants heard that we can impact public policy by working more closely with government officials; we can raise awareness through global projects with developing countries, drawing on the experiences of developed countries; seismologists can develop effective communication strategies in a post-earthquake environment; we can reduce losses through legislation that requires careful planning for major damaging events; we can build community support in vulnerable areas by launching 'grass roots' programs that engage school children, neighborhood communities, and the general public to effect systemic change; we can use tools such as the Internet to familiarize the population with methods of research aimed at earthquakes and related hazards; we can make preparedness easy by recognizing it as a personal responsibility and taking actions that will allow peace of mind and rapid recovery - doing just one thing to prepare is better than doing nothing at all; we can 'vaccinate' our homes from the effect of damaging earthquakes; and we can select from a wide range of programs and expertise offered by numerous organizations worldwide, all focused on reducing losses due to earthquakes.

Jill Andrews

22 Aug, Earthquake Preparation Process: Quantitative Method and Hypothesis Testing (W10)

Conveners: M. Wyss (USA), R. Console (Italy), D. Rhoades (New Zealand), J. Latoussakis (Greece)

The attendance at W10 was quite constant throughout at 80 to 90 people. The authors of all papers, except one, were present and delivered their lectures. The climax of the session came during the discussion I invited instead of the talk not given. Jackson took the floor for several minutes to show view graphs in response to some of the points Evison made in the first talk of the session. Then, I showed two overheads rebutting what Jackson said and pointing out to him that the other speakers of the session had aptly disproved his accusation in Science that no earthquake prediction research was quantitative. At this point, Mulargia got into the fray to defend the words of the 'gang of four' (Geller, Jackson, Kagan, and Mulargia), as he put it. It was a pity that we had to return to the regular session sequence of talks, although the next presentation by Ohtake was excellent and thoughtful.

At the beginning of the session, quantitative methods to test hypotheses were discussed. These were high-level theoretical lectures. In two talks on M8, the authors seemed confident that now M8 has to be accepted as working. In several presentations on quiescence, the existence of this phenomenon was documented and a couple of mechanisms explaining it were discussed. Bernard gave an overview of the GAIA project, which seems promising and well designed. Chesnokov discussed effects of anisotropy, and Ohtake constructed a convincing model for interdependence of a pair of earthquakes in Japan.

The only problem was that there was not enough time for discussion. So, discussion continued in the hallway.

Max Wyss

Conveners: V. Margaris (Greece), D. Rinaldis (Italy), G. Brady (USA), X. Goula (Spain)

The W11 workshop included some very interesting papers from engineering seismology point of view and the discussion, which followed, presented a great interest concerning the effects of the acquisition and processing procedures of the frequency content of the strong-motion records. Two basic categories of papers have been presented during the oral and poster presentations. The first one covers the instrumentation, networking and acquisition of the strong motion recordings from Public Works as bridges or specific accelerometer networks in seismic areas. The papers numbered 2485 and 2555 are related to this subject. The workshopwas attended by an average of about 50 geoscientists and engineers, and a fruitful discussion took place.

The second category of papers comprised the development and improvement of the various techniques of the data processing and analysis of strong motion records. Some new techniques of the data processing and correction of strong motion accelerograms were presented. The 2756 and 1640 papers had this content. Two papers (1182 and 2577) relating to the instrumentation in Public Works were not presented.

The subject of the W11 is actually very wide including the installation, maintenance of the strong motion instruments, the acquisition and processing of the accelerograph records and finally the application in engineering use. The participation of the scientists to the W11 Workshop was satisfactory, although most of the strong motion sessions were held during the first week of the IASPEI Meeting.

The W11 workshop associates with topics as propagation of the seismic waves, the site effects and the seismic source. Thus a greater number of geoscientists as well as engineers could participate in the next organizations of W11 workshop of IASPEI Meetings.

Basil N. Margaris

22 Aug, Comparison of Techniques for Computing Synthetic Seismograms for 3-D Global Earth Models (W12)

Conveners: H. Igel (UK), R. Geller (Japan), B. Romanowicz (USA)

Much of our progress in understanding the internal structure will depend on accurately modeling seismic wave propagation in generally heterogeneous elastic, possibly anisotropic and attenuating media. There are many different theoretical and numerical techniques to achieve this goal. The verification of these techniques is important to trust the structural implications resulting from inversion algorithms based on these techniques.

Prior to W12, a 3-D Earth model was made available on a WWW site (www.esc.cam.ac.uk/itg/COSY) as well as all relevant parameters for the seismic simulations. Several participants calculated synthetic seismograms for this test model and submitted them to the chairman prior to the meeting. The results were compared, analyzed, and presented at the meeting.

Oral and poster presentations ranged from various aspects of seismic forward modelling algorithms (Clevede, Mikhailenko, Kvasnicka, Geller, Takuechi, Martin, Thomsen, Megnin, Igel, Pointer, Du) to inverse modelling (Weber) and a summary of the results from the comparative study of global seismic modelling algorithms (Igel). After the session there was a lifely discussion on the continuation of the COSY project and the nature of 3-D test models, in particular their spectral properties. The suggestions will be incorporated in future test models.

It was felt by all participants involved in the development of 3-D algorithms that this verification initiative is crucial and valuable for their research and that such a workshop should be held again (efforts are underway to generate an informal working group which would meet at major meetings).

The direct outcome of the present workshop is a WWW page where 3-D global test models and the corresponding seismograms can be downloaded. This database will be extended and improved as our modeling efforts develop. It is planned that in addition to possible future 3-D reference Earth models, verified synthetic seismograms will be made available through this initiative.

Heiner Igel

25-26 Aug, Triggered/Induced Earthquakes (W13)

Conveners: H. Gupta (India), J. Gomberg (USA), P. Hatzidimitriou (Greece)

There were 21 oral and 19 poster presentations scheduled in 3 oral and 1 poster sessions. Harsh Gupta in his opening remarks underlined the importance of induced and triggered earthquakes in comprehending the earthquake processes.

Several new cases of RIS were reported including Kouris Dam, Cyprus (J. Markis), Katse Dam, South Africa (I. Saunders), Salante Dam, Switzerland (S. Sellami), and Thomson Reservoir, Australia (G. Gibson). Gold, potash, and coal mining induced seismicity was reported from South Africa (T. Miwa), Poland (S. Lasocki and S.J. Gibowicz), and Germany (K. Klinge). Monitoring of induced earthquakes by a network of 76 stations in the vicinity of KTB drilling site in Germany has indicated the depth of brittle- ductile transition zone (H.P. Harjes).

Nucleation of induced earthquakes in the vicinity of Koyna Dam, India, is being investigated by a recently deployed dense network of seismic stations (R.K. Chadha). Fifteen borewells of ~200 m depth have been instrumented to study in situ pore pressure fluctuations (H.J. Kumpel). A case is made for triggering of microearthquakes by the M 7.2 Kobe earthquake in a nearby mine (H. Ogasawra).

Several papers dealt with the mechanism of triggered/induced earthquakes (D.W. Simpson, F.F. Evison, S.J. Stacey, and others).

It was a very well attended workshop, the attendance being over 30 participants in each session.

Harsh Gupta

25 Aug, Advanced Geoinformation Technologies for Earthquake Hazard and Seismic Risk Assessment (W14)

Conveners: Y.S. Tyupkin (Russia) and V.G. Gitis (Russia), K. Stylianides (Greece), N. Voulgaris (Greece)

Seventeen reports were presented at the workshop. These reports allow us to analyze state of the art on new information technologies for earthquake hazard and seismic risk assessment.

Regional and thematic data base are created for information support of earthquake hazard and seismic risk assessment studies. For example, strain- deformation data base Ural's crust is available now. GIS technologies are used very active. In particular, GIS-based approach is used to the development of an expert tsunami data base. A user-friendly GIS-based multi-disciplinary microzonation approach has been designed and implemented in frame of the project AUTO-SEISMO-GEOTECH. GIS technology has also been applied to the problem of rock burst forecasting.

The artificial intelligent approach is applied successfully to regional classification of the epicenter location using single station and single component broad-band seismic records within the distance range 500-2000 km. This approach was used also for development decision support system for earthquake disaster relief. The combination of elements of GIS and expert system technologies was realized in the instrumental environment GEO that provide efficient intelligent support in sophisticated seismological and environmental applications such as seismic hazard assessment and earthquake prediction.

The problem of availability of data on earthquake hazard and seismic risk assessment distributed in different organizations of different countries was discussed. The idea of the creation of a virtual thematic network on the INTERNET basis as a solution of this problem was proposed.

Yu. Tyupkin

25 Aug, Manual of Seismological Observatory Practice (W15)

Conveners: P. Bormann (Germany), G. Choy (USA), J. Baskoutas (Greece)

The workshop consisted of:

A poster session with oral introduction from 10:30-12:00 (chaired by P. Bormann and F. Scherbaum) with 6 posters, all scheduled in the official program, with the exception of the poster by M. Hellweg et al. on 'Volcano observatory practice' since none of these authors attended the IASPEI 1997. The 'poster' by F. Scherbaum was presented as a PC demonstration. The poster by R. M. W. Musson was complemented by distributing 30 copies of the new Manual of Seismological Observatory Practice (NMSOP) chapter on: Intensity and Intensity Scales. All authors were present at their posters and there was a lively discussion with both members of the manual WG and other interested visitors.

Oral presentations chaired by P. Bormann and Jans Havskov on 5 topics as scheduled in the session program. For the first paper by E. Bergman, P. Bormann served as a proxy. The old manual structure and chapters already on the web could be demonstrated by a PC with Internet access in the meeting room MAC14. The access to the new manual web page was demonstrated the other day in conjunction with the meeting of the manual working group. The two presentations by P. Bormann were accompanied by several drafts of sections for the new manual related to the interpretation of core phases and to the bandwidth-dependent transformation of noise data from the spectral to the time domain and vice versa (with exercises and solutions). 15 copies were distributed for practical applications and comments before installing them in the manual web page. Also the paper by J. Fyer and J. Schweitzer on 'Seismic Arrays in the new MSOP' was complemented by a 40p. draft which is ready for insertion in the preliminary new manual pages on the web. The WS 15 was attended by up to 50 people (42 signed-up). There were several comments and questions from the audience and one complementary short contribution by Luciana Astiz from IRIS on an improved version of J. Peterson's New Global Low and High Noise Model.

P. Bormann

26 Aug, Long Period Studies of Lithospheric Structure and Engineering Seismology (W16)

Conveners: H. Bungum (Norway), G. Woo (UK), J. Kalogeras (Greece)

The rationale for this workshop was that a recent trend towards the construction of taller and longer engineering structures has given rise to an increasing earthquake risk exposure to long period ground motion. Also, seismic base isolation systems may soften drastically under strong earthquakes, causing a significant increase in the natural period of the isolated structure. To account for such effects the design engineer needs a reliable estimate of the site specific, long period ground motion.

The session included six oral contributions, starting with a study of the ground motion response for periods longer than 10 s in the strait of Messina (Panza, Michelini, Suhadolc) and a microzonation study from Grenoble, evidencing large, low frequency site effects, including geometrical effects (LeBrun, Bard, Hatzfield). This was followed by two papers based on a recent EC study, one describing a new data base, with prediction models, of large European earthquakes since the turn of this century (Bungum, Lindholm, Dahle), the other including engineering considerations of future design for long period structures in Europe (Woo). Then followed a paper on exploration of S-wave velocity of deep sediments using microtremor array techniques for estimation of long period ground motions (Yamanaka, Sato, Kurita, Seo), and finally one on problems relating to improvement of seismic resistance of buildings (Bugaevsky, Balashov).

These papers contributed all, in different ways, to the definition of the seismic input required for the development of state-of-the-art techniques in long period seismic design, which remains a safety issue poorly regulated in existing building codes.

Hilmar Bungum

26 Aug, The Global Seismic Hazard Assessment Program 1992-1997 (W17, Co-Sponsored by ICL/ILP)

Conveners: P. Basham (Canada), V.K. Gaur (India), K. Shedlock (USA), T. Tsapanos (Greece)

W17 provided the opportunity to review the progress achieved under GSHAP as this IDNDR demonstration project nears completion. Ten oral presentations reviewed the progress in the various GSHAP regions and test areas. Poster presentations displayed all of the detailed information on seismicity, seismic source zones, strong ground motion relations and hazard maps. It is evident that GSHAP has been highly successful in standardizing the seismic hazard methodology around the globe, and in providing state-of-the-art seismic hazard assessment in many regions where previous hazard estimates did not exist. A GSHAP Steering Committee meeting following the workshop made plans to compile a volume of the scientific results, a CD-ROM containing digital files of the hazard models and results, and a global seismic hazard map, as a final product. All of this information will also be available on a series of linked WWW home pages. These final compilations for the program should be available before the end of 1998. It is hoped that they can be maintained and built upon in future years (ref. IASPEI resolution).

Peter W. Basham

26 Aug, Instrumentation Prospects for the Future (W18)

Conveners: J. Berger (USA), K. Suyehiro (Japan), D. Fountoulis (Greece)

Over the past two decades two major changes in instrumental seismology - the replacement of analog with digital recording and the dramatic increase in the bandwidth and dynamic range of seismometers have occurred. This workshop discussed the emerging technologies that are likely to have a similar impact on instrumental seismology. Areas of discussion included: (1) the instrumentation of the ocean floor; (2) the integration of seismic and non-seismic sensors and their data - geodetic, magnetic, meteorological, infrasonic, hydroacoustic, and others; (3) advances in seismometry; and (4) telecommunications for global real-time data collection.

In the first oral session, the French efforts on geophysical ocean bottom observatories was discussed by J P Montagner. The Ocean Bottom Broadband Borehole Seismometer package for Global Ocean Seismic Network observations was described by J A Orcutt, F L Vernon followed by description of an inexpensive seafloor instrumentation system by J A Orcutt, S Constable, G Laske.

The discussion of instrumental developments of sensors for harsh environments continued with a presentation of space qualified seismometers for future planetary missions by P Lognonne, J F Karczewski, S Cacho, J Gagnepain- Beyneix, A Desautez, B Dole, N Striebig, H Richard, S Vincent, C Cavoit and finally a description of a seismic sensor for High Temperatures by K-H Jaeckel, R Stecher, E Unterreitmeier, W Ecke, J Schauer, R Willsch.

Plans for the French global seismographic network, GEOSCOPE were presented in a poster by G Roult, J P Montagner, J F Karczewski. Another poster reviewed a hundred years of seismic observation in Slovenia by R Vidrih, P Sini. The new Israeli seismic network was described by A Shapira, V Avirav while developments in earthquake monitoring systems and data transmission was reviewed by H N Srivastava. L Zimakov and P R Passmore described a new light-weight recorder for deep seismic sounding.

The second oral session began with an overview of Trends in Global Wireless Telecommunications and their Applications to Near Real-Time Data Access From the Global Seismographic Network was presented by J Berger. L Astiz described the Characteristic Low and High Noise Models From Robust PSE of Seismic Noise of Broadband Stations. A review of the Russian program on powerful vibrators and the future directions of this program was presented by A S Alekseev and A V Nikolaev. The final paper in this workshop described a refined GPS data analysis using the first data set for global network solution presented by E C Malaimani, J Campbell, B Goerres, S Smaritschnik

Jon Berger

Conveners: G.A. Sobolev (Russia), I. Main (UK), V.B. Smirnov (Russia), G. Tsokas (Greece).

19 oral and 11 poster communications were presented during the workshop by participants from 11 countries. The fundamental role of self-similarity and fractality for understanding of the statistical properties of seismicity were outlined in a set of presentations. The account of fractality allows to connect seismo-statistics with the fracture physics. Time variations of space and time fractal dimensions during aftershock sequences demonstrate the transition of seismicity from the uniform to the fractal state. Space variations of b-value found as a result of b-value tomography suggest that the heterogeneity of the crust is characterized by differences in the fractal properties. Method for estimation of the statistical significance of the fractal (correlation) dimension was putted forward. It allows to quantify the difference in the fractal structure for the clusters of induced seismicity. New method of catalogue declustering was proposed for investigation of the spatio-temporal scaling properties of seismicity on the base of multi-fractal approach. Universality and efficiency of the concentration criteria of failure were revealed. Self-similarity of the failure process was demonstrated both empirically and numerically.

Statistically significant correlation of the seismic and acoustic events with the external periodical loading processes was found both in the field and in the laboratory. Laboratory modeling showed that certain symptoms of the medium response to the external periodical loads can be used to estimate the onset of the instability stage in the fault zones of the Earth crust when analyzing the weak seismicity, Earth tides and vibroseis signals. Several authors came to conclusion that very small changes of stress can trigger the earthquakes in the metastable zones of Earth crust. It was shown that the dilatancy zones in the earthquake source and near the Earth's surface can be discovered using mathematical model for combined analysis of the multi- disciplinary geophysical fields. Retrospective application of the GEOTIME computer environment to the multi-parameter geophysical data revealed the existence of a localized precursor area near Tangshan earthquake and much more spread out zone before the Datong earthquake. The existence of global chains in seismic activity has been confirmed by computer analysis of earthquake catalogues. It was demonstrated that the stress field can be reconstructed as a result of study of micro-earthquake activity on the system of faults.

G. Sobolev

27 Aug, Thermal Regimes in the Continental and Oceanic Lithosphere (W20)

Conveners: C. Clauser (Germany), V. Cermak (Czech Republic), M. Yamano (Japan)

The workshop was intended as a forum for a wide spectrum of topics in continental heat , both continental and marine. Contributions presented accordingly varied interpretation of new data sets, re-interpretations of old data with techniques and numerical models of steady-state and transient heat flow in general. A total of five out of twenty-three contributions covered marine topics, while the remaining ~75% dealt with heat flow. Contributions were presented from four continents: Europe 13, North America 3, south America 1, Asia 5. Contributions highlighted the influence of topography and paleoclimate and their interference on the heat flow signal by 2D and 3D numerical simulations. A new and promising trend was shown in attempt to use (paleo) geothermal information from geology and petrology. In the discussion, which was very lively, it became apparent, that an important future task is to discriminate between shallow and deep sources of heat flow anomalies.

Splitting up the two thermal sessions, S9 and W20 in two different weeks had a noticeably negative effect on the attendance, as most participants were forced to decide which are the would attend due to increasingly limited travel. I urge IASPEI and IUGG to have the usually two thermal sessions in the same week in the future!

Christoph Clauser

28 Aug, Reducing Earthquake Losses in the Eastern Mediterranean Region (W21, Co-Sponsored by UNESCO)

Conveners: W. Hays (USA), B. Feigner (France), M.W. Jaradat (Jordan), E. Ibrahim (Egypt), J. Drakopoulos (Greece), D. Papanastasiou (Greece)

This session, comprised of oral and poster sessions, was convened on August 28, 1997. The primary focus was on sharing insights on location and magnitude determinations made during a portion of the ongoing Joint Seismic Observing Period (JSOP) in the Eastern Mediterranean region. Since JSOP was initiated in 1995, seismic network operators from Turkey, Lebanon, Syria, Cyprus, Jordan, Israel, Egypt, Saudi Arabia, and Yemen have cooperated with the Euro-Mediterranean Seismological Centre (EMSC) to share network data. Through this mechanism, each country now has continuing access to data from over 100 stations in the region.

The session was also used as a forum to: 1) discuss and plan the next meeting of the multi-national Gulf of Aqaba Work Group which is analyzing data from the Gulf of Aqaba earthquake of November 22, 1995, 2) discuss the scientific and technical issues associated with the construction of a simplified RELEMR ground shaking hazard map for inclusion in the Global Seismic Hazard Program World Map during 1998, and 3) develop a working concept and ideas for a meeting in Jordan next spring to plan joint calibration experiments. Attendees representing EMSC, Jordan, Israel, Egypt, Turkey, Spain, and the United States contributed to the oral and poster sessions. Thirty people attended and contributed to discussions during the oral sessions.

Walter Hays

28 Aug, Tsunami Sources (W22)

Conveners: C. Koutitas (Greece), V.K. Gusiakov (Russia), F. Imamura (Japan), S. Tinti (Italy), G.A. Papadopoulos (Greece)

The workshop on tsunamis has elucidated recent progress in tsunami research in Europe, USA and Japan. The state-of-the-art on the European research has been illustrated by a paper by Prof. Tinti, who emphasized the role of collecting data and assembling tsunami catalog for European seas, with special reference to the recent efforts performed in the framework of the international projects GITEC and GITEC-TWO: a unified European catalog of tsunamis is on the point of being completed and made available to the scientific community. Prof. Tinti further stressed that Italian research now and in the near future is being mainly focused in studying the major historical events by means of numerical tsunami simulations, in order to assess hazard and risk. A very important point is that numerical modeling can be used even to identify properties of the seismic source: in the case of the 1693 tsunami that invested the eastern Sicily coast, tsunami simulations were used to infer that the responsible fault is placed in the sector of the Malta-Hyblean escarpment facing Augusta (eastern Sicily).

The role of historical studies was proven by Prof. Tsuji who analyzed events occurred in 1498 in the Nankai and Tokai sea regions (Japan). These areas are known to have generated a series of large twin earthquakes (see 1707 and 1854 cases). The question to answer was if in 1498 only a single event or twin event occurred. Historical research, based on newly discovered Chinese sources, was able to demonstrate the occurrence of two earthquakes, the first on July 9 in Meio Nankai, generating a remarkable tsunami, and the second on September 20 1498 in Meio Tokai.

Tsunamis generated by volcanic activities have been touched by Dr. Bortolucci who studied the recent case (1988) of Vulcano island in the southern Tyrrhenian Sea (Italy). The small tsunami was generated by a landslide on the volcanic cone that entered marine waters. Modeling was based 1) on the simulation of the landslide evolution through a model based on a Lagrangian approach (i.e. the sliding mass is partitioned in a chain of interacting blocks) and 2) on the simulation of the tsunami generated by means of a shallow-water model.

Tsunami zoning as an important tool to define tsunami hazard and risk was illustrated by Dr. Gusiakov, who addressed the problem of selecting the appropriate space scale for the problem. By means of many data and examples he concluded that the general scheme of tsunami zoning for any particular coastal area should consist of at least two levels: small scale (1:1,000,000 or less) for evaluation of expected wave heights at some fixed isobath (say 50 m depth) and large scale (1:10,000) to obtain detailed inundation maps (run-up simulations).

The fundamental problem of establishing tsunami warning systems in the Mediterranean has been faced by Dr. Papadopoulos, who focused his attention on the Kithyra Strait area (southern Peloponnesus, Greece). He illustrated the study that is being carried out by NOA in the frame of the aforementioned project GITEC-TWO to evaluate the feasibility of a tsunami warning system, based on a network of broadband seismic sensors and of digital tide-gauges, real-time connected with a central processing system (24 hours operation) in Athens at the NOA headquarters.

A very interesting study on paleotsunamis in the Aegena Sea was described by Dr. Imamura. An international team formed by researchers from Japan, Greece and Turkey investigated tsunami traces in three sites, two in Turkey and one in the Santorini island). Analysis of samples taken from trenches showed evidence of new unknown tsunamis, and seems to disprove the occurrence of the Santorini explosion tsunami. This is a very extraordinary result that deserves, however, confirmation from further dating studies.

Dr. Ranguelov presented a comprehensive study on tsunamis in the Black sea, comparing his catalog with the recent tsunami list compiled by Dr. Nikonov. Differences are not relevant, but show that further joint research is needed to clarify and smooth discrepancies.

Tsunamis generated by earthquakes are reasonably associated with disturbance of the ocean thermal layering and with rising flux of deep cool ocean water. Low-temperature anomalies at the ocean surface are then to be expected after the occurrence of large open sea tsunamis. Dr. Levin showed that remarkable ocean cooling was detected through satellite images after the 1995 Mexico tsunami and the 1996 Solomon island tsunami. Anomaly amplitude was as large as 3 degree, with horizontal scale of about 500 Km and lifetime of several days.

Stefano Tinti

28 Aug, Exploiting Massive Seismological Data Sets: Theory and Practice (W23)

Conveners: R. Snieder (The Netherlands), P. Malischewsky (Germany), G. Nolet (USA), D. Panagiotopoulos (Greece)

The exploiting of massive seismological data sets is not a task unto itself, but serves the purpose of getting a deeper insight both into the Earth's interior and into the phenomenon of earthquakes. However, the present availability of an enormous amount of data also requires a special kind of handling for the distribution and the effective access to these data. Automatization and 'Networking the Networks' are the slogans. A part of the papers of this workshop were devoted just to these problems. Another essential part of the papers showed how massive seismological data sets together with refined theoretical and experimental conceptions yielded a better insight into geophysical phenomena. Finally, some papers were also devoted to the theory of wave propagation.

As a whole, the workshop demonstrated the necessity and importance of handling massive seismological data sets.

Guust Nolet

Other Scheduled Meetings


  • 20 Aug, Commission on Controlled Source Seismology (C1)
  • 21 Aug, Commission on Earthquake Hazard and Prediction (C2)
  • 27 Aug, Commission on Geodynamics and Tectonophysics (C3)
  • 21 Aug, International Heat Flow Commission (C4)
  • 17 Aug, International Ocean Network (C5, canceled)
  • 25 Aug, Commission on Practice (C6)
  • 25 Aug, Commission on Wave Propagation (C7)
  • 19, 20 Aug, European Seismological Commission (C8)
  • 24, 27 Aug, Federation of Digital broadband Seismograph Networks (C9)
  • 21 Aug, Commission for International Decade for Natural Disaster Reduction (C10)
  • 22 Aug, Committee for Developing Countries (C11)
  • 22 Aug, Commission on Education (C13)
  • 19 Aug, Asian Seismological Commission (C15)


  • 22 Aug, Sub-Commission on Earthquake Hazard and Risk (SC21, Earthquake Hazard and Prediction)
  • 22 Aug, Sub-Commission on Earthquake Prediction (SC22, Earthquake Hazard and Prediction)
  • 27 Aug, Sub-Commission on Modeling the Earthquake Source (SC23, Earthquake Hazard and Prediction)
  • 20 Aug, Sub-Commission on Strong Motion Seismology (SC24, Earthquake Hazard and Prediction)
  • 25 Aug, Sub-Commission on Anisotropy (SC71, Wave Propagation)
  • 25 Aug, Sub-Commission on Heterogeneity (SC72, Wave Propagation)
  • 19 Aug, Sub-Commission on Training (SC81, Education)

Working Groups

  • 20 Aug, Working Group on Seismic Hazard Assessment Techniques (WG21, Earthquake Hazard and Prediction)
  • 21 Aug, Working Group on Effects of Surface Geology on Seismic Motion (WG22, Earthquake Hazard and Prediction)
  • 20 Aug, Working Group on Regionalization (WG62, Practice)
  • 26 Aug, Working Group on Manual of Seismological Observatory Practice (WG63, Practice)
  • 20 Aug, Working Group on Personal Computers (WG64, Practice)
  • 20 Aug, Working Group on International Seismological Observing Period (WG65, canceled, Practice)
  • 20 Aug, Working Group on International Data Centers (WG66, Practice)

Special Interest Groups

  • 26, 27 Aug, Global Seismic Hazard Assessment Program (GSHAP) (SIG1)
  • 26 Aug, ORFEUS Workshop: Information and Waveform Dissemination (SIG2)
  • 19 Aug, ESC Working Group on Seismic Hazard Assessment: Seismic Ground Motion in Large Urban Areas (SIG3)
  • 25 Aug, IGCP-382: Seismotectonics and Seismic Hazard Assessment of the Mediterranean (SIG4)
  • 21, 22 Aug, EMSC/CSEM (SIG5)
  • 22 Aug, Working Group on Strong Motion Data (SIG7)
  • 21 Aug, Future of the Journal Geofisica Internacional (SIG8)
  • 21 Aug, EAEE-TG6 & ESC-WG4 (Joint Meeting) (SIG9)

Closing Plenary Session

28 August 1997

Present: Prof. C. Froidevaux (President) in the Chair and about 300 delegates and guests.

The President opened the meeting at 1415 and welcomed participants.

President's Report

The President reported that at this Assembly we had 1050 participants from 62 countries (396 European, 291 Greece, 200 Asia, 113 North America, 10 Africa, 10 Oceania, and 9 South America) and 1411 submitted abstracts.

The President noted that there were many IASPEI activities besides its General Assemblies. For example, there was a meeting on geodynamics sponsored by the Commission on Geodynamics and Tectonics in Germany only two weeks before this assembly. Next week there will be a meeting in Germany on megacities and risk, an emerging major theme for IUGG in future, that will be followed up with related meetings in Chile (IDNDR with IAVCEI) and Istanbul in 1998. In 1996 IASPEI, through its commissions, has sponsored meetings in many countries, including Zimbabwe (Bulawayo), USA (Stanford, Asilomar), UK (London), Czech Republic, Iceland (Reykjavik/ESC), and Kazakstan (Alama Ata/IDNDR).

The President also noted that IASPEI newsletters are issued periodically by the Association, the Commission for IDNDR, and the Committee for Developing Countries. He called attention to activities of the newly formed Asian Seismological Commission, including a Regional Assembly held at Tangshan, China, during 1-3 August 1996, and a similar assembly being planned at Hyderabad, India, in December 1998, and especially encouraged the participation of more Japanese scientists. The President noted IASPEI?s increased interest in promoting training courses under its Sub-Commission on Training. Finally, he called attention to areas where IASPEI cooperates with other IUGG associations, in particular the International Heat Flow Commission and (with IAVCEI) the Inter-Association Commissions on Volcano Seismology and on Physical and Chemical Properties of Materials of the Earth?s Interior.

Secretary-General's Report

The Secretary-General, Dr. E.R. Engdahl, reviewed the 1995 and 1996 Financial Reports for the Association. Major sources of income during this period were IUGG Allocations, Grants, and Sales of Publications. Major expenditures were Administration, General Assemblies, and support for IASPEI sponsored Symposia and Scientific Meetings. He noted that in future a significant decline in grant income is anticipated that can hopefully be offset by increased publications income.

The Secretary-General reported that the Association Newsletter is now being more widely distributed by e-mail. However, a hard copy version is also being mailed to scientists without Internet connections with the assistance of the National Geophysical Research Institute at Hyderabad, India. He noted that further development of the IASPEI Home Page on the World Wide Web is underway and that a IASPEI Brochure, which describes who we are and what we do, is now available both in hard copy and on the Home Page.

During the Assembly one IASPEI Bureau meeting was held jointly with the Local Organizing Committee and four business meetings of the IASPEI Executive Committee were held, the last of these with IASPEI commission chairs. In addition , the Secretary-General reported that most IASPEI commissions, sub-commissions, and working groups, as well as a number of special interest groups, held scheduled meetings during this assembly. He announced several important changes in commission structure that were confirmed by the IASPEI Executive Committee:

  • Committee on Developing Countries - The Committee Chair , R.D. Adams, resigned and has been succeeded by G. Gibson (Australia)
  • Commission on Wave Propagation - The Commission Chair, C. Thomson, resigned and has been succeeded by J. Park (USA).
  • Federation of Digital Broadband Seismograph Networks - The newly elected Chair is Y. Fukao, succeeding J-P. Montagner

The Secretary-General reported that progress had been made in developing the IASPEI scientific program for the 22nd General Assembly of IUGG and 30th General Assembly of IASPEI, to be held in Birmingham, England, 19-30 July 1999. As an experiment in developing the program for IASPEI sessions, the IASPEI Executive Committee has decided that the Association program should be based on scientific themes. For each theme there would be assigned a program group consisting of three persons that would include one member of the Executive Committee. Proposals are requested for topics within each theme to be used in constructing a broad scope for that theme. Papers would be submitted to themes and then would be assigned by the program group to appropriate topics as determined by the submitted abstracts. Conveners would then be assigned to theme topics as necessary to develop sessions.

The scientific themes and IASPEI Executive Committee member assigned to the group for each theme are:

  1. The nature of seismic sources and the prediction of earthquakes [Gupta]
  2. Seismotectonics [Engdahl]
  3. Strong ground motion, earthquake hazard and risk [Xie Li-Li]
  4. Earth structure and geodynamics (inc. heat flow) [Kennett/Fowler(ILP)]
  5. Physics and chemistry of Earth material (inter-association) [Jeanloz]
  6. Seismological observation and interpretation [Giardini]
  7. Education and outreach [Hamza]

The Secretary-General announced that Hanoi, Vietnam, has been selected by the Executive Committee as the venue for the 31st IASPEI General Assembly in 2001, which will be held jointly with IAGA. Dr. Engdahl reviewed the factors upon which the Executive Committee reached its decision. The joint assembly will be held during the last two weeks of August in a newly constructed fully air-conditioned Conference Center which will have large lecture rooms and other modern appointments. Near the Conference Centre there are Dormitory Houses for students which will be available to participants, restaurants providing meals at low prices, and hotels with a wide range of rates. The LOC will use Internet to communicate with participants and carry out the tasks of abstract submission and meeting pre-registration. The Registration Fee will be less than US$400 and travel assistance will be provided to participants who would not otherwise have support to attend. The Scientific Program for this Inter-Association Assembly will be developed at the 1999 IUGG General Assembly in Birmingham. The selection of the Hanoi venue was unanimously approved by voice vote.

Adoption of Resolutions

Prof. B.L.N. Kennett, Chairman of the Resolutions Committee, then proposed the Resolutions given below. They were accepted without modification.

Appointment of Nominations Committee

The President announced the composition of the Nominating Committee to propose a slate of officers at the 1999 General Assembly. The members are:

  • Prof. Claude Froidevaux (France, Chairman)
  • Prof. Shamita Das (United Kingdom)
  • Prof. Chen Yun-tai (China)
  • Prof. Kurt Lambeck (Australia)
  • Prof. Thomas Jordan (USA)

The President, First Vice-President, Second Vice-President, Secretary-General, and four additional Members of the Executive Committee should be nominated. Nominations should be sent directly to:

Prof. Claude Froidevaux Departement Terre-Atmosphere-Ocean Ecole Normale Superieure 24, rue Lhomond F-75231 Paris Cedex 05 FRANCE Tel: 33 1 44 32 22 13 Fax: 33 1 44 32 22 00 E-mail: froidevo@geophy.ens.fr

Other Business

There being no further business, the President once more thanked the Local Organizing Committee and expressed the hope that participants had enjoyed their stay in Greece.

The President closed the meeting at 1515.

IASPEI Resolutions Adopted

Thessaloniki, Greece

28 August 1997

Strong Ground Motion Data

Recognizing the critical importance of strong ground-motion data in the evaluation of seismic hazard analysis, earthquake resistant design and other aspects of seismic risk reduction,

IASPEI urges operators of seismic strong ground-motion instrumentation to make ground-motion recordings publicly available as soon as possible, for example by using the World-Wide Web.

Test Areas for Earthquake Prediction

Recognizing that research into earthquake prediction needs to be carried out over long time scales with extensive and detailed observation at substantial cost, and

aware that many nations face serious threats to their populations with limited resources and skills,

IASPEI urges the organization of additional multinational test areas in different tectonic settings where high level research efforts are already in progress, for example: Kamchatka (plate-subduction), Iceland (plate spreading), Yunnan (intercontinental strike-slip), Gulf of Corinth (continental rifting), Beijing (intra-continental) and

recommends that host countries welcome participants from all nations and in due course make the data available to the international research community in computer accessible form.

Global Seismic Hazard Assessment Project

Recognizing the substantial achievements on the five years of the Global Seismic Hazard Assessment Project (GSHAP)

IASPEI commends the compilation of a global assessment of seismic hazard,

urges all nations to collaborate to extend coverage to the full globe, and

recommends its Commissions and Committees to pursue the task in the years ahead.


Recognizing the importance of maintaining high quality expertise world- wide in earthquake engineering and its interface with seismology and

appreciating the unique contribution made by the Japanese Government to the International Institute of Seismology and Earthquake Engineering (IISEE) over nearly 40 years to training seismologists and earthquake engineers, particularly from developing countries,

IASPEI urges the continuation and expansion of support for the IISEE as a major contribution to training to aid the assessment and mitigation of earthquake hazard.


Recognizing the effort required to organize a General Assembly,

IASPEI thanks and congratulates the members of the Local Organizing Committee for a most memorable meeting in Thessaloniki.