Working Group on Event Location Using Multiple Events
Members: Peter Bormann, Jim Dewey, Soren Gregersen, Won-Young Kim, Klaus Klinge, Bruce Presgrave, Bob Uhrhammer, Karl Veith.
Chairman: Jim Dewey
I invited several people who were unable to participate. The group as it stands may lack some expertise or geographic representation that will eventually be critical to our success. In particular, I am bothered that we have, I believe, only one member (Karl) who has extensive knowledge of the perspectives of the nuclear-test-ban community, and no one from the IDC. I still have two invitations outstanding that, if accepted, would remedy these deficiencies. The WG also does not contain people working outside of the U.S. and Europe. I believe we can add members as we identify needed additional perspectives.
On the basis of comments I have received thus far, I would like to propose the following goals and timetable for the group. I have adopted the point of view suggested by several that the "standard" procedures for measuring amplitudes and periods should be those that replicate as much as possible the amplitudes and periods produced by widely-used mid-twentieth century seismographs.
The main purpose is to provide standards for making measurements from digital data to be used in calculating earthquake magnitudes. We will give highest priority to magnitude-types that appear frequently in current international bulletins produced by the NEIC and ISC or that are being produced by regional networks of digital seismographs: these magnitudes are those commonly denoted mb, MS, ML, MD, mbLg, and MW (from local and regional data). We may include more than one "standard" procedure for some general kinds of magnitude. We will document widely-used measurement procedures that we do not label as "standard."
---that depend in part on how measurements are made from digital data (abstracted from comments submitted by WG members). Most of these outcomes would not be the direct responsibility of the magnitude WG.
---seen from the perspective of the NEIC, that may affect how we go about our task
---based on comments already circulated by early WG members.
Agreeing on how the standards should be applied by the NEIC and ISC. There are "hard" approaches: e.g., the NEIC/ISC should use only certified standard measurements. There are "soft" approaches: e.g., the NEIC/ISC will encourage measurements to be made in the standard ways but will publish all contributed data and document the measurement practices of the stations for which they can obtain this information. Both hard and soft approaches can be defended, depending on the use that is to be made of the magnitude.
(can we aim to have these by mid-March?)
Members: B.Kennet, B.Engdahl, J.Havskov, J.Schweitzer, P.Bormann, D.Storchak
Chairman: Dmitry Storchak
The Working Group was set up 6 months ago in September 2001.
We have since:
We have originally planned to finish the job by 1 April 2000. At this point it becomes apparent, that the list is not going to be produced as planned. We believe it is not worth producing the list, which was not generally approved by a reasonable number of colleagues. We shall nevertheless still aim for it's completion two months after we got the desired response on the Second Draft Version.
Based on a considerable input to the work of the Group, I have invited Robin Adams to become a member of the WG. He has agreed
Members: E.A. Bergman, Bob Engdahl, Bondar, P. Firbas
Chairman: Bob Engdahl
The IASPEI reference event list has been carefully vetted and a new release is in preparation.
There has been some preliminary work on GT selection criteria for events with reporting stations at regional and teleseismic distances. We have assembled and vetted a database of about 1800 explosions and earthquakes globally whose locations are known to 5 km or better (GT5). These events have been relocated at fixed depth using stations at all distances with the EHB algorithm and the mislocations in km determined. These mislocations were compared to the secondary azimuth gap (the largest azimuth gap filled by a single station) both for explosions whose locations are known to 2 km and for explosions and earthquakes. In both cases, there are marked improvements in the percentage of events mislocated by 15 km or less (GT15) at secondary azimuth gaps of 180 and 130 degrees. More about this in the next report after we have performed further testing.
The IDC has informed us that reference events submitted through their calibration program will be released after certification.
Members: E. R. Engdahl, Paul G. Richards, Ray Willemann
Chairman: Paul G. Richards
Our work since the previous report of September 19, 2001, has been to acquire datasets of two types: first, sets of ground truth events (origin time, epicentre, depth, magnitude); second, sets of phase picks (regional, teleseismic). The purpose of such data acquisition, is to permit later evaluations of the performance of different algorithms for locating multiple events.
Thus, with help from Istvan Bondar we have acquired ground truth information for a set of mine-induced earthquakes at Lubin, Poland. For these events, we have also obtained the associated phase picks at IMS stations. Most of the picks are for regional waves recorded in Europe, but there are also some teleseismic picks.
Felix Waldhauser and Paul Richards at Lamont have begun joint efforts with two seismologists in China to study clusters of seismicity in three different regions of China (located with and without methods of multiple event location), and to relate the relocated events to fault structures.
Eric Bergman and Bob Engdahl at the University of Colorado have begun a similar effort with other seismologists in China to study clusters of seismicity in China using multiple event location techniques (HDC).
I anticipate that we shall see further progress in meetings held during a workshop being organized by NORSAR April 22-26 2002, which will attract several researchers working on multiple event location.