On September 18 th , 2021, our former colleague Dr. Dieter Seidl passed away at the age of 83. Dieter Seidl studied physics in Stuttgart, Germany, and joined the group of Prof. Dr. Stefan Müller in Karlsruhe for his PhD thesis on the analysis of seismic surface waves. In 1971 he changed to the formerly existing Seismological Central Observatory (SZGRF) in Erlangen, a branch of the Federal Institute for Geosciences and Natural Resources (BGR) in Hannover. There he worked as a scientist and prepared the theoretical foundation for the design and installation of the first digital broadband array on Earth, the Gr?fenberg Array on the Franconian Jura in Southern Germany. The 13 stations of the Gr?fenberg Array are still existing and delivering continuous data since 1976, providing a unique data set to the seismological community. Since the beginning of the 1980s, Dieter Seidl was heading the SZGRF until his retirement in 2003. He wrote numerous articles on the analysis of broadband seismograms and developed fundamental algorithms for the application of filter operations to digital seismic data. These methods still are the basis of modern processing techniques in seismic waveform analysis. In later years he focused on the seismological aspects of volcanism and conducted a number of measurements at volcanoes in South America. Thus, he contributed expert knowledge to the early recognition of critical states at volcanoes. Dieter Seidl always was a helpful colleague and promoted scientific discussions with his profound knowledge in geophysics. We will miss him.
Klaus Stammler, Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany