Observatories and Research Facilities for EUropean Seismology
Volume 2, no 1 March 2000 Orfeus Newsletter

Special issue on Rapid Moment Tensor determinations in Europe

Günter Bock1 and Torild van Eck2
1GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany.
2ORFEUS, c/o Seismology Division, Royal Netherlands Meteorological Institute, PO Box 201, 3730 AE De Bilt, The Netherlands.

The increasing amount of high-quality broad-band seismograph stations in Europe and in neighbouring areas will provide unprecedented opportunities for seismological research on the earthquake source and significantly improve services to the science community and to the public by releasing rapidly information on significant earthquakes.

The four articles in this ORFEUS Newsletters deal with these exciting new opportunities. While the articles give an account of ongoing work on moment tensor inversion at some institutions, this Newsletter does not provide a comprehensive overview of European activities on determinations of earthquake source parameters. However, we hope that the reports may help to initiate a kickoff for a broader forum on problems and results of earthquake source studies carried out at seismological institutions in the European-Mediterranean area. The editors of the ORFEUS Newsletter are certainly happy to provide a venue for presentations on this topic. We also wish to point to the forthcoming ESC General Assembly in Lisbon where a special session SSC-3 is dedicated to moment tensor determination. This would be certainly an appropiate venue for an informal exchange of ideas on this topic in addition to the more formal presentations in the session.

The majority of papers deals with methods for regional moment tensor (RMT) inversion. This is clearly appropiate for the European-Mediterranean area because strong (M > 5.5) earthquakes for which moment tensor solutions are reported, usually within 24 hours after the event, by the EMSC, Harvard, or the USGS do not occur frequently.

The contributions by Morelli et al. and Hofstetter et al. focus on earthquakes in the Mediterranean and Turkey. Braunmiller et al. give a detailed account of the source parameter determination of the November 12, 1999, Düzce earthquake for which they could provide a quick moment tensor solution 4 hours after the event. Many of the other examples presented deal with local and regional earthquakes. It is obvious that a very important point is the availability of broad-band data from a number of stations well distributed in azimuth about the epicentre. This requirement is not always met shortly after significant earthquakes as pointed out in the report by Bock on the rapid source parameter determination of the Izmit event of August 17, 1999. It is also clear that in many cases one has to work with data from more than one network. On a global scale, broad-band data become available for M > 5.5 events and some significant events below the M = 5.5 threshold through the Spyder® online data pools at IRIS DMC, ORFEUS and GEOFON. However, the station distribution for the global Spyder® systems is usually not suitable for reliable RMT solutions to be determined. Using regional network data is essential in these cases. Under favourable conditions it is possible to derive reliable RMT solutions for weak earthquakes down to Mw = 3.5 as demonstrated by Braunmiller et al. The contributions by Morelli et al, Braunmiller et al, and Hofstetter et al all indicate that completeness of RMT solutions for M > 4.5 earthquakes in the European-Mediterranean area is a realistic goal to be reached. Building a moment tensor catalogue for the European-Mediterranean region which is complete down to M = 4.5 or even 4.0 is a challenging task for the future. Such a regional database would be a most valuable addition to the Harvard catalogue of strong earthquakes. To achieve the goal it is appropiate to co-ordinate efforts by various groups in the European-Mediterranean region who are actively involved in moment tensor inversions. We hope that this and other topics can be discussed between interested people at the ESC Lisbon meeting.

page 2

Copyright © 2000. Orfeus. All rights reserved.