HR: 17:15h
AN: S52K-06    [PDF]
TI: Regional Moment Tensor Inversion With Application to the 2003 Algeria Earthquake
AU: * Braunmiller, J
EM: jochen@seismo.ifg.ethz.ch
AF: Swiss Seismological Service, ETH Zurich, Zurich, 8093 Switzerland
AU: Bernardi, F
EM: fabrizio@seismo.ifg.ethz.ch
AF: Swiss Seismological Service, ETH Zurich, Zurich, 8093 Switzerland
AU: Kradolfer, U
EM: kradolfer@seismo.ifg.ethz.ch
AF: Swiss Seismological Service, ETH Zurich, Zurich, 8093 Switzerland
AU: Giardini, D
EM: giardini@seismo.ifg.ethz.ch
AF: Swiss Seismological Service, ETH Zurich, Zurich, 8093 Switzerland
AB: Earthquake moment tensor (MT) solutions provide important parameters for seismotectonic studies and for calibrating earthquake size. The broadband seismic station network in the European-Mediterranean region allows MT analysis and since the year 2000 the Swiss Seismological Service provides regional MT solutions. For larger events ($M_{w}$ $\geq$ 4.8), we automatically determine MT solutions using near real-time available data. Our solutions provide accurate estimates of earthquake size, depth and deformation style that are available within 90 minutes after event occurrence. We post our results on the Web and disseminate them via the European-Mediterranean Seismological Center. Merging of near real-time data with off-line data available days to months after an earthquake allows routine MT analysis in the entire European-Mediterranean region from $25^{o}$N to $90^{o}$N and from $35^{o}$W to $55^{o}$E. For areas with dense station coverage, like Switzerland, events as small as $M_{w}$ = 3.5 are analyzed; in areas far from seismic stations, like the North Atlantic Ridge, the lower analysis threshold is near $M_{w}$ = 4.8. We determine about 200 MT solutions per year. The solutions are posted on the Web and are included in the ISC data base. For the recent, destructive earthquake in Northern Algeria on May 21, 2003, we provided 7 automatic MT solutions for the main shock and larger aftershocks. The mechanism, size, and depth estimates were later confirmed by Harvard CMT solutions for the largest events and by routine MT analysis. Routine analysis, in addition, allowed source parameter retrieval for several immediate aftershocks, that could not be analyzed automatically due to main event coda, and of many smaller events, where it is crucial to use all available waveform data to obtain a well constrained mechanism. All events were shallow and showed a thrust-type mechanism with NNW to N oriented P-axes (median $338^{o}$) parallel to the predicted Africa-Eurasia plate motion direction ($330^{o}$). The P-axes orientation of a single strike-slip event is consistent with the thrust events.
DE: 7215 Earthquake parameters
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting