TAILIEUCHUNG - Source investigation of a small event using empirical Green’s functions and simulated annealing

We propose a two-step inversion of three-component seismograms that ( 1) recovers the far-field source time function at each station and (2) estimates the distribution of co-seismic slip on the fault plane for small earthquakes (magnitude 3 to 4). The empirical Green’s function (EGF) method consists of finding a small earthquake located near the one we wish to study and then performing a deconvolution to remove the path, site, and instrumental effects from the main-event signal. The deconvolution between the two earthquakes is an unstable procedure: we have therefore developed a simulated annealing technique to recover a stable and positive source time function (STF) in the time domain. | Geophys. J. Int. 1996 125 768-780 Source investigation of a small event using empirical Green s functions and simulated annealing F. Courboulex 1 J. Virieux 1 A. Deschamps 1 D. Gibert2 and A. Zollo3 1 Geosciences Azur Université de Nice-Sophia Antipolis Rue A. Einstein 06560 Valbonne France 2 Geosciences Rennes I Avenue General Leclerc 35042 Rennes cédex France 3 Department di Geofisca e Vulcanoỉogia Università di Napoli Italy Accepted 1996 January 23. Received 1996 January 23 in original form 1994 October 21 SUMMARY We propose a two-step inversion of three-component seismograms that 1 recovers the far-field source time function at each station and 2 estimates the distribution of co-seismic slip on the fault plane for small earthquakes magnitude 3 to 4 . The empirical Green s function EGF method consists of finding a small earthquake located near the one we wish to study and then performing a deconvolution to remove the path site and instrumental effects from the main-event signal. The deconvolution between the two earthquakes is an unstable procedure we have therefore developed a simulated annealing technique to recover a stable and positive source time function STF in the time domain at each station with an estimation of uncertainties. Given a good azimuthal coverage we can obtain information on the directivity effect as well as on the rupture process. We propose an inversion method by simulated annealing using the STF to recover the distribution of slip on the fault plane with a constant rupture-velocity model. This method permits estimation of physical quantities on the fault plane as well as possible identification of the real fault plane. We apply this two-step procedure for an event of magnitude 3 recorded in the Gulf of Corinth in August 1991. A nearby event of magnitude 2 provides US with empirical Green s functions for each Station. We estimate an active fault area of to km2 and deduce a stress-drop value of 1 to 30 bar and an average slip of .

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