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Source investigation of a small event using empirical Green's functions and simulated annealing |
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| Authors: | F Courboulex J Virieux A Deschamps D Gibert A Zollo |
| Institution: | Géosciences Azur, Universitéde Nice-Sophia Antipolis, Rue A. Einstein, 06560 Valbonne, France;Géosciences, Rennes I, Avenue Général Leclerc, 35042 Rennes cédex, France;Departmento di Geofisca e Vulcanologia, Universitàdi Napoli, Italy |
| Abstract: | 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 0.02 to 0.15 km |
| Keywords: | Green's functions inversion Patras source time functions |