PRELIMINARY STUDY OF THE FOCAL PROCESS OF THE SEPTEMBER 12, 2009 EARTHQUAKE, LOCATED OFF THE COAST OF WESTERN CENTRAL VENEZUELA, USING BODY WAVES.

Abstract

This study investigates the rupture process of the September 12, 2009 earthquake (latitude: 10,69° N; longitude: 67,87o W; magnitude Mw = 6.3), which occurred in western central Venezuela, off the coast of Morón. Focal mechanisms solution from P and pP polarities shows a strike slip faulting, where one of the nodal planes has strike 272° (east-west orientation), dip 86° and slip angle -172°, and the other one has strike 181° (north-south orientation), dip 82° and slip angle -4°. Body waves show clear directivity effects, that are best explained assuming a rupture that propagated from east to west, implying that the first nodal plane is the fault plane. Using arrival times differences between pP and P phases, an average value of 12 km was obtained for the focal depth. Records of the P, pP, sP, pwP, swP, and multiples of the pwP and swP phases from six broad band stations and of the SH and sSH sismo del 12 de septiembre de 2009 phases from four broad band stations were modeled. To obtain a good fit between the observed and the synthetics records, it was necessary to take into account the topography of the water-crust interface of the epicentral region. The average seismic moment was estimated in 3.47E+18 Nm (6,29 Mw), the rupture length in 8.7 km and the stress drop in 52.5 bars.