ESTUDIO PRELIMINAR DEL PROCESO FOCAL DEL SISMO DEL 12 DE SEPTIEMBRE DE 2009, OCURRIDO FRENTE A LA COSTA CENTRO OCCIDENTAL DE VENEZUELA, UTILIZANDO ONDAS DE CUERPO
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Universidad Industrial de Santander
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Se investiga el proceso de ruptura del sismo del 12 de septiembre de 2009 (latitud: 10,69° N; longitud: 67,87° O; magnitud: Mw 6,3), ocurrido en la región centro-occidental de Venezuela, frente a la costa de Morón. A partir de polaridades P y pP se construyó el mecanismo focal que muestra un tipo de fallamiento rumbo-deslizante, con un plano nodal de rumbo 272° (orientación este-oeste), buzamiento 86° y ángulo de deslizamiento -172°, y otro plano de rumbo 181° (norte-sur), buzamiento 82° y ángulo de deslizamiento -4°. Los efectos de directividad, claramente observados en las ondas de cuerpo, permitieron determinar que el plano de falla es el de orientación este-oeste y que la ruptura se propagó en sentido de este a oeste. Usando la diferencia temporal de las llegadas entre la fases pP y P se obtuvo un valor promedio para la profundidad focal de 12 km. Se modelaron las señales correspondientes a las fases P, pP, sP, pwP, swP, y múltiples de la pwP y de la swP de seis estaciones banda ancha y las correspondientes a las fases SH y sSH de cuatro estaciones banda ancha. Para ajustar las señales sintéticas con las registradas fue necesario tomar en cuenta la topografía de la interfase agua-corteza de la región epicentral. El momento sísmico promedio se estimó en 3,47E+18 Nm (6,29 Mw), la longitud de ruptura en 8,7 km y la caida de esfuerzos sísmicos en 52,5 bars.
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.
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.
Keywords
Morón, seismic moment, focal mechanism, directivity, Morón, momento sísmico, mecanismo focal, directividad