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Geofísica internacional
versão On-line ISSN 2954-436Xversão impressa ISSN 0016-7169
Geofís. Intl vol.44 no.4 Ciudad de México Out./Dez. 2005
Articles
Source process and stress change associated with the 11 January, 1997 (Mw=7.1) Michoacán, Mexico, inslab earthquake
1Instituto de Geofísica, UNAM, Ciudad Universitaria, 04510 México D.F., México Email: masantoyo@correo.unam.mx
We study the source characteristics and the associated coseismic stress change of the January 11, 1997 Michoacán earth-quake, based on teleseismic, regional and near-source recordings. This event was located just beneath the ruptured zone of the 1985 Michoacán thrust event. From the inversion of teleseismic recordings, we obtain a nearly-vertical faulting at 35 km depth, a total source duration of 15 sec, a moment magnitude of Mw=7.1, and a mean rupture velocity of 2.8 km/sec. An analysis of teleseismic and local seismograms shows that the rupture had a strong directivity to the southeast, with a rather complex source-time function with two main subevents and a total duration of 13 sec. The dislocation distribution obtained from 2D kinematic linear inversion, using both local strong motion and broad-band teleseismic data, shows a complex rupture pattern with the main seismic moment release occurring in the southwest portion of the fault. A comparison between the coseismic Coulomb failure stress change during the main shock, and the location and mechanism of the aftershocks, suggests that post-event seismicity may have been triggered by the stress changes due to the main event.
KEY WORDS: Kinematic source inversion; Coulomb failure stress; earthquake interaction
Con base en registros sísmicos obtenidos a distancias locales, regionales y telesísmicas, estudiamos las características de la fuente y el cambio de esfuerzos asociado del sismo de Michoacán del 11 de enero de 1997. Este evento fue localizado justo bajo la zona de ruptura del gran sismo de subducción de Michoacán de 1985. De la inversión de datos telesísmicos, obtenemos una falla cercana a la vertical a 35 km de profundidad, con una duración total de la fuente de 15 segundos, una magnitud de momento sísmico Mw=7.1 y una velocidad de ruptura promedio de 2.8 km/seg. El análisis de registros locales y telesísmicos muestra que la ruptura presentó una fuerte directividad al sureste, con una función de tiempo de la fuente compleja, dos subeventos principales y una duración de 13 segundos. La distribución de dislocaciones sobre el plano de falla, obtenida a partir de inversión lineal cinemática 2-D y con datos locales y telesísmicos de banda ancha, muestra un patrón de ruptura complejo donde la mayor parte de la liberación de momento sísmico ocurre en la porción sureste de la falla. La comparación entre los cambios de esfuerzos de Coulomb cosísmicos debido al evento principal, y la localización y el mecanismo focal de sus réplicas, sugiere que la sismicidad post-sísmica pudo haber sido disparada por los cambios de esfuerzos debidos al sismo principal.
PALABRAS CLAVE: Inversión cinemática de la fuente; esfuerzos de Coulomb; interacción de sismos
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Received: January 20, 2005; Accepted: March 17, 2005
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