Teleseismic body-wave analysis of the 9 October, 1995 (Mw = 8.0), Colima-Jalisco, Mexico earthquake, and its largest foreshock and aftershock

Abstract

The source process of the October 9, 1995, Colima-Jalisco, Mexico, earthquake (Mw=8.0), and its largest foreshock and aftershock were determined from teleseismic body waves, using a least-squares inversion scheme. The three events are shallow-dipping, thrust-fault earthquakes, in agreement with the relative plate motions for Rivera-North America and Cocos-North America plate boundaries. Neither the foreshock nor the largest aftershock show significant differences in focal mechanism nor centroidal depth with respect to the average mechanism of the mainshock. The rupture of the mainshock began near the foreshock hypocenter and propagated, with a variable rupture velocity, towards the NW. The source-time function for this event shows four distinct episodes of energy release. About 50% of the moment was released at the northern end of the rupture, between 90 and 110 km from the epicenter. This rupture geometry is in agreement with crustal deformation observed inland using GPS measurements. However, the scalar seismic moment of the main shock obtained in this study (Mo=1.84×1020) is smaller with respect to the lower frequency CMT results reported by Harvard (Mo=1.15×1021).