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Seismicity and Stress in a Tectonically Complex Region: The Rivera Fracture Zone, the Rivera–Cocos Boundary, and the Southwestern Jalisco Block, Mexico

Centro de Sismología y Volcanología de Occidente-SisVOc , Universidad de Guadalajara–Centro Universitario de la Costa, Avenida Universidad 203, Puerto Vallarta, Jalisco 48280, México jjsanchez{at}pv.udg.mx fcornu{at}pv.udg.mx

Fault plane solutions for a group of 41 4.9M_w8.0 earthquakes between November 1980 and May 2007, extracted from the Global Centroid Moment Tensor Project catalog, are used to investigate spatial and temporal variations of stress in the south part of the Jalisco block (JB). Using rigorous statistical tests we decide on the quality and variability of the earthquake mechanisms and with the use of stress tensor inversion and cumulative misfit analysis find, at the 95% confidence level or more, significantly different regions and periods of stress regime. We conclude that the region located near (105° W, 18.43° N) appears as a particularly diffuse zone affected by various stress styles and that the period following the great M_w 8.0 earthquake on 9 October 1995 appears as a short-lived change in stress induced by the great shock. An important difference in seismicity and stress between the southern and northern regions is highlighted by the regular occurrence of earthquakes south of the JB, in stark contrast with the scarcity of seismicity with M_w>4.9 north of 19.36° N, a region that is illuminated with microseismicity when local temporal or permanent deployments of seismographs are used, as noted by previous studies.