Characteristics of seismicity in the coast and north of Jalisco Block, Mexico

Several studies of local seismicity were carried out between 1996 and 1998 on the coast and north of the Jalisco Block (JB) using a portable seismic network consisting of five Lennartz M88 seismographs with Le 3D (1 Hz) seismometers. The data from these studies, complemented with data from RESCO (Colima Seismic Network), is used to characterize three seismogenic zones in the region. One seismicity zone, located east of the Middle America Trench (MAT), under the continental plate, is associated with the interaction of the Rivera and North America plates, and can be characterized as a Double Seismic Zone (DSZ) with geometry suggesting a bending plate and, probably, oblique subduction; this pattern is clearer south of the 20°N parallel. A second zone of continental intraplate seismicity is located between Ameca and Amatlan de Canas, in the northeastern part of the study region, where the source depths vary from very shallow to about 35 km. The third zone is Bahia de Banderas where the stress pattern seems to be very complex; here we observe different types of seismic events: the first type consists of shallow events, located in the southern part of the Bay and a under continental area, that seems to be associated with the interplate (Rivera/North America) activity. A second event type with depths between 10 and 30 km, seems to be related to features that cross the Bay in an EW direction. In this zone, there is also a high shallow continental seismicity, which agrees with continental topographic features.