SEISMOTECTONICS OF JALISCO BLOCK, MEXICO

The Jalisco Block (JB) is one of the most complex tectonic areas in Mexico and one of less studied from a seismic point of view. By these between 1996 and 1998 several studies of local seismicity were carried out in the Coast and North of JB using a portable seismic network, we use these data complemented with data from RESCO Network to characterize at least four seismogenic zones in the region. One interplate seismicity zone which geometry suggest an oblique subduction, this is more clear at South of parallel 20°N. A second seismicity zone is observed in an area that seems to correspond to the bottom of the Rivera plate and the upper part of the oceanic mantle, this is also observed between 19° N and 20° N; these two zones are located at the East of the MAT, below of the continental plate. A third zone of continental intraplate seismicity located between Ameca and Amatlan de Canas where the depth of the events varies from very shallow to 35 km. The fourth zone is Bahía de Banderas(BB) where the stress pattern seems to be very complex, here we observe different types of seismic events: the first type are shallow events located at south of BB and under El Tuito area that seems to be associated to the interplate activity; a second type of events with depth between 10 and 45 km that seems to be related with features that cross BB in EW direction. In this zone we also observe shallow continental seismicity which agrees with continental structural features, on the basis of location and waveform of these events we identify three different families of seismos for these type of seismicity. In April 2002 began to transmit the stations of the first phase of Jalisco Telemetric Network located at the northwest of JB and at the area of Colima Volcano. The data of these stations jointly with the data from RESCO give us the minimum seismic stations coverage to initiate in a systematic and permanent way the study of the seismicity in this very complex tectonic region. A preliminary analysis of seismicity by the network confirms important features proposed by the microseismicity. Shallow seismicity at south and east of BB also suggest a complex stress pattern in this region of the JB, events at more than 30 km depth are located under the mouth of the bay and in face of it, a feature denominated Banderas Boundary mark the change of the seismic regime at north of this latitude (20.75°N).