HR: 1340h
AN: S43A-1053    [Abstracts]
TI: Microseismicity Studies in Northern Baja California: The Sierra Juárez Fault System
AU: * Frez, J
EM: jofrez@cicese.mx
AF: Centro de Investigacion Cientifica y Educacion Superior de Ensenada, POB 434843, San Diego, CA 92143 4843,
AU: Gonzallez, J
EM: javier@cicese.mx
AF: Centro de Investigacion Cientifica y Educacion Superior de Ensenada, POB 434843, San Diego, CA 92143 4843,
AU: Nava, F
EM: fnava@cicese.mx
AF: Centro de Investigacion Cientifica y Educacion Superior de Ensenada, POB 434843, San Diego, CA 92143 4843,
AU: Acosta, J
EM: jchang@cicese.mx
AF: Centro de Investigacion Cientifica y Educacion Superior de Ensenada, POB 434843, San Diego, CA 92143 4843,
AU: Carlos, J
EM: jaime@cicese.mx
AF: Centro de Investigacion Cientifica y Educacion Superior de Ensenada, POB 434843, San Diego, CA 92143 4843,
AU: Garcia-Arthur, R
EM: arthur@cicese.mx
AF: Centro de Investigacion Cientifica y Educacion Superior de Ensenada, POB 434843, San Diego, CA 92143 4843,
AB: The Sierra Juarez is one of the major, well defined, and active fault systems of northern Baja California. During two months of 2002, we installed 30 seismological stations (digital, three-components, Reftek instruments) between latitudes 31.6º N and 32.2º N, surrounding the most active part of this system as well as the SE segment of the San Miguel fault and the region in between. Almost half of the stations were installed in the Laguna Salada basin, located East of Sierra Juarez ranges and 1500 m below them. Observations resulted in 4200 high-quality hypocenter and ~500 focal mechanism determinations; magnitudes and rupture planes are still to be determined. For locating we use the Nava and Brune (1982) seismic structure, complemented with station residuals which are small and negative for stations located in the Sierra ranges. For stations installed in the Laguna Salada basin, residuals vary between 0.30s and -0.15s, with the exception of three sites where mean residuals reach -.50s. Seismic activity occurs either aligned (SE segment of the San Miguel fault) or in small clusters with radii ~1.5 km (elsewhere). Predominant depths are around 10 km with a secondary maximum at 5 km. Focal mechanism solutions show a consistent pattern which is common for all northern Baja California, with predominant strike-slip (a nodal plane striking in a NW-SE direction) and normal (T-axes mostly in EW direction) solutions. This pattern is interpreted as a transtensive regime consisting of strike-slip faults intercalated with extension zones; this pattern seems to be repeated at various scales. Also discussed are other details, like the interpretation of normal faulting in the scarp separating the Sierra Juarez ranges from the Laguna Salada basin, the dip of the fault planes, and interpretation of travel time residuals
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: 2007 Fall Meeting