HR: 0800h
AN: S51A-0129    [Abstracts]
TI: Microseismicity Studies in Northern Baja California, Mexico: the Agua Blanca Fault.
AU: * Frez, J
EM: jofrez@cicese.mx
AF: CICESE, P.O. BOX 434843, SAN DIEGO, CA 92143-4843 United States
AU: Acosta, J
EM: jchang@cicese.mx
AF: CICESE, P.O. BOX 434843, SAN DIEGO, CA 92143-4843 United States
AU: Nava, A
EM: fnava@cicese.mx
AF: CICESE, P.O. BOX 434843, SAN DIEGO, CA 92143-4843 United States
AU: Suarez, F
EM: fsuarez@cicese.mx
AF: CICESE, P.O. BOX 434843, SAN DIEGO, CA 92143-4843 United States
AU: Gonzalez, J
EM: javier@cicese.mx
AF: CICESE, P.O. BOX 434843, SAN DIEGO, CA 92143-4843 United States
AU: Arellano, G
EM: garellan@cicese.mx
AF: CICESE, P.O. BOX 434843, SAN DIEGO, CA 92143-4843 United States
AU: Carlos, J
AF: CICESE, P.O. BOX 434843, SAN DIEGO, CA 92143-4843 United States
AU: GarcĦa, R
EM: arthur@cicese.mx
AF: CICESE, P.O. BOX 434843, SAN DIEGO, CA 92143-4843 United States
AU: Alvarez, M
AF: PASSCAL INSTRUMENT CENTER, NEW MEXICO TECH, 100 EAST ROAD, SOCRRO, NM 87801 United States
AB: The Agua Blanca fault is major, conspicuous, well-defined, right-lateral strike-slip fault with a minor vertical component that extends from the Punta Banda Peninsula near Ensenada, in northern Baja California, to the San MatĦas Pass on the Main Gulf Escarpment. Regional catalogs from both the SCSN and RESNOM (ML $>$ 2.1) show an essentially inactive fault; however, some minor seismicity in the Punta Banda Peninsula and a clustered activity in Valle de la Trinidad, near the NW and SE ends of the fault, in addition of some scattered activity in between could be associated with it. It has been suggested that the Agua Blanca fault was originally related with the subduction of the Farallon plate. Besides, the fact that the fault cuts granitic intrusives together with results from trench studies indicate that the fault might be currently active. A detailed microseismicity survey of the Agua Blanca fault was carried out during two months in 2001 with 41 Reftek stations. About 140 very small events (ML $<$ 2.1) were located near the fault; most of them (103, depths mostly between 8 and 13 km, strongly clustered) are associated with Valle de la Trinidad. Less than 20 epicenters with depths mostly between 8 and 16 km, are less than 3 km from the fault surface trace, all of them at its central part. Focal mechanism determinations show mainly strike slip and normal solutions indicating a tensional regime, with a near N-S compressional axis, a result which agrees with those of our previous microseismicity studies in northern Baja California. Apart from earthquakes at the Valle de la Trinidad and a few epicenters located very near to the fault trace, the rest of them is scattered to the south of the Agua Blanca fault and in between this fault and the San Miguel fault system. These results indicate that there is important microseismic activity which is not associated with mapped faults in northern Baja California. In conclusion, our two month-long survey extends the picture of a relatively inactive (ML $>$ $\sim$0.8) Agua Blanca fault given by data from regional seismicity catalogs.
DE: 7230 Seismicity and seismotectonics
DE: 7205 Continental crust (1242)
DE: 1242 Seismic deformations (7205)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting