Geomorphic mapping and ground-penetrating radar survey of the Agua Blanca fault in Valle de Santo Tomas, Baja California, Mexico

The Agua Blanca fault is interpreted as an active, dextral strike-slip fault in northern Baja California about 100 km south from the U.S.-Mexico border. Tectonically, the Agua Blanca fault is associated with the San Andreas fault system, which comprises the main portion of the transform plate boundary between the Pacific and North American plates. Although there are estimated slip rates for the fault, there is no recorded seismicity. Geomorphic maps at a scale of ~ 1:5,000 were completed within the Valle Santo Tomas. Features characteristic of strike-slip faulting such as deflected streams and shutter ridges suggest the fault is still active and should not be considered abandoned. Ground-penetrating radar surveys were conducted in order to image the fault in the near surface. Based on the GPR data, it is apparent that a greater number of fault splays exist in the shallow subsurface than evidenced at the surface. This suggests that the detailed structure of the Agua Blanca fault consists of a complex system of fault splays and that a main fault strand and several subsidiary faults splays exist in Valle Santo Tomas.