Geologic mapping and ground-penetrating radar surveys of the Valle Santo Tomas segment of the Agua Blanca Fault, Baja California, Mexico

The Valle Santo Tomas is situated on a segment of the Agua Blanca fault (ABF) which is an ∼130 km WNW-ESE trending dextral strike-slip fault within the Pacific-North American (PAC-NAM) plate boundary. Although the ABF is thought to be active, evidence for recent seismic activity is scarce. In the Valle Santo Tomas geologic, geomorphic, and ground-penetrating radar (GPR) surveys were conducted to evaluate the fault segment for features that demonstrate recent movement. Features such as shutter ridges, diverted streams and fault scarps are observed and interpreted to indicate some degree of recent movement. The GPR survey further supports that the fault exists in the shallow subsurface as evidenced by offset beds, rotated hanging wall blocks and a negative flower structure indicating some degree of recent transtensional movement along the Valle Santo Tomas segment of the ABF.