--> --> Abstract: Geomorphic Mapping and Ground-Penetrating Radar Survey of the Western Segment of the Agua Blanca Fault, Baja California, Mexico, by S. R. Madsen and H. Alsleben; #90087 (2009).
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Geomorphic Mapping and Ground-Penetrating Radar Survey of the Western Segment of the Agua Blanca Previous HitFaultNext Hit, Baja California, Mexico

S. R. Madsen and H. Alsleben
Texas Christian University

The WNW-ESE trending Agua Blanca Previous HitfaultNext Hit, which is associated with the North American – Pacific plate boundary, traverses Baja California, Mexico near latitude 31º30’N for approximately kilometers and is commonly interpreted as a dextral strike-slip Previous HitfaultNext Hit. The Previous HitfaultNext Hit is divided into three right-stepping, 40 kilometers long segments. The westernmost segment, our study area, comes onshore at Punta Banda Ridge and bounds the southern edge of Valle Maneadero. A lack of recent seismicity along the Previous HitfaultNext Hit zone contrasts global positioning system data that supports slip rates of 3-4 millimeters per year.

Geomorphic expressions of the Previous HitfaultNext Hit suggest recent Previous HitfaultNext Hit activity and zones of highly-fractured rocks with intermittent zones of breccia and gouge better constrain the location of the main Previous HitfaultNext Hit trace, which juxtaposes Cretaceous beach deposits or Quaternary alluvium with Cretaceous volcanics. Although the geomorphology supports simple dextral motion, kinematic indicators suggest an additional normal-oblique component along the Previous HitfaultNext Hit.

To characterize the near-surface structure of the Previous HitfaultNext Hit zone, we completed 20 ground-penetrating radar transects across apparently faulted areas. This method reveals unexposed structural and stratigraphic relationships beneath the surface. Using 100 MHz antennas, depth penetration of 3-5 meters was achieved and potentially recently offset stratigraphic markers were recognized.

Our study shows that the western segment of the Agua Blanca Previous HitfaultNext Hit is an active, dextral-normal oblique Previous HitfaultNext Hit. The WNW-ESE orientation and the dextral-normal displacement make this Previous HitfaultNext Hit unique in this plate boundary system. We infer that the Previous HitfaultTop is currently accumulating strain and is likely to experience seismic activity in the future.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas