High-resolution seismic reflection data obtained across the Santa Monica fault in west Los Angeles reveal the near-surface geometry of this active, oblique-reverse-left-lateral fault. Although near-surface fault dips as great as 55?? cannot be ruled out, we interpret the fault to dip northward at 30?? to 35?? in the upper few hundred meters, steepening to ???65?? at 1 to 2 km depth. A total of ???180 m of near-field thrust separation (fault slip plus drag folding) has occurred on the fault since the development of a prominent erosional surface atop ???1.2 Ma strata. In the upper 20 to 40 m strain is partitioned between the north-dipping main thrust strand and several closely spaced, near-vertical strike-slip faults observed in paleoseismologic trenches. The main thrust strand can be traced to within 20 m of the ground surface, suggesting that it breaks through to the surface in large earthquakes. Uplift of a ???50,000-year-old alluvial fan surface indicates a short-term, dip-slip rate of ???0.5 mm/yr, similar to the ???0.6 mm/yr dip-slip rate derived from vertical separation of the oxygen isotope stage 5e marine terrace 3 km west of the study site. If the 0.6 mm/yr minimum, dip-slip-only rate characterizes the entire history of the fault, then the currently active strand of the Santa Monica fault probably began moving within the past ???300,000 years. Copyright 1997 by the American Geophysical Union.
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High-resolution seismic reflection profiling of the Santa Monica Fault Zone, West Los Angeles, California