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Environmental and Engineering Geoscience

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Proposed Revision of Marine Terrace Extent, Geometry, and Rates of Uplift, Pacific Palisades, California

¹ Exponent Failure Analysis Associates, 320 Goddard Street, Suite 200, Irvine, CA 92618
² URS Corporation, 2020 East First Street, Suite 400, Santa Ana, CA 92705

Marine terrace geometries provide a useful means to interpret the rate and style of uplift along emergent shorelines. In southern California, coastal uplift has been linked to activity on blind thrust or reverse faults. Two marine wave-cut platforms were identified in geotechnical investigations at the Getty Villa museum complex in Pacific Palisades, CA. Reconstruction of the late Quaternary geomorphic history at the Getty Villa allows assignment of the upper platform to the 320 ka oxygen-isotope Stage 9 Malibu terrace of W. M. Davis and P. W. Birkeland. The lower terrace is interpreted to be the 125 ka (Stage 5e) Pacific Palisades platform of J. T. McGill. The wave-cut platforms at the Getty Villa have been uplifted, tilted seaward, and possibly warped. They record late Quaternary uplift at a rate of about 0.3 mm/year and progressive seaward tilting at a rate of about 1°/40 ka since 320 ka. The elevations and geometries of the platforms differ markedly from earlier interpretations, necessitating a reinterpretation of marine terrace geometries throughout much of the Pacific Palisades area. The observed pattern of uplift and tilting suggests the Santa Monica Mountains blind thrust fault of J. F. Dolan and colleagues as the probable source of coastal uplift in this area since 320 ka. Only the central portion of the fault appears significantly active, however. Application of moment magnitude (M) regression equations of Dolan and colleagues indicate that the active portion is capable of generating M 7.0 earthquakes at a recurrence interval of about 6,800 years.

Key Words: Santa Monica Mountains Blind Thrust Fault • Coastal Uplift • Wave-Cut Marine Terrace • Pacific Palisades • Santa Monica Fault