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Structural Geometry and Slip of the Palos Verdes Fault, Southern California: Implications for Earthquake Hazards

Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street Cambridge, Massachusetts 02138 brankman{at}fas.harvard.edu

The Palos Verdes fault (PVF) is an active structure in southern California comprised of several segments that together form a complex fault system. The fault has been active since the Miocene and is a major regional seismic source. Using marine petroleum industry seismic data, we define the geometry of the fault and offsets of Tertiary stratigraphic units that constrain the along strike segmentation and slip rates on the fault system. In San Pedro Bay, patterns of deformed stratigraphic units suggest a deep fault geometry that dips moderately to the southwest and was initially formed as a Miocene normal fault. Plio–Pleistocene transpression resulted in the reactivation of this normal fault and its subsequent inversion with oblique, right-lateral reverse displacement. To the south, the Lasuen Knoll segment dips steeply to the northeast and is not a reactivated Miocene-age structure but rather formed in middle Pliocene time. Plio–Pleistocene transpression has linked these and other segments together to form the currently active PVF system. The resulting complex fault geometry and slip patterns suggest that the PVF is a highly segmented fault, which may rupture in moderate-size earthquakes that involve individual segments or large events that are able to propagate across significant geometric discontinuities. Estimates of moment magnitudes based on empirical relationships with rupture (fault) area indicate the possibility of M_w 6.6–6.9 earthquakes for single-segment ruptures and M_w 7.1–7.3 multisegment ruptures, with recurrence intervals ranging from 181 to 534 yr. Given the high inferred slip rates on the fault and its proximity to the urban population, these events pose significant earthquake hazards to metropolitan Los Angeles.