HR: 0800h
AN: T51D-1375    [Abstracts]
TI: Multiphase Deformational History, Kinematics, and Segmentation of the Palos Verdes Fault, Offshore Southern California
AU: * Brankman, C M
EM: brankman@fas.harvard.edu
AF: Dept of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Shaw, J H
EM: shaw@eps.harvard.edu
AF: Dept of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AB: The Palos Verdes Fault (PVF) forms the western boundary of the Los Angeles basin, California, and has one of the highest slip rates in the region, indicating that it may be a source of future large earthquakes. Using a dense grid of petroleum industry seismic reflection data and exploration well logs, we have mapped a series of stratigraphic horizons in San Pedro Bay south of the peninsula that we use to invert for permissible underlying fault geometries and displacements. The PVF is composed of several discrete but related segments which together reflect a complex and multiphase evolution of the fault system. Directly south of the Palos Verdes Peninsula, imaged hanging wall and footwall fault cut-offs indicate that at depths below about 5km the fault dips moderately to the southwest. Furthermore, a thick sequence of eastward-thickening Miocene strata west of the fault suggests that the PVF originally formed as a normal fault during Miocene extension/transtension. Contractional folding of younger strata, as well as structural duplication of the crystalline basement surface, indicates that the normal fault was subsequently inverted during Plio-Pleistocene transpression. In the upper 3-4 km, the fault is nearly vertical, presumably accommodating right-lateral strike-slip displacement. Approximately 20 km southeast of the Peninsula, the PVF changes character across a major geometric segment boundary as a second fault segment emerges and continues trending southeast. The second segment dips northeast and shows increasing reverse displacement along strike to the southeast. Growth strata in the hanging wall and emergent sea-floor folds indicate that contractional deformation began in Pliocene time and continues to the present. The varying geometry and structural character of the PVF along strike reflect the earlier structural elements which have been reactivated to form the present fault geometry. Furthermore, the segmentation of the PVF may impact hazard estimates in one of two ways: by restricting coseismic rupture and thus limiting maximum earthquake magnitude, or by rupturing on a series of discrete but interrelated fault segments to produce a more complex rupture than current hazard models consider. The non-vertical dip of the PVF at depth, and the dip-slip components of motion, may cause coseismic ground shaking that would differ from those produced by a simply, vertical strike-slip fault.
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
SC: Tectonophysics [T]
MN: Fall Meeting 2005