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[1] A regional west striking system of surface and blind faults transects northern metropolitan Los Angeles, separating the Santa Monica Mountains from two deep sedimentary basins. The surface faults include the Santa Monica, Dume, and Malibu Coast faults. The three-dimensional (3-D) geometries of these faults and deformed dated strata were examined in order to determine how oblique shortening is accommodated, how structural relief grows along a mountain front, and how block translation is related to block rotation. Industry seismic reflection, well, and outcrop data were used to construct digital structure-contour maps of several of these faults and three stratigraphic horizons that intersect them. These maps, swath bathymetry, digital elevation models, and seismicity were incorporated into a 3-D digital database. Modeling included new approaches to determining strike-slip displacement by separate analyses of shortening and structural relief in a restraining double bend. Stratigraphic thicknesses indicate Miocene extension across the Santa Monica and Dume faults, which have been reactivated as a single or linked moderately dipping arcuate fault that accommodates one coherent block motion via left-lateral and left-reverse displacement. Modeling indicates 5 km (+8/À1 km) of left-lateral displacement on part of the Santa Monica-Dume fault and $11°of clockwise rotation of the Santa Monica Mountains during the last $4 ± 1 m.y. Modern displacement rates modeled from GPS data are similar to our modeled post-$4 Ma rates of westward escape and clockwise rotation of the Santa Monica Mountains.

The Palos Verdes anticlinorium (PVA) is a 70 km‐wide, NW‐trending Pliocene‐Quaternary transpressional high that separates the onshore Los Angeles basin from the offshore San Pedro basin. The PVA southwest limb underlies a 70 km‐long SW facing seafloor escarpment. This escarpment is separated into two segments by a 6 km right step. It overlies two levels of NE dipping low‐angle thrust faults. These faults project beneath Los Angeles toward known SW verging blind thrust faults and may be the same regional faults. These conclusions are based on a detailed geometric representation constructed from a regional analysis of 5000 km of multichannel seismic reflection profiles, logs, and paleontology from 19 wells, published seafloor geology, and multibeam bathymetric data. Patterns of sedimentation and erosion indicate that folding of PVA initiated during Pliocene time and propagated southward, with folding of part of the southern PVA occurring during the Quaternary. Structural relief continues to grow with regional long‐term rock uplift of the PVA crest and ongoing subsidence in the adjacent basins. The low‐angle NE‐dipping faults beneath the PVA must be late Quaternary active in order to maintain hanging wall rock uplift above subsiding footwalls. Structural geometry requires that the underlying faults have slipped at 1.1–1.6 mm/yr over Quaternary time.

Linking beach tar with sources in a complex natural marine seepage area presents numerous challenges. Efforts at Coal Oil Point (COP), CA included beach tar distribution surveys, oil slick tracking, sampling, and chemical analysis, underwater scuba surveys, aerial surveys, and numerical modeling. Despite a wind from the east and current to the west, a slick was tracked initially north from its source, presumably due to spreading, then it drifted east, ending in a kelp bed off COP. Sample chromatograms showed mixing with another oil slick by the appearance of a heavier series of n-alkane peaks where the trajectory changed direction. Trajectory simulations suggested that interface currents were poorly described by parameterizations of wind and surface currents, and/or the existence of small-scale circulations not resolved by CODAR or the drift buoy. Detailed tar accumulation surveys covered 175-m (4400 m2) of COP beach where tar accumulation generally is greatest. Maximum total beach tar observed was 1.5 kg, with significant variability. Modeling suggested a similar source location for the three analyzed surveys. Analysis also suggested kelp canopies can play a significant roll in the arrival time and location of beach tar by blocking onshore transport. However, wind, current, and kelp conditions were such that much of the variability in tar accumulation for these surveys probably was from source emission variability.

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