New Kinematic Model for the Palos Verdes and San Pedro Basin Fault Zones in Santa Monica Bay, Offshore Southern California

Hogan, Phillip J.¹, Aaron Broughton¹, Kevin Smith¹, Mark Legg², Tom McNeilan¹, Robert R. Male³ (1) Fugro West, Ventura, CA (2) Legg Geophysical, Huntington Beach, (3) Woodside Natural Gas, Inc, Santa Monica, CA

High resolution seismic and geotechnical data collected for Woodside's OceanWay LNG project allow an improved understanding of the offshore Palos Verdes and San Pedro Basin fault zones in Santa Monica Bay. Both faults offset Latest Pleistocene and likely Holocene strata. A broad zone of deformation exists from the Shelfbreak down to the base of slope at the northeast margin of Santa Monica Basin.

The Palos Verdes fault zone on Santa Monica Shelf offshore LAX exhibits transtensional structures, including numerous left-stepping en echelon horsts and grabens. Farther north, the main trace of the Palos Verdes fault bends towards the west, more closely paralleling the structural grain of the Transverse Ranges to the north. The San Pedro Basin fault exhibits transpressional features, including popups and growth folding in late Quaternary strata.

The prehistoric Los Angeles River deposited a thick offlapping sequence of deltaic strata in northeastern Santa Monica Bay, which were subsequently cut by NW-trending strike-slip faults. Santa Monica Shelf was beveled off during glacially lowered sea levels 16-20k yBP. The beveled upper surface of the deltaic sequence is overlain by an undeformed coarse gravel layer deposited by the prehistoric Los Angeles River. The top of the pre-Holocene gravel marker horizon is not offset or disrupted by faults underlying most of the mainland shelf.

The collisional boundary of the Peninsular Ranges and Continental Borderland Provinces with the Transverse Ranges Provinces is thus characterized by both transpressional and transtentional structures on Santa Monica Shelf and Slope. A new kinematic model for this area is presented.