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Strike slip tectonics in the Inner California Borderlands, Lasuen Knoll, and the southern termination of the Palos Verdes fault

Jayne M. Bormann, Graham M. Kent, Neal W. Driscoll, & Alistair J. Harding

Submitted August 2015, SCEC Contribution #7981

Lasuen Knoll is a prominent bathymetric high in the Inner California Borderlands (ICB) that is bounded on the west by the northwest striking, right-lateral Palos Verdes fault. Lasuen Knoll is commonly interpreted to be a northwest trending, westward verging anticline that formed as a result of oblique right-lateral reverse slip on the northeast dipping, southernmost section of the Palos Verdes fault. However, interpretations of ICB structure are complicated by the overprinting of modern strike-slip deformation on topography formed as a result of large-scale extension and rotation during plate boundary reorganization 30-15 Ma and limited by the distribution of geophysical datasets.

We present observations from a focused, high-resolution 2D multichannel seismic (MCS) reflection and multibeam bathymetric survey to constrain the architecture of and tectonic evolution of Lasuen Knoll. We supplement our data with industry and USGS MCS surveys. We use sequence stratigraphy to identify discrete episodes of deformation in the MCS data and present the results in a fault map and tectonic model of the Palos Verdes fault, Lasuen Knoll, and the Carlsbad Ridge fault to the southeast.

We interpret the most recent deformation at Lasuen Knoll to result from right-lateral slip at the southern termination of the Palos Verdes fault. Mapping of structures within Lasuen Knoll shows an east-west trending series of compressional folds and faults thrusting sediments southward on to a preexisting structural high that extends more than 20 km southeast from Lasuen Knoll. The western margin of compressional deformation is sharply bounded by the Palos Verdes fault, with no evidence of compressional deformation southwest of the fault. South of Lasuen Knoll, the Palos Verdes fault becomes difficult to distinguish in the seismic data, suggesting that compressional deformation at Lasuen Knoll is related to the southern termination of the fault. The structural high that underlies Lasuen Knoll is bounded on its southeastern margin by the inactive Carlsbad Ridge fault. We interpret this structural high to be formed in part by a compressional, left-lateral stepover between the two strike slip fault systems. We acknowledge that the orientation of strike-slip faults in the ICB is likely influenced by inherited basement topography, and we conclude that modern fault geometry and plate boundary kinematics enhance this topographic structure at Lasuen Knoll.

Bormann, J. M., Kent, G. M., Driscoll, N. W., & Harding, A. J. (2015, 08). Strike slip tectonics in the Inner California Borderlands, Lasuen Knoll, and the southern termination of the Palos Verdes fault. Poster Presentation at 2015 SCEC Annual Meeting.