A new estimate of latest Quaternary slip on the offshore Anacapa-Dume Fault at Sycamore Knoll, Southern California Continental Borderland

Ethan F. Williams, Christopher M. Castillo, Simon L. Klemperer, Nicole Raineault, & Lind S. Gee

Published August 16, 2017, SCEC Contribution #7892, 2017 SCEC Annual Meeting Poster #127

At the boundary between the Western Transverse Ranges province and Inner Continental Borderland of Southern California, strain is partitioned across the sinistral-oblique Anacapa-Dume Fault system. As the offshore continuation of the Santa Monica-Raymond Fault system, an improved understanding of the Quaternary slip history of the Anacapa-Dume Fault has key ramifications for seismic hazard in the greater Los Angeles area. Sycamore Knoll, a wave-planed pop-up structure ~20 km west of Point Dume in the hanging wall of the north-dipping Anacapa-Dume Fault, stands out as an anomalous bathymetric high along the Southern California coast. We synthesize new and existing geophysical datasets, including multibeam backscatter/bathymetry and single/multichannel seismic, to study the morphology and tectonic implications of Sycamore Knoll. We identify a complete eustatic low-stand submerged marine-terrace package encircling Sycamore Knoll platform corresponding to the Last Glacial Maximum. The marine-terrace deposits and wave-planed surface of Sycamore Knoll seem to require a maximum late Quaternary uplift rate of 0.55 (+0.5/-0.3) mm/yr relative to sea-level. By combining our uplift rate with previous estimates of basin subsidence and a revised structural model of the Anacapa-Dume Fault, we determine a slip rate in latest Quaternary time of 1.50 (+0.5/-0.3) mm/yr and hence a rate of convergence across the Anacapa-Dume Fault of 0.60 (+0.2/-0.1) mm/yr. We additionally identify a system of radial fault structures cutting the surface of Sycamore Knoll that correlate well to newly mapped hydrocarbon seeps and suggest the potential for slope instability.

Citation
Williams, E. F., Castillo, C. M., Klemperer, S. L., Raineault, N., & Gee, L. S. (2017, 08). A new estimate of latest Quaternary slip on the offshore Anacapa-Dume Fault at Sycamore Knoll, Southern California Continental Borderland. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology