Paleoseismic Insights from Submarine Mass Transport Deposits in the San Nicolas Basin

Andrea Fabbrizzi, Alicia Sigworth, & Jillian M. Maloney

Submitted September 7, 2025, SCEC Contribution #14512, 2025 SCEC Annual Meeting Poster #TBD

The San Nicolas Basin, extending ~80×60 km and oriented N46°W, is aligned sub-parallel to the regional tectonic fabric of the Outer California Borderland. The northern margin displays an arcuate geometry, indicative of potential structural control by the East Santa Cruz Basin fault, whereas the relatively straight western margin suggests control by the Ferrelo fault zone. Novel high-resolution geophysical data acquired during cruise SR2502, including multibeam bathymetry and sub-bottom profiles, reveal a complex interplay between tectonic deformation and sedimentary processes shaping the basin floor. Analysis of these datasets has identified at least nine minor, repeated submarine mass transport deposits (MTDs) and one major near-surface landslide, referred to as the San Nicolas Slide, interbedded with hemipelagic sediments. These MTDs are interpreted as the result of earthquake-induced slope failure, providing a basis for reconstructing a paleoseismic record since the late Pleistocene. Spatial and temporal patterns of MTD emplacement suggest that both regional fault systems and local sources influenced slope instability. Evidence for quasi-instantaneous deposition of MTDs, associated with fault displacement and proximity to tectonic structures, supports a relationship between seismic ground shaking and submarine landslide initiation. These preliminary findings highlight the potential for applying “turbidity paleoseismology” across the Outer California Borderland. Ongoing and future work will include improved age constraints, as well as sedimentological and physical property analyses of core samples, to correlate dated events across adjacent basins. This approach offers new insights into the seismic history and geohazard potential of the Outer California Borderland.

Key Words
Fault-related landslides, Slope failure, California Borderland, San Nicolas Basin

Citation
Fabbrizzi, A., Sigworth, A., & Maloney, J. M. (2025, 09). Paleoseismic Insights from Submarine Mass Transport Deposits in the San Nicolas Basin. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Plate Boundary System (PBS)