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Neotectonics of the San Diego Trough and Coronado Bank fault systems, Inner California Borderlands

Jayne M. Bormann, Graham M. Kent, Neal W. Driscoll, Alistair J. Harding, James J. Holmes, Valerie J. Sahakian, & Steven G. Wesnousky

Submitted August 2014, SCEC Contribution #7984

Geodetic data indicate that faults offshore of Southern California currently accommodate 6-8 mm/yr of dextral Pacific-North American relative plate motion. In the Inner California Borderlands (ICB), modern strike-slip deformation overprints a prominent system of basins and ridges that formed during plate boundary reorganization 30-15 Ma. Despite its proximity to densely populated Southern California, the hazard posed by faults in the ICB remains poorly understood due to unknown fault geometry and loosely constrained slip rates.

The San Diego Trough fault and Coronado Bank fault systems are northwest striking, sub-parallel, right-lateral faults within the ICB system. We use reprocessed legacy 2D multichannel seismic (MCS) reflection data, newly acquired high-resolution 2D MCS reflection data, and multibeam bathymetry to constrain the architecture and evolution of these faults. We interpret the MCS data using a sequence stratigraphic approach to establish a chronostratigraphy and determine the relative recency of slip for the San Diego Trough and Coronado Bank fault systems.

Our new data refine assumptions about fault geometry and slip rates made in previous models of ICB deformation. Linear troughs that cut bathymetric highs along the trace of the Coronado Bank fault are geomorphic indicators that the fault has accommodated right-lateral strike slip deformation in the past. However, the MCS data show that younger, undeformed marine sediments onlap the bathymetric highs, which suggests that slip on the Coronado Bank fault has decreased over time. Additionally, a thick package of undeformed Late Pliocene sediments overlies the northern extent of the Coronado Bank fault; therefore, slip rate estimates based on kinematic linkage with the Holocene active Palos Verdes fault are unwarranted. To the west of the Coronado Bank fault, the San Diego Trough fault offsets young sediments between the US/Mexico border and the eastern margin of Avalon Knoll, where the fault is spatially coincident with the mapped trace of the San Pedro Basin fault. The length, linearity, and simplicity of the San Diego Trough fault trace suggest that this fault may accommodate a significant amount of modern ICB dextral deformation. Possible kinematic linkage between the San Diego Trough and San Pedro Basin faults increases the potential rupture length for earthquakes on either fault and may allow events nucleating on the San Diego Trough fault to propagate much closer to the LA Basin.

Bormann, J. M., Kent, G. M., Driscoll, N. W., Harding, A. J., Holmes, J. J., Sahakian, V. J., & Wesnousky, S. G. (2014, 08). Neotectonics of the San Diego Trough and Coronado Bank fault systems, Inner California Borderlands. Poster Presentation at 2014 SCEC Annual Meeting.