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Revised Offshore Mapping of Fault and Fold Deformation Associated with the Hosgri Fault Zone, the Point Buchon Fault and the Shoreline Fault

We present updated structural geologic mapping of fault-related deformation offshore San Luis Obispo Co., California.

23 Apr 2015
Michael Angell, Michael Buga, Jamey Turner, Janet Sowers, Stuart Nishenko


This effort builds on previous mapping conducted in 2012 (PG&E, 2014) with focus on characterizing linkages among the Hosgri Fault Zone (HFZ), Shoreline Fault (SLF), and the Point Buchon Fault (PBF), and deformation between the HFZ and the SLF and PBF. The datasets used for this revised map are two high energy exploration seismic surveys COMAP -1986; GSI-85), and three low energy, shallow (300 ms) high-res surveys (2010 USGS HR2D; 2011 PG&E HR2D; and 2011 PG&E HR3D). The previous mapping used only the 2010-2011 data. The N25°W-trending HFZ and the N67°W-trending central segment of the SLF appear to be connected by the N46°W-trending PBF. The northern PBF converges with HFZ on successive seismic profiles and is confidently located <150 m from the HFZ, suggesting PBF-HFZ physical intersection. The central and southern PBF is identified on 3D seismic time slice maps and HR2D lines to the south. The SE-most observation of the PBF is <1000 m along trend from the northwestern-most positive location of the SLF. The proximity and low angle of the projected intersection between the faults strongly suggests the PBF and the SLF are connected, thus the PBF may form a continuous structural link between the HFZ and the SLF. The region between the HFZ and the SLF/PBF contains three distinct systems of contractional deformation: (1) Thrusts close to and parallel with the HFZ; (2) deep “lower” thrusts that underlie large-scale anticlines oblique to the HFZ and PBF; and (3) a shallow “upper” fold and thrust system rooted into bedding-parallel detachments on the limbs and crests of the large anticlines. The contractional structures are cut and offset by high-angle faults at several locations, one of which has an apparent right-lateral offset of approximately 500 m to 1000 m.
There is no apparent deformation of the high angle faults by the contractional structures.


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