Project Abstract
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We developed new subsurface interpretations of the offshore Pitas Point fault system to define its possible connections with the adjacent Ventura, Red Mountain, and San Cayetano faults. The possible linkages among these faults is central to assessing the prospects for large, multi-segment thrust fault earthquakes in the region that have been proposed by paleoseismic and structural analyses of the onshore Ventura fault (Rockwell et al., 1988; Hubbard et al., 2014; McAuliffe et al., 2015; Grenader et al., 2015). Our analysis involved interpretation of 2- and 3-D seismic reflection surveys, well logs, and seismologic constraints to define subsurface fault and fold geometry. These interpretations were extended to depth using fault-related folding theories, and evaluated using structural balancing tests. Our results show that the Pitas Point fault shallows its dip with depth, consistent with the geometry of folded backlimb strata in its hanging wall. A range of lower fault dips are possible (0 to 20°N) based on balancing constraints. Notably, this inferred fault segment is located at a depth of 6.5-7.5km within the Miocene Monterey and Rincon shales. This is similar to the depth and stratigraphic position of the detachment inferred beneath the onshore Ventura fault (Hubbard et al., 2014), and located to the south of the Pitas Point fault in the eastern Santa Barbara Channel (Shaw and Suppe, 1994). Our interpretations favors a direct structural linkage between the Pitas Point and Ventura faults that, in turn, supports the prospect for large, multi-segment earthquakes that pose significant ground shaking and tsunami hazards. |
