Characterizing the 3D geometry of the Ventura-Pitas Point fault system and its implications for earthquake hazards in southern California

Jessica Don, Andreas Plesch, Mattie M. Newman, & John H. Shaw

Published August 13, 2018, SCEC Contribution #8411, 2018 SCEC Annual Meeting Poster #245

The Ventura-Pitas Point fault system, located in the western Transverse Ranges, is one of the largest earthquake sources in southern California with Holocene marine terraces suggesting that deformation occurs in discrete 7-9 meter uplift events (Rockwell et al., 1988; Hubbard et al., 2014; McAuliffe et al., 2015). Deformation of this scale is caused by large magnitude events that rupture multiple faults and pose significant ground shaking and tsunami hazards in southern California (McAuliffe et al., 2015, Ryan et al., 2015; Marshall et al., 2017). Recent studies have shown that the Ventura fault has a unique non-planar ramp-flat-ramp geometry that links at depth with several of the largest, fastest slipping faults in the area (Hubbard et al., 2014; Marshall et al., 2017; Levy et al., 2017).

We aim to characterize the geometry of the Pitas Point fault system, the direct offshore extension of the Ventura thrust in the Santa Barbara Channel, to further define the potential for large, multi-segment earthquakes. Previous studies have represented the Pitas Point fault with a planar geometry (e.g. Sorlien et al., 2000; 2015) which would limit its connection with other faults in the Santa Barbara Channel. In this study, we use 3D industry seismic reflection data from the Pitas Point and Dos Cuadras oil fields to directly constrain the fault geometry at depth. 2D seismic reflection data are used to extend our interpretations regionally to include the Oakridge and Blue Bottle trends. Extensive well control, including logs, horizon tops, and dipmeter, further constrain our interpretation.

We create a series of balanced cross sections using fault-related folding techniques and restoration modeling. These cross sections show that the Pitas Point fault system has a similar ramp-flat-ramp geometry to that of the onshore Ventura fault. This suggests that the Pitas Point fault also has linkages with other large faults at depth in the area. This improved fault geometry further supports the prospect for large, multi-segment ruptures and has implications for the associated hazards (such as ground motion and tsunamis) as well as geodetic strain and loading patterns.

Key Words
Pitas Point, Ventura, Santa Barbara Channel, fault system, 3D geometry, multi-segment ruptures

Don, J., Plesch, A., Newman, M. M., & Shaw, J. H. (2018, 08). Characterizing the 3D geometry of the Ventura-Pitas Point fault system and its implications for earthquake hazards in southern California. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology