Characterizing the 3D Geometry of the Ventura-Pitas Point Fault System in Southern California and its Potential for Large, Multi-Segment Earthquakes
Abstract
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 (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. The recent activity on the fault system is characterized using shallow spark seismic and bathymetry data (Perea et al., 2018). Extensive well control, including logs, horizon tops, and dipmeter, further constrain our interpretation. Through a series of balanced cross sections, created using fault-related folding and restoration modeling, we show that the Pitas Point fault system has a similar ramp-flat-ramp geometry to that of the onshore Ventura fault. We use these cross sections and the seismic reflection surveys to create a 3D fault model, which defines the lateral extent of the fault system and the nature of its linkage with the onshore Ventura fault and other large regional faults at depth. 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.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T13I0360D
- Keywords:
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- 7209 Earthquake dynamics;
- SEISMOLOGYDE: 7212 Earthquake ground motions and engineering seismology;
- SEISMOLOGYDE: 8110 Continental tectonics: general;
- TECTONOPHYSICSDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS