Poster #076, Earthquake Geology

Comprehensive 3D model of the Ventura-Pitas Point fault system and associated structures in the Santa Barbara Channel and Ventura basin for the CFM

Jessica Don, John H. Shaw, & Andreas Plesch
Poster Image: 

Poster Presentation

2021 SCEC Annual Meeting, Poster #076, SCEC Contribution #11530 VIEW PDF
The southern extent of the Western Transverse Ranges, in the Santa Barbara Channel and Ventura basin, is home to some of the fastest Holocene uplift and deformation rates in southern California. The faults that accommodate this deformation pose some of the largest deterministic seismic hazards in southern California. In particular, the Ventura-Pitas Point system shows evidence for large (M ≥ 7.5) paleoearthquakes (Hubbard et al., 2014; McAuliffe et al., 2015; Rockwell et al., 2016). While several recent paleoseismic studies have focused on the onshore Ventura fault, its offshore extension in the Santa Barbara Channel (the Pitas Point fault) is less well understood, particularly with respect its 3D geometry, slip rate, and linkages with other faults in the region.

We create a series of regional balanced cross-sections across the Pitas Point fault system in the Santa Barbara Channel and combine them with detailed mapping of seismic reflection data to produce a comprehensive 3D fault model. This work builds upon recent efforts by SCEC investigators that show the blind, north-dipping, onshore Ventura fault extends to depth in a ramp-flat-ramp structure and links with several of the largest and fastest slipping faults in the Transverse Ranges (Hubbard et al., 2014; Marshall et al., 2017).

Our analysis shows that the Pitas Point fault system has a crustal ramp-flat-ramp geometry that is similar to the Ventura fault, supporting their direct linkage. We also suggest that the Pitas Point fault system extends farther to the south as the Mid-Channel detachment, creating the Pitas Point and Mid-Channel anticlines. Combining this new 3D representation of the Pitas Point fault system with the Ventura thrust and other regional structures, we define the down-dip and lateral linkages of the Ventura-Pitas Point system with the Red Mountain and San Cayetano faults (Levy et al., 2019). This fault model represents a set of geometrically and kinematically viable alternative representations for the active blind-thrust and reverse faults in the Santa Barbara Channel and Ventura basin. Using this comprehensive regional fault model, we calculate potential earthquake magnitudes and show that if the system were to rupture in a multi-segment event, it could produce M7.5-8 earthquakes, further supporting paleoseismological evidence that the fault system ruptures in large-magnitude events. This set of fault models will be incorporated into the CFM for peer review this fall.