SCEC Award Number 12138 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Assessing the earthquake potential of the Ventura, Southern San Cayetano, and Pitas Point fault system: Characterizing subsurface fault geometry and forecasting strong ground motions
Investigator(s)
Name Organization
John H. Shaw Harvard University James F. Dolan University of Southern California
Other Participants Carl Tape (Univ. of Alaska), Tom Pratt (USGS), Andreas Plesch (Harvard), Judith Hubbard (Harvard)
SCEC Priorities 1a, 6b SCEC Groups Geology, GMP, USR
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 Our study investigates the activity, subsurface geometry, and earthquake potential of the Ventura thrust fault system. This fault underlies the Ventura Avenue anticline, which rises at a rate of ∼5 mm/yr and is one of the fastest uplifting structures in southern California (Rockwell et al., 1988). Moreover, the Ventura fault links several large, active thrust faults systems in the Transverse Ranges, including the San Cayetano fault to the east and the Red Mountain fault to the west. Our findings suggest that below 7.5 km depth, these faults may form a nearly continuous surface. Thus, our investigation of the Ventura faults also seeks to assess the likelihood that it ruptures in large (M > 7.6), multi-segment earthquakes that involve several of the major thrust fault systems in the Transverse Ranges. Such large earthquakes have been postulated based on large, episodic uplift events recorded in marine terraces along the western flank of the Ventura Avenue anticline (Rockwell, 2011). Due to the local geography and geology, such events would be associated with significant ground shaking amplification and strong regional tsunamis. Thus, we are also focused on developing a kinematic source model for the Ventura – Pitas Point fault system and generating numerical simulations of this rupture scenario to assess these hazards. These simulations are being developed using the spectral element method and the latest release of the SCEC Community velocity model (CVM-H 11.9).
Intellectual Merit This research helps to characterize a major seismic source in southern California, and the assess the possibility of multi-segment thrust fault ruptures in the Transverse Ranges. Through a coordinate approach involving several different disciplines (structural geology, paleoseismology, and seismology), we are also helping to develop and improve methods that can be used to define the earthquake potential of blind-thrust fault systems.
Broader Impacts This project included the training of two graduate students, including one woman who has just moved to a faculty position, and several undergraduates who helped with field data acquisition. The results characterize an important seismic source, and will be including in regional seismic hazard assessments that can be used to save lives and protect property in future earthquakes.
Exemplary Figure Figure 3: Perspective view of the faults in the Ventura region. (a) From the northwest, showing just the Ventura and Pitas Point faults, with the flat and ramp dipping down to the north, (b) from the northwest, showing those faults in the context of the regional structure, and (c) from the east, with the Lion/Southern San Cayetano fault semi-transparent. The San Cayetano fault is taken from the SCEC CFM (Plesch et al., 2007). The California coastline and the cities of Ventura and Santa Barbara are shown as a black line and black circles.