SCEC Award Number 11204 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Defining the slip rate, paleoseismology, and earthquake potential of the blind Western San Cayetano and Ventura fault system: Determining recent slip rates and paleo-earthquake ages and displacements
Investigator(s)
Name Organization
James F. Dolan University of Southern California John H. Shaw Harvard University
Other Participants McAuliffe, Lee (USC graduate student)
Pratt, Thomas L. (USGS Seattle)
SCEC Priorities A2, A3, A9 SCEC Groups Geology, USR, SHRA
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
 Following our 2010 SCEC-funded acquisition of high-resolution seismic reflection data across the loci of active folding at several sites along the southern San Cayetano-Ventura blind thrust system in the central Transverse Ranges, we began our acquisition of borehole data to define the slip rate and ages and displacements in ancient earthquakes along this major fault system. Our main 2011 study site was along Briggs Road near Santa Paula, CA. A transect of 6 cored boreholes and 4 CPTs revealed well-bedded stratigraphy along the southern flank of the SSCF forelimb. Together with planned 2012 boreholes, these results will allow us to characterize the geometry and ages of strata that have been deformed by late Pleistocene-Holocene earthquakes on the underlying SSCF blind thrust ramp.
Intellectual Merit There is a growing appreciation of the seismic threat posed by the system of large reverse faults that extend through the central and western transverse ranges. Although the potential for extremely large (Mw8) earthquakes exists along this system, relatively little is known about the likelihood of such earthquakes, or indeed about the specific earthquake behavior of any of these major faults. Our research aims to help define the slip rates of two of the largest of these faults - the blind southern San Cayetano fault and the associated Ventura fault - as well as the ages and displacements that have occurred in ancient earthquakes generated by these structures. Following our successful acquisition of high-resolution seismic reflection data across the loci of active folding above these faults, our initial borehole results from one site along the SSCF provide the first step in assessing the slip rate and earthquake record from this major, but poorly known seismic threat.
Broader Impacts The main goal of this project is to provide basic information about the state of activity, slipr ate, and past patterns of earthquake occurrence along two of the largest, fastest-slipping thrust faults in southern California. Currently, although these faults potentially represent some of the most dangerous seismic threats in southern california, (including the potential for generation of large, near-field tsunami), they are not well understood, precluding effective assessment of the hazard they pose. in addition, this project forms the basis for part of Lee McAuliffe's USC Ph. D. dissertation. The field work has also involved several USC and harvard graduate students, facilitating their training in the acquisition of a wide variety of geophysical and geologic data.
Exemplary Figure Figure 3: High-resolution seismic profile acquired this past summer at site 1 (Figure 1) across the active fold limb and synclinal axial surface associated with the tipline of the blind southern San Cayetano Fault. Green and red bars indicate locations of boreholes and CPT’s acquired during the summer of 2011. The new projected synclinal axial surface (~30 meters to the north of the initial location, and locations of three future boreholes are indicated.