SCEC Award Number 17024 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Crustal Architecture of the Western Transverse Ranges, Southern California: The Potential for Great Earthquakes
Investigator(s)
Name Organization
Thomas Rockwell San Diego State University
Other Participants Yuval Levy
SCEC Priorities 3a, 1a, 3b SCEC Groups SDOT, CXM, Geology
Report Due Date 06/15/2018 Date Report Submitted 06/20/2018
Project Abstract
 Details of the subsurface structure of the Western Transverse Ranges (WTR) of southern California is still under ongoing debate. Recent work found evidence for large earthquakes. This evidence combined with the community’s agreement that existing models can be improved, motivated us to study further the structure in the region. Our goal is to construct a balanced retro-deformable 3D model that will be in agreement with the full range of geologic and geodetic data. Towards achieving this goal, we initially constructed several shallow geologic cross-sections by compiling geologic data and reviewing / modifying existing models. These cross-sections have been added to with new sections to the west towards Point Conception, and together will be used interpolate a 3D model. We then used the Trishear module in MOVE to forward model the structure of the range to compare to the geologic sections with the purpose of testing different deep structural geometries that consistently reproduce the surface structure. The forward modeling predictions are in good agreement with the observed geology and deformation. Our results suggest that the Western Transverse Range is comprised of a southward verging imbricate thrust system, with the dominant faults dipping as a ramp-ramp to the north that steepen as they shoal from ~20˚ degrees at depth to ~60˚ near the surface. By including the full range of observations in our forward modeling efforts, we address fundamental questions regarding the structural geometry and kinematics of the region, which allows for a better understanding of earthquake and tsunami potential.
Intellectual Merit
The results of this work will provide a more consistent 3D model of the entire western Transverse Ranges for inclusion in the SCEC CFM, thereby providing a platform for modeling earthquakes in the Western Transverse Ranges. By doing so it will have a direct impact on an area in California which is inhabited by two million people. An additional contribution is the furthering of our understanding the 4D evolution of this region. A manuscript was submitted to Geology and is now in Review (Levy et al., In review).
Broader Impacts This project support PhD student Yuval Levy. Yuval trained on MOVE software, and has been teaching my MS students how to model in this environment. This project has broad impacts for understanding the earthquake potential of the Western Transverse Ranges, and explaining geologic observations of large uplift events, which could affect a large section of the central California coast both from seismic shaking and, potentially, tsunami inundation.
Exemplary Figure Figure 3. Comparison between data (upper cross section) and forward model (lower cross section) for cross section 2 (Figure 1) showing a good first order match between the two. Interpretation of the deeper data part is based on stratigraphic thickness from maps and Dibblee (1982). Ages are specified with black letters K - Cretaceous, E – Eocene, O – Oligocene, M – Miocene. Faults are specified with red letter: SCF – San Cayetano fault, SYF – Santa Ynez fault SSMF – South Sulfur Mountain fault, VF – Ventura fault, ORF – Oak Ridge fault. Black dashed line marks the brittle-ductile transition zone.