SCEC Award Number 16049 View PDF
Proposal Category Individual Proposal (Special Fault Study Area)
Proposal Title Crustal Architecture of the Western Transverse Ranges, Southern California
Investigator(s)
Name Organization
Thomas Rockwell San Diego State University
Other Participants Yuval Levy
SCEC Priorities 1a, 4a, 4b SCEC Groups Geodesy, Geology, USR
Report Due Date 03/15/2017 Date Report Submitted 03/14/2017
Project Abstract
The deep 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, which will be in agreement with the full range of geologic, geodetic, and seismicity data. For achieving this goal we constructed several preliminary cross-sections by compiling data and reviewed existing models. We then expanded these sections based on regional geologic mapping. These cross sections will be used with additional surface data to interpolate the 3D model. Our current interpretation is that the WTR, during the period of shortening, developed thrust fronts which propagated southward in time, similar to other fold-and-thrust belts worldwide. We interpret the nearly continuous overturned Tertiary stratigraphy of the Santa Ynez Mountains as a large anticlinorium that formed as an early thrust front over the (mostly) blind San Cayetano thrust, and that the thrust front propagated south with time to the Red Mountain fault and eventually to the currently active thrust front, the southward-vergent Pitas Point-Ventura fault. We further suggest that the steep dip angle and continued activity of the Red Mountain fault, as observed near the surface, is a result of northward rotation of the fault in the backlimb of the Ventura Avenue anticline, which has caused it to flexurally slip in the near surface.