SCEC Award Number 11122 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Characterizing Non-tectonic and Interseismic Deformation in the Ventura Basin Region, CA
Name Organization
Scott Marshall Appalachian State University Gareth Funning University of California Riverside Susan Owen National Aeronautics and Space Administration
Other Participants
SCEC Priorities A2, A5, A3 SCEC Groups Geodesy, CDM, LAD
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
Hager et al. [1999] and Donnellan et al. [1993] demonstrated that ongoing contractional deformation recorded by geodetic measurements in the western Transverse ranges of southern California is related to tectonic strain accumulation along active reverse faults that bound the Ventura basin. We find that all continuous GPS sites in the western Transverse ranges region, regardless of the geology of the local substrate (bedrock versus sedimentary basin fill), exhibit periodic seasonal motions; however, these periodic motions do not greatly affect velocity estimates and can be mathematically removed. While we have identified a few locations of potential non-periodic anthropogenic motion, we show that the large and ongoing anthropogenic deformation signals observed in the nearby Los Angeles basin are not seen to the same degree in the western Transverse ranges. Thus, most of the region’s GPS sites should yield reliable tectonic velocities. An interseismic model using the non-planar CFM surfaces and based on the technique of Marshall et al. [2009] has been created. The model is the first mechanical interseismic model of the region to use the geologically constrained CFM surfaces. The model produces surface velocities that largely agree with the GPS velocity field, and the best fitting locking depth (14 km) is similar to previous estimates [Hager et al., 1999]. The model predicts fault slip rates that generally agree with long term geologic estimates. Therefore, no slip rate discrepancies are apparent in the region. The model results also provide slip rate estimates for numerous otherwise unconstrained faults in the region.
Intellectual Merit This project contributes to the understanding of crustal deformation in southern California by using a novel three-dimensional mechanical modeling approach to simulate both interseismic and long-term deformation. Thus, this work will directly test whether any geologic/geodetic rate discrepancies exist in the western Transverse Ranges. Our modeling approach utilizes the CFM geometry and offers a quantitative assessment of the ability of the CFM to reproduce variations in slip and interseismic deformation in southern California. This work shows that that several proposed geodetic/geologic discrepancies are likely due to model simplifications, or site-specific slip rate estimates taken out of context and are, therefore, probably not real. Previous geodetic studies of the western Transverse Ranges did not attempt to separate tectonic and non-tectonic motions. Recent geodetic work in the Los Angeles basin suggests that many GPS sites have significant non-tectonic motions, which must be removed to reveal the true tectonic deformation rates. This work suggests that the large non-periodic and non-tectonic motions observed in the Los Angeles basin are not common in the western Transverse Ranges region.
Broader Impacts This work has fostered collaborations between researchers at the Jet Propulsion Laboratory, the University of California Riverside, and Appalachian State University. At Appalachian State University, PI Marshall has now begun training undergraduate students in GPS processing, dislocation modeling, and stress/strain theory. In 2011, this undergraduate student presented her work at the annual AGU meeting. Marshall is also currently training a Ph.D. student at the University of Massachusetts on GPS processing, and working with a Master’s student at the University of California Riverside. These efforts are aimed to produce future researchers that are better prepared for graduate school and the research community. Also, by training undergraduate students, interest and understanding of earthquake science is promoted. The results of this work will have a greater impact on society by more accurately characterizing the slip rates of faults, which in turn leads to improved seismic hazard estimates.
Exemplary Figure Figure 3. Comparison of a persistent scatterer InSAR dataset formed from 24 Envisat scenes to GPS velocities projected into the LOS of the Envisat satellite. The along track azimuth (T) and LOS (L) directions are shown with black arrows. Negative values represent motion away from the satellite. In general, we see only three potential sites of anthropogenic contamination: 1) northwest of site VNCO near the Ventura Avenue anticline where localized oil pumping is ongoing 2) in the greater Oxnard region where subsidence is likely due to aquifer drawdown 3) near site MPWD. The GPS and InSAR generally agree except for site TOST and sites in the northeast near the San Andreas fault.