SCEC Award Number 15079 View PDF
Proposal Category Collaborative Proposal (Special Fault Study Area)
Proposal Title High Resolution Geodetic Measurements of Deformation throughout the Ventura Special Fault Study Area Region
Name Organization
Scott Marshall Appalachian State University Susan Owen National Aeronautics and Space Administration Jet Propulsion Laboratory Gareth Funning University of California, Riverside
Other Participants
SCEC Priorities 4a, 4b, 4c SCEC Groups Geodesy, USR, SDOT
Report Due Date 03/15/2016 Date Report Submitted 03/13/2016
Project Abstract
In 2012, SCEC established the Ventura Special Fault Study Area (SFSA) largely based on recent work suggesting the potential for M7.5-8.0 earthquakes in the region [Rockwell, 2011; Hubbard et al., 2014; McAuliffe et al., 2015; Rockwell et al., in review]. This project is a continuation of a multi-year SCEC funded project aimed at both modeling the faults of and processing/analyzing GPS and InSAR data for the greater Ventura region.
For the fault modeling component of this study, we have produced a refined three-dimensional model based on the SCEC CFM5.0 including two alternative geometries for the Ventura fault. Mechanical models of the regional faults show no significant geologic/geodetic slip rate discrepancies. Based on comparison of model results to geologic slip rates alone, we cannot distinguish between the flat ramp and constant dip fault representations of the Ventura fault. Both produce slip rates at the sites of measurement that are compatible with existing geologic data.
For the geodesy component of this study, we have increased our GPS velocities from 52 to 127 total sites throughout southern California. We have also processed InSAR data from the Envisat and ERS satellites and produced two dense persistent scatterer datasets for the region. The GPS and InSAR both show potential deformation north of the Ventura fault that may be consistent with interseismic deformation on a shallow dipping fault (similar to the ramp model). Our ongoing efforts involve improving the geodetic data quality and modeling these potential interseismic deformation patterns.
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. A primary goal of the Ventura Special Fault Study Area (SFSA) is to determine the most likely fault structure for the region, and this work contributes to this effort by creating and directly testing an updated fault system geometry for the greater Ventura region using a physics-based method. Our approach offers a quantitative assessment of the ability of the CFM to reproduce variations in slip and interseismic deformation in southern California. Furthermore, the fault mesh produced in this study will be posted on PI Marshall’s website and provided for inclusion in a future release of the SCEC CFM. Several other research groups have already been provided the mesh for use in their respective works.
While deformation related to the strike-slip faults in southern California are relatively well-studied, deformation due to reverse and/or oblique slip faulting is poorly understood. The geodetic component of this project has and will provide several high-resolution InSAR datasets for the relatively poorly studied western Transverse ranges region of southern California. This work will also provide a GPS velocity dataset that has the effects of the larger and faster San Andreas (and other) faults removed. This will facilitate future studies of the slower slipping (but still hazardous) faults in southern California, including the Los Angeles and Ventura basin regions.
Broader Impacts This work has fostered collaborations between researchers at the Jet Propulsion Laboratory, the University of California Riverside, Harvard University, and Appalachian State University. At Appalachian State University, PI Marshall now routinely trains undergraduate students in GPS/InSAR processing, dislocation modeling, and stress/strain theory. Marshall recently trained a Ph.D. student at the University of Massachusetts on GPS processing, and is currently working with two undergraduate geology students at Appalachian State University on fault modeling and geodesy. One student is modeling the faults of the Los Angeles region using the CFM, while the other is processing GPS time series to determine seasonal aquifer motions. 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 an 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. Persistent scatterer InSAR data from the Envisat satellite downsampled to 200 m spacing using a median filter. The largest deformation signals are near the northwestern end of the data where the ground is rapidly subsiding due to hydrocarbon extraction. The gradual increase in line of sight velocity from southwest to northeast is dominantly due to interseismic deformation on the San Andreas Fault. A zone of line of sight velocity increase is labeled with a dashed path that may be due to interseismic deformation associated with the Ventura fault, but this region has steep topography and is partly vegetated, so the InSAR data is noisy. This zone partly overlaps with a zone of uplift identified in the GPS data (Figure 1a).