SCEC Award Number 14055 View PDF
Proposal Category Individual Proposal (Special Fault Study Area)
Proposal Title Deformation and Fault Slip Rates in the Ventura Basin and Western Transverse Ranges
Investigator(s)
Name Organization
Kaj Johnson Indiana University
Other Participants
SCEC Priorities 1a, 1b, 4a SCEC Groups SDOT, Geodesy, SoSAFE
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 The far-field, regional loading rate constrained by geodetic data is a critical component to Ventura Special Fault Study Area (SFSA) project. To this end, we have incorporated existing and newly acquired geodetic data from the western Transverse Ranges into a regional kinematic model of present-day deformation rates. We use a kinematic method in which a long-term horizontal and vertical velocity field is constructed assuming slip on faults in elastic plate over an inviscid fluid. The interseismic deformation field is modeled with backslip on the faults in an elastic halfspace. We also account for vertical surface motions due to San Joaquin Valley water withdrawal following Amos et al. (2014). In the forward model, slip is imposed on the faults. Using Monte Carlo Metropolis methods, we invert the geodetic data for slip rates and coupling, constrained by the upper and lower slip rate bounds in the UCERF3 geologic model. We adopt the UCERF3 fault geometry. The horizontal GPS velocity field is from UCERF3, and the vertical GPS and InSAR velocity field is from Bill Hammond (2014 SCEC grant). We find significant shortening across the Transverse Ranges of ~10 mm/yr. This is shortening attributed only to motion along faults in western Transverse Ranges, after removing contributions from the San Andreas and other large strike-slip faults as well as far-field loading. The summed reverse-slip rate across the Transverse Ranges along a profile through Ventura is >15 mm/yr with 8-10 mm/yr across the Ventura Basin (Oak Ridge and Ventura Faults).
Intellectual Merit The far-field, regional loading rate constrained by geodetic data is a critical component to Ventura Special Fault Study Area (SFSA) project. We have incorporated existing and newly acquired geodetic data from the western Transverse Ranges into a regional kinematic model of present-day deformation rates. We also account for vertical surface motions due to San Joaquin Valley water withdrawal following Amos et al. (2014). We invert the geodetic data for slip rates and coupling, constrained by the upper and lower slip rate bounds in the UCERF3 geologic model. We find significant shortening across the Transverse Ranges of ~10 mm/yr. This is shortening attributed only to motion along faults in western Transverse Ranges, after removing contributions from the San Andreas and other large strike-slip faults as well as far-field loading. The summed reverse-slip rate across the Transverse Ranges along a profile through Ventura is >15 mm/yr with 8-10 mm/yr across the Ventura Basin (Oak Ridge and Ventura Faults).
Broader Impacts This project contributes directly to improved understanding of the seismic hazard in the western Transverse Ranges and, in particular, the Ventura and Santa Barbara regions.
Exemplary Figure Figure3. Inversion results. a. Modeled and observed shortening rates across the western Transverse Ranges. b. Inferred reverse-slip rates. Model mean and 99% confidence interval of reverse slip rate on dipping faults is shown. The maximum allowable rate is 6 mm/yr for all reverse faults. Note ~10 mm/yr of present-day shortening across western Transverse Ranges. The summed slip rate across A-A’ is >15 mm/yr. About 8-10 mm/yr occurs across
the Ventura Basin (Oak Ridge and Ventura
faults).