Spatial and Temporal Variations in Strain Rates in the Western Transverse Ranges, California
Abstract
We determine the spatial and temporal variations in strain rates in the Transverse Ranges of southern California by combing data from 52 continuous GPS sites in the Plate Boundary Observatory network with InSAR time series. To characterize periodic seasonal motions in the GPS time series, phases and amplitudes of annual and semiannual motions are estimated for each GPS station. We remove these seasonal terms, and then perform Principal Component Analysis on the residual time series to remove common-mode errors. We find that seasonal GPS motions are not strongly dependent on local substrate geology. To quantify the spatial patterns of deformation in greater detail than GPS can provide, we use a persistent scatterer InSAR (PSI) data set comprised of 23 ENVISAT ASAR scenes. The PSI data were derived using the software package, StaMPS [Hooper et al. 2004]. The PSI data show potential anthropogenic subsidence in the Oxnard/Ventura area as well as at a location just south of the Oak Ridge. A highly localized zone of subsidence is also present along the Ventura Avenue anticline, where ongoing petroleum extraction is occurring. Comparison of the InSAR and the GPS projected into the InSAR line of sight, shows general agreement. The relative lack of significant non-tectonic motions in the western Transverse Ranges is in stark contrast to the nearby Los Angeles basin where anthropogenic motions dominate many InSAR scenes. To determine the local tectonic deformation rates, we remove strain associated with the nearby San Andreas fault using a rectangular dislocation model. Direct inversion of the GPS velocities into a triangulated network with variable strain/rotation rates produces a generalized map of variations in tectonic strain rates. The strain rate map shows the largest strain rates to be near the central Ventura basin with rates generally decreasing westward towards the Santa Barbara Channel. To determine compatible regional fault slip rates, we use a forward mechanical model based on the technique of Marshall et al. [2009] that utilizes fault surfaces defined by the Southern California Earthquake Center Community Fault Model. The mechanical model is generally compatible with geologic slip rates as well as the geodetic deformation patterns in the region. Areas of largest mismatch occur near the Ventura basin, where the modeled homogeneous rock stiffness is much higher than the seismic velocity structure suggests.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.G51B1097M
- Keywords:
-
- 1209 GEODESY AND GRAVITY / Tectonic deformation;
- 1211 GEODESY AND GRAVITY / Non-tectonic deformation;
- 1242 GEODESY AND GRAVITY / Seismic cycle related deformations;
- 8107 TECTONOPHYSICS / Continental neotectonics