Annual Meeting - SCEC.org

Poster Abstracts | Group 1 – CDM
interferograms (InSAR). We investigate the potential of compliant zones (CZ), areas with reduced
elastic moduli compared to ambient rock, to explain the radar observations. We derive an iterative
procedure that evaluates the three-dimensional deformation due to the presence of faults in an
arbitrary heterogeneous half space, with vertical as well as lateral variations in elastic properties.
The latter are modeled with equivalent body forces and equivalent surface traction in a
homogenized elastic medium. Displacement field in the computational volume is obtained in the
Fourier domain using semi-analytic Greens' functions. We find that CZs in the ECSZ along the
Rodman, the Calico and the Pinto Mountain faults can explain simultaneously InSAR data for the
Landers and the Hector Mine earthquakes. InSAR data require a 60% reduction in effective rigidity
in the Pinto Mountain CZ accompanied by a 7% increase in Poisson's ratio compared to ambient
crust. Large wavelength of LOS displacements around the Pinto Mountain fault is best modeled
with a CZ extending to at least 9km depth. Best fit for the Rodman and the Calico CZs, north of
Galway Dry Lake, is obtained for a 4.5km deep CZ, with a 60% reduction in shear modulus and 0%
and 20% increase in Poisson's ratio for the Calico and the Rodman CZ, respectively. We find that
required effective rigidity reduction in the Calico CZ, south of Galway Dry Lake is less dramatic
than in the northern segment, demonstrating possible along-strike variations of effective elastic
moduli within a long CZ. Best model thickness for the Mojave desert CZ varies between 0.8 and
1.5km. These observations suggest pervasive and widespread damage around active crustal faults.
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MODELING SENSITIVITY OF GPS NETWORKS TO GROUND DEFORMATION IN
SOUTHERN CALIFORNIA Williams NR, and Lohman RB
We generated strain and error models from Global Positioning System (GPS) data for the Southern
California (SoCal) Fault System and quantified the impact of potential new campaign observations.
We explored varying levels of spatial smoothing to determine shear strain and dilation, and
performed Monte Carlo tests to determine the expected variance on these values. Extending the
temporal span of GPS observations for individual stations will decrease model errors and result in
better estimates on strain or other model parameters. This improvement factor can determine
which GPS stations in SoCal would most benefit the geophysical modeling of Southern California
faults if resurveyed. We conducted similar tests on determining slip rate and errors of some of the
major SoCal faults. We converted these results to files viewable in Google Earth and made them
available on a public website for easy distribution and visualization. Future work may include a
comparison to updated models from Crustal Motion Map version 4 to determine the accuracy of
estimated error improvements.
1-113
NEW GEODETIC DATA FOR CRUSTAL DEFORMATION IN THE SAN BERNARDINO
MOUNTAINS Velasquez CM, and McGill SF
Global Positioning System (GPS) data in the vicinity of the San Bernardino Mountains are
minimally existent. At 16 survey sites GPS data were gathered for a time span of twenty-four hours
or more. At remotely located survey sites data were gathered for two to five continuous days.
Differences in rates at the various benchmarks will be used to infer the amount of elastic strain that
is accumulating due to faults in the vicinity. The measurements that have been collected are
currently being processed at the University of Arizona by Rick Bennett and Joshua Spinler. When
combined with prior data collected in 2005, the new data will provide the first GPS velocity vectors
for many parts of the San Bernardino Mountains.
In addition to collecting new GPS data, one-dimensional elastic modeling of data from SCEC’s
Crustal Motion Model version 3 (CMM3) was conducted along a transect through the San
128 | Southern California Earthquake Center