Annual Meeting - SCEC.org

Poster Abstracts
breakage weakens the ability of a granular material to support a shear stress, even though grain breakage accounts for only a
small fraction of the total energy dissipation.
HIGH-FREQUENCY AMBIENT NOISE TOMOGRAPHY USING INDUSTRIAL SEISMIC ARRAY IN LONG
BEACH, CALIFORNIA (B-063)
F. Lin and R.W. Clayton
The ambient noise cross-correlation method has now routinely being applied to study shallow earth structure. Here we
present the preliminary result of such application on an industrial array in Long Beach, California. The data was recorded by
NodalSeismic Inc. The pilot study contains about 150 stations with 72 hours of data on each of the four local streets (Cherry
Ave., Redonde Ave., Spring St., and Willow St.). After temporal normalization and spectrum whitening, cross-correlations are
calculated and clear signals, which can be associated with air waves and surface waves, are observed between 1 and 20 Hz
frequency. We perform frequency-time analysis (FTAN) to study the dispersion property of the observed signals. Besides
demonstrating the applicable of the ambient noise method in a suburban area, we also present potential complexities in
observed cross-correlations due to persistent regional noise sources.
GEODETIC SLIP RATES IN THE SOUTHERN SAN ANDREAS FAULT SYSTEM: INVESTIGATION OF THE
EFFECTS OF HETEROGENEOUS ELASTIC STRUCTURE (A-057)
E. Lindsey and Y. Fialko
We investigate the importance of fault geometry and crustal heterogeneity on estimates of slip rates and locking depths of the
Southern San Andreas fault (SAF) and San Jacinto fault (SJF). Previous estimates of geodetic slip rates in the Salton Sea region
based on dislocation models have generally inferred a higher slip rate on the SAF (21-26 mm/yr) compared to the SJF (12-19
mm/yr). The inferred geodetic slip rate on the SAF is higher than recent geologic estimates representing average slip rates on
time scales of 10^4-10^6 years. We investigate to what extent the geodetically inferred slip rate might be biased by incorrect
assumptions about the fault geometry and neglect of spatial variations in crustal rigidity. To address this issue, we use a
forward model that incorporates heterogeneous elastic moduli computed from the SCEC CVM-H seismic tomography model
of Southern California. In our inversions we allow for a non-vertical SAF and a "blind" segment of the SJF, the previously
suggested southern continuation of the Clark fault. The models are compared to surface velocities derived from a combination
of all available continuous and campaign GPS sites in the region, processed in a consistent North American fixed frame
(NAFD), and InSAR data spanning 18 years (1992-2010). These data sources are strongly complementary: while InSAR
provides higher spatial resolution in the near-fault region, we find that GPS sites located more than 10 locking depths from the
fault are required to resolve the trade-off between locking depth and fault slip rate. The parameter space is examined using an
efficient Monte Carlo algorithm which approximates the joint probability distribution for the model parameters and allows for
a formal evaluation of uncertainties and trade-offs. We estimate slip rates of 15(+/-2) mm/yr for the Southern San Andreas
fault and a total of 23(+/-3) mm/yr for the two closely spaced branches of the southern San Jacinto fault, in reasonable
agreement with geologic estimates. The locking depths are estimated at 9(+/-3) km and 16(+/-3) km for the SAF and SJF,
respectively. The incorporation of realistic elastic properties serves to increase the estimated locking depths on both faults by
2-3 km, and decreases the estimated slip rate on the San Andreas fault by several mm/yr in comparison to a homogeneous
elastic model.
SEISMIC SOURCE CHARACTERIZATION FOR THE LADWP VAN NORMAN COMPLEX AND ISSUES TO
CONSIDER FOR UCERF3 IN THE NORTHERN SAN FERNANDO VALLEY, CA (A-125)
S. Lindvall, C. Kemp, J. Unruh, and D. O'Connell
A new seismic source model was developed to support the seismic hazard evaluation of the Los Angeles Department of Water
& Power (LADWP) existing and proposed water storage, treatment, and conveyance facilities at the Van Norman Complex
(VNC) located in the northern San Fernando Valley. The LADWP is the largest municipal utility in the USA and nearly 75% of
the city’s annual water supply flows through the VNC, which makes these reservoir, embankment, water treatment, and
pipeline facilities critical to the City of Los Angeles. The VNC site, which lies in one of the most tectonically complex areas of
the Transverse Ranges, has experienced strong near-field ground motions in both the 1971 M6.7 San Fernando and 1994 M6.7
Northridge earthquakes that ruptured faults adjacent to and beneath the VNC. The new seismic source characterization
focused on detailed assessments of these and several other local fault sources that contribute most significantly to the VNC
seismic hazard. The new seismic source characterization included the reprocessing and interpretation of nine oil-industry
seismic reflection profiles in the northeastern San Fernando Valley to map subsurface strands of the Verdugo, Mission Hills,
196 | Southern California Earthquake Center