Annual Meeting - SCEC.org

Funning et al. resurveyed 19 GPS
sites in the Anza gap region along
the San Jacinto fault and processed
these data to extend position time
series for these sites. These data
have made possible new or revised
velocity calculations for GPS sites
in this region. In the event of a San
Jacinto fault earthquake, these
velocities will be required in order
to obtain accurate coseismic and
postseismic displacement
measurements. Improved
interseismic velocities will also
prove valuable for refining models
strain accumulation, and thus
seismic hazard, in the vicinity of
the San Jacinto fault.
GPS data collection in the Anza
gap region is complemented by the
variety of observations recorded at
the Piñon Flat Observatory (PFO).
With partial support from SCEC,
Wyatt et al. maintained and
operated the PFO, which includes a
longbaseline strainmeter, assisted
other groups with operation and
testing of various seismic
instruments, and continued
SCEC Research Accomplishments | Report
Figure 8. M7.2 El Mayor-Cucupah coseismic displacements (black arrows) from campaign
GPS surveys.(Sandwell et al., 2010)
processing and archiving longbaseline strain data. These data show intriguing trends during the initial months following the
El Mayor Cucapah earthquake that may reflect slow slip on the San Jacinto fault.
Oskin et al. developed a test to distinguish between two end-member models of long-term earthquake temporal clustering
and applied it to the southern San Jacinto fault. One end-member is that clustering occurs due to changes in the brittle fault
strength, and this would predict anti-correlated slip rate behavior of individual fault strands. Alternatively, clustering can
result from changes in loading by the ductile lower crust which would predict correlated slip rate behavior of fault strands. To
test these models they estimated slip rates at six sites along strands of the San Jacinto fault using two independent dating
techniques to reduce potential bias in the results. Their results indicate there is a strong slip rate gradient along the San Jacinto
fault with the slip rate decreasing to the southeast where slip is transferred from the Clark fault strand to the Coyote Creek
fault and Salton Trough. The slip rates estimated for the Clark and Coyote Creek faults both show an increase over time
suggesting that the change is due to an increase in fault zone loading.
Weldon et al. completed mapping of the north branch of the San Andreas fault in the San Bernardino Valley and prepared for
sample collection for cosmogenic dating to be conducted in the summer of 2011. These data will be used to determine the slip
rate on this fault branch, a structure for which little slip rate information exists despite its important role in assessing the
geodetic/geologic slip rate discrepancy and seismic hazard in this region.
Kilb inspected the spectra for triggered earthquakes in the wavetrain of large amplitude teleseismic events and demonstrated
that these triggered events are similar to typical shallow earthquakes in the same region (the Salton Sea) rather than having
frequency characteristics expected of triggered tremor.
2011 SCEC Annual Meeting | 45