Annual Meeting - SCEC.org

Poster Abstracts | Group 2 – Earthquake Geology
commonly has significant age inheritance. Furthermore, most of the archeologic dates are based on
composite samples, which may have a spread of age components. While there seems to be a
general consensus that there have been multiple fillings and dessications in the past 1000-1500
years, a definitive late-Holocene chronology has yet to be developed. Here we present a new
chronology using the radiocarbon ages, stratigraphic lacustrine correlation and historical data from
sites across the entire Cahuilla basin. We have compiled over 350 radiocarbon ages from
paleoseismic trenches and archeological sites above and below the lake highstand. We have sorted
and placed each date in stratigraphic context to its relationship with lacustrine and non-lacustrine
periods using its sample location, elevation, depositional context (i.e., anthropogenic, geologic),
type of material and source of the material dated. The stratigraphic occurrence of multiple lakes at
higher elevations relative to lower elevations has provided additional constraints regarding the
timing and length of individual highstands, as well as information on partial desiccations. Finally,
we add historical constraints to lake levels provided by diaries and maps of European expeditions
within the region. Based on these data, the most recent lake is interpreted as three sub-high stands
with two partial desiccations between about AD 1600 and 1720. Lake 2 (reported as lake 3 at
paleoseismic sites close to the shoreline) dates to the period of about AD 1400-1500. The third major
lake inundated the basin in the 13th century, whereas a protracted generally dry period persisted
between about AD 700 and 1200, with brief lakes inferred around the AD 1150 and 1000.
2-039
A GPS RESURVEY OF THE ANZA GAP REGION, CALIFORNIA: PREPARATION
FOR AN EARTHQUAKE ON THE SAN JACINTO FAULT Millar AZ, and Funning GJ
There is a significant probability within the coming decades of rupture along the San Jacinto Fault,
which has been seismically active in the past century. With this in mind, the goal of our
SCEC/SURE study is to increase preparedness for several possible earthquake scenarios along the
San Jacinto fault focusing specifically on the Anza, San Bernardino Valley and San Jacinto Valley
segments, the region in which the Earthquake Processes group at UC Riverside would likely be
first responders in the event of an earthquake.
Key components involved in the project include resurveying GPS benchmarks throughout
Riverside and San Bernardino Counties and using elastic deformation models to devise postearthquake
response strategies that emphasize and prioritize particular GPS benchmarks. Initially,
eighteen benchmarks were selected to be resurveyed over the course of the summer based on the
year in which they were last surveyed (the most recent being in 2001) and for their locations
relative to the surface fault traces and to those of continuous GPS and recent campaign sites. The
original list of benchmarks has since been modified to reflect the outcome of reconnaissance work,
and following the running of simple forward and inverse models. Additionally, we have created
detailed site descriptions for each benchmark that will be posted on the Web at the conclusion of
the project.
2-040
PALEOSEISMOLOGIC EVIDENCE FOR MULTIPLE HOLOCENE EARTHQUAKES
ON THE CALICO FAULT: IMPLICATIONS FOR EARTHQUAKE CLUSTERING IN
THE EASTERN CALIFORNIA SHEAR ZONE Ganev PN, Dolan JF, Oskin ME, Owen LA,
and Le KN
New paleoseismologic data from the Calico fault reveal evidence for the occurrence of at least
three, and probably four, surface ruptures during the Holocene. This new data set strongly
reinforces earlier suggestions that seismic strain release across southern California may be highly
clustered in time and space. Two fault-perpendicular trenches were excavated in the town of
158 | Southern California Earthquake Center