Annual Meeting - SCEC.org

Poster Abstracts
We will present the systematic difference of ZH ratio measurements depending on the different area and S-wave structure due
to the inversion using ZH ratio measurements.
THE SCEC-USGS DYNAMIC EARTHQUAKE RUPTURE CODE VERIFICATION EXERCISE (A-115)
R.A. Harris, M. Barall, R. Archuleta, B. Aagaard, J.P. Ampuero, D.J. Andrews, V. Cruz-Atienza, L. Dalguer, S. Day, N.
DeDontney, B. Duan, E. Dunham, A.A. Gabriel, P. Galvez, Y. Kaneko, Y. Kase, J. Kozdon, N. Lapusta, S. Ma, P.M. Mai, H.
Noda, D. Oglesby, K. Olsen, and S. Somala
We summarize recent progress by the SCEC-USGS Dynamic Rupture Code Verification Group. In February 2011 we held our
most recent workshop where we examined how SCEC and USGS researchers spontaneous-rupture computer code results
agree (or disagree) when computing benchmark scenarios for dynamic earthquake rupture. Our recent benchmarks were a 2D
case of thermal pressurization and 2D and 3D cases of slip-weakening friction on branched vertical strike-slip faults set in an
elastic medium.
Since our February 2011 workshop, we have officially archived the results of the TPV12 and TPV13 Extreme Ground motion
normal-fault benchmarks that were used in our new paper Harris, R.A., M. Barall, D.J. Andrews, B. Duan, E.M. Dunham, S.
Ma, A.-A. Gabriel, Y. Kaneko, Y. Kase, B. Aagaard, D. Oglesby, J.-P. Ampuero, T.C. Hanks, N. Abrahamson, Verifying a
Computational Method for Predicting Extreme Ground Motion, Seismological Research Letters, Vol. 82, No. 5,
September/October 2011. The online archive allows newcomers (and veterans) to conduct new TPV12 and TPV13 extreme
ground motion simulations while at the same time we are preserving the results that are described in our journal publication,
for scientific repeatability.
In the fall of 2011, our group will embark on our next benchmark exercises, both of which will assume a slip-weakening
framework. One new benchmark will involve heterogeneous initial stresses on a planar vertical strike-slip fault set in an
elastic medium, using a stress-conditions methodology that is updated from the 2010 100-runs exercise. A second new
benchmark will involve more-homogeneous initial stresses on branching faults that are this time set in a medium that allows
for plastic yielding.
For more information please visit our website: scecdata.usc.edu/cvws
PRELIMINARY PALEOSEISMIC RESULTS FROM THE ECHO PLAYA TRENCH SITE ON THE CENTRAL
GARLOCK FAULT, CHINA LAKE NAWS, NEAR RIDGECREST, CA (A-133)
R.D. Hartleb, C.D. Kemp, A. Lutz, E.K. Frost, and S.C. Lindvall
Investigation of a new paleoseismic trench site along the central Garlock fault at Echo Playa on the China Lake Naval Air
Weapons Station exposed evidence for at least four, and as many as six, surface-rupturing earthquakes. The Echo Playa site is
located within a roughly 150-m-wide and 1.5-km-long transtensional step-over that has formed a closed basin fringed by
alluvial fan and colluvial deposits that grade basinward into laterally continuous playa sediments. Numerous subdued northand
south-facing fault scarps are recognized between the playa edge and the ridges of the step-over. These faults generally
deform bedrock or coarse alluvial fans, although two fault strands have formed low scarps along the playa margin. Two
trenches opened at Echo Playa across these playa margin faults exposed roughly 5 m of generally conformable stratigraphy,
recording several episodes of fan progradation and lacustrine/palustrine transgression along the playa margin.
Evidence for four surface-rupturing earthquakes is preserved within a roughly 30-m-wide zone of distributed deformation
where correlative sets of faults and fissure fills terminate upward at the base of laterally continuous stratigraphic horizons.
The distributed nature of deformation here has produced very small individual offsets that indicate different combinations of
lateral and normal slip components. Age estimates for strata that bracket each rupture are pending radiocarbon analyses of
detrital charcoal and optically stimulated luminescence analyses of fine-grained playa deposits. Initial age estimates based on
an assumption of reasonable sedimentation rates and the observed lack of soil development suggest that these four to six
surface-rupturing earthquakes occurred during the Holocene.
Echo Playa is the easternmost paleoseismic trench site along the Garlock fault, and data from this site are expected to provide
a basis for developing an earthquake chronology for the eastern Garlock fault, which is currently not well characterized. These
data also will provide an important opportunity to refine estimates of earthquake chronology, fault rupture length, and
recurrence intervals along the central and western Garlock fault, contributing to an improved understanding of seismic
hazard in southern California.
2011 SCEC Annual Meeting | 173