Annual Meeting - SCEC.org

Poster Abstracts | Group 1 – ShakeOut
are an important step in the development of a complete and consistent set of updatable data layers
for evaluating geologic hazards in southern California at regional and sub-regional scales.
Susceptibility maps classify surficial geologic materials based on the likelihood that the materials
will undergo liquefaction and ground failure in an earthquake. We used geologic maps from 43
sources that represent the best regional geologic mapping available and supplemented these maps
locally with airphoto interpretation. Because digital large- to medium-scale maps do not cover the
entire 8-county study area, we started with the 1:250,000-scale materials map of Wills and Clahan
(2006) and supplanted these data with higher resolution maps in the urbanized areas where
ground failure would most likely affect the built environment. For liquefaction, the map units were
assigned to five susceptibility classes, following the system presented by Youd and Perkins (1978).
For landslides, the units were binned into 3 classes and then intersected with slope data to produce
a 10-category assignment modified from Wilson and Keefer (1985). The map of the water table was
constructed using measurements at over 37,000 localities and binned into 10 depth classes. In
practice, the process of translating geologic map units into corresponding susceptibility classes is
difficult because many geologic map units do not adequately reflect the depositional environments
and material properties that are critical to inferring susceptibility. Where classification was
ambiguous, we tended to classify conservatively so as not to underestimate any potential hazard.
Following classification, any differences that may have been present across map boundaries were
reconciled using expert judgment in order eliminate any major map boundary discontinuities.
1-045
SHAKEOUT SIMULATIONS: VERIFICATION AND COMPARISONS Bielak J, Graves
RW, Olsen KB, Taborda R, Ramirez-Guzman L, Day SM, Ely GP, Jordan TH, Maechling PJ,
Urbanic J, Juve G, and Roten D
For the past three years we have presented results of several large-scale earthquake simulations
run by different research groups, but our verifications have been limited to qualitative
comparisons. This work presents a preliminary verification of three simulation sets for the
ShakeOut earthquake scenario, version 1.1, an Mw 7.8 earthquake on a portion of the San Andreas
fault in southern California. Two of the simulation sets use a finite difference approach while the
third one uses finite elements. The verification is done in a quantitative manner by means of the
goodness-of-fit criteria proposed by Anderson (2004) and the misfit criteria proposed by
Kirstekova et al. (2006). The results indicate good agreement between the three implementations
and the metrics of the comparisons for ten selected locations throughout the region signal that the
agreement can be regarded as excellent according to the scale defined by Anderson. All three
groups used a common discrete representation of SCEC's Community Velocity Model (CVM,
version 4). Discrepancies observed among the different synthetics are associated to intrinsic
differences between the numerical methods used and their implementation by each simulation
group. We conclude that the three schemes are consistent, reliable, and sufficiently accurate for
future large-scale simulations.
1-046
SHAKEOUT-D: GROUND MOTION ESTIMATES USING AN ENSEMBLE OF LARGE
EARTHQUAKES ON THE SOUTHERN SAN ANDREAS FAULT WITH SPONTANEOUS
RUPTURE PROPAGATION Olsen KB, Day SM, Dalguer LA, Cui Y, Zhu J, Mayhew JE,
Maechling PJ, Jordan TH, Chourasia A, and Okaya DA
We simulate ground motion in southern California from an ensemble of 7 spontaneous rupture
models of large (Mw7.8) northwest-propagating earthquakes on the southern San Andreas fault
(ShakeOut-D). Median rock-site 3 sec spectral accelerations follow the Next Generation
92 | Southern California Earthquake Center