Annual Meeting - SCEC.org

Seismology
Group 2 – Seismology | Poster Abstracts
2-103
GEOTECHNICAL SITE CHARACTERIZATION IN CALIFORNIA Yong A, Hough SE,
Schwarz S, Yu E, Louie JN, and Wills CJ
The recent 29 July 2008 Mw5.4 Chino Hills earthquake generated moderate shaking intensities and
provided a reminder that we live in earthquake country. In support of scientific efforts to better
understand and predict ground motions, we continue efforts to improve geotechnical site
characterizations in California. First, we report updates to our MySQL-based site characterization
repository introduced two years ago at the 2006 SCEC Annual Meeting. The PHP-based webaccessible
table (http://sitechar.gps.caltech.edu/table.php) has been updated to a version
(http://sitechar.gps.caltech.edu/table2.php) that includes site information for 17 seismograph networks,
for a total of 782 individual seismic stations. The table now includes the predicted Vs30, or average
shear wave velocities in the upper 30 m (Wills et al., 2000; Wills and Clahan, 2006), along with the
reported elevation of the station sites. In addition, a total of 69 observed Vs30 measurements were
acquired through the SeisOpt®ReMi (refraction microtremor; ©2007 Optim Inc.) surface wave
dispersion analysis method. These measurements, located at SCSN (Southern California
Seismographic Network) station sites, are now included in the database. Although available and
preserved in the previous version (http://sitechar.gps.caltech.edu/table.php), the updated table no
longer provides geologic descriptions of each site. Finally, users can also retrieve site information
through a link on the Southern California Earthquake Data Center Research Tool website
(http://www.data.scec.org/research.html). To explore the reliability of estimated Vs30 values, we
regress the observed (SeisOpt®ReMi) values against the predicted values from both the Wills et
al. (2000) and the Wills and Clahan (2006) data sets. We find correlation coefficients of just under
0.6 for both models. Significant imprecision in predicted Vs30 values is expected and can be
attributed to the natural variability of Vs within geologic units and to the lack of precision in the
small-scale statewide maps. It is clear that, while state-wide maps indicate reasonable Vs30 trends
across a region, additional Vs30 measurements, more detailed maps and more detailed site
categories are needed for detailed microzonation. Further studies to determine the predictive
performance of other site characterization proxies (topographic slope and distance from hard rock)
and a combination of proxies (geology with topographic slope as terrain units) are under way.
2-104
PRODUCTS AND SERVICES AVAILABLE FROM THE SOUTHERN CALIFORNIA
EARTHQUAKE DATA CENTER (SCEDC) AND THE SOUTHERN CALIFORNIA
SEISMIC NETWORK (SCSN) Yu E, Chen S, Chowdhury F, Hutton K, Given D, Hauksson E,
and Clayton RW
Currently the SCEDC archives continuous and triggered data from nearly 3000 data channels from
375 SCSN recorded stations. The SCSN and SCEDC process and archive an average of 12,000
earthquakes each year. The SCEDC provides public access to these earthquake parametric and
waveform data through its website http://www.data.scec.org and through client applications such as
STP and DHI. This poster will describe the most significant developments at the SCEDC in the past
year.
Increased data holdings:
• Beginning Jan 1, 2008 the SCEDC began continuously archiving high sample rate channels of 80
sps or 100 sps.
2008 SCEC Annual Meeting | 197