[Withdrawn] Evaluation of Vs30 at Southern California Edison Substations Using S-Wave Refraction Tomography and Multichannel Analysis of Surface Waves
Date: 4/26/2019
Time: 11:00 AM
Room: Pine
Southern California Edison (SCE) provides electricity to more than 15 million people in 15 southern California counties by maintaining a vast network of transmission lines and substations, many of which are susceptible to strong ground shaking from earthquakes. To better understand the potential for amplified ground shaking at several of those sites with co-located strong motion recording stations, we evaluated VS30, the time-averaged shear-wave velocity in the upper 30 m of the subsurface. Ground motion models and ground motion prediction equations (GMPEs) use VS30 as a parameter to account for site amplification and site conditions; the parameter is also used to classify soil stiffness, which is widely used in building codes. To evaluate lateral variability in VS30 at each site, we conducted 2-D active-source seismic surveys, recording body and surface waves along linear profiles (118 to 174 m long) near the strong motion recording stations. We used sledgehammer (3.5-kg) and accelerated weight-drops (45-kg angled and 226-kg vertical) at each shot point co-located with 4.5-Hz (vertical- and horizontal-component) geophones at 2-m spacing along the profiles. We used 2-D refraction tomography and Multichannel Analysis of Surface Waves (MASW) methods to evaluate shear-wave velocities, from which we calculated VS30 at every meter along the seismic profiles. Our results show that VS30 varies by as little as 30 to as much as ~ 200 m/s along individual seismic profiles. We also found that VS30 nearest to strong motion stations can be up to 46% lower or 41% higher than VS30 within 50 m of the strong motion stations, suggesting 1-D VS30 may not accurately capture true site conditions at many strong motion sites due to lateral changes in subsurface materials and structures, which imply SCE substations may experience greater or smaller shaking than indicated by the co-located strong motion stations.
Presenting Author: Joanne H. Chan
Authors
Joanne H Chan jchan@usgs.gov U.S. Geological Survey, Menlo Park, California, United States Presenting Author
Corresponding Author
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Rufus D Catchings catching@usgs.gov U.S. Geological Survey, Menlo Park, California, United States |
Mark R Goldman goldman@usgs.gov U.S. Geological Survey, Menlo Park, California, United States |
Coyn J Criley ccriley@usgs.gov U.S. Geological Survey, Menlo Park, California, United States |
Robert R Sickler rsickler@usgs.gov U.S. Geological Survey, Menlo Park, California, United States |
Luther M Strayer luther.strayer@csueastbay.edu California State University, East Bay, Hayward, California, United States |
[Withdrawn] Evaluation of Vs30 at Southern California Edison Substations Using S-Wave Refraction Tomography and Multichannel Analysis of Surface Waves
Category
Methods for Site Response Estimation