Peak ground velocity spatial variability revealed by dense seismic array in southern California

Journal of Geophysical Research B: Solid Earth
By: , and 

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Abstract

Understanding and modeling variability of ground motion is essential for building accurate and precise ground motion prediction equations, which can net site‐specific characterization and reduced hazard levels. Here, we explore the spatial variability in peak ground velocity (PGV) at Sage Brush Flats along the San Jacinto Fault in southern California. We use data from a dense array (0.6 x 0.6 km2, 1,108 geophones, station spacings 10‐30 m) deployed in 2014 for ~1‐month. These data offer an opportunity to study small scale variability in this region. We examine 38 2≤ML≤4.2 earthquakes within 200 km of the array. Fault strands and a small basin impact the ground motions, producing PGV variations up to 22% of the mean and a 40% reduction in P and S wave near‐surface velocities. We find along‐fault rupture directivity, source, and path effects can increase PGVs by 167%. Surface PGV measurements exceed the co‐located borehole station (depth 148 m) PGV by factors of 3‐10, confirming the impact on PGV from near surface fault structures, basins, topography, and amplifications from soft sediments. Consistently we find high PGVs within the basin structure. A pair of ~co‐located ML2.6 events produce repeatable PGV values with similar spatial patterns. The average corner frequencies of these two events are 11‐16 Hz and viable measurements of stress drop can differ by 6.45MPa. Within this small array, the PGV values are variable implying spatial extrapolation of PGV to regions of known faults and basins, even across a small area, should be done with caution.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Peak ground velocity spatial variability revealed by dense seismic array in southern California
Series title Journal of Geophysical Research B: Solid Earth
DOI 10.1029/2019JB019157
Edition Online First
Year Published 2020
Language English
Publisher American Geophysical Union
Contributing office(s) Earthquake Science Center
Country United States
State California
Other Geospatial Sage Brush Flats, San Jacinto Fault
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