Temporal and Spatial Variation in Ambient Seismic Noise in the Charleston Region

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Cobb, Savannah E
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Charleston has a high earthquake hazard, and understanding site response in the region is important for earthquake preparedness. Previous studies have revealed a 1-3 Hz peak in horizontal-to-vertical spectral ratios (HVSRs) on the Charleston peninsula. These studies also found that the amplitude of this response varies with surface geology and, at a few locations, with time of day. The objective of this study is to study the spatial and temporal variation of the 1-3 Hz peak amplitude in Charleston using recently acquired seismic data. In Summer 2015, the United States Geological Survey (USGS) recorded up to 7 hours of daytime ambient seismic noise from ten arrays of up nine to ten Nanometrics Trillium Compact seismometers placed throughout the Charleston region. I computed HVSRs using 1-hour-long time segments when all seismometers in an array were recording. I analyzed variation in HVSRs by hour and by station to determine if spatial variation or temporal variation in the amplitude of the 1-3 Hz peak was more significant. I found that spatial variation in ambient seismic noise was consistently much greater than temporal variation in ambient seismic noise for all stations. Therefore, the observed spatial variation in the 1-3 Hz HVSRs from this and the previous studies is a robust observation relatively unaffected by the time of day when data were collected.
Charleston, seismic noise, seismology, spatial, temporal, variation, earthquake, seismicity, ambient seismic noise