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Compilation of Geologic and Seismic Velocity Characteristics at Advanced National Seismic System Strong Motion Accelerometer Sites

December 9, 2021

Near-surface site characteristics are critical for accurately modeling ground motion, which in turn influences seismic hazard analysis and design of critical infrastructure. Currently, there are many strong motion accelerometers within the Advanced National Seismic System (ANSS) that are missing this information. We use a Geographic Information Systems (GIS) based framework to intersect the site coordinates of approximately 5,500 ANSS accelerometers located throughout the United States and its territories with geology and velocity information. We consider: (1) surficial geology from digitized geologic maps (Horton, 2017; Wilson et al., 2015; Sherrod et al., 2007; Bawiec, 1999; Saucedo, 2005; Bedrossian et al., 2012; Washington Geological Survey, 2019; Washington Division of Geology and Earth Resources; 2016; Franczyk, et al., 2020; and Wagner et al., 2002), (2) measurements of the shear-wave velocity in the upper 30 m (VS30) at seismic stations (McPhillips et al., 2020; Yong et al., 2016), (3) three different VS30 proxies based on geology (Wills et al., 2015), terrain (Iwashashi and Pike, 2007; Yong et al., 2012; Yong, 2016), and a hybrid approach that utilizes regional VS30 map insets or topographic-slope-based proxy mosaics (Allen and Wald, 2007; Thompson et al., 2014; Heath et al., 2020), (4) VS30 values utilizing a combination of measurements and proxies from the Next Generation of Ground-Motion Attenuation Models (i.e., NGA-West2, NGA-East, and NGA-Subduction (Seyhan et al., 2014; Goulet et al., 2018; Bozorgnia et al., 2020)), and (5) additional site characteristics where available, including liquefaction susceptibility (Knudsen et al., 2000; Witter et al., 2006; CUSEC Association of the State Geologists, 2008; Madin and Burns, 2012; Palmer et al., 2004), VS profile data from the University of California, Los Angeles (UCLA) Shear-wave Velocity Profile Database (VSPDB) (Ahdi et al., 2017), regional VS30 information (Williams et al., 1999); fundamental site period (fpeak) (Gospe et al., 2020), National Earthquake Hazard Reduction Program (NEHRP) site class (Building Seismic Safety Council, 2003), borehole geologic information (Jeschke et al., 2019), physiographic province (Fenneman and Johnson, 1946), basin amplification (Petersen et al., 2019), and peak ground acceleration and horizontal spectral response acceleration from regional National Seismic Hazard Models (Petersen et al., 2019; Wesson et al., 2007; Klein et al., 2001; Mueller et al., 2003; and Petersen et al., 2014). This compilation will help populate seismic station information webpages, like those of the Center for Engineering Strong Motion Data (strongmotioncenter.org), providing users the option to quickly obtain and utilize a variety of VS30 measurements, VS30 proxy-based estimates, and assigned NEHRP site classes. The collective availability of this information will improve our understanding of the ground motions recorded at ANSS accelerometers from both previous and future significant earthquakes. This additional station information will increase the usefulness of strong motion data and ultimately improve ground motion models used in seismic hazard estimates.

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