This data release provides the global mosaic of the time-averaged shear-wave velocity in the upper 30 m (Vs30) described by Heath and others (2020). This map uses the Wald and Allen (2007) slope-based Vs30 as the basemap, and regional take precedence where they are available.

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 US and its territories with geology and velocity information. We consider: (1) surficial geology from digitized geologic maps, (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 (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)) (5) Regional liquefaction, subsurface and seismic site class data as available. 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 National Earthquake Hazard Reduction Program (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 also improve ground motion models used in seismic hazard estimates.

The dataset is consisted of travel-time records in SEG2 format recorded using multi-station arrays near 6 seismographic stations located in southern California. A table in the spreadsheet (vs30data.SCE.FINAL01.xlsx) summarizes the data collection. Included in the dataset are figures showing incremental results supporting the resultant modeled shear-wave velocity (Vs) profile and estimated time-averaged Vs in the upper 30 m of the subsurface (Vs30). Incremental results include plots of the picks of fundamental mode dispersion curve, the modeled Vs profile and estimated Vs30, and the empirical and theoretical dispersion curves.

In June of 2011, the U.S. Geological Survey acquired high-resolution P- and S-wave seismic data across the mapped (Schussler, 1906) trace of the San Andreas Fault zone at San Andreas Lake in unincorporated San Mateo County, California. Our seismic survey consisted of seismic reflection, refraction, and guided-wave data along a 60-m-long profile. To acquire the reflection and refraction data we co-located shots and geophones, spaced every meter along the profile. We used 59 SercelTM L40A, P-wave (40-Hz vertical-component) geophones (sensitivity of 22.34 volts/meter/second) to record 59 P-wave shots and 59 SercelTM L28-LBH, S-wave (4.5-Hz horizontal-component) geophones (sensitivity of 31.3 volts/meter/second)to record 59 S-wave shots. We generated P-wave data using a charge from a Betsy SeisgunTM, with the charge placed approximately 0.4 meters (16 inches) beneath the ground surface. The charge consisted of an 8-gauge, 400-grain, blank shotgun shell. S-wave sources were generated by horizontally striking an aluminum block with a 3.5-kg sledgehammer. We acquired fault-zone-guided-wave data using approximately one pound of explosives within a mapped trace of the San Andreas Fault, approximately 1.74 km NNW of the recording arrays. The explosives were placed in a 5-cm (2 inch) diameter borehole approximately 3-meter (10 feet) deep. All data were recorded using a 60-channel Geometrics Stratavisor NX-60TM seismograph with a 24-bit analog-to-digital converter and a roll-along descaling factor, and the output data are in SEG-Y format (Barry et al, 1975). Each in-line shot was recorded for two seconds, with data recording starting 100 ms before the actual time of the shot. Data were recorded at a sampling rate of 0.5 ms, or 2000 samples per second. This report provides the metadata needed to analyze the seismic data. References Barry, K.M., Cavers, D.A. and Kneale, C.W., 1975, Recommended standards for digital tape formats: Geophysics, vol. 40, no. 2, p. 344-352. Schussler, H., 1906, The Water Supply of San Francisco, California, Before, During, and After the Earthquake of April 18, 1906 and the Subsequent Conflagration: Martin B. Brown Press, New York, 103 pp.

This data release provides a map of the time-averaged shear-wave velocity in the upper 30 m (Vs30) for California using the method described by Thompson and others (2014). There are two adjustments to the algorithm described by Thompson and others (2014), which is built on the geology-based Vs30 map by Wills and Clahan (2006). In this data release, we use the Wills and others (2015) updated geology-based Vs30 map. The second change is that we have adjusted the kriging procedure so that measured Vs30 values do not affect the predictions across distinctly different geologic units.

The updated 2018 National Seismic Hazard Model includes new ground motion models, aleatory uncertainty, and soil amplification factors for the central and eastern U.S. and incorporates basin depths from local seismic velocity models in four western U.S. (WUS) urban areas. These additions allow us, for the first time, to calculate probabilistic seismic hazard curves for an expanded set of spectral periods (0.01 s to 10 s) and site classes (VS30 = 150 m/s to 1,500 m/s) for the conterminous U.S. (CONUS), as well as account for amplification of long-period ground motions in deep sedimentary basins in the Los Angeles, San Francisco Bay, Salt Lake City, and Seattle regions. Ground motion data for 2, 5, and 10 percent probability of exceedance in 50 years have been derived from these hazard curves.Two sets of data are available: (1) 0.05 by 0.05 degree gridded hazard data for the CONUS and (2) 0.01 by 0.01 degree gridded hazard data for WUS basins. Note that both sets of data contain basin amplification in deep sedimentary basins in the WUS. The 0.01 degree by 0.01 degree data simply provides a higher resolution dataset than then 0.05 degree by 0.05 degree dataset. This dataset is discussed in the journal article titled: "The 2018 update of the US National Seismic Hazard Model: Additional period and site class data" by Shumway et al. (2021) located at https://doi.org/10.1177/8755293020970979. First Posted - October 7, 2019 Revised - February 2020 (ver 1.1) Revised - May 2021 (ver 1.2)

A model of the lower seismogenic depth distribution of earthquakes in the western United States was developed to support models for seismic hazard assessment that will be included in the 2023 USGS National Seismic Hazard Model. This data release presents a recalibration using the hypocentral depths of events M>1 from the Advanced National Seismic System Comprehensive Earthquake Catalog from 1980 to 2021. For higher precision and better resolution in the model, the data were supplemented with seismicity from southern California that was relocated by Hauksson and others (2012). Along the San Andreas Fault, the deepest seismogenic depths are located at 23 km around the Cholame segment, whereas the shallowest depths are located at about 10 km along the Rogers Creek and Macaama faults. In the western United States outside of California, the depth varies between 10 and 25 km with an average around 14 km.