VS30, the time-averaged shear-wave velocity (VS) to a depth of 30 meters, is a key index adopted by the earthquake engineering community to account for seismic site conditions. VS30 is typically based on geophysical measurements of VS derived from invasive and noninvasive techniques at sites of interest. Owing to cost considerations, as well as logistical and environmental concerns, VS30 data are sparse or not readily available for most areas. Where data are available, VS30 values are often assembled in assorted formats that are accessible from disparate and (or) impermanent Websites. To help remedy this situation, we compiled VS30 measurements obtained by studies funded by the U.S. Geological Survey (USGS) and other governmental agencies. Thus far, we have compiled VS30 values for 4,369 sites in the United States, along with metadata for each measurement from government-sponsored reports, online databases, and scientific and engineering journals. Most of the data in our VS30 compilation originated from publications directly reporting the work of field investigators. A subset consisting of 20 percent of VS30 values was previously compiled by the USGS and other research institutions. VS30 originating from these earlier compilations were crosschecked against published reports when clarification was needed. Both downhole and surface-based VS30 estimates are represented in our VS30 compilation. Most of the VS30 data are for sites in the western contiguous United States (3,128 sites); 682 VS30 values are for sites in the Central United States; 267 VS30 values are for sites in the Eastern United States and Puerto Rico; 15 VS30 values are for sites in Alaska; 30 VS30 values are for sites in Hawaii. The remaining 247 sites are in the vicinity of Vancouver, Canada.

The multi-period BSE-1E and BSE-2E response spectra for the 2023 ASCE 41 Standard are derived from the downloadable data files. For each site class, 5% in 50 year uniform hazard spectral accelerations and 20% in 50 year uniform hazard spectral accelerations are provided for 22 spectral periods.

The multi-period BSE-1E and BSE-2E response spectra for the 2023 ASCE 41 Standard are derived from the downloadable data files. For each site class, 5% in 50 year uniform hazard spectral accelerations and 20% in 50 year uniform hazard spectral accelerations are provided for 22 spectral periods.

The multi-period BSE-1E and BSE-2E response spectra for the 2023 ASCE 41 Standard are derived from the downloadable data files. For each site class, 5% in 50 year uniform hazard spectral accelerations and 20% in 50 year uniform hazard spectral accelerations are provided for 22 spectral periods.

Site characterization, with the goal of measuring VS30, was performed at 27 strong motion stations across Central and Southern California. These stations, belonging to the National Strong Motion Program, spanned four counties and varied geophysical environments. Primarily employed were the Simplified Site Characterization Procedures (SSCP) as an efficient yet robust method for measuring VS30. The active-source SSCP were designed for Rayleigh-wave MASW analysis, while the passive-source methods were designed with ESAC analysis in mind. Also employed along the El Centro Array were conventional large-array MASW and ambient microtremor techniques, and HVSR site characterization techniques.

The “Database of Central and Eastern North American Seismic Velocity Structure” involves the compilation of one-dimensional (1D) seismic velocity-depth functions for central and eastern North America (CENA). The present database is an update of the report by Chulick and Mooney (2002) who present a compilation and statistical analysis of 1D seismic velocity-depth functions for North America and its margins. All seismic velocity-depth functions are extracted from peer-reviewed journal articles, with 86% derived from active-source seismic refraction profiles and the remaining 14% from receiver functions or local earthquake tomography models. No reanalysis of the original seismic field data was undertaken. The database of Chulick and Mooney (2002) covered a much larger region than central and eastern North America. In 2013 the USGS focused on augmenting the Chulick and Mooney (2002) database to update the coverage specifically for central and eastern North America. This augmented compilation was done to help characterize the seismic site response at the locations of nuclear power facilities and was a deliverable specified by a USGS-Nuclear Regulatory Commission Inter-agency Work Agreement, which can be found at https://www.nrc.gov/docs/ML1428/ML14280A412.pdf. Each seismic velocity-depth function is specified by its unique latitude and longitude and consists of the published crustal model for the subsurface Earth layers at that location, with each layer specified by compressional-wave velocity, shear-wave velocity, thickness, and depth. Each entry also includes other information, such as: elevation, geologic province, age of last significant thermo-tectonic activity, and the principal seismic methodology used to determine the velocity-depth function. Chulick, G.S., and Mooney, W.D., 2002, Seismic Structure of the Crust and Uppermost Mantle of North America and Adjacent Oceanic Basins: A Synthesis, Bulletin of the Seismological Society of America, vol.92, no.6, p.2478–2492.