Gridded earthquake ground motions for the 2023 AASHTO Design Specifications

For designing bridges to safely resist earthquakes, the 2023 editions of the AASHTO (1) Guide Specifications for LRFD Seismic Bridge Design, (2) LRFD Bridge Design Specifications, and (3) Guide Specifications for Seismic Isolation Design provide risk-targeted design ground motions via this data release and the corresponding USGS Seismic Design Web Services. The web services spatially interpolate the gridded ground motions of this data release for user-specified latitudes and longitudes. The attached files below for 8 site classes each provide risk-targeted spectral accelerations (in units of g) for a grid of latitudes and longitudes and 22 spectral periods, including 0.0 seconds for peak ground acceleration (denoted SA0P0). The spectral accelerations for Site Class BC and spectral periods of 0.0, 0.2, and 1.0 seconds were directly derived from the USGS seismic hazard curves released in the "Associated Item"; from these three values, the spectral accelerations for the other site classes and spectral periods were derived indirectly via the FEMA P-2078 "Procedures for Developing Multi-Period Response Spectra at Non-Conterminous United States Sites," because corresponding USGS hazard curves were not yet available for Alaska.