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). To compare these risk-targeted spectral accelerations with uniform-hazard counterparts analogous to those in previous editions of the AASHTO Design Specifications, corresponding risk coefficients are also provided (for all of the site classes in a single ZIP file). The risk coefficients are ratios of the risk-targeted divided by uniform-hazard spectral accelerations, with the latter for a 7% probability of being exceeded in 75 years. The risk-targeted and uniform-hazard spectral accelerations were both derived from the truncated USGS seismic hazard curves released in the "Associated Item."