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 Guam and the Northern Mariana Islands.

为设计可安全抵御地震作用的桥梁，2023版美国公路与运输官员协会（AASHTO）的三项规范，即（1）《LRFD抗震桥梁设计指南规范》、（2）《LRFD桥梁设计规范》以及（3）《隔震设计指南规范》，通过本次数据发布及对应的美国地质调查局（USGS）抗震设计网络服务，提供了面向风险目标的设计地震动参数。
该网络服务可根据用户指定的经纬度，对本次发布的网格化地震动数据进行空间插值计算。
下述附件文件共覆盖8类场地类别，每类文件均针对一组经纬度网格与22个频谱周期，提供了以g为单位的风险目标谱加速度（Spectral Acceleration，SA），其中0.0秒周期对应峰值地面加速度，记为SA0P0。
BC类场地、0.0秒、0.2秒及1.0秒周期对应的谱加速度，直接取自“关联项目”中发布的美国地质调查局地震危险性曲线；基于该三类参数，其余场地类别与频谱周期的谱加速度均通过美国联邦应急管理局（FEMA）P-2078《美国非本土大陆场地多周期反应谱制定规程》间接推导得出——因关岛及北马里亚纳群岛暂无对应美国地质调查局的地震危险性曲线。