INCORPORATING 3D GEOLOGY INTO SEISMIC HAZARD FOR THE ATLANTIC AND GULF COASTAL PLAINS

Several studies at the urban and small region scale have successfully incorporated 3D geology mapping into earthquake hazard models and maps for use in building codes, emergency planning, and seismic hazard mitigation. We are developing a 3D geology model for the Atlantic and Gulf Coastal Plain to be used in improving the U.S. Geological Survey’s (USGS) National Seismic Hazard Model (NSHM) for those larger regions. The Atlantic and Gulf coastal plains have very thick sediments (up to 12 km) over bedrock that contribute significantly to the response to earthquake ground shaking. We started with the simplified coastal plain amplification model of Mueller (1999, 2008) based on surface geology and sediment thickness. This initial model has been incorporated, along with basic geotechnical and seismological information, into the current 2018 USGS NSHM for the coastal plain region. We will present these initial coastal plain seismic hazard maps and comparisons to the 2018 USGS national seismic hazard maps. For our initial 3D geology model, ground motions on sediments are amplified at long periods relative to the standard national seismic hazard maps used in building codes. Compared to the standard hazard maps at short periods, ground motions above 0.2 g tend to be more greatly deampified, and ground motions below 0.2g tend to be more greatly amplified. We will also discuss how we are updating the Mueller (1999, 2008) 3D geology model using available boring information and 3D hydrogeological models to improve these initial seismic hazard maps. This research works toward the goal of improving models for predicting ground motion amplifications and seismic hazards in the Central and Eastern United States.