A HIGH RESOLUTION, LOCAL-SCALE CHARACTERIZATION OF LG ATTENUATION IN THE ROCKY MOUNTAIN–CENTRAL UNITED STATES TRANSITION ZONE

Notable regional-scale differences in seismic attenuation exist across the continental United States, and it is well established that the attenuation of Lg-phase waves is greater west of the Rocky Mountains than east of the Rocky Mountains. However, there is considerably less clarity in delineating the boundary or defining the transition in attenuation between the Western U.S. (WUS) and the Central and Eastern U.S. (CEUS), as few near-field strong motion observations exist in the CEUS. Utilizing Lg-phase waves recorded at regional distances (110-1100 km) at ~300 seismic stations from Oklahoma to central Nevada, we compute the path-averaged apparent quality factor (the inverse of attenuation) Q, source terms, and local amplification factors at one-octave frequency bands centered on the frequencies 0.75, 1.0, 3.0, 6.0, and 12.0 Hz. We use all raypaths and first assume a single Q to derive source and receiver terms. Subsequently subdividing the study area into distinct physiographic regions allows us to quantify the average path-averaged Q in the Basin and Range, Colorado Plateau, Rocky Mountains, and Great Plains. This high-resolution, local-scale analysis of Q is a crucial component for modeling the variation of ground motion prediction equations (GMPEs), and our refined Q(f) model will provide valuable insight into local-scale attenuation mechanisms and supplements the attenuation component of the USGS National Crustal Model, which will lead to improved ground motion characterization in the USGS National Seismic Hazard map.