Progress on Building a USGS National Crustal Model for Seismic Hazard Studies

Date: 4/26/2019

Time: 08:45 AM

Room: Vashon

The USGS National Crustal Model (NCM) is being developed to assist in the modeling of seismic hazards across the conterminous United States by improving estimates of site response in the USGS National Seismic Hazard Model. Improved hazard assessments may also be used for planning and risk assessments but are not intended for site-specific engineering applications. We are currently in Phase 1 of the project, which covers the western United States west of -100 degrees longitude. In Phase 2, we will complete the NCM in the central and eastern U.S.&

The NCM is composed of geophysical attribute-depth profiles on a 1-km grid from which can be extracted metrics needed for ground motion models. Quantities of immediate interest are the time-averaged shear-wave velocity in the upper 30 meters and the depths to 1.0 and 2.5 km/s shear-wave velocity. The NCM has the flexibility to provide additional metrics such as fundamental frequency, a fully frequency-dependent site response function derived from 1D, 2D, or 3D analyses, or 3D geophysical volumes for wavefield simulations. The NCM may also benefit other aspects of seismic hazard analysis including better accounting for path-dependent attenuation and geometric spreading and more accurate estimation of earthquake source properties such as hypocentral location and stress drop.

Each geophysical profile within the NCM is based on subsurface geology, pressure, and temperature coupled with mineral and rock physics theory and porosity and attenuation models. The primary elements used to construct the NCM are: 1) depth to bedrock and basement; 2) 3D geologic framework; 3) petrologic and mineral physics database; 4) 3D temperature model; 5) calibration of a porosity and attenuation model; and 6) validation. These elements make use of a host of geology, borehole, gravity, and seismic datasets and are detailed in separate reports. The first primary element of the NCM is published as a USGS Open-File Report. Elements 2 through 4 are in review, and the methods for calibration and validation are in development.

Presenting Author: Oliver S. Boyd

Authors