Grids in support of the U.S. Geological Survey Thermal Model for Seismic Hazard Studies

A 3D temperature model is constructed in order to support the estimation of physical parameters within the USGS National Crustal Model. The crustal model is defined by a geological framework consisting of various lithologies with distinct mineral compositions. A temperature model is needed to calculate mineral density and bulk and shear modulus as a function of position within the crust. These properties control seismic velocity and impedance, which are needed to accurately estimate earthquake travel times and seismic amplitudes in earthquake hazard analyses. The temperature model is constrained by observations of surface temperature, temperature gradient, and conductivity, inferred Moho temperature and depth, and assumed conductivity at the base of the crust. The continental plate is assumed to have heat production that decreases exponentially with depth and thermal conductivity that exponentially changes from a surface value to 3.6 W/m-K at the Moho. The oceanic plate cools as a halfspace with a geotherm dependent on plate age. Under these conditions and the application of observed surface heat production, predicted Moho temperatures match Moho temperatures inferred from Pn velocities, on average. As has been noted in previous studies, high crustal temperatures are found in the western United States, particularly beneath areas of recent volcanism. In the central and eastern United States, elevated temperatures are found from southeast Texas, into the Mississippi Embayment, and up through Wisconsin.