Seismic hazards in the Basin and Range province, United States

Deformation rates determined for the Basin and Range province using geodetic data agree within uncertainties with scalar moment rate estimates from a 146-year earthquake catalog. This agreement suggests that the rate of historic earthquakes within the province provides a reasonable estimate for the long-term rate of seismicity. Geological estimates of deformation rates are lower than that of geodesy or seismicity due to limited data.; We focus on a particular, small region for more detailed analysis of ground motion prediction and amplification. The Reno-Sparks urban region (population ∼400,000) is located in a fault-controlled basin that is about 13 km wide and 21 km long. Despite the small basin size and depth, local basin effects are significant. Both data and synthetic modeling show that the 3D basin structure strongly influences ground motion within the basin. Site characteristics are assessed at twenty-one seismic stations in the region. Shallow shear wave velocities are measured using the refraction microtremor (ReMi) technique (Louie, 2001). Average velocities to depths of 30 m and 100 m are compared with local geological and soil classifications. Generalized geological classifications show some variations in unit averages of the measured velocities, variations between units are much smaller than the standard deviations of velocities within units having multiple measurements. Predictions of site velocities based on soil weight percent of gravel, sand, silt, and clay fall within +/-20% of measured values for all but two of the 21 sites. Ground motions from local earthquakes are used to ascertain empirical site amplification effects within the basin relative to a nearby rock site using the soil to rock spectral ratio technique. Most site response functions within the basin are mainly flat, but do show relative amplification. Some sites do show resonant peaks. These empirical site effects are compared with site conditions evaluated using average shallow shear wave velocities and local geological classifications. While the geology rock group has a lower mean amplification, the separation with those of the sedimentary groups not large. The Vs30 groups have distinct means that are well separated, indicating that velocity is a useful predictor of amplification.