Earthquake Hazard Class Mapping by Parcel in Las Vegas Valley

Clark County, Nevada completed the very first effort in the United States to map earthquake hazard class systematically through an entire urban area. The County and the City of Henderson contracted with the Nevada System of Higher Education to classify about 500 square miles including urban Las Vegas Valley, and exurban areas considered for future development. The Parcel Map includes 10,721 surface-wave array measurements that classify individual parcels on the NEHRP hazard scale. We introduce a C+ Class for sites with Class B average velocities but soft surface soil. The measured Parcel Map shows a clearly definable C+ to C boundary on the west side of the Valley. The C to D boundary is much more complex. Using the parcel map in computing shaking in the Valley for scenario earthquakes is crucial for obtaining realistic predictions of ground motions. Despite affecting only the upper 30 meters, the Vs30 geotechnical shear-velocity from the Parcel Map shows clear effects on 3d shaking predictions computed at frequencies from 0.1 Hz to 1.0 Hz.