Earthquake Hazard Class Mapping by Parcel in Las Vegas Valley

摘要

Clark County, Nevada has completed the Nation's very first effort to map earthquake hazard class systematically through an entire urban area. The map will be used in development and disaster response planning, in addition to its direct use for building code implementation and enforcement. The County and the City of Henderson contracted with the Nevada System of Higher Education to classify about 550 square miles of Las Vegas Valley. The Parcel Map includes more than 10,000 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. We computed using our "ShakeZoning" process 50 separate earthquake scenarios, yielding estimates of earthquake ground shaking in Las Vegas Valley based on physics and geology rather than on statistics. Despite affecting only the upper 30 m, the Vs30 geotechnical shear-velocity from the Parcel Map shows clear effects on 0.1-Hz to 0.3-Hz shaking predictions.