Las Vegas Valley Seismic Response Project

Jornada shot recorded at Squires Park, Las Vegas, NV

Project Investigators

Lawrence Livermore National Laboratory	University of Nevada Las Vegas	Nevada Seismological Laboratory, University of Nevada Reno
Dave McCallen Arthur Rodgers Shawn Larsen	Barbara Luke: Department of Civil and Environmental Engineering Catherine Snelson: Department of Geoscience Wanda Taylor: Department of Geoscience	John Anderson John Louie

Introduction	Background	Geologic and Tectonic Setting
LVVSRP Studies	Newspaper Articles	More Information

Introduction

The Las Vegas Valley Seismic Response Project (LVVSRP) focuses on charaterizing the Las Vegas Valley (LVV) and its response to seismic ground motion. Sources of seismic ground motions includes those generated by earthquakes and nuclear testing, in the event it resumes at the Nevada Test Site. A multidisciplinary team of seismologists, engineers and geoscientists are working towards understanding and integrating their findings on different aspects of the LVV. These individual studies range from understanding and modelling the basin stucture to characterizing the seismic response of structures.

Background

Las Vegas Valley, Nevada is a northwest trending valley situated in the southern portion of the Basin and Range province of western North America. It is a broad sedimentary basin composed primarily of Quaternary alluvial deposits (Tabor, 1982). Recent studies by Slemmons et. al. (2001) have shown that eight tectonically driven faults are located within the valley and are capable of producing earthquakes of Mw5-7.0.

The city of Las Vegas, Nevada is a rapidly growing community located within the Las Vegas basin. Understanding and assessing the seismic hazards of the city and surrounding area are vital in mitigating disaster for earthquakes. Quaternary faults located within close proximity to the city in conjunction with the nearby Death Valley fault system are sources of potential earthquakes capable of producing strong ground motions within the basin. Studies by Su, et. al. (1998) have shown that strong ground motions in alluvial basins from sources up to 300 km away can be overwhelmingly destructive, as was the case with Mexico City in 1985.

The Federal Emergency Management Agency (FEMA) has characterized the city of Las Vegas as located in an area of high seismic risk. From a FEMA HAZUS calculation based on a M6.9, estimated damages and total lost are expected to be approximately $28 million (Perry and O'Donnell, 2001). Increased awareness, stricter building codes and more studies are needed to carefully assess the seismic hazards of Las Vegas Valley.

Geologic and Tectonic Setting

Las Vegas Valley is geographically bounded by the Spring Mountains to the west, Frenchman Mountain to the east, the McCullough Range to the south, and the Sheep and Las Vegas ranges to the north. Extensional tectonics associated with the Basin and Range province of western North America helped to form the basin (Tabor, 1982). This extension has resulted in a series of normal and strike-slip faults that cut across the region including the inactive Las Vegas Shear Zone (LVSZ), a right lateral strike-slip fault and the left-lateral Lake Mead fault system (LMFS) as well as a series of more recent Quaternary normal faults (Figure 1). Many faults within the basin have been interpreted to be a result of subsidence, but recently eight of these faults have since been shown to be tectonically driven (Slemmons et al., 2001). It is suspected that more faults are present, but have yet to be identified in the Las Vegas basin.

Geophysical studies by Langenheim, et. al. (2001) have characterized preliminary basin geometries and thickness of basin fill based on gravity, drillhole and seismic reflection data. Results have indicated that the deepest areas of the basin are located in the northeast section of the valley with a maximum basin thickness of 5 km (Figure 1).

Figure 1. Topographic map of the Las Vegas Valley. Blue lines are in-active Miocene strike-slip faults and transfer faults. Red lines are Quaternary normal faults that cut across the basin that have recent offsets. Thin black lines are the basin thickness contours from Langenheim et al. (2001) model.