SEISMICITY OF THE SOUTHERN NEVADA REGION

We present an overview of the historical seismicity of southern Nevada from an updated regional earthquake catalog. Recent moderate events include the 1966 M 6.0 Caliente earthquake, the 1992 M 5.6 Little Skull Mountain earthquake in southern NTS, the 1992 M 5.8 St. George, Utah earthquake, and the 1999 M 5.6 Scottys Junction earthquake near Goldfield. The broad east-west zone of seismicity at about 37N extending eastward from the Eastern California Shear Zone into Utah has been termed the Southern Nevada Seismic Belt. This zone includes several moderate historical earthquakes in the Goldfield region, NTS area seismicity, activity of the Pahranagat Shear Zone north of Las Vegas, and the Caliente region in eastern Nevada. Persistent activity in the Boulder City - Lake Mead area, including two M 3.7 events in 1988, may be associated with the Mead Slope fault and a number of M 5+ earthquakes in the 1940s correlated with filling of Lake Mead. The M 3.5 earthquakes on November 9, 1989, and February 3, 2001, within the Las Vegas basin were widely felt and are a reminder that active faults exist in urban Las Vegas. The ability to characterize the seismicity and active structures (dependent on catalog completeness and location accuracy) is challenging due to the variability in the regional seismic monitoring network and the large uncertainties in the historical record. Whereas the NTS region has benefited from comprehensive seismic monitoring, improvements are needed in characterizing potential source zones capable of generating damaging ground motions in the Las Vegas area and along the I15 corridor. ANSS strong motion and broadband instruments provided through Lawrence Livermore National Lab have been installed in Las Vegas Valley to better understand the response of the basin to earthquake ground motions; however, improved regional monitoring is needed to maintain a quality earthquake catalog and effectively evaluate active tectonic processes in the region.