Earthquake location data for the southern Great Basin of Nevada and California: 1984 through 1986

This report presents data in map and table form for earthquake parameters such as hypocentral coordinates and magnitudes for earthquakes located by the southern Great Basin Seismic network for the time period January 1, 1984, through December 31, 1986. These maps show concentrations of earthquakes in regions previously noted to be seismically active, including the Pahranagat Shear Zone, Pahroc Mountains, southern Nevada Test Site, Timber Mountain, Black Mountain, Gold Mountain, Montezuma Range, and Grapevine Mountains. A concentration of earthquake activity in the Reveille Range was observed in 1986, in a previously inactive area. The northern Nevada Test Site had fewer earthquakes than a comparable area of the southern Nevada Test Site, indicating that the low-yield nuclear testing program is not currently triggering significant numbers of aftershocks. Eight microearthquakes occurred at Yucca Mountain during the 1984-1986 monitoring period. Depths of focus for well-located earthquakes continue to indicate a bimodal distribution, with peaks at 1 to 2 and 8 to 9 km below sea-level and a local minimum at 4 to 5 km. Focal mechanisms range from strike slip to normal slip. No dependence of slip mode on depth or magnitude is evident. 8 refs., 46 figs., 5 tabs.