A high-resolution seismic CHIRP investigation of structure and tectonic activity in Pyramid Lake, Nevada

Abstract

The structurally complex transition between the Pacific and North American plate and more specifically the Sierran microplate and the Basin and Range, known as the Walker Lane Belt in the north and the eastern California shear zone in the south, is observed through seismic, geodetic, and geologic data (Ichinose et al., 2003; Unruh et al., 2003; Argus and Gordon, 1991; Thatcher et al., 1999; Bennett et al., 2003; Svarc et al., 2002; Oldow, 2003; Hammond and Thatcher, 2004; Dokka and Travis, 1990; Wesnousky 2005a; Hammond et al., 2011). This 100-km-wide belt of seismicity and active strike-slip faulting accommodates ∼20% (Thatcher et al., 1999; Thatcher et al., 2003; Hammond et al., 2011; Faulds et al., 2005) or ∼12.4 mm/yr of relative motion between the two microplates (Bennett et al., 2003; Dingler et al., 2010.) Pyramid Lake straddles the margin between the northern Walker Lane and the northwest Basin and Range. Recent sediments within several large lakes in this region express very well this complex structural transition. In June 2010, the University of Nevada, Reno; Scripps Institution of Oceanography; and the United States Geological Survey, Salt Lake City collected high-resolution (sub-meter) seismic CHIRP data in Pyramid Lake, Nevada. Faults were beautifully expressed in the images that allowed correlation between horizons in CHIRP profiles and the chronostratigraphic framework acquired from five sediment cores. This produced, for the first time, a complete fault map of the Pyramid Lake region and a seismic history of the lake as well as slip rates to classify earthquake hazards in the nearby Reno metropolitan area. Successful imagining of the lake revealed a system of much more complexity than originally anticipated. Repeating flips in structural polarity within the basin and segmentation of the East Pyramid Lake fault (referred to as the Lake Range fault in this paper) supports the notion that the Pyramid Lake basin provides a natural laboratory to study the details of transtensional deformation.