PRELIMINARY PSEUDO 3-D IMAGERY OF THE STATE LINE FAULT, STEWART VALLEY, NEVADA USING SEISMIC REFLECTION DATA

The State Line fault (SFS) system is located in the central Basin and Range region and has recently been included as part of the Eastern California Shear zone (ECSZ). The SFS consists of three main segments: the Mesquite, Pahrump and Armargosa segments. The Pahrump segment, located in Stewart Valley, Nevada is made up north-west trending dextral strike-slip faults that run parallel to the Nevada-California border. Previous geologic and geophysical studies conducted in and around Stewart Valley, located ~90 km from Las Vegas, Nevada, have constrained the location of the SFS to within a few kilometers.

The goals of this project were to use seismic methods to definitively locate the northwestern most trace of the SFS and produce pseudo 3-D seismic cross-sections that can then be used to characterize the subsurface geometry and determine the slip of the State Line fault. During July 2007, four seismic lines were acquired in Stewart Valley: two normal and two parallel to the mapped traces of the SFS. Presented here are preliminary results from the two seismic lines acquired normal to the fault. These lines were acquired utilizing a 144-channel geode system with each of the 4.5 Hz vertical geophones set out at 5 m intervals to produce a 595 m long profile to the north and a 715 m long profile to the south. The vibroseis was programmed to produce an 8 s linear sweep from 20-160 Hz. These data returned excellent signal to noise and reveal subsurface lithology that will subsequently be used to resolve the subsurface geometry of the SFS. This knowledge will then enhance our understanding of the evolution of the SFS as whole. Knowing how the State Line fault has evolved gives insight into the stick-slip fault evolution for the region and may improve understanding of how stress has been partitioned from larger strike-slip systems such as the San Andreas fault.