NEW EVIDENCE SUPPORTING PROBABLE EARTHQUAKE NUCLEATION SITE ALONG THE CENTRAL MAYNARD LAKE FAULT WITHIN THE LEFT-LATERAL PAHRANAGAT SHEAR ZONE, NEVADA, USA

The eastern part of the rift segment boundary zone between the Northern (NBR) and Central Basin and Range (CBR) sub-provinces consists of the Miocene-Quaternary left-lateral Pahranagat shear zone/fault system (PSZ) on the SW and the Caliente-Enterprise zone on the NE. Delineation of the style and timing of deformation, and kinematics within this boundary zone is essential to understanding the development of the Basin and Range. Here, we focus on the PSZ, specifically the Maynard Lake fault (MLF), the southern of three major left-lateral faults in this zone that lies about 115 km N of Las Vegas, Nevada. Published maps suggest that Miocene-Quaternary activity occurred along the MLF. Evidence for Quaternary motion includes geodetic data and seismic epicenters. New 1:12,000 scale mapping of the central MLF reveals a NE-striking, left-lateral transfer fault zone between two distinct normal fault sets to the north and south. These distinct fault sets are made up of steeply dipping, primarily N-S-striking normal faults that cut Miocene rocks, but differ in distribution and number of faults.

Quaternary slip along the central MLF is shown by fault scarps, and offset Quaternary deposits and geomorphic features. A Quaternary fault exposure in the western part of the study area reveals a few meters of dip-slip offset within one of the youngest Quaternary alluvial fans along the fault zone. Along the majority of the central MLF, multiple fault strands are exposed. These strands exhibit subtle scarp development over a distance of ~4 km along strike. Minor scarp heights can be attributed to the strike-slip offset, which is evidenced by offset features of older alluvial fans. In contrast to this multiple stranded fault section, the MLF is a single strand or narrow zone that lacks Quaternary motion to the SW and NE of the study area. We suggest that earthquake nucleation within the PSZ could possibly occur along the central portion of the MLF because recent offset in Quaternary units indicates recent fault activity there, but not nearby.

In summary, the central MLF, on the southern side of the NBR-CBR boundary zone is a transfer fault that accommodates strain from steeply dipping NS-striking normal faults to the N and S which developed during the Miocene, but continues to be active in the Quaternary along some sections, thus posing a seismic hazard.