Seismically-Induced Lateral Spreads Detected in Airphotos and Subsurface Investigation, Dixie Valley, NV

Paleo-lateral spreads, dated 2,000 to 2,500 years ago, have been identified by previous researchers in Dixie Valley, Nevada, a seismically active area of central Nevada which is bound to the west by the Stillwater Range and to the east by the Clan-Alpine Range. The study area is located between the Stillwater Range faults and the basin playa, and is composed of alluvial fan material washed down from the westward bounding Stillwater Range and of beach gravel, sands and fines from the eastward bounding pluvial Lake Dixie. Slope failures have occurred on slopes as low as approximately 3 degrees and, in the absence of a free face, have resulted in the crumpling of lake sediments at the passive toe. Preliminary field work shows the presence of sand boils and fissures, which are consistent with liquefaction and lateral spreading. Detailed seismic cone penetration testing and split-tube samples from drilling at the three sites within the lateral spreads show low-strength clays in the subsurface at one site and fine sands and clay at the other sites, complicating a simple seismically- induced liquefaction process. On-going geotechnical investigations and slope modeling will establish failure surfaces and failure mechanisms at all three sites.