Investigation and analysis of paleo-seismically induced lateral spreading mechanisms in Dixie Valley, Nevada.

摘要

Paleo-lateral spreads, dated between 2,000-2,500 years ago and interpreted by previous researchers to be due to seismically-induced liquefaction, have been investigated in Dixie Valley, Nevada. The study area, in the Central Nevada Seismic Belt within the Basin and Range province, is bound to the west by the Stillwater Range and to the east by the Clan-Alpine Range. The failure examined in this study is one in a zone of failures located between the Dixie Valley fault system---the range front fault system for the Stillwater Range---and the basin playa 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.;Field studies and the subsurface drilling investigation complicated the scope of the project as a result of the unanticipated discovery of extensive clays suggesting that failure could be the result of seismically-induced cyclic failure and sliding block failure in addition to simple liquefaction failure. Field and laboratory soil analyses were performed to measure soil properties to use in analysis for all three failure modes. An additional complication discovered during laboratory analyses was the variation of clay strength with overburden and moisture content.;Field methods included standard penetration testing (SPT), cone penetration testing (CPT), hand trenching and augering and slope profiling by laser range finder. Laboratory methods included particle size distribution, plasticity index analysis, soil classification by the Unified Soil Classification System and direct shear testing. Slope failure analyses included limit equilibrium of several liquefaction and cyclic failure methods for both SPT and CPT data and modeling a cross-section for sliding block failure.;Results from failure analyses and modeling indicate that all three modes of failure are possible given the range of earthquake magnitudes experienced in the region. The morphology of the failures may indicate the different failure mechanisms, which requires future investigation.