The engineering properties of alluvial/colluvial fault scarp soils in the western Basin and Range, and their influence on fault scarp morphology/dating

Abstract

Both field and laboratory studies of the alluvial/colluvial soils, derived from various lithologies, that comprise the 1954 Dixie Valley – Fairview Peak fault scarps and the 1915 Pleasant Valley fault scarps of west- central Nevada show that the engineering properties of these soils play a significant role in the development of scarp morphology. Laboratory shear tests demonstrate that the cohesive strengths (C) of these scarp soils increase in an approximately linear manner with increasing ratio of free face to total scarp height (R) . Comparable linear relationships exist between the bulk densities (Y,) and the b Rg ratios for the two study areas. In both cases, the v correlation coefficients between the soil engineering parameters and the Rg ratios are high. The peak friction angles ( (J)^) and the Rg ratios for the Dixie Valley-Fairview Peak study area also exhibit a linear trend and a high correlation coefficient, but, those of Pleasant Valley do not. This is probably due to the smaller sampling base of the latter. Such results help explain the often abrupt changes in the free face/total scarp height ratios observed along fault scarps at the boundaries between differing soil types.