Determination of translational landslide slip surface depth using balanced cross sections
Kim M. Bishop
California State University Department Geological Sciences, Los Angeles, CA, United States
An apparently little-recognized but powerful technique for determining slip surface depth of translational landslides is the use of balanced cross-sections. Conceptually, the method is simple and the necessary parameters can be determined without subsurface exploration. To determine the depth of the slip surface for a given landslide, a longitudinal cross-section through the approximate center of the slide is drawn. From the cross section, the area of the depression (zone of depletion) formed at the head of the slide above the listric part of the slip surface is determined. The displacement along the planar (translational) part of the slide is also determined, either by direct field measurement or by some indirect method. Finally, the depth of the slip surface is determined by dividing the area of the depression by the displacement. Determining the slip surface displacement is likely to be the most uncertain aspect of the method. In some cases, the displacement can be determined directly by measurement of offset features such as roads, fences, or surface drains. However, in many, if not most cases, the displacement must be determined by indirect methods such as using displacements found along the scarp(s) of the landslide. In using scarps, the style of internal deformation of the slide mass is important. Styles of deformation include penetrative shear strain and/or the slippage along discrete shear planes. Based on the displacement determined from the scarp(s), a reasonable calculation of the slip surface depth can be made.
This record provided courtesy of AGI/GeoRef.
