EFFICACY OF GEOPHYSICAL METHODS IN IDENTIFYING AND CHARACTERIZING LANDSLIDES AT DIFFERENT STAGES OF DEVELOPMENT

Abstract – The use of geophysical techniques such as seismic refraction and electrical resistivity (ER) have gained popularity in the modeling of subsurface structures over the last two decades. Such non-invasive techniques are considered highly reliable in the imaging of hydrologic barriers as well as in the field of petroleum geology, however they have not been as widely used to study structures such as landslides. Our research aims to assess the effectiveness of seismic and ER surveying techniques in identifying and characterizing landslides at different stages of development. In order to make this assessment we conducted surveys on slopes with known and historical landslide activity, slopes with suspected landslide activity, and slopes of high landslide susceptibility with no known activity. Landslide susceptibility was modeled in ArcGIS using a frequency-ratio method where peak ground acceleration, mean annual precipitation, elevation, lithology, slope, aspect, and ground cover are considered in the calculation of a Landslide Susceptibility Index. This technique was used to create a full landslide susceptibility map of Arizona so that slopes with high landslide susceptibility where no known activity had occurred could be identified for further geophysical assessment. Our results indicate that geophysical methods work very well in identifying and characterizing landslides at different stages of development. Landslide slip surfaces and offset features were identifiable on slopes with historical and suspected landslide activity. On high susceptibility slopes with no known activity, geophysical methods provided a better assessment of landslide development beyond topographic/field observations by allowing us to image potential future failure surfaces.