Test Of High-Resolution Seismic Reflection And Other Geophysical Techniques On The Boup Landslide In The Swiss Alps

Abstract

Complementary geophysical surveys on large landslides help reveal geologic structures and processes, and thus can help devise mitigation strategies. The combined interpretation of these methods enhance the result of each data set interpretation and makes it possible to derive a geological model of the landslide. We chose a test site on the Boup landslide (Wallis, western Swiss Alps) to test high-resolution seismic reflection surveys combined with ground penetrating radar (GPR), electromagnetic (EM) and electrokinetic spontaneous potential (SP) measurements. The results of the high-resolution seismic surveys suggest that the sliding is within a gypsum layer at 50 m depth and not as previously believed along a deeper (70 m) gypsum-shale boundary, also mapped seismically. Inversion of electromagnetic profiles (EM-34) with constraints from seismic data provided a model cross-section of conductivity values of the landslide (20-25 mS/m) and of the surrounding stable ground (10-15 mS/m), and it helped outline their boundary at depth. The accurate surface location of the landslide limit could be detected with electromagnetic measurements of shallower depths of investigation (EM-31). Positive PS anomalies revealed an upward flow of mineralised waster interpreted to follow the lateral boundary of the Boup landslide on its east side. Limited success was obtained with GPR profiling. This method can be hampered by conductive shallow layers, and its successful application on landslides is expected to be strongly site dependant.