Test of high-resolution seismic reflection and other geophysical techniques on the Boup landslide in the Swiss Alps

Complementary geophysical surveys on large landslides help reveal geologic structures and processes, and thus can help devise mitigation strategies. T he combined interpretation of these methods enhance the result of each data set interpretation and makes it possible to derive a geological model of t he landslide. We chose a test site on the Boup landslide (Wallis, western Swiss Alps) to test high-resolution seismic reflection surveys combined with ground penetr ating radar (GPR), electromagnetic (EM) and electrokinetic spontaneous pote ntial (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 alon g a deeper (70 m) gypsum-shale boundary, also mapped seismically. Inversion of electromagnetic profiles (EM-34) with constraints from seismic data pro vided 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 outl ine their boundary at depth. The accurate surface location of the landslide limit could be detected with electromagnetic measurements of shallower dep ths of investigation (EM-31). Positive PS anomalies revealed an upward flow of mineralised water interpreted to follow the lateral boundary of the Bou p landslide on its east side. Limited success was obtained with GPR profili ng. This method can be hampered by conductive shallow layers, and its succe ssful application on landslides is expected to be strongly site dependant.