Landslide characterization using active and passive seismic imaging techniques: a case study from Kerala, India

The unusually intense precipitations of the 2018 monsoon triggered numerous landslides in the Western Ghats region, southwest of India. Although the landslides caused no casualties, significant damage to property and infrastructure was observed. We present, as a case study, the results of active and passive seismic prospecting at two of those landslides with the goal of characterizing them, in a first application of shallow seismic exploration to landslides in the region. Our deployments included both sites perturbed by the landslides and unperturbed slopes adjacent to them with the purpose of identifying possible structural differences between slopes that underwent landsliding from slopes that were not affected. We analyze seismic sections obtained using the multi-channel analysis of surface waves technique and compare the results with seismic noise analyzed using seismic interferometry. We show that different analyses give similar results. The lateral variations observed in the shear-wave velocity distribution below the different profiles are well correlated with dominant frequency determined from seismic noise horizontal-to-vertical spectral ratios. Our measurements were taken after the landslides occurred. In hindsight, our results suggest that soil thickness played a major role in the triggering of landslides.