DC resistivity and seismic refraction define surface ruptures in tropical soils - A case study of La Bonita, Antioquia, Colombia

Landslides are a major and frequent natural hazard in Colombia. In particular, the areas close to Medellin city in the Colombian Andes have recorded many landslides. At "La Bonita" sector, many events occurred in recent years and there is evidence of slow deformation at slopes. Nevertheless, understanding and delineating the subsoil rupture or slip surface is difficult due to the heterogeneity of landslide materials. Getting information about the weathering layers in tropical soils that may contribute to landslide initiation is often simplified and addressed by a single geophysical technique. Nowadays, it is a common practice to perform geoelectrical and seismic surveys to obtain more accurate characterization of slopes subsurface features. Even if those two techniques provide complementary information of the subsurface, interpretation of the rupture surface may not always be clearly defined using independent analysis. This is particularly true for tropical soils, which due to their weathering processes form highly heterogeneous subsurface features. In this research, we make use of a joint inversion of the two techniques. We assume that both methods sense the same underlying lithology along a co-located transect and use a cross-gradient approach to link the electrical resistivity and seismic velocity structures. We carried out a longitudinal and transverse 2D joint inversion using data acquired across a landslide in La Bonita and validated the reliability of the result with synthetic models. We found that the joint inversion methodology contributes to a more accurate delineation of the subsurface features in comparison to separate 2D inversions from DC resistivity and seismic refraction alone. This shows that joint acquisition and inversion of electrical resistivity and seismic refraction data are a promising tool for decreasing uncertainty on defining the rupture surface of landslides in tropical soils.