Slow movements observed with in situ and remote-sensing techniques in the central zone of Chile

Slow movement processes correspond to slow to extremely slow deformation in slopes. Slow movement is often known to be the cause of severe damage to structures and infrastructures. In the Northern Biobio hillside (NBH), many slow movements were not previously identified, which led to building damage. To evaluate their triggering factors, we use two complementary techniques: interferometry of synthetic aperture radar (InSAR) and electrical resistivity tomography (ERT). We observed deformation patterns using SAR data derived from PALSAR-1 during a year that exhibited extreme rainfall (2006). We established that reactivation of slow movements occurs during extreme rainfall periods, which can be observed through deformation patterns. ERT inversion results reveal a formation of silt and clay layers. Our results indicate the existence of slow movement processes close to densely populated areas. An interpretation of InSAR and ERT results showed that during extreme rain events, soil saturation occurs. The silt layer loads the hillslope and the clay layer acts as a lubricant below the silt.