Linking large-volume landslides with potential neotectonic activity of the Pocuro fault system, Central Andes (32°-33°S)

Abstract

The link between large-volume landslides and a potential seismic source has not been extensively tackled in the seismic central Chile even though many mega-landslides have been triggered historically by earthquakes. In this research, an inventory of prehistoric landslides was developed on the western border of the Andes Principal Cordillera, identifying 41 large-volume landslides along main regional structures of the Pocuro Fault System. Among them, 8 landslides were selected to determine a probable seismic source. Slide modelling was performed by reconstructing the topography previous to failure obtaining geotechnical parameters from compressive strength tests and RMR-GSI values collected during field work. Slope stability models were carried out by implementing pseudostatic limit equilibrium analyses in slopes where critical accelerations for sliding were determined. Back-analysis applying inversely Ground Motion Models to nearby mapped faults and topographic amplification depicted cases where a coseismic origin of the landslides is likely. Several faults of the Pocuro Fault System are identified as possible seismogenic sources of the instabilities, suggesting neotectonic activity of this Quaternary fault system, consistent with recent paleoseismological studies in the area and the occurrence of high magnitude earthquakes in this region.