A multidisciplinary approach to the evaluation of the mechanism that triggered the Cerda landslide (Sicily, Italy).

Abstract

The present paper describes a multidisciplinary approach to the evaluation of a seismically triggered landslide that occurred in the Cerda area (Italy) on September 6, 2002, about 1 h after an earthquake took place in the south Tyrrhenian Sea. The study was focused on an analysis of the role of the seismic input in triggering the landslide, in view of the evidence that no other mass movement was recorded in the adjacent areas despite geological and geomorphological spatial homogeneity. The studied area is located on a slope of the western flank of the Fiume Imera Settentrionale (Northern Sicily), which is made up of clayey–arenitic rocks. The slope inclines gently but is not uniform due to fluvial, gravitative, and rainwash processes. Field data dealing with global positioning system (GPS), geology, geomorphology, geophysics (vertical electrical sounding, or VES), and geochemistry (soil gas fluxes and composition) were acquired and analysed in order to investigate the cause–effect relationships between the earthquake and the mass movement. The GPS survey allowed us to map the ground failures that have also been classified on the basis of their kinematical meaning (i.e., compressive, distensive, or transcurrent structures). The geological analysis revealed outcropping rocks and tectonic structures. The geomorphologic survey highlighted the presence of preexisting landslide bodies. The geophysical survey detected a buried surface located at a depth of about 100 m . Finally, the geochemical survey showed that the gas released from the displaced mass came from a shallow depth and was not related to any active fault system. The abovementioned information allowed us to interpret the landslide event as a partial reactivation of a preexisting landslide body that was triggered by the earthquake.