NUMERICAL MODELLING OF EARTHQUAKE-INDUCED ROCK LANDSLIDES: THE 1783 SCILLA CASE-HISTORY (SOUTHERN ITALY)

The coastal M. Pacì rock-avalanche occurred on 6th February 1783, near the village of Scilla (southern Calabria) and involved a subaerial volume of about 5·106 m3. This landslide produced a tsunami wave responsible for more than 1500 human life losses near Marina Grande beach. A geomechanical characterization of both the intact rock and the rock mass outcropping in the landslide slope was performed in order to obtain an engineering-geology model of the landslide according to an equivalent-continuum approach. Dynamic numerical modelling by FDM code FLAC 6.0 was performed to back-analyse the landslide occurrence during the 1783 seismic sequence. At this aim reference synthetic accelerometric ground motions were derived from strong motion records, taking into account both source and energy features of the 5th an 6th February mainshocks and local expected response spectra. In order to force the numerical model, levelled-energy multifrequencial equivalent signals were obtained from these reference records by experiencing the new LEMA_DES approach. The results of modelling show a post-seismic trigger of the rock-avalanche, related to the second mainshock of the seismic sequence, and are in good agreement with the present-day field evidences of the landslide scar area. In addition, no landslide results in the present M. Pacì slope by applying an equivalent input derived for the 1908 Reggio and Messina earthquake. The performed numerical analyses demonstrate the reliability of: 1. an equivalent-continuum approach to derive geomechanical properties of intensely jointed rock masses for numerical modelling of rock landslides; 2. levelled-energy multifrequencial equivalent signals derived from reference recordings; 3. the experienced approach for previsional analyses of landsliding, involving rock masses in highly seismic areas.