Numerical simulations of the ground deformation recorded in the historical town of Gerace during the seismic events in Calabria (1783)

The case history presented is referred to the historical town of Gerace, located in Calabria (Southern Italy) on a cliff constituted by soft rocks overlying a thick clay shale, characterised by continuous erosion processes affecting ground deformation and slope instability. Some of these phenomena may be attributed to the unusual sequence of five strong earthquakes (M= 5.1 to 6.9) occurred at the beginning of 1783; the present study aims to reproduce by numerical modelling the entire seismic sequence. The reference input motions were obtained by means of a seismic hazard analysis carried out through both a ‘macroseismic’ and a ‘seismogenic’ approach. The geotechnical characterisation of the different soils was obtained by combining data taken from field (Down-Hole, MASW, SASW) and laboratory static and dynamic (RC, CTS) tests. The seismic response of the cliff and valley area was simulated by one-dimensional total stress (EERA) and two-dimensional effective stress (FLAC) analyses. The results of both methods permitted to assess the influence of the topography on the site response; also, the effective stress analyses permitted to justify the occurrence of accumulated large deformations following the seismic sequence, reported by the chronicles.