The 1997 Umbria-Marche (Italy) earthquake sequence: relationship between ground deformation and seismogenic structure

Abstract

A field survey performed during the 1997 Umbria-Marche earthquake sequence led us to recognize ground and pavement ruptures associated with the three largest shocks (M>= 5.7). The ruptures are concentrated in narrow bands that, in part, are on and near previously mapped high-angle normal fauts. The geometry of the ground deformation is consistent with the NE-trending extension indicated by CMT focal solutions of the mainshocks. The distribution of aftershocks suggests that the three mainshocks occurred on ~40 degree SW-dipping normal faults. Geological investigations, modelling of expected coseismic elevation changes, and seismic data, suggest that the surface deformation is not the direct result of primary rupture of faults at depth.