Moment Tensor Inversion of the 1978 Ferruzzano Earthquake (Southern Italy)

We present a new study of the Ferruzzano earthquake occurred on March 11th, 1978 in the southern Calabria region. The Ferruzzano earthquake is the most recent moderate-to-major earthquake occurred in the high seismic risk area of southern Calabria (south Italy). Previous information available from the literature on this earthquake is quite contrasting and not well framed in the regional seismotectonic scenario. A new moment tensor solution has been estimated by using a time-domain algorithm properly implemented to analyze data recorded before the advent of the digital era. To do this we selected and digitized seismograms, mainly collected from the SISMOS Project, coming from several stations distributed in the Euro-Mediterranean region. Moreover, we estimated a new hypocentral location by using original bulletin data and a non-linear probabilistic earthquake location technique working with 3D velocity models. A carefully evaluation of data quality and stability of the results were made, by also performing several inversion tests. The obtained results indicate that the 1978 earthquake is characterized by a ca. N-S trending normal faulting mechanism and its moment magnitude is about 4.7, significantly lower than previous estimates. The faulting mechanism now appears well framed in the regional seismotectonic scenario. In addition to the intrinsic interest in this earthquake, the 1978 event can be considered a test-case to prove that digitized seismograms may be successfully used to study also relatively small earthquakes (i.e., Mw<5) of the past.