Aeromagnetic investigation of southern Calabria and the Messina Straits (Italy): Tracking seismogenic sources of 1783 and 1908 earthquakes

摘要

Southern Calabria and the NE corner of Sicily (Italy) were struck in 1783 and 1908A.D. by two of the most catastrophic earthquakes ever in European history. Although it is generally acknowledged that the seisms were yielded by normal faults rupturing the upper crust of the Calabria-Peloritani terrane, no consensus exists on seismogenic source location and orientation. Here we report on a high-resolution low-altitude aeromagnetic survey of southern Calabria and Messina Straits. In southern Calabria we document a broad weakly positive (5-10nT) anomaly zone interrupted by three en echelon SW-NE null to negative magnetic anomaly corridors. Euler deconvolution and magnetic modeling show that the anomaly pattern is produced by a 1-1.5km thick crustal layer located within 3km depth. This layer is offset by a 25km long NE trending fault that corresponds to the Armo normal fault, recently inferred to be the source for the 1908 earthquake. Few kilometers to the south, we also document a subparallel and previously unrecognized fault, entering the Messina Straits and likely joining the Armo fault at depth. Further east, we model a 40km long normal fault, probably extending northeastward for additional 40km, running along the south Calabria axis from Aspromonte to the Serre mountains and partly following the 18km long surface rupture witnessed by Deodat de Dolomieu after the 1783 earthquake. Thus, aeromagnetic data suggest that the sources of the 1783 and 1908 earthquakes are en echelon faults belonging to the same NW dipping normal fault system straddling the whole southern Calabria.