The 1905 Calabria, Southern Italy, Earthquake: Hypocenter Location, Causative Process, and Stress Changes Induced in the Area of the 1908 Messina Straits Earthquake

We used the Bayloc seismic location method for the nonlinear hypocenter location of the 8 September 1905 southern Calabria earthquake that several investigators identified as the strongest earthquake ever to occur in Italy, and for which quite different views exist concerning location, magnitude, and the causative process. Our offshore, 35-55-km deep location of the event, jointly with literature information concerning the same earthquake and the local structure of crust and upper mantle, leads us to suggest that the earthquake may have been generated by rupture of the bending zone of the Ionian subduction slab with a seismic event magnitude as large as 7.5. By computation of the coulomb stress change produced around the source by this earthquake, we find that it may have played a significant role in the generation of the magnitude 7.1 earthquake which struck the Messina Straits area, a few tens of kilometers south, only three years later (December 1908). The 1905 seismic dislocation occurring in the most arcuate part of the pulled-by-gravity descending slab is proposed here to have caused the 1908 earthquake by inducing positive changes of coulomb stress of the order of 0.1-0.4 MPa on the shallow normal faults of the overriding plate in the Messina Straits area.