Seismological contribution to STEP fault detection in the Calabian subduction zone, south Italy

Abstract

The Calabrian Arc system (southern Italy) is characterized by the presence of the southeast-ward retreating Ionian slab subducting beneath the southern Tyrrhenian region. Recent intermediate tomographies indicated that the Ionian slab is continuous in depth beneath the central part of the Arc (central Calabria-Messina Straits), while detachment of the deep portion of the subducting structure may have already taken place beneath the edges of the Arc itself (southern Apennines and Sicilian Maghrebides). Geophysical investigations, including seismic tomography, gravity analyses, earthquake and geologic data, led us to better identify the transitional zones between different subduction modes in correspondence of the NWtrending seismogenic faults of Tindari and Crotone Basin, respectively. According to the model introduced by GOVERS & WORTEL (2005) and adopted also by other investigators for describing the dynamics at the borders of retreating subduction slabs, we suggested that these seismogenic faults may work as Subduction-Transform Edge Propagator (STEP) faults in the Calabrian subduction system. In order to investigate these STEP fault zones, we have applied in the present study the waveform inversion method known as Cut And Paste (ZHAO & HELMBERGER, 1994; ZHU & HELMBERGER, 1996) for computation of seismic moment, depth and focal mechanism of earthquakes with magnitude greater or equal to 3 occurred in the Calabrian Arc region between 2004 and 2011.