Earthquake focal mechanisms, seismogenic stress fields, and seismotectonic features of the Calabrian Arc, south Italy

Crustal earthquake focal mechanisms are reconsidered for the Calabrian Arc, southern Italy, where heterogeneous seismotectonic domains occur and where the causative faults of several destructive earthquakes are still unknown. An up-to-date database of earthquake focal mechanisms as reliable as possible is compiled by evaluating the quality metadata of existing mechanisms increased by 17 newly-computed ones. A total of 164 mechanisms are selected and included in the database: 142 mechanisms elaborated by waveform analysis and 22 mechanisms elaborated by using P-wave first motions of earthquakes with good network coverage and no less than 14 records. The database includes focal mechanisms from earthquakes down to a minimum of magnitude 2.6, for the mechanisms from waveform analysis, and of magnitude 1.7, for the mechanisms from P-wave first motion. Focal data from the database are grouped into five subsets and inverted to obtain the seismogenic stresses in the study area. Results are compatible with three major tectonic domains subject to markedly different regional stresses along the Arc. Two transitional domains are also found separating the three major domains. The transitional domains, which are located on top of the Ionian subducting slab edges, are likely forced in their horizontal transfer kinematics by the different tectonic regimes occurring in the adjacent major domains rather than by the regional tectonics. This differential tectonics is at least in part interpreted as the surface expression of the different deep mechanisms occurring in correspondence of the narrow Ionian slab and their lateral edges.