Seismogenic stress field estimation in the Calabrian Arc region (south Italy) from a Bayesian approach

Crustal earthquake focalmechanisms are investigated in the Calabrian Arc region,where thewesternMediterranean subduction process is close to ending and the residual Ionian subducting slab affected by gravitational roll-back produces a strong variation of faulting regimes at shallowdepth along the local section of the convergentmargin. An updated database of earthquake focal mechanisms has been compiled by selecting the best-quality solutions available in the literature and in catalogs, and by adding 17 new solutions estimated in the presentwork. A total of 164 mechanisms are included in this database, 142 computed by waveform inversion and 22 by analysis of P-wave first motions from earthquakes with good network coverage and no less than 14 records. 60% of the solutions included in the database have never been used for regional-scale geodynamic investigations before the present study, and this makes the compiled database substantially new for our application. Focal mechanisms have been inverted for stress tensor orientations to obtain the principal stress axes over the study region. Results are compatible with three major tectonic domains subject to markedly different regional stresses along  the arc. These three domains are separated by two transitional domains, which are located on top of the Ionian subducting slab edges and are likely forced in their horizontal transfer kinematics by the different tectonic regimes occurring in the adjacentmajor domains rather than by the regional tectonics. This along-arc 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. Open tectonic questions are emphasized and proposed for future studies.

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