Crustal structure of seismic gap areas: The case of the Pollino (Italy) and Thessaly (Greece) sequences.

Knowledge of the crustal structure of potentially hazardous but long-silent seismic gaps is crucial for seismic hazard mitigation. The occurrence of seismic sequences provides a valuable opportunity to illuminate the properties of the area. We present the results of analyses of the elastic and inelastic properties of two seismic gap areas: the Pollino area (Italy) and the Thessaly area (Greece). The first area was affected by a long-lasting sequence characterised by more than 10000 earthquakes with a predominant swarm-like behaviour and, to a lesser extent, as a mainshock-aftershock sequence following the two main events (ML 4.3 and ML 5.0) that occurred late in the sequence, about two years later. In the second case study, the aftershock sequence, following three medium-intensity events (Mw 6.3, Mw 6.0 and Mw 5.6), dissipated in less than a month during March-April 2021. Seismic tomography and detailed relocation of seismic events were performed for both sequences, with the results then being compared with geological, geophysical and satellite information available for the areas. This work is supported by PRIN-2017 MATISSE project, No. 20177EPPN2, funded by Italian Ministry of Education.