Catalog of 3D DD Locations of the Irpinia Micro-Seismicity from 2008 to 2022

The micro-seismicity catalog was obtained by analyzing a 89 data set consisting of about 2400 micro-earthquakes, with local magnitude (ML) ranging 90 between 0.5 and 3.2. These events were recorded by 42 ISNet and INGV stations from August 2005 to December 2022. We used manually picked first P- and S-wave arrival times from ISNet bulletin (http://isnet-bulletin.fisica.unina.it/cgi-bin/isnet-events/isnet.cgi), and integrated manually picks from INGV stations. Initially, we located the events with a probabilistic method (NLLoc, Lomax et al. 2009) and a 3D velocity model optimized for the area (De Landro et al., 2022), which allowed to obtain a first location catalog with an average RMS residual of 0.15 s and location errors smaller than 2 km. Successively, we refined the absolute 3D location with the double-difference approach (HypoDD, Waldauser & Ellswort, 2000) by using catalog (CT) and cross-correlation (CC) differential times (Schaff & Waldauser, 2005). The final residual RMS was 0.008 s for CC data and 0.03 s for CT data. The final location errors were within 100 meters for most of the events.

Moreover, we provided the composite focal mechanisms of four clusters of this new micro-seismicity catalog. Similarly to Muzellec et al. (2023), we evaluated, for selected hypocenter clusters, the composite focal mechanisms by usinf FPFIT (Reasenberg, 1985) and integrating the polarities of co-located events for the construction of more constrained mechanisms. Furthermore, we integrated four additional focal mechanisms of single events. These were selected among the focal mechanisms available from the ISNet bulletin and refined by using the 3D location. To validate this selection, we compared them with those obtained by De Matteis et al. (2012), in which the author performed an extensive analysis of focal mechanisms and refined the stress field of the Irpinia region.