GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 - POSTER GNGTS 2023 Soon after the wastewater reinjection, microseismicity was recorded with over 1000 events with Magnitude < 2.2 (Valoroso et al., 2009; Improta et al., 2015; Stabile et al., 2016), and it was interpreted as wastewater injection-induced seismicity reactivating small inherited faults into the reservoir (Buttinelli et al., 2016). Part of the microseismicity recorded in the southwestern portion of the VA, close to the MMFS southern branches, has also been defined as RIS (Reservoir Induced Seismicity) and associated with the water level changes in the nearby artificial Pertusillo lake (Valoroso et al. 2009; Rinaldi et al., 2020; Piccozzi et al., 2022). INGV has been charged by the Italian oil and gas safety authority (DGS-UNMIG) to monitor the VA seismic activity, ground deformations, and pore pressure changes, according to the governmental monitoring guidelines (ILG; Dialuce et al., 2014; Braun et al., 2020). For that challenging task, INGV established a dedicated working group (CMS, Centro di Monitoraggio del Sottosuolo, http://cms.ingv.it ) . The CMS operates the real-time acquisition and offline analyses of seismic data recorded at 56 seismic stations associated with six public and private local seismic networks.  (VA, VD, IX, IV, TP, GE). The completeness magnitude of this virtual network reaches Mc=0.2 (Braun et al., 2022). One of CMS's most important tasks is to investigate whether industrial hydrocarbon operations can cause significant stress changes within the upper crustal volume and their potential ability to induce or trigger seismic events. This analysis follows the guidance suggested in ILGs, which involve the application of a traffic light system TLS after the location of seismic events occurring within domains of interest around the VA reservoir.  A side question to be fully unraveled is also defining an accurate structural setting of the VA, evidencing which faults, with surface expression (e.g., MMFS and EAFS), can be defined as active. For this reason, the CMS recently started several multidisciplinary research activities flanking the monitoring task of the high-resolution hypocenter location. CMS is developing: i) a new reconstruction of a 3D geological model of the VA based on the reinterpretation of a large dataset of 2D/3D seismic reflection profiles; ii) the revision of an accurate and local 3D velocity model based on the velocity analysis of the seismic dataset and the geophysical well logs in VA, to be used for both depth conversions of seismic interpretation and seismological applications; iii) a broad geological and geophysical fieldworks aimed to recognize and characterize the active and capable faults of the area. Here we present the general results of this work, focusing on the relative location of seismic events, that occurred between March 2020 and June 2022, through a double-difference (DD) location algorithm. We used the hypocenters catalog obtained during the CMS routine absolute locations analyses to infer interesting relationships between the distribution of local seismicity and the structural setting of the area in the uppermost crust ( depth < 6km). This work aims to contribute to understanding the VA’s active tectonics identifying potentially seismogenic faults with clear signs of recent activity at the surface and their relation with the preexisting structures.