Multi-sensor monitoring of a transient event in the Gran Sasso aquifer, Italy.

A novel approach in monitoring the inner dynamics of mountains, massifs, and of the Earth crust in general, involves hydrogeological measurements, as well as new generation multi-component seismic stations. Several hydrogeological stations monitor the water parameters of the large Gran Sasso aquifer. This is especially important when the instrumentation used has a high sensitivity and is able to access frequencies below 1 mHz, opening the possibility of observing very slow signals of local origin. For several years, the ring laser gyroscope GINGERINO is operative inside the underground Gran Sasso laboratory (LNGS-INFN), and monitors the local Earth angular velocity around the vertical axis. Together with the co-located GIGS broadband seismometer (seismic stations of national network of INGV), it constitutes a 4C seismic station; the 4 degrees of freedom put together give insight into the inner movements of the Gran Sasso massif, that find correspondence in measurements conducted on the groundwater of the aquifer. In particular, the hydrogeological interpretation of the slow dynamics of the period since May to August 2023, and of the powerful mountain bang event of August 14 is consistent with data from GINGERINO. The final large bang event was also detected by the GIGS broadband seismic station and accelerometer station of RAN (National Accelerometer Network of Civil Protection Department). Furthermore, in the underground laboratories the bang event was recorded by an acoustic sensor and the groundwater hydraulic pressure monitor shows an anomaly exactly when the bang event occurred. Finally, the monitoring data of the groundwater at the boundary of the Gran Sasso aquifer also reveal anomalies linked to the bang event.