Source parameter analysis of microearthquakes recorded around the underground gas storage in the Montello-Collalto Area (Southeastern Alps, Italy)

The study of seismic source parameters is crucial for understanding the origin of seismicity and retrieving in- formation on the energy balance and the stress involved in earthquake rupture processes. In active tectonic areas, where underground industrial activities are carried out, such parameters may help to understand whether earthquakes are induced, triggered, or natural. The Montello-Collalto area (Southeastern Alps) is located in an active tectonic environment and hosts a depleted natural reservoir used to store gas. Since 2012, a high-quality seismic network monitors the microseismicity occurring around the underground gas storage reservoir to un- derstand if the storage activity might induce seismicity. In this paper, we estimate the source parameters of low magnitude events representative of the seismicity occurring in the area surrounding the reservoir. The analysis includes a preliminary removal of the site effects, specifically computed within this study, from all the records. Then, using a parametric multistep inversion scheme, we estimate the seismic moment, the corner frequency and the static stress drop, that can be set as reference for the microseismicity occurring in the study area. All the investigated earthquakes show low seismic efficiency compatible with overshoot processes, which is typical of natural (i.e., tectonic) earthquakes. Our procedure can be implemented in other tectonic regions hosting un- derground industrial activities to support the decisional processes related to real-time monitoring.