Microseismic portrait of the Montello thrust (Southeastern Alps, Italy) from a dense, high-quality seismic network

The Montello thrust is part of a complex system of the active southeastern front of the Alps in northeastern Italy. An underground gas-storage facility operates in the anticline at the hanging wall of this thrust system. The Collalto Seismic Network was designed to monitor the induced microseismicity and natural earthquakes around this storage. We analyzed the first 6 yr seismic catalog, containing 1635 earthquakes with -0.8 <= M-L <= 4.5 localized with an enhanced 1D velocity model. The clearly aligned seismicity pattern depicts the Montello thrust as an similar to 1000 km(2) plane, gently dipping to the northwest and locally interrupted by high-angle faults, which are nearly perpendicular to the main plane. The observed seismicity suggests a creeping behavior of the main thrust at seismogenic depth (5-13 km). However, we cannot exclude the possibility some parts of the system not microseismically active might be locked and under loading stress condition. Finally, we did not observe a space-time correlation between the microseismicity and the anthropogenic activity occurring in the reservoir. Supplemental Content: Table of hypocentral parameters and fault-plane solutions, graphical output related to fault-plane solutions, and seismicity map and cross-section for events occurred in the study area from 1 January 2012 to 31 October 2017.