The Irpinia Near Fault Observatory: A Cutting-Edge Infrastructure Exploring the Interplay Between Earthquakes, Deep Fluids and Climate Forcing

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The Irpinia Near Fault Observatory (INFO) is a state-of-the-art infrastructure for monitoring seismic activity in the Southern Apennines, a region of high seismic hazard that experienced the 1980 M 6.9 Irpinia earthquake. Managed by the University of Naples, the observatory operates the dense ISNet seismic network, including 30 strong-motion and short-period sensors, 9 broadband seismometers, as well as geodetic and geochemical stations from INGV. Data and products are openly shared through the EPOS platform and the FRIDGE community portal. INFO also serves as a testbed for the Geo-Inquire project, providing unique transnational access for geophysical surveys and real-time analysis.Fifteen years of continuous seismic monitoring have uncovered a strong correlation between the hydrological loading of shallow karst aquifers, GNSS-measured surface deformation, changes in elastic properties of subsurface, and seismicity rates at depths where large historical earthquakes have nucleated. Velocity and attenuation tomography have further revealed the pervasive presence of deep fluids, with evidence of reservoirs likely containing CO₂ and brine.Despite these findings, the background seismicity in the area appears sparse, with hypocenters distributed irregularly within the graben system bounded by the faults responsible of the 1980 earthquake. To better understand the microseismicity pattern and its relationship with the major fault structures, we deployed a temporary dense network of 20 arrays (10 stations each) for one year (DETECT experiment), alongside with a Distributed Acoustic Sensing (DAS) system monitoring a 20 km fiber-optic cable.Advanced machine learning detection techniques, applied to data from the dense monitoring network, expanded the standard seismic catalog by a factor of eight, producing a dataset comparable to a decade of traditional observations. The enhanced catalog revealed that seismic events follow the seasonal hydrological loading, predominantly cluster at depth, forming small sequences of aftershocks (magnitude

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