Consiglio Nazionale delle Ricerche, IGAG, Rome, Italy

The SEISMOFAULTS project (www.seismofaults.it) was set up in 2016 with the general plan of exploring the seismicity of marine areas using deep seafloor observatories. The activity of the first two years (Seismofaults 2017 and 2018) consisted of the installation of a geophysical-geochemical temporary monitoring network over the Ionian Sea floor. Eleven ocean-bottom seismometers with hydrophones (OBS/H) and two seafloor geochemical-geophysical multiparametric observatories were deployed to: (1) identify seismically active faults; (2) identify potential geochemical precursors of earthquakes; and (3) understand possible cause–effect relationships between earthquakes and submarine slides. Furthermore, five gravity cores were collected from the Ionian Sea bottom and ~4082 km of geophysical acquisition, including multibeam and single channel seismic reflection data, were acquired for a total of 4970 km2 high-resolution multibeam bathymetry. Using Niskin bottles, four water column samples were collected: two corresponding at the location of the two multiparametric observatories (i.e., along presumably-active fault zones), one corresponding at a recently discovered mud volcano, and one located above a presumably-active fault zone away from the other three sites. Preliminary results show: (1) a significant improvement in the quality and quantity of seismological records; (2) endogenous venting from presumably active faults; (3) active geofluid venting from a recently-discovered mud volcano; and (4) the correct use of most submarine devices. Preliminary results from the SEISMOFAULTS project show and confirm the potential of multidisciplinary marine studies, particularly in geologically active areas like southern Italy and the Mediterranean Sea.

Early in the morning of 24 August, 2013, following by hours the drilling of a shallowborehole in the same spot, a new fumarole producing emissions of CO2-rich gas, water, and mud suddenly appeared at a crossroad along the fenced area of the Fiumicino international airport of Rome, Italy. Similar episodes have been scientifically documented or simply reported in recent and past years. To understandwhy gases are easily entrapped in the shallow subsurface of the Fiumicino area, we used five borehole cores drilled by us, analyzed the stratigraphy of these and other nearby cores, acquired a 2D seismic refraction tomogram, and performed chemical and isotopic analyses of water samples collected from aquifers intercepted by two drilled boreholes. Our boreholes were realized with proper anti-gasmeasures as,while drilling, we recorded the presence of pressurized gases at a specific permeable gravel level. Results showthat, in the study area, gases become mainly entrapped in a mid-Pleistocene gravel horizon at about 40–50 m depth. This horizon contains a confined aquifer that stores the endogenous upwelling gases. The gravel is interposed between two silty–clayey units. The lower unit, very hard and overconsolidated, is affected by fractures that allow ascending gases to bypass the otherwise impermeable shale, permeate the gravel, and dissolve into the aquifer. In contrast, the upper unit is impermeable to fluids and seals the gaspressurized aquifer, which therefore constitutes a source of hazard during human activities such as well drilling, quarrying, and various building-related excavations. As the stratigraphy of the Fiumicino area is very common in large portions of the densely populated Roman area and as the adjacent volcanic districts are hydrothermally active, we conclude that phenomena similar to that observed at Fiumicino could again occur both at Fiumicino and elsewhere in the surrounding region. As a prompt confirmation of our conclusion, we signal that, while writing this paper, new artificially-triggered degassing phenomena occurred off Fiumicino in connection with the construction of the new harbor.