GNGTS 2021 - Atti del 39° Convegno Nazionale

79 GNGTS 2021 S essione 1.1 border between northeastern Italy and western Slovenia - a complex overlap of thrust (Alpine) and transpressive (Dinaric) structures - is the most favorable to fault valve behavior, according to Sibson (2020), and it connects highly permeable dolomitic limestones with low permeable fine-grained limestones and flysch formations. In the interseismic period, high-pressure fluids can therefore accumulate at the base of a fault zone, below a low permeability barrier; the move- ment of the fault, closely related to seismic events, can break the impermeable barrier and allow the diffusion of the fluid into the surrounding environment (Fig. 2). The hypothesis of a contribution of meteoric waters in the region, characterized by karst phe- nomena both on the surface and at depth, cannot be excluded a priori. However, in the hypothe- sis of a deep source, we estimated the flow rate necessary to maintain the overpressure both for the transient analyzed here and for that reported by Rossi et al . (2018), following the approach of David et al . (1994). The fluid flow values ​necessary to maintain the calculated pore pressure val- ues ​vary between 0.013 and 0.65, minimum for the formation of Cenozoic Calcari Grigi, very little permeable, and maximum for the more permeable Triassic Dolomia Principale, comparable with other observations in other contexts. A flow rate of 5.8 · 10 5 -2.8 · 10 6 m 3 / year in the case of the Dolomia Principale would be sufficient to maintain the high pressure, which would be reduced to 1.7 ∙ 10 4 -1.1 ∙ 10 5 m 3 / year whence gray limestones were involved. Our research provides new Fig. 1 - IMF8 for the four stations, in a variable area mode (black area: the positive signal), in the direction in which the transient is maximum and positive. A gain of 10 4 is applied to the GG signal to allow comparison with the other stations. Vertical axis: time (years). The trace interval is proportional to the distance from the calculated source (red star). The traces located to the west of the source of the transient (red star) are on the left, while GG, to the east of the source, on the right.