GNGTS 2022 - Atti del 40° Convegno Nazionale

178 GNGTS 2022 Sessione 1.3 APPLICATION OF GRAVITATIONAL GROUNDWATER FLOW SYSTEMS TO IRPINIA AREA (SOUTHERN APENNINES, ITALY): PERSPECTIVES AND IMPLICATIONS E. Vitagliano, N. D’Agostino Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy In recent decades, gravity-driven groundwater flow models have been applied to a variety of scientific disciplines, such as hydrogeology, geotechnics, geothermal exploration, or environmental protection, and has provided successful results in terms of understanding the processes involved and predicting their effects. Herein, this geologic agent (Tóth, 1999) was applied to the southern Apennines to study the effect of groundwater circulation on various observational data (seismicity, geodesy) along the Irpinia Fault Zone (IFZ). The relationship between hydrologically-driven strain and temporal variation in seismicity has been recently addressed along fault segments activated during the 1980 M S 6.9 Irpinia earthquake (D’Agostino et al. , 2018). The integration of continuous Global Positioning System (CGPS) data with hydro-meteorological and seismicity information has shown that low-magnitude events (−0.1 ≤ML ≤3.9) along the IFZ are correlatedwith seasonal andmultiannual hydrological signals. In addition, the extensional strain transient measured at several CGPS stations is characterised by seasonal oscillations and inter-annual trends in phase with hydrological recharge of karst aquifers. These correlations suggest the occurrence of horizontal seasonal dilation in late spring/early summer, strongly controlled by groundwater dynamics. The points described suggest the emergence of key questions, such as: what path can meteoric water trace from inflow to outflow and what depth can it reach during the infiltration/ migration process? How does it interact with the different layers (aquifer, aquitard, aquiclude) over time? What is the role of normal fault planes and thrust sheets as barriers or conduits for fluid circulation? How can pressure increment due to the hydrodynamic process interacting with the pressure regime of the rocks resulting in hydraulic leaking and fluid losses? In this work, a multi-disciplinary approach to investigate the proposed issues is presented. First, regional groundwater flux (i.e., flow nets and intensities) and fluid-potential field were evaluated by applying the most frequently used equation, which combines Darcy’s law with the equation of continuity and describes saturated flow under steady state and transient conditions (Hubbert, 1940; Lusczynsky, 1961; Tóth, 1978). Within the flow domain, the distributions of hydraulic head and flow were calculated by solving Laplace’s equation under appropriate boundary conditions. According to Tóth’s theory (Toth, 2009), flow patterns are calculated with respect to boundary conditions and head configuration. Moreover, final results depend on three main basin features: water-table relief, basin depth and macro-scale heterogeneity due to variations in rock permeability. Within the study, the variations of the water table were formulated based on the topography of the study area and reconstructed by testing various functions (e.g., sine wave, moving average, polynomial function), while the regional groundwater gradient was assumed from available wells and previous or analogue hydrogeological studies. The head formulation was treated in terms of both elevation/ depth and pressures. In particular, the latter annotation allowed dynamic water pressure increments to be calculated and then compared to vertical pressure profiles available from exploration wells. These wells also allowed the definition of key petrophysical parameters (i.e., permeability, porosity, density, temperature) useful for identifying the physical properties of aquifers, aquitards and aquiclude, in relation to the site. The geometry of the flow domain was reconstructed using geological and structural studies available in the literature (e.g. Improta et al. , 2003; Nicolai and Gambini, 2007), plus reports prepared by Oil Companies that operated in the area during 1978-2002. Although the study is still in progress, the work aims to present the multidisciplinary approach used, with particular emphasis on the role of pressure data in the treatment of fluid