Combined geophysical approach for subsurface structural mapping and modeling in Badrouna –Sidi Ismail intramontane plain (Northwestern Tunisia): Hydrogeological implications

Groundwater investigation requires a structural framework that delineates tectonic features influencing aquifer geometry and characteristics. This study aims to model the subsurface geology of the Badrouna–Sidi Ismail intramontane plain through the integrated analysis of gravity data and vertical electrical soundings. The gravity analysis employs a suite of complementary processing techniques. Upward continuation is applied to separate residual from regional anomalies, while first and second vertical derivatives are used to enhance shallow anomalies and delineate their edges. To refine structural interpretation, additional methods—including total horizontal derivative, analytical signal, tilt angle, theta angle, normalized tilt angle, horizontal gradient tilt, and directional derivatives—are utilized to trace tectonic boundaries. Euler deconvolution is further applied to estimate the burial depths of the identified structures. The resulting maps highlight high gravity anomalies in the northern part of the study area, suggesting the existence of dense buried formations, likely composed of Eocene and Triassic carbonates. Gravity interpretation also reveals several lineaments with varying orientations and estimated depths ranging between 500 and 1, 000 m. The 2.5D gravity model indicates that the Mio-Plio-Quaternary aquifer overlies an Eocene aquifer, and that the detected lineaments may correspond to tectonic faults, which facilitate deep groundwater infiltration and hydraulic contact with Triassic formations. This configuration accounts for the elevated salinities—exceeding 50 g/L—observed in certain localities. Correlation of geoelectrical models with borehole data across different directions highlights notable variations in the depth and thickness of the Mio-Plio-Quaternary water reservoirs, which predominantly align with the gravity-defined lineaments. These findings provide a robust structural basis for understanding groundwater flow paths and salinization patterns in the study area.