Hydrothermal system operating mechanism by 3D gravimetric inversion and Vertical Electrical Soundings: Case of Hammam Righa hot springs, central Algeria

Abstract

The Hammam Righa thermal site is one of the most important in the central part of the Tellian Atlas in Algeria, where the temperature of the thermal water reaches 68 °C. It is located between the Mitidja Basin to the northeast and the Upper Chelif Basin to the southwest, at about 100 km to the SW of Algiers.In order to characterize the Hammam Righa hydrothermal system and propose a geostructural model that regulates it, a multimethod-multiscale geophysical study was carried out and a three-dimensional gravity data inversion was completed using VOXI Earth Modeling™. 237 gravity data stations covering an area of about 36 km2 and 70 Vertical Electrical Soundings (Schlumberger, AB = 1000 m) covering an area of about 2.5 km2 were collected around the thermal discharge area.The different processing results of the Vertical Electrical Soundings and the gravimetric data allowed us to define the characteristics of the hydrothermal system (geothermal reservoir depth, heat source and faults system). The Hammam Righa thermal springs are structurally controlled by deep NE-SW direction faults that ramify towards the surface. The thermal waters flow into the geothermal reservoir, which is located in the Jurassic formation at a depth of approximately 1300–1500 m, and emerges near the surface from the Upper Cretaceous. The 3D gravity inversion model reveals a dense body with an average density of 2.78 g/cm3 at around 500 m depth, likely to be the source that ensures water heating process and associated with the region's Miocene volcanism.