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Geothermal Anomaly Detection Using Potential Field Geophysical Data in Rahat Volcanic Field, Madinah, Saudi Arabia

Essam Aboud*, Faisal Alqahtani, Nabil Elmasry, Murad Abdulfarraj, Helmy Osman

Rahat volcanic field is the longest and oldest Cenozoic volcanic field in the Kingdom of Saudi Arabia, located along the Red Sea coast. Three historical eruptions have occurred at the northern part of this volcanic field: The fissure eruption (641 AD), historical eruption (1256 AD), and unknown location eruption (AD 1293). Addition, the area is characterized by swarm area since 1999. Recently, the elevation of temperature in water wells around Rahat volcanic field indicates that there is a source of heat at a certain depth. Gravity and magnetic data were collected for various purposes, volcanic hazards, mineral exploration, and geothermal exploration. Also, few boreholes were drilled for exploration by the Ministry of Environment, Water, and Agriculture. These datasets are analyzed for the purpose of understanding the subsurface thermal structure where the main objective of this research is to locate the most probable geothermal resources causing the elevated water temperatures in the water wells. Results indicate that underneath the historical eruption and fissure eruption, toward west, there is a geothermal anomaly at depths of 3-4 km with an area of about 35 km². This anomaly was mapped from density and susceptibility variations in rock samples, analysis of gravity and magnetic data, and the 3D inversion of gravity data. We recommend carrying out MT surveys to model the geothermal reservoir. In addition, the area is characterized by basin like structural system trending in northwest direction, parallel to the Red Sea trend.