Unraveling the Geothermal Potential of Corbetti Caldera Using Integrated Geophysical Methods, Central Main Ethiopian Rift.

Abstract

Bisrat Kebede, Abera Alemu, Hailemichael Kebede, Enatfenta Melaku, Dejene Feyissa, Guta Legesse

In this paper integrated geophysical techniques, involving electrical resistivity, gravity and magnetic surveys have been carried out over the Corbetti Caldera in the central Main Ethiopian Rift (CMER) to verify the geothermal potential of the caldera. Corbetti geothermal prospect is located at about 250 km south of Addis Ababa and 20km from Awassa city and the area is bounded by Lake Awassa to the south and Lake Shalla to the north with geographic location between latitude 7.170N-7.250N and longitudes 38.300E-38.470E. The Corbetti Caldera is characterized by Quaternary volcano-tectonic activity which is mainly silicic volcanism and a resurgent caldera structural system. Quaternary volcanism is associated with a wide spread of steaming ground and fumarolic activity which could confirm the existence of a heat source at depth. Fifty six (56) VES points, 200 gravity and about 200 magnetic data have been used and analyzed. The results are presented as magnetic, gravity and electrical counter maps for qualitative interpretation. Constrained gravity and magnetic 2D model and results obtained from the geoelectric section were made for quantitative interpretation. The complete Bouguer gravity anomaly in conjugation with the total magnetic field anomaly map of the area indicates the existence of intrusion beneath the caldera, i.e. the highest Bouguer gravity anomaly resulting from the higher density of the intrusion. Correspondingly the shallower heat source caused by this intrusion is characterized by the lowest magnetic anomaly response. Results from vertical electrical soundings along profile-2 indicate the presence of a middle thicker conductive zone which is associated with the increase in temperature and alteration of rocks. Apparent resistivity map for AB/2=1810m and AB/2=2700m shows low resistivity anomaly follows the eastern and northern caldera rim, stretching north of the caldera towards Lake Shalla.

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