Application of Gravity, Magnetic and Electrical Resistivity Methods for Geothermal Investigation at the Corbetti Caldera, Main Ethiopian Rift, Ethiopia

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Addis Ababa University


In this thesis work 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 about 250 km south of Addis Ababa and 20kms from Awassa 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. The Quaternary volcanism is associated with a wide spread of steaming ground and fumarolic activity which evidenced the existence of a heat source at depth. 56 VES points, 200 gravity and about 200 magnetic data have been used and analyzed and results are presented as magnetic, gravity and electrical counter map for qualitative interpretation and also gravity and magnetic 2-D model constrained with Geoelectric section for quantitative interpretation. The complete Bouguer gravity anomaly in conjugation with 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 indicates the presence of middle thicker conductive zone which is associated with the increase in temperature and alteration of rocks and 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. Based on the joint analysis of data from these geophysical methods and thermal manifestations in the area, the area has the potential for large scale electrical power development. Besides, additional geophysical methods are proposed to further reinforce the outcome of the study.



Application of Gravity, Magnetic and Electrical Resistivity, Methods for Geothermal Investigation, Corbetti Caldera, Main Ethiopian Rift, Ethiopia