Magnetic anomaly patterns and volcano-tectonic features associated with geothermal prospect areas in the Ziway-Shala Lakes basin, Central Main Ethiopian Rift

The Ziway-Shala Lakes Basin is a structural depression found in the Main Ethiopian rift being associated with Cenozoic volcanism, faulting and sedimentation activities. The Aluto-Langano volcanic complex is one of the geothermal prospect sites found in this basin and is currently being exploited for geothermal power production. Although it contradicts with the previous research results, recent observations using magneto-telluric method reveal nonexistence of a heat source beneath the Aluto volcano. Instead existence of a strong conductor possibly a magmatic heat sources claimed to occur beneath the Silti Debre Zeyet Fault Zone that lays far NW of the Aluto volcanic complex. In this study, ground based magnetic survey is carried out to map magnetic anomaly patterns and structural features associated with the Aluto-Langano. The volcano-tectonic features are extracted from the differentially pole reduced total magnetic field anomaly map and its derivative maps compiled by applying upward continuation, first vertical derivative and tilt derivative filters. Interpretation of the complied anomaly maps reveal existence of a heat conduction structural path along a traverse running from the Aluto-Langano geothermal to the Silti Debre Zeyte Fault zone and laying between 1.5 km and 3 km depths. This result could be taken to prove the most likely heat source feeding the Aluto-Langano geothermal field is found at about the locality of the Silti Debre Zeyte Fault Zone. The research work also identified magnetic lineaments most of which oriented in the direction of pre-existing Mesozoic structures and in the direction of thermally altered structures.