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 within the central Main Ethiopian Rift and contains Cenozoic volcanism, faulting and sedimentation. Within this region, the Aluto-Langano volcanic complex is currently being exploited for geothermal power production. In contrast to previous geophysical studies, recent magnetotelluric (MT) investigations reveal the nonexistence of a heat source beneath the Aluto-Langano geothermal field. Instead, the MT study revealed a low resistivity region to the northwest of Aluto beneath the Silti Debre Zeyet Fault Zone (SDFZ) which may be the magmatic heat source. To aid in determining the volcano-tectonic features within the Basin magnetic data were analyzed. The analysis included creating a differentially reduced to the pole total magnetic field anomaly map and then applying upward continuation, power spectral analysis, 2D-Werner Deconvolution, 2D forward modeling, first vertical derivative and tilt derivative filters. Interpretation of the anomaly maps and the depth analyzes suggests the existence of a heat conduction path is structurally controlled along a trend from the Aluto-Langano geothermal field to the SDFZ and occurring between depths 1.5 km and 3 km. Additionally, most of the magnetic lineaments are oriented in the direction of pre-existing Mesozoic structures and in the direction of thermally altered structures.