Dimensionality and Directionality Analysis of MT Data to Image Geothermal Systems in Kiejo-Mbaka Geothermal Field, SW Tanzania

Abstract

The Kiejo-Mbaka geothermal field is located close to the eastern margin of the Karonga rift basin and is part of the Rungwe Volcanic Province (RVP), where the East African Rift System (EARS) splits up into its Western and Eastern branches in southern Tanzania. The area is characterised by an Intrusive Precambrian gneiss metamorphic basement complex (MIT), that either sub-crops or outcrops along the NW-trending and SW-dipping Mbaka fault. Kilambo hot springs manifest and flow just along the Mbaka fault, the highest Swift-skew, phase-sensitive skew and ellipticity were observed in the Mbaka ridge area, where these parameters indicated strong 3-D characters starting from frequencies of about 1 Hz at relatively greater depth, which indicates the necessity for 3-D inversion in order to know the deeper part of the study area. Greater variability in the induction arrows direction and module are well evinced. YX-Phases are out of quadrant greater than (90 deg) and apparent resistivity curves for the TM-modes are greater than that of TE-modes for many of the MT stations lying on the Mbaka ridge area, as an implication of high resistivity zones beneath the Mbaka ridge regions, with a strike directions probably close to x-axis. On the other hand, the reason for the latter may be a possible current channelling that is strongly within the ridge area, owing to topographic effects. The lowest Swift-skew, phase-sensitive skew, ellipticity and shortest induction arrow lengths are on the Mbaka river plain, west to south-west of the Mbaka fault, and on the eastern plateau of the Mbaka escarpment, indicating 1D/2D characters for short period ranges at relatively shallow depth, therefore, 1-D/2-D inversion may probably represent the shallow portion of the study area.