||Ronald VERAVE, Nathan MOSUSU, and Philip IRARUE
||1D inversion, 1D Layered Model, Geoelectric Layers, IX1D, Resistivity, Schlumberger array, Talasea (Garua) Geothermal Field,
||World Geothermal Congress
||Four Schlumberger resistivity soundings were conducted at the Talasea (Garua) geothermal field as a preliminary study by the Mineral Resources Authority to test whether the ABEM Terrameter SAS1000 resistivity equipment would be able to detect geoelectric layers corresponding to geothermal activity. The resistivity data were processed by Interpex IX1D program using one-dimensional (1D) inversion to model the vertical variations of subsurface resistivity at depths of less than 200 m. The data were interpreted to show four geoelectric layers: a top thin layer of varying resistivity values (17 to 688 Ωm) interpreted as a mixture of volcanic sediments comprising of gravel, sand, silt, ash and clay; a second layer of moderately low resistivity values (20-50 Ωm) comparable to moderately altered volcanic sediments whose conductivity is due to pore fluid conduction, ; a third layer has anomalously very low resistivity of ≤2 Ωm and is related to low temperature (50-200°C) alteration in the smectite-zeolite zone; and a fourth layer shows a highly resistive layer which was poorly modeled. Resistivity data observed outside geothermal fields interpreted the second layer as the ground water aquifer zone. Comparison of resistivity values modeled for the moderately low resistivity layer from the current study and past ground water investigations revealed Talasea geothermal field most probably has high heat flow. This is supported by extensive surface manifestations and the shallow detection of the very low resistivity zone. The lateral extent of the anomalously very low resistivity was restricted to the orientation of a suspected fault identified through visual interpretation of the 3D models generated in ERDAS ER Mapper in the Wavua manifestations. The thickness of this layer was not adequately modeled due to breaks and distortions of the measured data at longer electrode spacing.