The objective of this paper is to investigate how electrical resistivity changes as electromagnetic waves penetrate deep into the subsurface of Lili-Sepporaki geothermal prospect, using Magnetotelluric data. Lili Sepporaki is an andesitic-trachytic volcanic-rich area located in western Sulawesi-Indonesia. Magnetotelluric data was processed using SSMT2000 and MTEditor software programmes. Results show that resistivity of rocks generally increases with decreasing frequency, that is; less than 100 Ohm-m for frequencies greater than 100 Hertz; and fluctuates between 100 -1000 Ohm-m for frequency range 1- 0.1 Hertz. Resistivity also increases with depth of penetration of electromagnetic waves. Weathering, hydrothermal alteration, and many times fluids increase the conductivity of rocks. A low resistivity anomaly is seen around the hot spring, northwards. Presence of fluids in an intensively fractured volcanic rock lowers its resistivity. In the future, another Magnetotelluric sounding should be carried with much more measurement stations followed by a three-dimensions interpretation.
Keywords: Magnetotelluric, electromagnetic, SSMT2000, MTEditor, alteration.