Resitivity Structures of Bonjol Geothermal Prospect, Indonesia, Derived from Magnetotelluric Data

Abstract

The Bonjol geothermal area is situated on a segment of the Sumatran fault zone (SFZ), Indonesia. During 2009 magnetotelluric (MT) measurements were carried out on the area with the aim of extracting resistivity features related to geothermal reservoirs of the area. MT data were collected from 25 measurement stations along 4 lines trending SW – NE and processed using robust algoritms. Processed MT data were computed with Non Linear Congugate Gradient Method to produce two-dimensional models of electrical resisitivity. The resistivity models show pronounced resistivity contrasts elongated to SFZ trending NW-SE. The resitivity models revealed the presence of shallow low resistivity zone to depth of about 800 m due to low-temperature clay minerals as indicated by shallow drillings. This low resistivity is followed by moderate to high resistivity zone, which may indicate high-temperature geothermal system at depth.