DC Resistivity analysis was carried out in the Sibayak geothermal using Schlumberger Vertical Electrical Sounding (VES) during a preliminary study in 1990. The resistivity data has been processed conventionally using one-dimensional (1-D) inversion to estimate vertical variation of resistivity related to hydrothermal activity at shallow depths of less than 1 km. Subsequently, the inversion results were correlated to develop a 2-D resistivity section; afterwards, it was combined with the MT data processing result. However, the results of 1-D inversion of DC resistivity are not fully satisfactory for actual 3-D structures such as geothermal systems. Therefore, we have re-processed the same Schlumberger VES data set by performing a 2-D inversion based on ABIC least squares method. The 2-D inversion result shows a more realistic feature in terms of geological structure. Caldera boundaries and a dome-like structure of the low resistivity are clearly determined, indicating an up-flow zone around fractures in the southeast direction of the Sibayak Mountain. By tuning and improving the interpretation method, we accomplished descriptions of the shallow subsurface conditions in the Sibayak geothermal field. These results can be used to improve the understanding of the shallow subsurface conditions in the Sibayak geothermal field.

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