Electrical resistivity structure of Danau Ranau geothermal prospect area based on integrated 3-D Inversion of impedance tensor and tipper vector.

• Three-dimensional magnetotelluric inversion was carried out to understand the geothermal system in Danau Ranau geothermal Area, Sumatera, Indonesia. • The dimensionality analysis based on the magnetotelluric phase tensor indicate a spatial complexity and asymmetricity in lateral and vertical direction, which suggests the need of inverting all the MT transfer function components including impedance and tipper. • The resulting model recovers the spread of highly conductive impermeable cap rock in the shallow depth, as well as localizes the more resistive zone seated below the summit of Mt. Seminung, which serves as the reservoir for the geothermal fluids. • The existing faults in the west and northern parts of the area act as channels for the outflow manifestations, while ones in the southern parts serve as the path for meteoric fluids infiltrations. Subsurface electrical resistivity distribution needs to be revealed to explore the geothermal potential in The Danau Ranau prospect area, as the components in geothermal systems could be easily characterized by their resistivity contrasts. The magnetotelluric method is a geophysical method commonly used to perform this task. This paper performs a three-dimensional inversion based on the complete component of magnetotelluric transfer functions, including impedance tensor and tipper vector. Prior dimensionality analysis using phase tensor revealed that the MT data contains a high dimensionality distortion and shows significant horizontal geoelectrical variations. The analysis suggests using the MT full components in the inversion process to effectively recover all the geoelectrical features in such a geologically complex area. The three-dimensional inversion was then carried out after taking control of the model mesh dimension and the regularization parameter. The 3-D resistivity model showed an overburden layer with varying resistivity in the shallow depth. In the subsequent layer, a conductive anomaly representing impermeable cap rock is distributed from the center to the northern and western parts of the study area, bordered by faults and manifestations. The reservoir zone is located under the center of Mount Seminung at an approximate depth of 1500 m. The heat source is expected to be the residual eruption magma of the volcano, which sits far under the reservoir zone and is unreachable by the MT signal. All the findings agree with the existing geological and geochemical survey data and can explain the hydrothermal activities in the Danau Ranau geothermal prospect area. [ABSTRACT FROM AUTHOR]