DIMENSIONALITY ANALYSIS OF MAGNETOTELLURIC DATA AND ITS IMPLICATIONS ON THE SUBSURFACE RESISTIVITY DISTRIBUTION IN CANDI DUKUH GEOTHERMAL FIELD AND ITS SURROUNDINGS, CENTRAL JAVA

• Main Author: Maswah, Fauziah
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/53585
• Institution: Institut Teknologi Bandung

Magnetotelluric (MT) method plays an important role in geothermal exploration. This method can characterize the components of geothermal system such as reservoir and clay cap. However, Prior to MT data modeling, determining the direction of the geoelectrical strike must be performed. Dimensionality analysis and determination of geoelectrical strike direction were applied to the Candi Dukuh Geothermal Field, Central Java. The previous study on MT in Candi Dukuh Geothermal Filed did not apply the rotation of the MT data, which can lead the ambiguous interpretation. Therefore, this study aims to analyze the dimensionality of the MT data and its implications for the subsurface resistivity model of the study area. The applied dimensionality analysis consisted of Zstrike parameter, phase tensor, and induction arrow. In this study, geoelectrical strike is validated with geological data, first horizontal derivative (FHD) and second vertical derivative (SVD) from gravity data analysis. The validated geoelectrical strike direction is used to rotate the MT data. The result from MT analysis, geology, and gravity shows that the geoelectric strike of the study area is about N15°E and agrees well with the NE-SW structure of the study area. The result from 2D inversion shows the presence of conductive layer as clay cap (<10 ohm.m) distributed around Telomoyo Mountain and the north part of the study area with the thickness is about 500 - 1000 m. The resistive layer found underlying clay cap is indicated as reservoir zone with the top of the reservoir estimated at an elevation of 700 m to -500 m. From the interpretation of the resistivity model, it is known that the application of MT data rotation to the geoelectrical strike direction results smaller RMS error and gives a model that can qualitatively explain the geological conditions of the subsurface in the study area.