MAGNETOTELLURIC DATA PROCESSING AND 1-D INTERPRETATION ON VOLCANIC GEOTHERMAL SYSTEM

• Main Author: Verson Tumanan, Trian
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/60906
• Institution: Institut Teknologi Bandung

Earth’s thermal energy in any localized geological setting can be extracted from induced circulating fluids, which is geophysical exploration method, that is magnetotelluric method, is used to image the reservoir structure of sub-surface in order to identifies the heat source. The source of energy in magnetotelluric method is the natural electromagnetic field that have a frequency range from about 10-5 Hz to 105 Hz. Magnetotelluric method has two assumption to investigate Earth’s properties and the deepness, which is the quasi-stationary approximation and plane wave hypothesis. These two assumption generates the solution of electric and magnetic field equation from Maxwell’s equation in case of an homogeneous structure to obtain skin depth and relation between electromagnetic field response at given frequencies and characteristic of conductivity distribution of the underlying materials by magnetotelluric transfer functions. In the 1-D Earth’s model, Schmucker-Weidelt’s transfer function is used to formulate the apparent resistivity and phase. Apparent resistivity and the impedance phase would be processed in processing magnetotelluric data through data acquisition that records variations of electric and magnetic fields on the Earth’s surface. Time series analysis such as spectral analysis can be used for estimating the complex spectral coefficients of the various field quantities so that magnetotelluric transfer function can be estimated. Magnetotelluric data, which has been processed to become apparent resistivity and phase, will be inverted in 1-D to obtain resistivity distribution of subsurface. In this research, there are eleven magnetotelluric data measurement points located in the x region which are processed with robust processing in SSMT2000 and the transfer function results will be estimated using MTEditor. The results of magnetotelluric data processing looks smooth for the frequency range more than 1 Hz and looks random and have a large error bar for the frequency range less than 1 Hz. The inversion process is carried out through Interpex 1-D Sounding Inversion and visual interpretation of the resistivity subsurface distribution is carried out through Surfer. Based on the interpretation of the subsurface resistivity model, the characteristics of x region have a volcanic geothermal system, where there is heat source and reservoir layer for greater resistivity (20 – 100 ????m) and the clay cap and sediment for lower resistivity (<10 ????m). Keyword