1-D VELOCITY MODEL DETERMINATION BASED ON SURFACE WAVE DISPERSION CURVE ANALYSIS AND INVERSION IN PATUHA GEOTHERMAL FIELD

• Main Author: Aria Santoso, Michael
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/54038
• Institution: Institut Teknologi Bandung

Geothermal energy is one of the energy sources that is currently widely developed. Indonesia has 127 volcanoes because it is close to the plate subduction path so that it has a high enough geothermal potential. The need to know the depth location of each geothermal system component such as heat source (source rock) and reservoir are most vital for better understanding of a geothermal field and how the knowledge is utilized for future prospects. In this study, surface wave phenomena from the activity of regional earthquakes is used to analyze its dispersion curves prior to obtain 1-D velocity structure of the subsurface through the inversion of dispersion curves. The data used in this study are regional earthquake catalog data, which event has ts-tp > 3 seconds at the Patuha Geothermal Field in the month of January-March 2018 timeframe. Earthquake data that are used were recorded using 9 borehole type seismometers spread across the study area. Picking of dispersion curve points is done using Sval software based on the signal analysis by exploiting the science behind time-frequency analysis using multiple-filtering technique to determine the dispersion curve. The Sval software works by searching dispersion points with calculating the spectrograms of the waveform. Continuity criterion of the dispersion curve is also apllied on the program for better dispersion points selection. Determination of the 1-D velocity structure of the subsurface will then use the inversion of dispersion curve based on the Isometric method, which method are used for solving weakly non-linear problems for more robust result. From the inversion the seismic velocity of Vs, at elevation of 1.5 km Vp and Vs values tend to rise which can be associated with the presence of caprock, the Vp and Vs values tend to drop at elevation of 0.5 km which can be associated with the presence of a reservoir, and high Vp and Vs values at -0,5 elevation km can be associated with the presence of a heat source