3D Seismic Tomography to Image the Subsurface Structure of "IY" Geothermal Field Using Double-Difference Method and Waveform Cross-Correlation: Preliminary Results

"IY" Geothermal Field is located in southern part of Bandung, West Java, Indonesia. This geothermal field is dominated by liquid and vapour conditions. In this study, we used microearthquake (MEQ) waveform and catalog data around the geothermal field to determine 3D seismic velocity through tomography inversion. The data was recorded by 15 stations around "IY" geothermal field area. During ten months of recording, there were 926 MEQ events have been identified. We conducted 3D subsurface seismic velocity by using double difference tomographic (tomoDD) in order to delineate structure around the reservoir. To improve the distribution of initial hypocenter from catalog data, we relocated the MEQ hypocenters using double difference method and waveform cross-correlation to enhance P-and S-wave arrival times as input for tomographic inversion. We updated catalog data and applying threshold of coefficient value that we used is around 0.72-0.822, depends on updated waveforms from cross-correlation method. From 15 stations, there are two stations used threshold value above 0.8 for P-wave and two stations for S-wave, whereas other stations used value of 0.72-0.8. The ongoing process, is to determine seismic velocity structure by applying tomographic inversion. We also know the clustering events near well in geothermal field. The result shows the relocated MEQ hypocenters with 3D velocity model to delineate of geothermal reservoir zone, such as brine and steam, depends on the value of Vp, Vs, and Vp/Vs ratio structures. (paper)