Preliminary Estimation of Geological Structure Based on Relocated Hypocenter of Microearthquake: Case Study at “X” Geothermal Field

Abstract

Generally, analysis of geological structure in the geothermal field is carried out using remote sensing methods, geological mapping, and gravity analysis. These methods can provide the distribution of geological structure on the surface but cannot provide information on whether the structure is active or not. This study aims to utilize improved hypocenter location which can be used to delineate the distribution of active faults. This is useful for obtain a better interpretation of geological structures in geothermal areas. Hypocenter locations are determined by picking the arrival time of the P-wave and S-wave. This method sometimes leads to uncertainty of hypocenter location due to subjectivity of picking arrival time. The double-difference method is applied with additional input pairing events from waveform cross-correlation (WCC) to overcome the uncertainty of hypocenter location. The result shows 3 microearthquake clusters formed in the western, central, and eastern parts of the “X” Geothermal Field. The cluster formed in the western area shows that there are two orientations of conjugated hypocenter distribution with the orientation of NW-SE and NE-SW. These hypocenters reveal the presence of geological structures which provide permeability pathways for fluids rising in the western part of the geothermal field. Multiplet-clustering analysis in the middle cluster which coincides with the reservoir zone shows two different sub-clusters indicating the possibility of two different sources mechanism working in the area. By integrating all the analysis and hypocenter distribution, these methods provide a better interpretation of structure’s distribution in the “X” Geothermal Field.