IDENTIFICATION OF GEOLOGICAL STRUCTURES BASED ON RELOCATED MICROEARTHQUAKES USING DOUBLE-DIFFERENCE METHOD: A STUDY AT “GORGJESS” GEOTHERMAL FIELD

Abstract

Geological structures (faults) play a crucial role in the utilization of geothermal fluids within a reservoir. During the exploration stage, geological structures act as fluid pathways to the surface, which are observed as surface manifestations. Moreover, these structures can be considered as drilling targets due to their role in controlling fluid permeability within the reservoir. One of the geophysical methods that can be employed to identify geological structures is the Microearthquake (MEQ) method. This method utilizes P- and S-body waves recorded at seismic stations, which are generated by mechanical failures along fractures or faults, known as microearthquake events. In this study, MEQ data were relocated using the double-difference method to obtain high precision hypocenter locations for identifying fault structures in the “Gorgjess” Geothermal Field. The dataset used spans from January 1 to April 4, 2018, recorded by 11 seismic stations within the field. Phase arrival picking of P- and S-waves was performed automatically using EQTransformer, followed by event association using the GaMMA (Gaussian Mixture Model Associator) algorithm, and initial hypocenter determination using NonLinLoc. A total of 228 MEQ events were identified and subsequently relocated using the double-difference method. Of these, 113 events were successfully relocated based on event pair distances and arrival time misfits that were relatively close to zero, indicating consistency between observed and calculated data. The relocated hypocenter results reveal the presence of dominant NE–SW trending structures, namely the Ciwidey and Patuha Faults.