Identification of Micro-Earthquake Hypocenters using Geiger and Coupled Velocity-Hypocenters Methods

Abstract

The accuracy location of hypocenter is needed to determine the subsurface character beneath a geothermal area. The study used 73 micro-earthquake events; each micro-earthquake event was classified based on the time difference between the P and S waves (ts-tp) that had values ≤ 3seconds, the magnitude of micro-earthquake ≤ 3SR and each micro-earthquake event was recorded at least by 3 observer stations. We inverted selected P and S travel times from 11-unit seismic stations on X geothermal area. The initial hypocenter location was determined using Geiger method. The result of the Geiger method's initial hypocenter location was then used as the input to determine the accurate hypocenter location in the following method, Coupled Velocity-Hypocenters method. Other parameters were also used on this second method, including hypocenter location, 1-D velocity model, origin time, vp/vs ratio, zshift and the station correction. The distribution of hypocenter locations of micro-earthquakes obtained using the second method was better than the results from Geiger method. This result is supported by the Coupled Velocity-Hypocenters average RMS error value, which was smaller, only 0.19 seconds, compared to the Geiger method, which had an average RMS error of 0.74 seconds. The hypocenter location of the relocation was more clustered in the reservoir area, precisely in the production well, and in the heat source area. The hypocenter location in the production well area indicates fluid flow through the fracture from the permeable zone.