DETERMINING HYPOCENTRAL PARAMETERS OF EARTHQUAKES OCCURRED IN THE GYEONGSANG BASIN, KOREA USING THE GA-MHYPO

KIM, W., and HAHM, I.K., Univ., Dept. of Earth and Environmental Sciences, Gyeongsang National Univ., Jinju, 660-701, Korea, wookim@gsnu.ac.kr.

85 earthquakes occurred in the Gyeongsang Basin, Korea were relocated using the GA-MHYPO (Kim et al., 2005). The GA-MHYPO was developed from the HYPO-71 by employing the genetic algorithm (GA), the two-point ray tracing, and a new weighting factor. The GA searches the best fitting velocity structure which minimizes the error between observed (true) traveltimes and calculated ones. The two-point ray tracing (Kim and Baag, 2002) reduces ray path error between the source and the receiver. The new weighting factor which represents the degree of focal-depth information is described in terms of the take-off angle at the source, and improves the accuracy of the focal depth and origin time (Hahm et al., 2005). The GA-MHYPO yielded very accurate hypocentral parameters for the synthetic data without and with noise. The newly determined hypocentral parameters of this work were compared with those determined by the Korea Institute of Geology and Materials (KIGAM) using LOCSAT (Bratt and Bache, 1988). The newly determined epicentral distribution is closely correlated to linear structure while the one by the KIGAM is not. The newly determined focal-depths are quite different from those by the KIGAM.