THE 20 JANUARY 2007,M W 4.5, ODAESAN, KOREA, EARTHQUAKE

Abstract

Results of analyses for the source parameters and ground responses of the 20 January 2007 Odaesan earthquake, Korea, are presented. We use the ground velocity and acceleration data recorded at the regional seismic stations located in southern Korea. For the determination of hypocenter and origin time, we use the program HYPO71 which has been generally used for the hypocenter determination of local earthquake and perform a depth phase analysis using arrival time difference ofP n andsP n waves. The focal mechanism is obtained using a grid search algorithm with the polarities of the observedP g, Pn andSH waves. The moment magnitude (M w) and dynamic stress drop are estimated using an iterative integral method with broadband seismic data. The estimated source parameters of the Odaesan earthquake are as follows: origin time 11∶56∶53.48 in UTC, latitude 37.686°N, longitude 128.589°E, focal depth 12.1 km,M w 4.5, dynamic stress drop 77.4 bars, the fault plane 19.69°, 69.74° and −165.02°, the auxiliary plane 284.40°, 75.97° and −20.91° in strike, dip and rake, respectively. Considering geological characteristics around the epicenter, the fault plane solution with the strike angle of 19.69° is consistant with that of the existing Woljeongsa fault. The largest peak ground acceleration (PGA), 0.157 g, was recorded at the DGY station located 7.5 km east of the epicenter. The maximum instrumental intensity is estimated as VII in the Modified Mercalli Intensity (MMI) scale.