Geosciences Journal

The Association of Korean Geoscience Societies (한국지질과학협의회)
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The 20 January 2007, $M_w$ 4.5, Odaesan, Korea, earthquake

Jo, Nam-Dae;Baag, Chang-Eob

  • Published : 20070300
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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 accelerationdata recorded at the regional seismic stations located in southernKorea. For the determination of hypocenter and origin time, weuse the program HYPO71 which has been generally used for thehypocenter determination of local earthquake and perform adepth phase analysis using arrival time difference of Pn and sPnwaves. The focal mechanism is obtained using a grid search algo-rithm with the polarities of the observed Pg, Pn and SH waves. Themoment magnitude (Mw) and dynamic stress drop are estimatedusing an iterative integral method with broadband seismic data. Theestimated source parameters of the Odaesan earthquake are as fol-lows: origin time 11:56:53.48 in UTC, latitude 37.686°N, longitude128.589°E, focal depth 12.1 km, Mw 4.5, dynamic stress drop 77.4bars, the fault plane 19.69°, 69.74° and -165.02°, the auxiliary plane284.40°, 75.97° and -20.91° in strike, dip and rake, respectively.Considering geological characteristics around the epicenter, thefault plane solution with the strike angle of 19.69° is consistantwith that of the existing Woljeongsa fault. The largest peak groundacceleration (PGA), 0.157 g, was recorded at the DGY stationlocated 7.5 km east of the epicenter. The maximum instrumentalintensity is estimated as VII in the Modified Mercalli Intensity(MMI) scale. Key words : the 20 January 2007 Odaesan earthquake, focal mech-anism, depth phase, dynamic stress drop, seismic moment, momentmagnitude, peak ground acceleration, instrumental intensity

Keywords

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