Fault rupture directivity of Odaesan Earthquake (M=4.8, '07. 1. 20)

오대산지진(M=4.8, '07. 1. 20)의 단층파열방향성

  • Yun, Kwan-Hee (Environmental & Structural Lab., Korea Electric Power Research Institute)
  • 연관희 (한전전력연구원 환경구조연구소)
  • Published : 2008.05.31

Abstract

Fault rupture directivity of the Odaesan earthquake, which was inferred to be the main cause of the high PGAvalue (> 0.1 g) unusually observed at the near-source region, was analyzed by using the data from the nearby (R < 100 km) dense seismic stations. The Boatwright's method (2007) was adopted for this purpose in which the azimuth and takeoff angle of the unilateral rupture directivity function could be estimated based on the relative peak ground-motions of seismic stations resulting from the nature of the rupture directivity. In this study, the approximate values of the relative peak ground-motions was derived from the difference between the log residuals of the point-source spectral model (Boore, 2003) for the main and secondary events based on the Random Vibration Theory. In this derivation, the spectral difference for a frequency range between the source corner frequencies of main and secondary events was considered to reflect only the effect of the fault directivity. The inversion result of the model parameters for the fault directivity function showed that the fault-plane of NWW-SEE direction dipping steeply to the North with high rupture velocity near upward in SE direction is responsible for the observed high level of ground-motion at the near-source region.

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