Geophysics and Geophysical Exploration (지구물리와물리탐사)

Korean Society of Earth and Exploration Geophysicists (한국지구물리·물리탐사학회)
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Near-surface P- and S-wave Velocity Structures in the Vicinity of the Cheongcheon Dam

청천댐 주변의 천부 P파 및 S파 속도구조

  • Received : 2013.01.14
  • Accepted : 2013.06.12
  • Published : 2013.08.31
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Abstract

On and near the 23-m high earthen Cheongcheon dam in Boryeong City, Korea, short seismic refraction and surface-wave profiles were conducted using a 5-kg sledgehammer. From vertical and horizontal components of the seismic waves, near-surface P-wave velocities (${\nu}_p$) and S-wave velocities (${\nu}_s$) were derived by inverting first-arrival refraction times and dispersion curves of Rayleigh waves. Average ${\nu}_p$ and ${\nu}_s$ for the Jurassic sedimentary basement were determined to be 1650 and 950 m/s at a depth of 30 m directly beneath the dam and 1650 m/s and 940 m/s at a depth of 10 m at the toe of the dam, respectively. The dynamic Poisson's ratio for these strata were therefore in the range of 0.24 to 0.25, which is consistent with ratios for consolidated sedimentary strata. Near a 45-m borehole 152 m downstream from the dam crest, an SH tomogram indicates a refraction boundary with an average ${\nu}_s$ of 870 m/s at depths of 10 ~ 12 m. At this site, the overburden comprises the upper layer with relatively constant ${\nu}_p$ and ${\nu}_s$ around 500 and 200 m/s, respectively, and the lower layer in which both ${\nu}_p$ and ${\nu}_s$ increase with depth almost linearly. The dynamic Poisson's ratios for the overburden were in the range of 0.30 to 0.43.

높이 23 m인 보령시 청천댐 상부와 인근에서 5 kg 해머를 이용하여 소규모 굴절법 및 표면파 탐사를 실시하였다. 인공 지진파의 수직 및 수평성분을 초동주시 토모그래피 및 레일리파 분산곡선 역산을 통하여 천부 P파속도(${\nu}_p$)와 S파속도(${\nu}_s$) 구조를 파악하였다. 중생대 퇴적암질 기반암의 평균 ${\nu}_p$와 ${\nu}_s$는 댐마루 30 m 깊이에서 각각 1650 m/s와 950 m/s, 하류쪽 댐체 끝 지점 10 m 깊이에서 각각 1650 m/s와 940 m/s로 분석된다. 이 층들의 동포아송비는 0.24 ~ 0.25의 범위로, 고화된 퇴적층의 값과 일치한다. 댐체로부터 152 m 하류지점의 깊이 45 m 시추공 부근에서의 SH파 굴절법 토모그램은 10 ~ 12 m 깊이에 평균 vs가 870 m/s인 임계굴절면이 존재함을 보여준다. 이 지역에서는 덮개층의 ${\nu}_p$와 ${\nu}_s$가 각각 500 m/s와 200 m/s인 상부층과 깊이에 따라 속도가 거의 선형으로 증가하는 하부층으로 구성되어 있다.

Keywords

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