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상시미동 및 원거리 지진 자료로부터 구한 화천 지진관측소의 천부 횡파속도구조

Near-surface Shear-wave Velocities Derived from Microtremors and Teleseismic Data at the Hwacheon Seismic Station

  • 투고 : 2013.07.09
  • 심사 : 2013.08.26
  • 발행 : 2013.08.31

초록

화천 지진관측소의 시추주상도와 56일간 기록한 상시미동자료 및 3개 원거리 지진이벤트($M_w{\geq}6.0$)를 이용하여 천부 횡파속도(${\nu}_s$)를 구하였다. 지표에서 기록한 상시미동자료의 수평성분/수직성분 스펙트럼비로부터 10 m 두께의 토양층의 ${\nu}_s$(${\nu}^s_s$= 296 m/s)를 결정하였다. 지표로부터 시추공 센서가 설치된 96 m 깊이까지의 평균 ${\nu}_s$($\bar{\nu}_s$= 1,309 m/s)는 3개의 원거리 지진이벤트를 지표 및 시추공 센서로 기록한 자료들의 스펙트럼 상관도로 계산하였다. 이렇게 계산한 ${\nu}^s_s$$\bar{\nu}_s$값을 이용하여 계산한 기반암의 ${\nu}_s$는 2,150 m/s이며, 30 m까지의 평균 ${\nu}_s$는 696 m/s이다. 화천 관측소 부지는 비교적 양호한 것으로 판단되며, 이 연구를 통해 구해진 천부 ${\nu}_s$는 향후 지반의 부지증폭효과 및 지진재해의 정량적 평가에 활용될 수 있다.

We estimated near-surface shear-wave velocity (${\nu}_s$) at the Hwacheon seismic station using a geologic log of a well, microtremors recorded during a period of 56 days, and records of three teleseismic events ($M_w{\geq}6.0$). The vs of the 10-m thick soil layer (${\nu}^s_s$= 296 m/s) was determined from horizontal-to-vertical spectral ratios of microtremors recorded at the surface. The average ${\nu}_s$ ($\bar{\nu}_s$= 1,309 m/s) from the surface to the 96-m depth of a borehole sensor, was computed using spectral coherence analyses of data recorded by surface- and borehole-sensors for the three teleseismic events. Using these calculated values of ${\nu}^s_s$ and $\bar{\nu}_s$, the computed bedrock ${\nu}_s$ is 2,150 m/s and the time-averaged ${\nu}_s$ to a 30-m depth is 696 m/s. Accordingly the Hwacheon seismic station is regarded as a relatively good site. The deduced near-surface ${\nu}_s$ can be used for further quantitative evaluation of site amplification and earthquake hazard.

키워드

참고문헌

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