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2019 Vol.29, Issue 1

Research Article

Characterizing Fracture System Change at Boreholes in a Coastal Area in Korea for Monitoring Earthquake

지진감시를 위한 국내 해안지역 시추공 내 단열계 변화 특성

Jae-Yeol Cheong1
,
Se-Yeong Hamm2*
,
Soon-Il Ok3
,
Hyunjin Cho3
,
Soo-Gin Kim3
,
Sul-Min Yun4
정 재열1
,
함 세영2*
,
옥 순일3
,
조 현진3
,
김 수진3
,
윤 설민4
1Korea Radioactive Waste Agency, Team Head
2Dept. of Geological Sciences, Pusan National University, Professor
3Korea Radioactive Waste Agency, Manager
4Dept. of Geological Sciences, Pusan National University, PhD Student
1한국원자력환경공단, 팀장
2부산대학교 지질환경과학과, 교수
3한국원자력환경공단, 과장
4부산대학교 지질환경과학과, 박사과정
*Corresponding Author
31 March 2019. pp. 1-12
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Abstract

Earthquake can change underground stress condition around the hypocenter and affect the fracture systems of the rocks. In Korea, the M5.8 Gyeongju earthquake on September 12, 2016 and M5.4 Pohang earthquake on November 15, 2017 occurred inside the Yangsan fault zone and possibly affected the fracture systems in the Yangsan fault zone and nearby rock masses. In this study, the characteristics of the fracture system (fracture orientation, number of the fractures, fracture spacing and aperture, dip angle, fracture density along depth, and relative rock strength) of the rocks in the low/intermediate level radioactive waste repository site located in the coastal area of the East Sea are analyzed by the impact of the Gyeongju and Pohang earthquakes using acoustic televiewer data taken from the boreholes at the radioactive waste repository site in 2005 and 2018. As a result of acoustic televiewer logging analysis, the fracture numbers, fracture aperture, and fracture density along depth overall increased in 2018 comparing to those in 2005. This increase tendency may be due to changes in the fracture system due to the impact of the earthquakes, or due to weathering of the wall of the boreholes for a long period longer than 10 years after the installation of the boreholes in 2005. In the borehole KB-14, on the whole, the orientation of the fractures and the average fracture spacing are slightly different between 2005 and 2018, while dip angle and relative rock strength in 2005 and 2018 are similar each other.

Keywords
Gyeongju earthquake
Pohang earthquake
acoustic televiewer logging
fracture system characteristics
coastal area

지진은 진원지 주변의 지반의 응력상태를 변화시키고, 암반의 단열계에 영향을 미칠 수 있다. 국내에서 2016년 9월 12일과 2017년 11월 15일에 각각 발생한 지진규모 5.8의 경주지진과 지진규모 5.4의 포항지진은 양산단층대와 관련되며, 양산단층대 및 인근 지역 암반의 단열계에 영향을 미쳤을 가능성이 있다. 본 연구에서는 동해안 지역에 위치하는 중 ‧ 저준위 방사성폐기물 처분장 부지 내 암반의 단열계 특성(방향성, 주향에 따른 절리개수, 절리간격, 절리간극, 경사각, 심도 구간별 절리빈도, 상대 암반강도)이 경주지진 및 포항지진에 의해서 영향을 받았는지를 분석하기 위하여 부지내 감시공에서 2005년과 2018년에 실시한 초음파 주사검층자료를 비교·분석하였다. 초음파 주사검층 분석 결과, 주향에 따른 절리개수, 절리간극, 심도 구간별 절리빈도는 2005년보다 2018년에 대체로 증가하였다. 이러한 증가는 지진의 영향으로 인한 단열체계의 변화로 인한 영향이거나, 2005년 감시공 설치 이후 10년 이상의 오랜 기간 나공 상태에서 공벽의 풍화로 인한 것일 수도 있다. 또한 KB-14공에서 전체 절리의 방향성과 절리의 평균 간격이 2005년과 2018년 사이에 다소 차이를 보이고 있으나, 절리면 경사와 상대 암반강도는 전반적으로 2005년과 2018년이 유사하게 나타났다.

키워드
경주지진
포항지진
초음파 주사검층
단열계 특성
해안지역
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Information
  • Publisher :Korean Society of Engineering Geology
  • Publisher(Ko) :대한지질공학회
  • Journal Title :The Journal of Engineering Geology
  • Journal Title(Ko) :지질공학
  • Volume : 29
  • No :1
  • Pages :1-12
  • Received Date : 2019-02-19
  • Revised Date : 2019-03-16
  • Accepted Date : 2019-03-21
  • DOI :https://doi.org/10.9720/kseg.2019.1.001
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