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Research Article

Analysis of Geological Structure of Volcanic Rock Mass in Ulleung-do using Variations of Magnetic Anomaly

자력탐사 자기이상 분석을 활용한 울릉도 화산암체 지질구조 특성 해석

Ki-Beom Kim1
,
Man-Il Kim2*
김 기범1
,
김 만일2*
1Department of Earth and Environmental Sciences, Andong National University, Adjunct Professor
2Forest Engineering Research Institute, National Forestry Cooperative Federation, Principal Researcher
1안동대학교 지구환경과학과, 겸임교수
2산림조합중앙회 산림공학연구소, 책임연구원
* Corresponding Author
31 December 2018. pp. 619-630
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Abstract

The purpose of this study is to investigate the existence of faults and intrusive rocks in the volcanic rock mass of Ulleung-do using magnetic anomalies. The magnetic survey data show that basaltic (mafic) rocks have high magnetic anomalies and that trachytic (felsic) rocks have low magnetic anomalies, implying that the anomaly distributions can be used to distinguish between different volcanic rock types that may be covered by regolith (such as alluvial and colluvial deposits) and other sedimentary layers. Our results show that basaltic rocks are not present within the Nari caldera. However, outside the caldera, the occurrence of high magnetic anomaly values of >1000 γ is presumed to reflect the existence of basaltic craters or volcanic vents that formed prior to the eruption of the trachytic rocks. In particular, the area with anomaly values of >1000 γ in the vicinity of Namyang-ri, southwest of Ulleung-do, is interpreted as having a high probability of hosting a crater and vent originating from mafic volcanism.

Keywords
magnetic survey
magnetic anomaly
volcanic rock mass
basaltic rocks
trachytic rocks

울릉도 화산암체 내 단층 및 관입암체의 존재 여부 등을 파악하기 위한 목적으로 자력탐사를 실시하고 이의 정성적인 해석을 통해 자기이상 변화를 분석하였다. 울릉도 전역에 대한 자력탐사 자료 분석결과, 염기성암인 현무암질암류는 높은 자기이상을 나타내고 산성암인 조면암질암류는 낮은 자기이상을 나타내었다. 이들 자기이상은 모두 울릉도 화산암체의 암상과 대체로 잘 일치하며 화산암의 종류에 따라 대비를 이루고 있어 자기이상 분포의 상호 분석을 통한 전석, 충적층, 퇴적층 등으로 피복되어 있는 지역의 암상 구분에 활용 가능이 가능하다. 또한, 나리칼데라에서 현무암질암류가 관찰되지는 않으나 1,000 γ이상의 높은 자기이상이 분포하는 것은 조면암질암류의 분출 이전에 형성된 현무암질암류로 이루어진 화구 및 화도에 의한 것으로 추정된다. 나리칼데라 이외 지역에서 나타나는 높은 자기이상의 분포지역 중 일부는 화구 및 화도로 추정이 가능하며 울릉도 남서쪽의 남양리 부근에 분포하는 큰 규모의 1,000 γ 이상의 높은 자기이상은 현무암질암류의 화구 및 화도 가능성이 클 것으로 사료된다.

키워드
자력탐사
자기이상
화산암체
현무암질암류
조면암질암류
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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 : 28
  • No :4
  • Pages :619-630
  • Received Date : 2018-10-31
  • Revised Date : 2018-11-06
  • Accepted Date : 2018-11-10
  • DOI :https://doi.org/10.9720/kseg.2018.4.619
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