The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY (한국해양학회지:바다)

The Korean Society of Oceanography (한국해양학회)
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Gas Hydrate Occurrence in the Southwestern Slope of the Ulleung Basin, East Sea, Inferred from Seismic Evidence

동해 울릉분지 남서 사면지역에서 탄성파 특징으로부터 유추한 가스 수화물의 존재 가능성

  • 홍종국 (한국해양연구원 해양환경 기후연구본부) ;
  • 유해수 (한국해양연구원 해양환경 기후연구본부) ;
  • 주형태 (한국해양연구원 해양환경 기후연구본부) ;
  • 한상준 (한국해양연구원 해양환경 기후연구본부) ;
  • 최동림 (한국해양연구원 장목분원)
  • Published : 2001.11.30
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Abstract

A high resolution Chirp seismic profile and a multichannel seismic reflection profile were analysed to study the possibility of gas hydrate presence in the southwestern upper slope of the Ulleung Basin. The Chirp profile shows acoustic turbidity, acoustic void, and pockmarks, suggesting the presence of shallow gas in the sediments .Slope failures appear to have occurred in association with decomposition of gas hydrated sediments. A bottom-simulating reflector (BSR) is seen in subbottom depths of 60 to 110 m below the seafloor at water depths of 750 to 1130 m. The sediments above BSR are characterized by acoustic blanking probably due to amplitude reduction caused by a mixture of gas hydrate with sediments. The interval velocity above the BSR is 1,650 m/sec and it drops abruptly to 1,080 m/sec below the BSR. The sediment column between seafloor and the BSR thins with increasing water depth, which is very closely related to increasing geothermal gradient with increasing water depth in the Ulleung Basin.

고해상 Chirp 자료와 다중채널 탄성파 자료를 이용하여 울릉분지 남서 상부대륙사면지역에 가스수화물의 존재 가능성에 대해 분석하였다. Chirp 자료에서 퇴적층내 천부 가스의 분포를 지시하는 음향혼탁상, 음향 공백상, 그리고 포크마크가 보인다. 가스수화물의 분해와 관련된 것으로 생각되는 사면붕괴 구조도 확인된다. BSR이 수심 750${\sim}$1130m사이 지역에서 해저면 아래 60${\sim}$110m부근에 발달한다. BSR위의 상부퇴적층은 음향 블랭킹 양상을 보이는데, 이는 퇴적물과 가스수화물의 혼합에 의한 진폭 감소의 결과로 해석된다. 탄성파 자료 속도분석으로부터 계산된 지층의 구간속도는 BSR위의 퇴적층이 1,650m/sec이고 아래 퇴적층은 1,080m/sec을 나타낸다. BSR 상부의 퇴적층 두께가 수심이 증가할수록 얇아지는 양상은 울룽분지의 지열류량이 수심의 증가와 함께 증가하는 발달분포와 매우 밀접한 관계가 있을 것으로 예상된다.

Keywords

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