The sea layer in marine Controlled-Source Electromagnetic (mCSEM) survey changes the conventional definition of apparent resistivity which is used in the land CSEM survey. Thus, the development of a new algorithm, which computes apparent resistivity for mCSEM survey, can be an initiative of mCSEM data interpretation. First, we compared and analyzed electromagnetic responses of the 1D stratified gas hydrate model and the half-space model below the sea layer. Amplitude and phase components showed

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... proper results for computing apparent resistivity than real and imaginary components. Next, the amplitude component is more sensitive to the subsurface resistivity than the phase component in far offset range and vice versa. We suggested the induction number as a selection criteria of amplitude or phase component to calculate apparent resistivity. Based on our study, we have developed a numerical algorithm, which computes appropriate apparent resistivity corresponding to measured mCSEM data using grid search method. In addition, we verified the validity of the developed algorithm by applying it to the stratified gas hydrate models with various model parameters. Finally, by constructing apparent resistivity pseudo-section from the mCSEM responses with 2D numerical models simulating gas hydrate deposits in the Ulleung Basin, we confirmed that the apparent resistivity can provide the information on the geometric distribution of the gas hydrate deposit. 서 론 우리나라 동해지역의 가스 하이드레이트는 미래의 석유 대 체에너지원으로 주목받고 있으며, 다채널 탄성파 탐사와 물리 검층, 코어분석등을 통해 그 부존이 확인되었다(유동근 등, 2008; 김길영 등, 2010). 기존의 가스 하이드레이트 탐사에 주 로 사용된 탄성파 탐사는 BSR (bottom simulating reflector)과 같이 가스 하이드레이트의 부존 가능성을 시사하는 탄성파 지 시자를 이용하거나 음향 임피던스(acoustic impedance)와 같은 탄성파적 특성(seismic attribute)을 이용하여 가스 하이드레이 트의 부존가능지역을 추정하고, 가스 하이드레이트를 함유하