日本地球惑星科学連合2018年大会

講演情報

[EJ] ポスター発表

セッション記号 S (固体地球科学) » S-GL 地質学

[S-GL29] 泥火山と地球化学的・地質地形学的・生物学的関連現象

2018年5月24日(木) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:浅田 美穂(国立研究法人海洋研究開発機構)、土岐 知弘(琉球大学理学部)、井尻 暁(国立研究開発法人海洋研究開発機構、共同)、辻 健(九州大学工学研究院)

[SGL29-P04] 自動速度解析で明らかになってきた日本周辺のガス層

*辻 健1Chhun Chanmaly1 (1.九州大学工学研究院)

The submarine mud volcano could be related to the gas reservoir and hydrate widely distributed around the Japanese Island. To investigate gas reservoir, we performed a high-resolution seismic velocity analysis to 3D seismic data using a method of conventional semblance spectra via automatic velocity picking algorithm. The high-resolution velocity models allow us to elucidate several gas reservoirs around the Japanese Island. In the Kumano forearc basin off the Kii peninsula, we found several gas reservoirs as low P-wave velocity zone. The results revealed that gas hydrate-bearing sediments above the BSR and free gas-bearing sediments below the BSR are characterized by P-wave velocities of 1900-2500 m/s and 1000-1800 m/s, respectively. The P-wave velocity of gas reservoir is lower than that of seawater (1500m/s). Then, the velocity model was converted into gas hydrate and free gas saturation using rock physics approaches. The results indicated that saturation of gas hydrates ranges from 0% to 45% in the pore space, and highly concentrated around the outer ridge where faults are densely developed. Additionally, concentrations of free gas ranging from 0% to 20% in the pore space are widely distributed below BSRs and are considerably high above ridge structure generated by displacement of large fault splayed from the deep plate boundary décollement. Based on these results, we suggest that the accumulations of gas and/or hydrates are further controlled by fault movements in the accretionary prism beneath the forearc basin. Therefore, these factors generated by intensive tectonic movements in the plate subduction zone control the distribution and saturation pattern of gas hydrate and free gas formations.