东海天然气水合物地热研究及其环境意义

依据地热资料研究天然气水合物稳定带厚度在东海海域的分布情况。东海在地质构造上位于新生代环太平洋构造带西部边缘岛弧的内侧,又是欧亚板块、太平洋板块和菲律宾海板块的相互作用带。依据国际热流委员会(IHFC)提供的东海地热数据,经过统计确定出该区域的热流分布,热流平均值为121·0mW/m2,最小值为73·0mW/m2,最大值为168·0mW/m2。同时利用天然气水合物温压模型计算了稳定带厚度,数据显示稳定带厚度平均值为92·2m,最小值为1·4m,最大值为190·6m,薄于其他已经发现的海洋天然气水合物稳定带厚度(约400m)。天然气水合物大部分分布在条件适宜的陆坡和岛坡上,冲绳海槽底部水合物稳定带厚度相对较薄。统计分析表明本区热流值与水合物稳定带厚度相关性很差,相关系数仅有0·12。这是由于天然气水合物所在海域水深较浅时,海底温度的变化迫使运算所应用的非线性方程影响因子迅速积累,从而导致相关系数降低。最后结合东海陆坡的地质条件,探讨了在天然气水合物存在的情况下,陆坡失稳的可能性及其造成的环境影响。

A geothermal study of gas hydrates in the East China Sea and its environmental implications

We calculate the thickness of gas hydrate stable zone (GHSZ) in the East China Sea, which is located at the convergent margin between the Eurasian plate, the Pacific plate and the Philippine Sea plate. This research is based on the heat flow data provided by the International Heat Flow Commission (IHFC). The heat flow measurements suggest that the East China Sea is characterized by a relatively high average heat flow of about 121.0 mW/m~2, ranging from 73.0 to 168.0 mW/m~2. The results indicate that the average thickness of GHSZ in the study region is 92.2 m, ranging from 1.4 m to 190.6 m, which is smaller than the 400 m thickness at other GHSZ sites of natural marine gas hydrate occurrences in the world. Mostly, gas hydrates are concentrated in the sediments of continental slopes and trench areas. Statistical tests show that the heat flow values in the area are not in good agreement with the thickness of GHSZ, because the correlation coefficient is 0.12. This could be explained by the fact that seafloor temperature exerts a substantial influence on theoretical solutions of the non-linear equations for the thickness of GHSZ, when the depth to sea floor is shallower than 1 100 m. We conclude that gas hydrate dissociation is most likely to cause seafloor collapse, resulting in the venting of a large amount of greenhouse gas, especially methane, in the East China Sea.