东北太平洋Cascadia陆缘Orca滑坡触发机理的数值模拟  

Modelling of triggering of Orca submarine landslide, Cascadia margin, northeast Pacific

作　　者：何雯[1] 曹运诚[1] 陈多福[1] HE Wen;CAO Yuncheng;CHEN Duofu(Shanghai Engineering Research Center of Hadal Science and Technology,College of Marine Sciences,Shanghai Ocean University,Shanghai 201306,China)

机构地区：[1]上海深渊科学工程技术研究中心,上海海洋大学海洋科学学院,上海201306

出　　处：《海洋地质与第四纪地质》2023年第1期180-189,共10页Marine Geology & Quaternary Geology

基　　金：国家重点研发项目“中国海域冷泉系统演变过程及其机制”(2018YFC0310006);国家自然科学基金项目“南海北部冷泉和天然气水合物发育区海底浅表层沉积物碳循环数值模拟”(41730528),“马里亚纳弧前海底蛇纹岩泥火山无机成因甲烷形成水合物的条件及潜力分析”(41776050),“冲绳海槽海底冷泉-热液系统相互作用及资源效应”(91858208)。

摘　　要：海底温度和海平面变化可以引起海底天然气水合物分解,导致沉积物孔隙内形成超压,改变沉积物有效应力从而触发海底滑坡。本文建立了与此相关的海底滑坡产生的数值模型,并应用于东北太平洋Cascadia陆缘14~9 kaBP期间发生的Orca滑坡形成过程研究。模拟结果显示在最近18 ka海平面逐渐上升的大背景下,18~14 kaBP期间底水温度升高引起其后的天然气水合物稳定带底界快速上移,并在13.7 kaBP达到1.18 m/ka的高底界上移速率,此时Orca地区稳定带底界粗颗粒层内的高饱和度天然气水合物发生分解,产生114 kPa的流体超压,使地层安全系数显著小于1,触发海底滑坡。因此,海底温度升高引起高饱和度天然气水合物分解可能是东北太平洋Cascadia陆缘Orca海底滑坡的主要触发因素。Bottom-water temperature variations and eustatic sea-level fluctuations may cause decomposition of marine gas hydrate and excess pore pressure in sediment, which leads to a subsequent decrease in effective stress of the sediment, and eventually results in submarine landslides. A numerical modeling of the mechanism of such slope failure was developed herein, and was applied to the study of Orca Slide that occurred between 14 and 9 kaBP on the Cascadia margin in the northeast Pacific. The modeling results show that with the rising sea level in the last 18 ka, the base of hydrate stability zone(BHSZ) experienced a fast upward movement whose rising rate peaked to 1.18 m/ka at 13.7 kaBP due to continuous bottom-water warming during 18~14 kaBP. Meanwhile, an excess pore pressure of 114 kPa was formed in the coarsegrained layers in the BHSZ of Orca Slide as a result of gas hydrate decomposition, which then significantly reduced the factor of safety of the strata to less than 1, thereby triggering the submarine landslides. Therefore, highly saturated hydrate decomposition caused by the bottom-water temperature rise may be the main triggering mechanism of Orca submarine landslide.

关 键 词：海底滑坡 水合物分解 流体超压 滑坡触发机理 Cascadia陆缘Orca滑坡 

分 类 号：P736[天文地球—海洋地质]