Contrasting hydrological and mechanical properties of clayey and silty muds cored from the shallow Nankai Trough accretionary prism
Contrasting hydrological and mechanical properties of clayey and silty muds cored from the shallow Nankai Trough accretionary prism
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南海海槽浅层增生棱柱取芯的粘土和粉质泥的水文和力学特性对比
DOI：
10.1016/j.tecto.2013.01.008
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发表时间：
2013
期刊：
影响因子：
2.9
通讯作者：
A
中科院分区：
文献类型：
--
作者：
Takahashi;M.;Azuma;S.;Uehara;S.;Kanagawa;K. and Inoue;A
在南海海槽315号考察站C 0002点南海海槽浅水增生棱柱体中取心的两个泥质样品，其水文力学性质存在明显差异。在围压、孔隙水压力和接近原位条件的温度下，粘土质泥浆样品的渗透率较低，为2.92×10− 19 m2，而粉质泥浆样品的渗透率较高，为2.29×10− 18 m2。在此条件下，轴向位移速率为10μm/s的三轴压缩实验表明，粘土质泥浆样品的破坏强度较低，为14.2MPa，随后缓慢破坏，持续约40 s，而粉质泥浆样品的破坏强度较高，为20.1MPa，随后在约5 s内快速破坏。轴向位移速率在0.1、1和10μm/s之间逐级变化的摩擦实验表明，粘土质泥浆试样的稳态摩擦力（μss <$0.25）远低于粉质泥浆试样（μ ss <$0.53）。虽然这两种样品都表现出速度强化，但前者的稳态摩擦的速度依赖性比后者大三倍以上。粘土质和粉砂质泥样品的水文和力学性质的这种对比，在这项研究中揭示了以下的影响，在浅泥为主的南开海槽增生棱镜的变形和断层。变形可能导致孔隙压力的增加，从而导致粘土质泥浆的强度降低，但不会导致粉质泥浆的强度降低。断层优先发生在较弱的粘土质泥中，其缓慢破坏可能导致缓慢滑动。在粘土质泥中形成的断层是软弱的，容易再活化，但稳定，不孕震。反之，强度较强的粉质泥一旦发生断层，其快速破坏就可能变成地震滑移。在粉质泥中形成的断层很强，不易再活化，但可能不稳定，有孕震性。
Two mud samples cored from the shallow (≈1000mbsf) Nankai Trough accretionary prism at Site C0002 of IODP Expedition 315 are found to be distinctly different in hydrological and mechanical properties. At confining pressures, pore water pressures and temperatures close to their in situ conditions, a clayey mud sample has lower permeability of 2.92×10−19m2, while a silty mud sample has higher permeability of 2.29×10−18m2. Triaxial compression experiments at these conditions and an axial displacement rate of 10μm/s reveal that the clayey mud sample exhibits lower failure strength of 14.2MPa followed by a slow failure lasting for ≈40 s, while the silty mud sample exhibits higher failure strength of 20.1MPa followed by a rapid failure within ≈5 s. Friction experiments at these conditions and axial displacement rates changed stepwise among 0.1, 1 and 10μm/s reveal that the clayey mud sample has a much lower steady-state friction (μss≈0.25) than the silty mud sample (μss≈0.53). Although both samples exhibit velocity strengthening, the former has more than three times larger velocity-dependence of steady-state friction than the latter. Such contrasting hydrological and mechanical properties of the clayey and silty mud samples as revealed in this study suggest the following implications for deformation and faulting in the shallow mud-dominant Nankai Trough accretionary prism. Deformation results in a possible increase in pore pressure, and hence, in strength reduction in clayey mud, but not in silty mud. Faulting would preferentially occur in the weaker clayey mud, and its slow failure may result in a slow slip. Faults formed in clayey mud are weak and easily reactivated, but stable and not seismogenic. In contrast, once the stronger silty mud is faulted, its rapid failure may become a seismic slip. Faults formed in silty mud are strong and not easily reactivated, but possibly unstable and seismogenic.