Mechanical characterization of slope sediments: Constraints on in situ stress and pore pressure near the tip of the megasplay fault in the Nankai accretionary complex
Mechanical characterization of slope sediments: Constraints on in situ stress and pore pressure near the tip of the megasplay fault in the Nankai accretionary complex
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DOI：
10.1029/2011gc003556
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发表时间：
2011-08
期刊：
影响因子：
3.7
通讯作者：
I. Song;D. Saffer;P. Flemings
中科院分区：
文献类型：
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作者：
I. Song;D. Saffer;P. Flemings
我们对日本西南部南海增生杂岩体的一个主要无序逆冲断层的上盘取芯的泥岩样品进行了力学测试，（1）了解形成断层带的斜坡沉积物的固结和剪切行为以及上部几公里的这一重要构造特征的围岩，（2）限制地应力和孔隙压力，这两个控制俯冲带变形过程的基本参数是众所周知的难以测量的。我们对取自 20-150 mbsf 深度的一组样品进行了变形实验，包括 6 次单轴固结试验和 1 次各向同性固结试验。对于其中三个测试，我们在固结后进行了不排水三轴压缩测试。我们的结果表明，原位孔隙压力是静水压力，在沉积和埋藏过程中，有效水平应力约为有效垂直应力的 41%。结合钻井过程中记录的井眼故障分析，我们的实验数据使我们能够定义完整的应力张量，包括该主要断层带上盘的原位最小和最大水平应力的大小。最大水平应力大小与沉积和单轴埋藏的预期相当，而最小水平应力低于该值。这表明（1）浅沉积部分在埋藏期间或之后受到与海沟近平行的延伸，（2）与板块汇聚相关的应力并未在这些浅沉积物内有效传递。
We performed mechanical tests on mudstone samples cored in the hanging wall of a major out of sequence thrust fault in the Nankai accretionary complex prism, SW Japan, (1) to understand the consolidation and shear behaviors of slope sediments that form the fault zone and wall rock of this important structural feature in the upper several kilometers, and (2) to constrain in situ stresses and pore pressure, two fundamental parameters governing deformation processes in subduction zones, which are notoriously difficult to measure. We conducted deformation experiments on a suite of samples taken from depths of 20–150 mbsf, including six uniaxial consolidation tests and one isotropic consolidation test. For three of these tests, we conducted undrained triaxial compression testing following consolidation. Our results suggest that in situ pore pressure is hydrostatic and that during sedimentation and burial, the effective horizontal stress is ∼41% of the effective vertical stress. In combination with analysis of wellbore failures documented during drilling of the borehole, our experimental data allow us to define the complete stress tensor, including the magnitude of in situ minimum and maximum horizontal stresses, in the hanging wall of this major fault zone. The maximum horizontal stress magnitude is comparable to that expected for sedimentation and uniaxial burial, whereas the minimum horizontal stress lies below this value. This suggests (1) that the shallow sedimentary section was subjected to extension subparallel to the trench during or following burial and (2) that stresses associated with plate convergence are not effectively transmitted within these shallow sediments.