(Table 1) Petrological description and consolidation properties of ODP Site 186-1150 and Hole 186-1151A

In order to determine the shear parameters of the forearc sedimentary strata drilled during Ocean Drilling Program Leg 186, West Pacific Seismic Network, Japan Trench, eight whole-round samples were selected from different depths in the drilled sections of Sites 1150 and 1151. Whereas Site 1150 lays above the seismically active part of the subduction zone, Site 1151 is situated in an aseismic zone. The aim of the triaxial tests was, apart from determination of the static stress strain behavior of the sediments, to test the hypothesis that the static stress strain parameter could differ for each sites. In order to simulate undrained deformation conditions according to the high clay mineral content of the strata, consolidated undrained shear tests were performed in a triaxial testing setup. Measurements of water content, grain density, organic content, and microtextural investigations under the scanning electron microscope (SEM) accompanied the compression experiments. After the saturation and consolidation stages were completed, failure occurred in the compression stage of the experiments at peak strengths of 280-7278 kPa. The stiffness moduli calculated for each sample from differential stress vs. strain curves show a linear relationship with depth and range between 181 and 5827 kPa. Under the SEM, the artificial fault planes of the tested specimen only show partial alignment of clay minerals because of the high content of microfossils.

为测定西太平洋地震网、日本海沟大洋钻探计划（Ocean Drilling Program，ODP）186航次所钻取的弧前沉积地层的剪切参数，研究人员从1150和1151两个钻孔站位的不同深度选取了8块整芯样品。其中1150站位位于俯冲带地震活跃段上方，而1151站位则处于无震带内。本次三轴试验的目标，除明确沉积物的静态应力-应变行为外，还旨在验证“不同站位的静态应力应变参数可能存在差异”这一假说。鉴于该地层黏土矿物含量较高，为模拟不排水变形条件，研究人员采用三轴测试装置开展了固结不排水剪切试验。配合压缩试验，研究人员还开展了含水率、颗粒密度、有机质含量测定，以及扫描电子显微镜（Scanning Electron Microscope，SEM）下的微观结构观测。在完成饱和与固结阶段后，试验在压缩阶段发生剪切破坏，峰值强度介于280~7278 kPa之间。根据差应力-应变曲线计算得到的各试样刚度模量，与深度呈线性相关，取值范围为181~5827 kPa。在扫描电子显微镜观测下，由于微化石含量较高，受试试样的人工断层面仅表现出黏土矿物的部分定向排列。