High-velocity frictional properties of a clay-bearing fault gouge and implications for earthquake mechanics
High-velocity frictional properties of a clay-bearing fault gouge and implications for earthquake mechanics
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DOI：
10.1029/2007jb005551
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发表时间：
2008-10-03
影响因子：
3.9
通讯作者：
Shimamoto, T.
中科院分区：
文献类型：
--
作者：
Brantut, N.;Schubnel, A.;Shimamoto, T.
使用高速旋转剪切装置研究了来自中位构造线（日本西南）的天然高岭石凿岩样品的摩擦特性，并使用光学和电子（扫描和透射）显微镜观察了变形样品。对于 1 m s(-1) 的滑移速度和 0.3 至 1.3 MPa 的法向应力，观察到了显着的滑移弱化行为。变形样品的 X 射线衍射分析和对纯高岭石的额外高速摩擦实验表明高岭石在滑移过程中脱水。临界滑移减弱距离 D-c 约为 1 至 10 m。假设 D-c 是热参数而不是与真实特征长度相关的参数，则这些值被外推到更高的法向应力。计算表明，在量纲上，D-c 与 1/sigma(2)(n) 成正比，其中 sigma(n) 是施加在断层上的正应力。推断的 D-c 值范围从 10 MPa 正应力下的几厘米到 100 MPa 正应力下的几百微米。显微镜观察显示，局部非晶化和晶粒尺寸急剧减小（降至纳米级），集中在厚度约为 1 至 10 μm 的狭窄区域。断裂能 G(c) 是根据力学曲线计算出来的，并与由于晶粒尺寸减小而产生的表面能以及矿物学转变的能量进行比较。我们表明，大部分断裂能要么转化为热量，要么转化为辐射能。然后根据几个断层带的矿物学和孔隙力学数据评论了地震滑动过程中粘结水热脱水的地球物理后果，这往往表明在大多数地下断层和俯冲洋壳的含水岩石中必须考虑到这种现象。
Frictional properties of natural kaolinite-bearing gouge samples from the Median Tectonic Line (SW Japan) have been studied using a high-velocity rotary shear apparatus, and deformed samples have been observed with optical and electron (scanning and transmission) microscopy. For a slip velocity of 1 m s(-1) and normal stresses from 0.3 to 1.3 MPa, a dramatic slip-weakening behavior was observed. X-ray diffraction analysis of deformed samples and additional high-velocity friction experiments on pure kaolinite indicate kaolinite dehydration during slip. The critical slip-weakening distance D-c is of the order of 1 to 10 m. These values are extrapolated to higher normal stresses, assuming that D-c is rather a thermal parameter than a parameter related to a true characteristic length. The calculation shows that dimensionally, D-c proportional to 1/sigma(2)(n), where sigma(n) is the normal stress applied on the fault. The inferred D-c values range from a few centimeters at 10 MPa normal stress to a few hundreds of microns at 100 MPa normal stress. Microscopic observations show partial amorphization and dramatic grain size reduction (down to the nanometer scale) localized in a narrow zone of about 1 to 10 mu m thickness. Fracture energy G(c) is calculated from the mechanical curves and compared to surface energy due to grain size reduction, and energies of mineralogic transformations. We show that most of the fracture energy is either converted into heat or radiated energy. The geophysical consequences of thermal dehydration of bonded water during seismic slip are then commented in the light of mineralogical and poromechanical data of several fault zones, which tend to show that this phenomenon has to be taken into account in most of subsurface faults and in hydrous rocks of subducted oceanic crust.