Fluid transport properties in sediments and their role in large slip near the surface of the plate boundary fault in the Japan Trench
Fluid transport properties in sediments and their role in large slip near the surface of the plate boundary fault in the Japan Trench
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DOI：
10.1016/j.epsl.2013.08.052
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发表时间：
2013-11
影响因子：
5.3
通讯作者：
W. Tanikawa;T. Hirose;H. Mukoyoshi;O. Tadai;Weiren Lin
中科院分区：
文献类型：
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作者：
W. Tanikawa;T. Hirose;H. Mukoyoshi;O. Tadai;Weiren Lin
流体输运性质如渗透率和孔隙度是影响地震发生的重要参数。我们测量的运输性能的浅沉积物样品的板边界附近的日本海沟在IODP远征343在围压高达40 MPa。来自浅板块边界断层的样品的渗透率非常低，为10− 20 m 2，相当于10− 10 m 2 s− 1的水力扩散率。在板块边界的断裂带的核心渗透率和孔隙度低于直接覆盖的沉积物和周围的完整的沉积物，这表明板块边界断层可以作为一个障碍，流体流动。浅盘边界断层的低渗透性和高孔隙压缩性，即使在初始剪切应力较低时，也会由于流体加压和摩擦加热而产生很大的动态断层弱化潜力。我们的研究支持这样的假设，即在东北地震期间，断层面上的热加压有助于促进俯冲带浅部的极大滑动。由于断裂带的渗透性比周围沉积物低，粘土含量较高，因此，粘土矿物脱水产生的深部孔隙压力比俯冲洋壳的持续流体流入更能合理地解释断裂带上浅强斑的形成，而俯冲洋壳的持续流体流入并不影响断裂带的深部孔隙压力。虽然有许多可能的断层弱化机制，但当滑动开始时，即使在较浅的深度，热加压也可以相对有效地起作用。因此，我们的研究结果支持在东北地震的浅层滑动热增压的作用。
Fluid transport properties such as permeability and porosity are significant parameters that affect earthquake generation. We measured the transport properties of shallow sediments sampled around the plate boundary near the Japan Trench during IODP Expedition 343 at confining pressures up to 40 MPa. The permeabilities of samples from the shallow plate boundary fault were very low at 10− 20 m 2, equivalent to a hydraulic diffusivity of 10− 10 m 2 s− 1. Permeability and porosity in the core of the fault zone at the plate boundary were lower than those in the immediately overlying sediments and the surrounding intact sediment, suggesting that the plate boundary fault can act as a barrier for fluid flow. Low permeability and high pore compressibility in the shallow plate boundary fault create a strong potential for dynamic fault weakening due to fluid pressurization with frictional heating, even when the initial shear stress is low. Our investigation supports the hypothesis that thermal pressurization on the fault plane helped facilitate the extremely large slip in the shallow part of the subduction zone during the Tohoku earthquake. As the fault zone has a lower permeability than the surrounding sediments and a higher clay content, pore pressure generation at depth by dehydration of clay minerals can explain formation of the shallow strong patch on the fault more reasonably than continuous fluid influx from the subducting oceanic crust, which does not affect pore pressure at depth in the fault zone. Although there are many possible mechanisms of fault weakening, thermal pressurization can act relatively efficiently as slip begins, even at shallow depths. Therefore our results support the role of thermal pressurization in shallow slip during the Tohoku earthquake.