Permeability control on transient slip weakening during gypsum dehydration: Implications for earthquakes in subduction zones
Permeability control on transient slip weakening during gypsum dehydration: Implications for earthquakes in subduction zones
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DOI：
10.1016/j.epsl.2016.02.015
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发表时间：
2016-05-15
影响因子：
5.3
通讯作者：
Mariani, Elisabetta
中科院分区：
文献类型：
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作者：
Leclere, Henri;Faulkner, Daniel;Mariani, Elisabetta
最近的实验室实验中出现了一个冲突，即脱水反应是否会促进俯冲带的不稳定滑动，从而导致地震。尽管由于孔隙流体压力增加，反作用产生机械弱化，但这种弱化与稳定和不稳定滑移都有关。在这里，提出了监测脱水反应期间强度、渗透率、孔隙流体压力、反应进程和微观结构演变的新结果，以确定机械不稳定所需的条件。使用石膏和具有恒定正应力的直接剪切样品组件进行三轴实验，所述正应力允许在滑动期间测量渗透率。试验是在70 ~ 150 ℃的温度梯度和不同的有效围压（50、100和150 MPa）和速度（0.1和0.4 μ m·s（-1））下进行的。结果表明，石膏脱水为钙钛矿导致了受孔隙流体压力和渗透率演化控制的瞬态稳定滑移弱化。在脱水开始时，孔隙压实促进的低渗透率导致孔隙流体压力增加和稳定的滑移减弱。在反应过程中的钙钛矿含量的增加显示了与R-1里德尔剪切和A叶理面的发展有关的脱水的明显证据，其中钙钛矿优先沿沿着这些结构定位。强度大于石膏的钙钛矿的持续产出为新形成的孔隙提供了支撑骨架，从而导致渗透率增加、孔隙流体压力下降和断层强度增加。在脱水反应之后，变形的特征在于在完全脱水的反应产物上的不稳定滑动，其由在高于类似于140 ℃的温度下的镁橄榄石的从速度加强到速度减弱行为的转变以及变形沿沿着窄Y剪切面的局部化控制。这项研究强调了在脱水反应过程中触发不稳定性所需的一般条件。它表明，孔隙流体压力的建设脱水反应与本地化的速度减弱反应或脱水相沿着剪切面是必要的地震触发。(C)2016作者由爱思唯尔公司出版
A conflict has emerged from recent laboratory experiments regarding the question of whether or not dehydration reactions can promote unstable slip in subduction zones leading to earthquakes. Although reactions produce mechanical weakening due to pore-fluid pressure increase, this weakening has been associated with both stable and unstable slip. Here, new results monitoring strength, permeability, pore fluid pressure, reaction progress and microstructural evolution during dehydration reactions are presented to identify the conditions necessary for mechanical instability. Triaxial experiments are conducted using gypsum and a direct shear sample assembly with constant normal stress that allows the measurement of permeability during sliding. Tests are conducted with temperature ramp from 70 to 150 degrees C and with different effective confining pressures (50, 100 and 150 MPa) and velocities (0.1 and 0.4 mu m s(-1)). Results show that gypsum dehydration to bassanite induces transient stable-slip weakening that is controlled by pore-fluid pressure and permeability evolution. At the onset of dehydration, the low permeability promoted by pore compaction induces pore-fluid pressure build-up and stable slip weakening. The increase of bassanite content during the reaction shows clear evidence of dehydration related with the development of R-1 Riedel shears and A foliation planes where bassanite is preferentially localized along these structures. The continued production of bassanite, which is stronger than gypsum, provides a supporting framework for newly formed pores, thus resulting in permeability increase, pore-fluid pressure drop and fault strength increase. After dehydration reaction, deformation is characterized by unstable slip on the fully dehydrated reaction product, controlled by the transition from velocity strengthening to velocity-weakening behaviour of bassanite at temperature above similar to 140 degrees C and the localization of deformation along narrow Y-shear planes. This study highlights the generic conditions required to trigger instabilities during dehydration reactions. It shows that pore-fluid pressure buildup during dehydration reactions associated with the localization of a velocity-weakening reacting or dehydrated phase along shear planes is necessary for earthquake triggering. (C) 2016 The Authors. Published by Elsevier B.V.