Large earthquakes and slow slip events typically nucleate along plate boundaries near the depth limit of the seismogenic zone, which is also recognized as the brittle‐plastic transition zone (BPT). High V_p/V_s ratios are commonly observed at the BPT in subduction zones, indicating the presence of aqueous fluid in pore spaces. We conducted experiments to investigate the rheology of quartz with different fluid fractions at deformation conditions that cross the BPT. The strengths of quartz aggregates with fluid‐filled porosities of 5–25 vol% are significantly lower than predicted by wet quartzite flow laws, and decrease with increasing fluid fraction. Recovered samples deformed in the ductile regime exhibit S‐C´ mylonitic structures characterized by elongate grains, shear localization and fluid segregation. Variations in strength are explained by a combination of a constitutive law for dislocation creep that includes the geometric effects of fluid fraction, a friction law that includes the effect of fluid fraction through its role on the real area of contact, and an empirical function to describe the smooth brittle‐plastic transition. Our results indicate that the presence of fluid‐filled porosity promotes significant weakening in shear zones, and that variations in fluid fraction (together with temperature) can explain transitions in the spectrum of slip behaviors observed along plate boundaries.

中文翻译：

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脆性塑料过渡带流体过饱和断裂带的流变学

大地震和缓慢滑动事件通常沿着靠近地震发生带深度极限的板块边界成核，该区域也被认为是脆性塑性过渡带（BPT）。高V _p / V _s通常在BPT的俯冲带中观察到比率，表明孔隙空间中存在含水流体。我们进行了实验，以研究在穿过BPT的变形条件下，不同流体分数的石英的流变特性。充填孔隙率为5–25 vol％的石英骨料的强度显着低于湿石英岩流定律所预测的强度，并且随着流体分数的增加而降低。在延展状态下变形的回收样品显示出S‐C´淀粉样结构，其特征是细长的晶粒，剪切定域和流体偏析。强度的变化通过位错蠕变的本构定律的组合来解释，该定律包括流体分数的几何效应，摩擦定律包括流体分数通过其对实际接触面积的作用而产生的影响，以及描述光滑的脆塑性转变的经验函数。我们的结果表明，充满流体的孔隙度的存在促进了剪切带的显着减弱，流体分数（随温度变化）的变化可以解释沿板块边界观测到的滑移行为谱的转变。