Fluid overpressure from the water released by subducted sediments and oceanic crust is an important mechanism for generating earthquakes via brittle failure and frictional instability. If unstable, such fault materials may also host diverse fault reactivation mechanisms from slow slip events to moderate-sized earthquakes in cold subduction zones. We examine this hypothesis for glaucophane gouge - a key index minerals for blueschist facies - at lower confining stresses where behavior is poorly understood. We measure friction and stability at temperatures of 100°C–500°C and effective normal stresses of 50–200 MPa, to explore the controls of temperature, stresses and excess pore fluid pressures on fault friction. The frictional coefficient of glaucophane at representative temperatures and stresses is ∼0.70, insensitive to temperature but with a slight increase at lower effective stresses. Elevating temperature promotes a transition from velocity-strengthening to weak velocity-weakening behavior, indicating the destabilizing effect of high temperature downdip in subduction zones. Reducing effective normal stress or concomitantly elevating pore fluid pressure further strengthens the velocity-weakening response and would be manifest as moderate-sized earthquakes. Our results support the potential for enhanced unstable sliding of glaucophane gouges at lower effective stresses and blueschist facies temperatures - with weak to moderate velocity-weakening responses upon fluid pressurization vital for understanding the abundance of slow slip to moderate-sized earthquakes apparent in cold subduction zones.

中文翻译：

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海绿石凿孔在蓝片岩温度下的摩擦强度和摩擦不稳定性支持从慢滑事件到中等规模地震的不同断层滑移模式


俯冲沉积物和海洋地壳释放的水中的流体超压是通过脆性破坏和摩擦失稳产生地震的重要机制。如果不稳定，这种断层材料也可能承载着不同的断层再激活机制，从慢滑事件到冷俯冲带的中等规模地震。我们检查了海绿石凿孔的这一假设 - 蓝片岩相的关键指标矿物 - 在行为知之甚少的较低围压下。我们在 100°C–500°C 的温度和 50–200 MPa 的有效法向应力下测量摩擦和稳定性，以探索温度、应力和过孔流体压力对断层摩擦的控制。在代表性温度和应力下，海绿膜的摩擦系数为 ∼0.70，对温度不敏感，但在较低有效应力下略有增加。升高的温度促进了从速度增强到弱速度行为的转变，表明俯冲带高温下降的不稳定作用。降低有效法向应力或同时提高孔隙流体压力会进一步加强速度减弱响应，并表现为中等规模的地震。我们的结果支持在较低的有效应力和蓝片岩相温度下海绿石凿槽增强不稳定滑动的潜力 - 流体加压时的弱到中速弱化响应对于理解冷俯冲带中明显的慢滑到中等规模地震的丰富性至关重要。