Abstract In order to clarify the weakening mechanism of quartz rocks at subseismic slip rates of 0.1–10 cm/s, we conducted two series of rotary-shear friction experiments at a normal stress of 1.5 MPa and equivalent slip rates (Veq) of 0.1–10 cm/s; one on intact agate controlling background temperature (TBG) and atmosphere, and the other on intact agate and silica-gel gouge monitoring temperature (T) adjacent to the slip surface or the gouge layer. In the former experiments at Veq = 1 cm/s, agate samples at room TBG showed similar steady-state friction coefficients (μss = 0.62–0.63) irrespective of humid or dry condition in the latter case of which hydration of amorphous wear materials was hampered, while agate sample at TBG = 100 °C exhibited weakening to μss ≈ 0.35. In the latter experiments, μss of both intact agate and silica-gel gouge decreased with increasing Veq from 0.6–0.7 at Veq = 0.1 cm/s to 0.03–0.16 at Veq = 10 cm/s, while the maximum T increased with increasing Veq from 25–28 °C at Veq = 0.1 cm/s to 88–93 °C at Veq = 10 cm/s. Spikes of high friction followed by T maxima and subsequent weakening suggest that slip at strong asperity contacts induced frictional heat, which in turn resulted in weakening. These two series of friction experiments indicate that the frictional strength of quartz rocks at subseismic slip rates is controlled by temperature, which increases by frictional heating, but not by wear materials of hydrated amorphous silica or silica gel. Indentation strength of quartz is much higher than that of other common rock-forming minerals so that much more amount of frictional heat would be induced at asperity contacts in quartz rocks than in other rocks, which is likely responsible for weakening of quartz rocks at subseismic slip rates.

中文翻译：

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由于摩擦加热，石英岩在亚地震滑动速率下变弱，但不会被水合无定形二氧化硅或硅胶耐磨材料润滑

摘要 为了阐明亚震滑移率为 0.1~10 cm/s 时石英岩的弱化机制，我们在法向应力为 1.5 MPa、等效滑移率（Veq）为 0.1~ 10 厘米/秒；一个在完整的玛瑙控制背景温度 (TBG) 和大气，另一个在完整的玛瑙和硅胶凿监测温度 (T) 附近的滑移表面或凿层。在 Veq = 1 cm/s 的前一个实验中，无论潮湿或干燥条件如何，TBG 室中的玛瑙样品都显示出相似的稳态摩擦系数（μss = 0.62–0.63），在后者的情况下，无定形耐磨材料的水合作用受到阻碍，而 TBG = 100 °C 的玛瑙样品表现出减弱到 μss ≈ 0.35。在后面的实验中，完整玛瑙和硅胶凿的 μss 随 Veq 从 0.6–0.7（Veq = 0.1 cm/s）增加到 0.03–0.16（Veq = 10 cm/s）而降低，而最大 T 随 Veq 从 25–28° 增加而增加Veq = 0.1 cm/s 时的 C 到 Veq = 10 cm/s 时的 88–93 °C。高摩擦的尖峰，然后是 T 最大值和随后的减弱表明在强粗糙接触处的滑动会引起摩擦热，这反过来又导致减弱。这两个系列的摩擦实验表明，石英岩在亚地震滑动速率下的摩擦强度受温度控制，温度随摩擦加热而增加，但不受水合无定形二氧化硅或硅胶磨损材料的影响。