水热作用条件下蛇纹石断层泥的摩擦强度和速度依赖性及其地震地质意义
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摘要
在恒定的正应力和孔隙压力、不同温度下测量了三种蛇纹石断层泥摩擦强度的速度依赖性。在室温下，纤蛇纹石具有很低的摩擦系数（０．２～０．２５），而利蛇纹石和叶蛇纹石的摩擦系数较高，分别为０．３９和０．４５左右。在２５～２００℃范围内，温度变化对纤蛇纹石和叶蛇纹石强度的影响不明显，而利蛇纹石的摩擦系数随温度升高明显增加。室温下，三种蛇纹石的摩擦在较快的滑动速率下表现为微弱的速度弱化，而在较慢的滑动速度下为明显的速度强化，温度的提高有促使速度弱化向速度强化转变的趋势。研究表明，蛇纹石的存在有利于断层的无震蠕动，但这种影响可能主要限于浅部；尽管纤蛇纹石是最软弱的造岩矿物之一，但仍不足以解释圣安德烈斯断层的软弱性
The velocity-dependence of frictional strength of serpentine gouges has been measured at constant normal stress of 110 MPa, pore pressure of 10 MPa, temperature 25, 100 and 200℃, and at sliding rate ranging from 0.001 to 10μm/s. At 25℃, the coefficient of friction of chrysotile gouge is very low ( μ ≈0.2～0.25), while lizardite and antigorite gouge are much stronger, with μ ≈0.39 and 0.45, respectively. The frictional strengths of chrysotile and antigorite gouges change little with a temperature increase to 200℃, whereas the strength of lizardite gouge increases substantially with increasing temperature. At 25℃, all three gouges show a transition from weak velocity weakening at high slip rates to velocity strengthening at low slip rates. With increasing temperature, the velocity dependence of each gouge shifts towards more positive values, especially at high slip rates. Based on this study and previous results, we suggest that the presence of serpentine in the fault zone may contribute to the occurrence of stable creep rather than earthquakes, but this effect may be limited to shallow depths. Although chrysotile is one of the weakest rock-forming minerals, it is still too strong to explain the weakness of the San Andreas fault deduced from heat flow data.
The velocity-dependence of frictional strength of serpentine gouges has been measured at constant normal stress of 110 MPa, pore pressure of 10 MPa, temperature 25, 100 and 200℃, and at sliding rate ranging from 0.001 to 10μm/s. At 25℃, the coefficient of friction of chrysotile gouge is very low ( μ ≈0.2～0.25), while lizardite and antigorite gouge are much stronger, with μ ≈0.39 and 0.45, respectively. The frictional strengths of chrysotile and antigorite gouges change little with a temperature increase to 200℃, whereas the strength of lizardite gouge increases substantially with increasing temperature. At 25℃, all three gouges show a transition from weak velocity weakening at high slip rates to velocity strengthening at low slip rates. With increasing temperature, the velocity dependence of each gouge shifts towards more positive values, especially at high slip rates. Based on this study and previous results, we suggest that the presence of serpentine in the fault zone may contribute to the occurrence of stable creep rather than earthquakes, but this effect may be limited to shallow depths. Although chrysotile is one of the weakest rock-forming minerals, it is still too strong to explain the weakness of the San Andreas fault deduced from heat flow data.
引文
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