This paper reports friction experiments performed on samples collected from the earthquake-hit region of the Longmenshan fault zone(LFZ).The materials tested consisted of simulated gouges prepared from intact clay-rich mudstone and sandstone, a calcite limestone, and a natural fault gouge from a trenched, surface rupture cutting the mudstone and sandstone.The clay-rich samples, including the natural fault gouge, were dominated by illite and quartz.In the experiments, 1 mm thick gouge layers were sheared between saw-cut driver blocks, using a triaxial testing machine at conditions corresponding to 2 km depth in the LFZ.Temperature was varied from 25 ℃ to 150 ℃ and, to investigate the velocity dependence of friction, the shear displacement rate between 1.22 and 0.122 μm/s was stepped.The results show that the natural fault gouge was more illite-rich and much weaker than the protolith mudstone and sandstone, and showed a steady-state friction coefficient of 0.4 compared with 0.6 for the latter.The limestone fault gouge displayed values of 0.6 - 0.7.All samples, except the limestone, showed stable, velocity-strengthening slip.The limestone showed velocity-strengthening at 25 ℃ -50 ℃, but quasi-static oscillations at 100 ℃-150 ℃ along with velocity-weakening behavior at 150 ℃.The result is applied to discuss the role of the sedimentary rocks studied during events such as the Wenchuan earthquake; and it is argued that the clay-rich sediments of the region may have a damping effect upon ruptures propagating from depth; whereas the limestone may accelerate propagation, producing significant stress drops.%对采自四川龙门山断裂带(LFZ)地震发生区段的样品进行摩擦滑动实验研究,得到一系列实验结果.实验样品包括用富含黏土的完整泥岩和砂岩制备的模拟断层泥、由富含方解石的灰岩制备的模拟断层泥和一种天然断层泥.其中,天然断层泥是通过人工探槽方法采自于穿过泥岩和砂岩层的地表破裂中.富含黏土矿物的样品主要由伊利石和石英组成.在实验中,将1 mm厚的断层泥夹于具有倾斜锯切面的围岩之间,在三轴实验系统中对其进行剪切变形实验,实验条件与龙门山断裂带2 km深处的条件相一致.实验温度范围为25 ℃～150 ℃,同时为了研究摩擦强度的速度依赖性,对剪切位移的速度实施1.22～0.122 μm/s的阶跃式变化.分析结果表明,天然断层泥比原岩的泥岩和砂岩更富含伊利石,而且强度比原岩弱得多.天然断层泥的稳态摩擦系数约为0.4,而原岩则约为0.6.另外,灰岩断层泥的摩擦系数为0.6～0.7.除了灰岩,所有样品均表现为稳定、速度强化的滑动行为.灰岩在25 ℃～50 ℃表现为速度强化,但是在100 ℃～150 ℃时表现为准静态的振荡,在150 ℃时显示速度弱化行为.运用此次实验结果讨论沉积岩在类似于汶川地震这样的地震事件中所起的作用,指出该区域富含黏土的沉积层可能对从深部扩展而来的破裂扩展有阻尼作用,而灰岩则有可能会加速破裂的传播,同时产生明显的应力降.
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