Abstract: In this paper, we report friction experiments performed on natural fault gouge samples embedded in granitic rock from drilled core by a project entitled "the Longmenshan Fault Shallow Drilling(LMFD)". Compared with other natural fault gouge, this yellow-greenish gouge(YGG)is dominantly chlorite-rich. The maximum content of chlorite reaches 47%in the YGG. To understand the frictional properties of the YGG sample, experiments were performed at constant confining pressure of 130MPa, with constant pore pressure of 50MPa and at different temperatures from 25℃ to 150℃. The experiments aim to address the frictional behavior of the YGG under shallow, upper crustal pressure, and temperature conditions. Compared with previous studies of natural gouge, our results show that the YGG is stronger and shows a steady state friction coefficient of 0.47~0.51. Comparison with previous studies of natural gouge with similar content of clay minerals indicates a sequence of strengths of different clay minerals:chlorite > illite > smectite. At temperatures up to 150℃ hence depths up to~8km in the Longmenshan region, the YGG shows stable velocity-strengthening behavior at shallow crustal conditions. Combined with the fact of strong direct velocity effect, i.e., (a-b)/a>0.5, faults cutting the present clastic lithology up to~8km depth in the Longmenshan fault zone(LFZ)are likely to offer stable sliding resistance, damping co-seismic rupture propagating from below at not-too-high slip rates. However, as the fault gouge generally has low permeability, co-seismic weakening through thermal pressurization may occur at high slip rates(>0.05m/s), leading to additional hazards.

Key words: chlorite-rich fault gouge, velocity strengthening, stable sliding, shallow portion of Longmenshan fault zone

摘要： 文中针对龙门山断层浅层钻探获取的花岗岩体中的断层泥进行了摩擦滑动实验研究。这种断层泥与其他天然断层泥相比，绿泥石的质量分数很高，约为47%。为研究这种黄绿色断层泥在断层浅部低正应力条件下的摩擦滑动性质，选取的实验条件：围压130MPa，采用围压恒定控制，温度25~150℃，孔隙水压50MPa。通过对比其他天然断层泥的实验结果发现，该断层泥强度较高，稳态摩擦系数在0.47~0.51之间。通过与已有的黏土总质量分数相当但矿物不同的天然断层泥的摩擦系数数据对比，表明不同的非云母层状硅酸盐矿物的摩擦强度排序为：绿泥石 > 伊利石 > 蒙皂石。文中的实验条件对应龙门山地区温度不超过150℃，深度不超过8km的浅层地壳环境，实验结果表明该天然断层泥在整个温度范围内均呈速度强化特征，在摩擦滑动中处于稳定状态。但是断层泥的渗透率很低（<10^-19m²），在高速摩擦滑动时可能会发生热压作用。基于此可得出结论：龙门山断裂带的切过已有的深度不超过8km的碎屑原岩的断层可能产生稳定黏滞滑动的阻力，不会自发地震成核，而在后期高速摩擦滑动（>0.05m/s）时可能会发生同震弱化，形成一定的灾害叠加。

关键词: 富含绿泥石断层泥, 速度强化, 稳定滑动, 龙门山断裂带浅部