龙门山断裂带金河磷矿剖面断层泥的低速至高速摩擦性质研究  

Low-to high-velocity frictional properties of the Longmenshan fault gouges retrieved from the Jinhe shallow drilling cores

作　　者：李晓慧 姚路[1] 马胜利[1] 杨晓松[1] LI XiaoHui, YAO Lu, MA ShengLi, YANG XiaoSong(State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, Chin)

机构地区：[1]中国地震局地质研究所地震动力学国家重点实验室,北京100029

出　　处：《地球物理学报》2018年第5期1741-1757,共17页Chinese Journal of Geophysics

基　　金：地震动力学国家重点实验室自主研究课题(LED2014A06);开放基金课题(LED2016B04);国家自然科学基金(41404143)项目共同资助

摘　　要：本文对龙门山断裂带金河磷矿浅钻岩芯中的三种断层泥开展了低速到高速摩擦滑动的实验研究,并对实验变形样品开展了BET比表面积研究.摩擦实验在干燥和孔隙水压条件下开展,速率范围涵盖20μm·s^(-1)~1.4m·s^(-1).实验结果显示,三种断层泥在干燥条件下的摩擦性质差别不大,但在孔隙水压条件下,三者的中低速摩擦强度与层状硅酸盐矿物的种类而非总含量紧密相关,蒙脱石和伊利石相比绿泥石更能有效地弱化断层.三种断层泥在孔隙水压条件下存在中低速率域的速度强化,暗示着对断层的加速滑动存在一定的阻碍作用.孔隙水压下,黄绿色和灰绿色断层泥的初始动态弱化非常迅速并伴随断层泥层的瞬时扩容,凹凸体急剧加热导致的局部热压作用可能是造成这种力学行为的物理机制.在经历高速滑动之后,三种断层泥在干、湿条件下的BET比表面积都显著降低,暗示着可能发生了颗粒烧结.中低速域内,孔隙水的存在使得断层泥呈现分散式的剪切变形,BET比表面积的增加因此比干燥条件下更加明显.对表面能的估算表明,颗粒磨碎所消耗的能量至多不超过摩擦力做功的8%,暗示着断层作用中颗粒磨碎所占的能量比例较低.In this study,low-to high-velocity friction experiments were conducted on the three kinds of fault gouges retrieved from the shallow drilling hole penetrating the Longmenshan fault zone near Jinhe outcrop.BET surface area of the experimentally deformed samples was also studied to constrain the energetics of grain crushing during frictional slip.The friction experiments were performed under both room dry and pore pressure conditions,at slip rates ranging from 20μm·s^（-1） to 1.4 m·s^（-1）.Results show that the frictional properties of the three gouges are similar under dry condition.However,under pore pressure condition,the frictional strength of the three gouges atlow-to intermediate-velocities is closely related to the types rather than total contents of clay minerals—smectite and illite could lower gouge friction more effectively than chlorite.All the three gouges show velocity strengthening at low-to intermediate-velocity regime,suggesting a mechanical barrier to accelerating slip during seismic rupture propagation.The yellow-greenish and gray-greenish gouges both show extremely rapid dynamic weakening that is contemporaneous with transient dilatancy of gouge layers at the slip rate of 1.4 m·s^（-1） under pore pressure condition.Local fluid pressurization triggered by flash heating probably could explain such mechanical behavior.At the high slip rate of 1.4 m·s^（-1）,the three gouges show clear reduction in BET surface area under both dry and wet conditions,suggesting the occurrence of grain sintering.At the lowto intermediate-velocity regime,the presence of pore water tends to distribute the shear deformation within the entire gouge layer,making more increases in BET surface area in wet samples than that in dry samples.Moreover,surface energy estimates reveal that the energy consumed by grain crushing is less than 8% of the frictional work in all the friction experiments,suggesting the energy partition for grain crushing is small during seismic faulting.

关 键 词：低速至高速摩擦性质 BET比表面积 地震断层运动中的能量分配 动态弱化 龙门山断裂带 汶川地震 

分 类 号：P313[天文地球—固体地球物理学]