现场大尺度摩擦实验中观测到的断层泥中的塑性变形波

本文介绍了在断层区的岩体中进行的现场大尺度摩擦实验。实验的目的是探索地壳中变形波的存在。实验结果表明,在加载时断层泥屈服时间不一致,加载一端的断层泥先屈服,然后屈服范围逐步扩大,此过程相应于塑性变形波在断层泥中的传播。实验测得试件中塑性变形波波速约为2—3 cm/min,实际相当于10—16km/year。     

岩石高速摩擦实验的进展

文中简述了地震动力学国家重点实验室近年来在岩石高速摩擦实验方面的进展。为了深化断层与地震力学研究,实验室建设了一套旋转剪切低速-高速摩擦实验装置,可开展滑动速率介于板块运动速率(cm/a量级)至地震滑动速率(m/s量级)的岩石摩擦实验,其中高速摩擦性能填补了实验室的技术空白。以此为依托,围绕汶川地震断层带力学性质研究,开展了一系列高速摩擦实验。结果表明,龙门山断裂带断层泥的高速摩擦性质具有一致性,其高速滑动下显著的滑动弱化必定在汶川地震中极大地促进了破裂的扩展;断层弱化的主导机制是与摩擦生热相关的过程,包括凹凸体急速加热弱化和热压作用;断层泥在经历高速滑动弱化之后摩擦系数可在5~10s内恢复0.4,断层强度的快速恢复是同震主破裂带余震减少的原因之一。基于对实验装置现状和现有成果的分析,展望了近期实验室岩石高速摩擦的发展方向。     

岩石高速摩擦实验与地震物理过程

简述了最近20年来国内外岩石高速摩擦实验研究领域的进展和动态:岩石高速摩擦实验技术的发展实现了对高滑动速率、大位移的地震过程的实验模拟;其结果揭示了岩石和断层泥在地震滑动速率下的力学性状,深化了对断层滑动弱化机制、临界滑动距离、以及地震发生过程的认识和理解;实验在假玄武玻璃成因方面取得了重要进展,并提出了断层发生地震滑动可能留下的其它地质证据,可望为研究断层滑动性状与地震物理过程提供新的思路和信息.岩石高速摩擦实验今后的发展方向主要包括:发展具有加温系统和孔隙压系统的岩石高速摩擦实验装置,研究水热作用下岩石和断层泥的高速摩擦性状;室内实验和地震资料分析相结合研究断层滑动和地震机制;室内实验和野外地质调查相结合探索断层发生地震错动的地质证据等等.     

含水粘土断层泥的现场大尺度剪切实验

为了研究水分对断层泥抗剪特性的影响,在湖北省当阳县砂岩岩体中的天然断层带上进行了现场大尺度的剪切实验。实验用直剪法进行。试体的尺度为30×50×60cm~3。以含水粘土断层泥的天然断层面为剪切面。剪切面的面积为3000cm~2。先对试体在一个确定的正应力下进行剪断实验,然后继续对它在不同的正应力下进行摩擦实验。实验表明,剪断实验表现为塑性破坏及随后的位移强化现象。摩擦实验的摩擦强度略高于剪切破坏强度。剪切破坏强度方程为:τ=0.03+0.30σ。其中σ为正应力,τ为剪应力。单位均为MPa。     

辉长岩摩擦实验中断层泥的剪切组构及成因

模拟断层泥的摩擦实验对地震的成核及断层带变形组构的研究具有重要意义。文中对辉长岩摩擦实验中的断层泥变形组构及形成机理进行了研究 ,以期从实验室角度来理解地壳深部断层活动的性质和特点。断层泥剪切组构中的边界剪切带 ,R1,Y剪切面比较发育 ,T裂隙次之 ;R2 ,P ,X剪切面不发育。R1面与边界面的夹角较小 ,平均在 1 1°左右 ,为单剪变形过程中达到破裂极限状态时形成的 1组库仑破裂面。分析表明R1面密度随正应力的增加而明显增高。而在相同的正应力下 ,随温度的增高 ,R1面的密度也有增加的趋势。当温度高于 5 0 0℃时 ,断层带内的斜长石出现塑性变形特征 ,R1剪切面与矿物的压性面理组成典型的S -C组构     

脆塑性转化带Carrara大理岩断层稳定性的实验研究

为探究脆塑性转化带断层的力学性质和滑动稳定性,本文采用干燥的Carrara大理岩预切断层(saw-cut)样品,在气体介质三轴高温岩石力学实验仪上开展了摩擦实验研究,实验温度70～400℃,围压30～100 MPa,位移速率在0.08μm·s^-1, 0.4μm·s^-1, 2μm·s^-1之间切换.实验力学数据揭示,不同围压下Carrara大理岩断层摩擦系数随温度变化规律不同：低围压(30 MPa)下,摩擦系数随温度升高先增大后减小,中高围压(≥70 MPa)下摩擦系数则表现为随温度先减小后增大.断层摩擦滑动行为在100～300℃的范围内表现出由稳定的速度强化转化为不稳定的速度弱化,且在400℃左右重新转变为稳定的速度强化.实验后断层滑动面形貌和微观结构分析表明,稳定滑动断层面为高反射镜面,擦痕清晰;黏滑断层面为有光泽的凹凸不平的表面;最高围压下蠕滑的断层面粗糙无光泽,擦痕不可辨别.本文认为受温度激活的塑性变形过程逐步主导了岩石变形,对断层激活发生不稳定滑动至关重要,而高围压则会抑制断层的不稳定滑动.本研究结果不仅为识别野外...     

岩石摩擦-滑动中的声发射b值动态特征及其地震学意义

双剪试验的结果表明,岩石摩擦滑动过程中的AE b 值动态曲线可归纳为锯齿状和台柱状两类,分别对应于不规则粘滑和规则粘滑.滑动瞬间滑面上摩擦系数变化△μ的分布决定岩石的滑动方式,不均匀分布易发生不规则粘滑.均匀分布易引起规则粘滑;破裂和滑动是摩擦滑动过程中的两类AE 机制,两类AE 的能量分别与破裂面面积及△μ成正比.研究结果提示,平直光滑的地震断层可能显示出特征地震的发震特点.     

龙门山断层带浅钻花岗岩中断层泥的摩擦本构参数

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(10-19m~2),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。     

断层同震滑动的实验模拟——岩石高速摩擦实验的意义、方法与研究进展

岩石摩擦实验是断层力学和震源物理实验研究中主要的手段之一.传统低速率的岩石摩擦实验与以之为基础建立的速率状态变量摩擦本构关系理论体系,对于认识断层摩擦滑动稳定性和地震成核等地震成因机制问题具有重要意义.近20年来,断层力学领域兴起了用于模拟断层同震动态滑动的岩石高速摩擦实验.这种新的实验模拟方法揭示出断层同震滑动存在明显的摩擦生热效应,断层的力学性状主要表现为显著的滑移弱化和速度弱化,断层带物质在断层高速滑移过程中经历了各种复杂的物理化学变化.这些研究成果对于认识和评估断层同震弱化机制、断层带强度、地震能量分配、断层破裂模式、断层愈合等问题均具有重要启示.本文对岩石高速摩擦实验的意义、方法与研究进展进行了总结,提出了目前的前沿性问题和值得开展的工作.     

龙门山断裂带断层岩在水热条件下的摩擦滑动特性实验研究

为了探索断层岩石在断层带不同温度和压力条件下其摩擦强度和摩擦滑动稳定性对于断层活动性的影响,我们采集了龙门山断裂带地震发生区段出露的自然断层泥样品和后山断裂带韧性剪切带中的富含层状硅酸盐矿物的糜棱岩样品进行了水热条件下的摩擦滑动实验研究。我们根据自然断层泥样品的XRD分析结果选取了5种具有不同矿物组合及含量的自然断层泥样品并在50MPa的初始围压和25℃～150℃的温度条件下进行了摩擦滑动实验。     

海原断裂带断层泥摩擦特性的研究

用双剪法对海原断裂带5个点的13种断层泥的摩擦滑动特征进行的实验研究表明,海原断裂带的断层泥的存在有助于消除粘滑与增大摩擦强度,五个点断层泥的摩擦系数平均值分别是0.760(景泰),0.728(哈思山),0.669(大沟门),0.644(剌儿沟),0.684(蔡祥堡)。     

FRICTIONAL PROPERTIES OF A NATURAL FAULT GOUGE FROM DRILLED CORES IN THE LONGMENSHAN FAULT ZONE CUTTING GRANITIC ROCK

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.     

从断层泥石英颗粒的微观形貌研究八宝山断裂带的活动性

北京八宝山断裂带主要由八宝山内支、外支断裂和黄庄-高丽营断裂组成。根据野外地质资料和室内研究,认为八宝山内支断裂是燕山期的逆掩断层,已不具活动性,而外支断裂是一条规模和断距都不大的正断层,只有黄庄-高丽营断裂才是活动断层,它错断了中更新统黄土。 为了获得更多的有关八宝山断裂带活动性的资料,我们采用Kanaori提出的一种判定断层活动性的新方法,通过扫描电镜观察了八宝山断裂带的6个断层泥样品和4个有关地层中的石英颗粒表面微结构,所得结果与野外宏观地质资料相吻合     

断层泥在孕震过程中的作用

本文用粘弹性理论,探讨了老断层失稳扩展型地震的孕育过程中,断层泥的作用问题.得到了如下结果:即使区域背景场和扰动场保持不变,断层局部应力场仍会因断层泥的蠕变而变化.其中切向应力分量σ0_ηη(t),在其它所有分量都缓慢衰减的同时缓慢增大.一旦这个应力分量在断层尖端附近的极大值点,积累至大于岩石的断裂强度,断层的失稳扩展便会从这点发生.与空腔断层相比,断层泥使σ0_ηη(t)的突变过程变成了缓慢渐近过程,并使σ0_ηη(t)的渐近值有所降低,因而会推迟和减少地震的发生.文中还讨论了断层失稳扩展方向等问题.      

虹口八角庙-深溪沟炭质泥岩同震断层泥的X射线衍射分析结果

5.12汶川地震同震地表破裂带在虹口八角-深溪沟一带主要出露于三叠系须家河组的炭质泥岩中,同震断层泥在颜色、结构上与老断层泥和围岩类似。通过开挖探槽,系统采样,采用粉晶X射线衍射定量分析方法,研究了同震地表破裂带的围岩、断层角砾岩、老断层泥和新断层泥的矿物成分特征。同震断层泥的主要成分为石英和黏土矿物,含微量长石和白云石;断层泥的显著特征为高黏土矿物含量,从同震断层泥、老断层泥、角砾岩到围岩黏土矿物含量依次降低,黏土矿物以伊利石和伊蒙混层为主,含微量绿泥石和高岭石,矿物组成明显比地表破裂带北段同震断层泥简单。不同颜色的同震断层泥成分略有不同,黑色断层泥中伊利石含量明显高于白色断层泥;老断层泥中含有方解石和白云石,而同震断层泥不含方解石,只含微量白云石。同震断层泥中伊蒙混层高含量表明,在本次地震错动中有富含K的流体参与。     

THE GEOLOGICAL AND ROCK MECHANICAL DISTINCTION EVIDENCE BETWEEN STICK-SLIP AND CREEP IN HOST ROCK SEGMENTS OF FAULT

Paleo-seismic and fault activity are hard to distinguish in host rock areas compared with soft sedimentary segments of fault. However, fault frictional experiments could obtain the conditions of stable and unstable slide, as well as the microstructures of fault gouge, which offer some identification marks between stick-slip and creep of fault. We summarized geological and rock mechanical distinction evidence between stick-slip and creep in host rock segments of fault, and analyzed the physical mechanisms which controlled the behavior of stick-slip and creep. The chemical composition of fault gouge is most important to control stick-slip and creep. Gouge composed by weak minerals, such as clay mineral, has velocity weakening behavior, which causes stable slide of fault. Gouge with rock-forming minerals, such as calcite, quartz, feldspar, pyroxene, has stick-slip behavior under condition of focal depth. To the gouge with same chemical composition, the deformation mechanism controls the frictional slip. It is essential condition to stick slip for brittle fracture companied by dilatation, but creep is controlled by compaction and cataclasis as well as ductile shear with foliation and small fold. However, under fluid conditions, pressure solution which healed the fractures and caused strength recovery of fault, is the original reason of unstable slide, and also resulted in locking of fault with high pore pressure in core of fault zone. Contrast with that, rock-forming minerals altered to phyllosilicates in the gouges by fluid flow through degenerative reaction and hydrolysis reaction, which produced low friction fault and transformations to creep. The creep process progressively developed several wide shear zones including of R, Y, T, P shear plane that comprise gouge zones embedded into wide damage zones, which caused small earthquake distributed along wide fault zones with focal mechanism covered by normal fault, strike-slip fault and reverse fault. However, the stick-slip produced mirror-like slide surfaces with very narrow gouges along R shear plane and Y shear plane, which caused small earthquake distributed along narrow fault zones with single kind of focal mechanism.     

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

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20 μm·s^-1~1.4 m·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.     

AN EXPERIMENTAL STUDY ON THE PROCESS OF INTERGRANULAR PRESSURE SOLUTION OF PLAGIOCLASE GOUGE UNDER HIGH TEMPERATURE AND PRESSURE: METHOD AND PRELIMINARY RESULTS

To understand the mechanism of lower-crust earthquake and slow slips, it is necessary to study the frictional properties of mafic rocks and their major rock-forming minerals. Previous studies have performed a series of experimental researches on gabbro, basalt and their major constituents. According to the results of previous experiments, frictional sliding of plagioclase under hydrothermal conditions(100~600℃)shows a property of velocity weakening, and the experimental results show that both the direct rate effect parameter(a)and the healing effect parameter(b)increase with temperature, a typical feature for thermally-activated processes. Velocity weakening means property of a shear band that has a stronger friction healing effect than the direct rate effect in the rate and state friction constitutive framework, and the healing effect(b value)in constitutive relation mainly reflects the increase in contact area with time under hydrothermal conditions, with some minor effect of structural changes. Since the microphysical mechanism of feldspar minerals at the contacts is mainly brittle cataclasis for temperatures below 600℃, the significant frictional healing effect in this case can only be explained by the mechanism of pressure solution. In order to determine if the dissolution process of plagioclase actually occurs on the laboratory time scale, we conducted hydrostatic experiments on plagioclase powder samples under hydrothermal conditions whereby frequent contact switch between particles seen in frictional sliding experiments can be avoided, making the observation on the dissolution sites possible. Experimental temperatures were 400℃ and 500℃, with confining pressure of 90~150MPa, pore pressure of 30MPa, with 2mm initial thickness of fault gouge. The mechanical data show that a creep process occurred in the plagioclase fault gouge in the experimental temperature and pressure range; and the microstructures of the experiment show that precipitation of new grains is prevalent as the product of pressure solution process between plagioclase particles. At the same time, it is observed that the contact points have an appearance similar to fused, fuzzy structure as signatures of dissolution. The results of our experiments provide a definite experimental evidence for the healing mechanism in friction of plagioclase and for the theoretical relation between unstable slip and the pressure solution process. The results of the experiments are summarized as follows: (1)Drainage rate of pore water in plagioclase gouge was high in the first few hours of experiment, but gradually decreases over time for both temperature and pressure series of experiments slowing down to a steady state. This feature indicates that there is a creep process that evolves inside the plagioclase gouge. In the temperature-series experiments, the drainage rate of the pore water in the plagioclase gouge at 400℃ is relatively low than the cases for higher temperatures. Thus, the applied temperature is positively correlated with the creep of plagioclase gouge. (2)Scanning electron microscopy(SEM)observations of the experimentally deformed samples were performed on thin sections cut along the sample axis. Firstly, from the images of microstructure, it was found that the degree of particle fracture became more significant at a higher effective pressure, with smaller pore volume between particles. In the temperature-series experiments it was found that the degree of compaction of plagioclase gouge increased with increasing temperature. Precipitation of plagioclase grains in layered structures was generally observed in high-magnification images, indicating the presence of pressure solution processes. Contact points were also found to be in a state of ambiguity that seems to be a fused morphology, but the details of the structure remain to be determined by further observations. The above results indicate that the pressure solution process of plagioclase particles can occur on a typical laboratory time scale, and the results of this study provide robust experimental evidences for the theory that links between pressure solution and the mechanism of frictional healing and unstable slips for plagioclase.     

THE VITRINITE REFLECTANCE OF FAULT ROCKS FROM THE WENCHUAN EARTHQUAKE FAULT ZONE: CONSTRAINTS ON FRICTIONAL PROPERTIES OF THE FAULT DURING THE EARTHQUAKE

The temperature rise caused by frictional heating during seismic slip is able to indicate dynamic frictional properties of the seismic fault,which provides an approach to understand the dynamic process and energy budget of an earthquake.The residual indicators of frictional heating within the fault zone also can be taken as an evidence for seismic events.The vitrinite reflectance is a commonly-used geothermometer in the coal,oil and gas industries.It also has some potential applications in the studies of fault rock and fault mechanics.We studied vitrinite reflectance (VR) of fault rocks collected from surface outcrops of the Wenchuan earthquake fault zone in this paper.The measured data reveal that the VR of fault rocks are affected by fault motion,and there is a trend that the VR increases towards the fault core,which indicates the effects of frictional heating.The VR of fault rocks from the Bajiaomiao outcrop is much higher than those from the Shenxigou outcrop,which probably suggests the difference in fault activity at the two outcrops.Our study also suggests that systematic measurement of VR across the fault zone is helpful in identifying slip zones and determining their widths.From the VR measurement on an oriented specimen containing the slip surface of the Wenchuan earthquake from the Shenxigou outcrop,we observed anomalous high VR values in two black-colored slip zones of about 2mm in width near the slip surface.The numerical calculation shows that the maximum temperature rise on the fault plane near Shenxigou was probably less than 162℃ during the Wenchuan earthquake,which means the dynamic fault strength was quite low.These estimations are roughly in accord with the results from the high-velocity frictional experiments.