FRICTIONAL SLIDING OF PLAGIOCLASE GOUGE UNDER LOWER-CRUST TEMPERATURE AND RELATIVELY LOW EFFECTIVE NORMAL STRESS

The discovery of tremors on the lower crust portion of the San Andreas Fault has attracted more attention on the mechanical properties of the lower crust in recent years, and some experimental studies have been carried out to understand the mechanical behavior. Previous experiments under effective normal stresses of 200MPa have shown that pyroxene and plagioclase mineral separated from the gabbro and their mixtures all show velocity weakening in the lower-crust temperature range, which results in unstable slip when frictional sliding is the dominant deformation mechanism. This work is to examine whether the velocity-weakening behavior of plagioclase gouge also applies to relatively lower effective normal stress. Our experiments were performed under effective normal stress of about 100MPa, with a constant confining pressure control, with pore pressure of 30MPa and temperature of 100℃ to 600℃. We found that the frictional sliding of plagioclase are basically the same with the previous results obtained under effective normal stress of 200MPa, both of which show velocity weakening over the entire temperature range. The only difference is the out-of-trend drop of constitutive parameter a at 600℃ for the lower effective normal stress of 100MPa. It is thus concluded that reducing the effective normal stress has little effect on the sliding stability of plagioclase, and the previous conclusion made for mechanical behavior of the lower crust that unstable slips are possible therein also applies to the lower effective normal stress of 100MPa.     

温度压力孔隙压力对断层泥强度及滑动性质的影响

在不同的压力、温度和孔隙压力下进行了含四种不同断层泥标本的强度试验。碎屑型断层泥对压力很敏感,对温度无反应,对孔隙压力的反应符合有效应力律。粘土类断层泥则对温度和孔隙压力有明显响应。这些力学性质的差别反映了具体变形机制的差别     

热水条件下角闪石断层泥的摩擦滑动性质——与斜长石断层泥的对比

基于速率与状态依赖性摩擦本构关系理论框架,在热水条件下研究了角闪石断层泥的摩擦滑动性质并与闪长岩的另一种主要矿物斜长石的摩擦滑动性质进行了对比.摩擦实验是在三轴实验系统上完成,有效正应力200 MPa,孔隙压力30 MPa,并将加载速率在1.22 μm/s和 0.122 μm/s之间实施了切换.结果表明角闪石的摩擦系数均值为0.70±0.01,随着温度增加没有系统性的变化,整体低于斜长石的摩擦系数(0.75±0.01);计算与实验表明,角闪石和斜长石的摩擦系数的体积分数加权平均值与闪长岩的摩擦系数基本一致;角闪石在实验温度范围内(100～614 ℃)显示速率强化(a-b>0),与斜长石在整个温度范围内的速率弱化(a-b<0)正好相反;角闪石的速率依赖性在整个实验温度范围内无系统性的变化.     

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.     

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

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     

高温高压下红河断裂带断层泥力学性质的研究

断层泥在室温高压下的应力-应变曲线呈非线性、线性等阶段性变形,在高温高压下则呈非线性变形,两者均表现出渐进破坏。含水量、矿物成分和温压条件对变形特征和破坏强度有重要影响。曲线的初始弹性模量小于有效弹性模量。断层泥在温度T≥400℃和σ_3≥300MPa时发生岩化,据此岩化温压条件可估计出未岩化断层泥存在深度将不超过10—15km。由于断层泥具渐进破坏特征,故在高温高压条件下断层泥有利于断层活动呈现稳滑     

流体对石灰岩断层摩擦滑动影响的实验研究

在气体介质三轴高温岩石力学实验仪器上,采用意大利Scaglia Bianca石灰岩,在温度50～300℃、围压150MPa,含50MPa孔隙压、无孔隙压含饱和水和完全干燥三种条件下,开展摩擦滑动实验.实验力学数据和显微结构表明,完全干燥样品在120℃时出现慢滑移,实验样品中没有出现溶解与沉淀.无孔隙压含饱和水条件下,100℃、120℃、150℃条件下出现典型的慢滑移,实验样品中含有微弱的溶解与沉淀;300℃条件下出现黏滑,实验样品中出现沉淀.在含50MPa孔隙压条件下,50℃时的实验表现为典型的稳滑,实验样品中以溶解为主;在100～150℃时,出现慢滑移,实验样品中以溶解为主,沉淀为辅;在200～300℃时,出现典型黏滑,实验样品中以沉淀为主.实验结果表明,石灰岩断层泥摩擦滑动稳定性随温度变化,受流体中碳酸钙的溶解和沉淀作用控制,因此,流体中矿物质的饱和度这一化学性质对断层带的摩擦强度和摩擦滑动稳定性具有显著影响.     

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.     

热水条件下黑云母断层泥的摩擦强度与稳定性

黑云母是自然界常见的层状硅酸盐矿物,其摩擦系数不高且化学稳定性好,对其摩擦性质的关注可能会对弱断层的研究有所帮助.本次工作选取的实验温度条件对应于典型地壳强度模型中脆塑性转化带的范围,为300 ℃和400 ℃.有效正应力为200 MPa,孔隙水压包括10 MPa和30 MPa,在此条件下对黑云母模拟断层泥进行摩擦实验研究.实验得出黑云母的摩擦系数平均在0.36左右.速度依赖性随温度升高速度弱化的程度增强,表现为300 ℃为十分微弱的速度弱化,而在400 ℃出现了黏滑行为,代表了更强的速度弱化.显微结构中同时出现了脆性剪切变形和塑性扭折变形,但决定宏观力学性质的显然是脆性剪切变形.在黑云母存在的情况下,本研究的实验结果有助于理解大陆地壳脆塑性转化带中地震的可能性和弱断层深部的变形机制、宏观力学行为以及地震活动.     

白云母对岩盐断层带摩擦速度依赖性影响的实验研究

为更好地理解层状硅酸盐对断层强度、滑动速度依赖性及地震活动特征的影响,利用双轴摩擦实验对含白云母岩盐断层带在干燥及含水条件下摩擦的速度依赖性进行了实验研究,并观测了摩擦滑动过程中的声发射,分析了断层带的微观结构.实验结果表明,干燥条件下含白云母岩盐断层带在0.1 ～ 100μm/s的速度范围内表现为黏滑和速度弱化,增大σ2会使断层带从速度弱化向速度强化转化,速度依赖性转换出现在0.1 μm/s,其中断层滑动表现为稳滑或应力释放时间较长的黏滑事件;含水条件下含白云母岩盐断层带在0.05 ～0.01μm/s的速度范围内表现为速度强化,0.1 ～10μm/s的速度范围内表现为速度弱化,50～100μm/s的速度范围内又转换为速度强化行为.含白云母岩盐断层带在干燥条件下一次黏滑伴随一个或一丛声发射事件,而在含水条件下与稳滑相对应,滑动过程中并未记录到声发射事件.显微结构观察表明,速度弱化域的主要变形机制是岩盐颗粒的脆性破裂和局部化的滑动;干燥条件下,速度强化域的主要变形机制是岩盐颗粒的均匀破裂;含水条件下2个速度强化域对应不同的微观机制,高速域的速度强化受控于岩盐颗粒在白云母相互连结形成的网状结构上的滑动及其均匀碎裂作用,而低速域的速度强化还受岩盐的压溶作用控制.通过与岩盐断层带摩擦实验结果对比可知,白云母的存在对于燥岩盐断层带摩擦滑动方式和速度依赖性没有显著影响,而在含水条件下白云母的存在使得岩盐断层带滑动趋于稳定.实验结果为分析含层状硅酸盐断层的强度和稳定性提供了依据.此外,在速度依赖性转换域上观察到的应力缓慢释放的现象进一步证实了在岩盐断层带摩擦滑动过程中观察到的现象,这对慢地震机制研究具有参考意义.     

热水条件下花岗质糜棱岩的摩擦滑动实验研究

为了探讨大陆地壳断层深部的力学性质,我们选择了采自红河断裂带的糜棱岩作为实验样品,进行热水条件下的高温高压摩擦滑动实验.实验在一个以气体为介质的高温高压三轴实验系统中进行.实验条件是：有效正应力为200 MPa;孔隙水压为30 MPa（在400 ℃到600 ℃之间为超临界水条件）;温度为100 ℃到600 ℃;轴向加载的速率范围从0.04 μm/s到0.2 μm/s再到1 μm/s.实验结果表明：（1）当温度小于300 ℃时,糜棱岩的摩擦强度随着温度的上升而增大;当温度大于300 ℃时,糜棱岩的摩擦强度随着温度的上升而减小.这种趋势和以往花岗岩的摩擦滑动数据基本一致;（2）糜棱岩在200 ℃和400 ℃时表现为速度弱化,其余温度下为速度强化;（3）糜棱岩与已有花岗岩的摩擦滑动数据并不完全一致;（4）花岗质糜棱岩速度弱化向速度强化转变的温度在430 ℃附近,以此我们可以推测：在变形机制为摩擦滑动的深部条件下,地震成核的深度范围可以比以往的估计更深.     

断层脆塑性转化带的强度与变形机制及其流体和应变速率的影响

野外、实验和地震数据表明:浅部地壳的变形以脆性破裂为主,深部地壳的变形以晶体塑性流动为主.在这种认识的基础上,提出了地壳变形的2种机制模型,即发生脆性变形的上部地壳强度基于Byerlee摩擦定律以及发生塑性变形的下部地壳强度基于幂次蠕变定律.而位于其间的脆塑性转化带的深度与浅源地震深度的下限具有很好的一致性.然而,二元结构的流变模型局限性在于其力学模型过于简单,往往过高估计了脆塑性转化带的强度.问题的根源在于对脆塑性转化带的变形机制的研究已有很多,但没有定量的力学方程来描述脆塑性转化带强度;而且以往对断层脆塑性转化带的研究主要集中在温度引起的脆塑性转化方面,对因应变速率和流体对脆塑性转化的影响方面的研究也比较薄弱.对断层带内矿物变形机制研究表明,某些断层带脆塑性转化发生在相同深度(温度和压力)内,发生脆塑性转化的原因是应变速率的变化,而这种变化被认为与地震周期的同震、震后-间震期蠕变有关,这种变化得到了主震-余震深度分布变化的证实.对断层流体特征分析表明,断层带内可能存在高压流体,这种高压流体会随断裂带的破裂及愈合而周期性变化,在地震孕育及循环中起着关键性作用.高压流体的形成(裂隙愈合)有多种机理,其中,压溶是断层带裂隙愈合的主导机制之一.研究在水作用下的压溶,可以对传统的摩擦-流变二元地壳强度结构及其断层强度进行补充与修正.通过以上分析,认为有必要通过野外变形样品和高温高压实验,深入研究应变速率及流体压力对断层脆塑性转化的影响,同时,通过实验建立压溶蠕变的方程,近似地估计脆塑性转化带的强度.     

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.     

蒙脱石的脱水作用对断层摩擦本构行为的影响

利用高温双轴摩擦装置，研究了含蒙脱石的断层带在不同温度下摩擦滑动的速度依赖性，以期了解脱水作用对摩擦行为的影响。结果表明，断层带摩擦强度随温度而升高，而速度依赖性较为复杂，以１．４ｕ／ｓ为界，室温和１００℃时，低滑动速率下表现为微弱的速度弱化，高滑动速率下则表现为速度强化；２００℃时均为速度强化；３００℃时高滑动速率下仍为速度强化，但低滑动速率下转变为速度弱化；４００℃以上，均为明显的速度弱化。摩擦行为的变化与脱水过程及相应的断层物质变形方式的变化密切相关     

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)。     

断层物质测年的热释光研究

断层物质ＴＬ测年的关键，是断裂运动产生的温压效应能否使断裂带内某些矿物原贮存的ＴＬ能量完全释放而“归零”。为此，进行了不同条件的高温、高压和位移速率变化等的模拟断裂运动的实验。结果表明，断裂运动产生的摩擦增温是使断层面上矿物ＴＬ强度减弱的主要因素。讨论了摩擦增温值与断裂运动时剪应力大小、断层泥厚度和断层位移间的关系，并得到了野外断层面上实际测试的证实。据此研究成果，还对小湾坝区Ｆ＿７断裂的活动时代进行了测定     

EXPERIMENTAL STUDY ON THE EFFECT OF WATER ON THE STRENGTH AND DEFORMATION MECHANISM OF CARRARA MARBLE AT HIGH TEMPERATURE

We performed deformation experiments using Carrara marble in dry and wet conditions under temperature of 400~700℃ and confining pressure 300MPa with two different strain rates. Water contents of deformed samples were measured using FTIR spectroscopy. The microstructure and deformation mechanisms of samples were observed under optical microscopy, scanning electron microscopy and energy spectroscopy analysis. The mechanical data show that samples display strain hardening at 400℃, and transition to steady creep at temperature from 500~700℃. The strength of marble reduced gradually with elevated temperatures or decreased strain rate. However, water effect to the strength of the marble is significantly weak. Microstructures observed show that the deformation is cataclastic flow in dry samples, fracture and pressure solution in wet samples at 400℃. Samples underwent brittle-plastic transition at 500℃. Dislocation glide is major deformation mechanism for dry samples at 600℃. Dislocation climb and dynamic recrystallization are major deformation mechanism for wet samples at 600℃ and for all wet samples and dry samples at 700℃. Lower strain rate and higher water content could promote the process of pressure solution and diffusion as well as dynamic recrystallization.     

剪切破裂与粘滑——浅源强震发震机制的研究

周口店花岗闪长岩的高温高压三轴实验和理论分析表明,剪切破裂和摩擦滑移具有类似的孕育过程和发生机制。剪切破裂贯通强度就是一种摩擦强度。剪切破裂和摩擦滑移各自都有渐进式和突发式之分。突发式摩擦滑移是已有断层的粘滑滑移。突发式剪切破裂则是完整岩石的初始粘滑滑移。考虑到地壳温度随深度增加,完整岩石剪裂强震要求较高的围压,因此,多数浅源强震的发震方式很可能是已有断层的粘滑     

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.     

高温高压下蒙脱石显微变形与力学性质的研究

通过研究高温高压条件下蒙脱石的变形特征和机制,着重阐述了蒙脱石的显微变形特征与温度压力之间的关系,以及对应力-应变的影响。研究表明,在围压为200M Pa条件下,温度升高将导致蒙脱石的变形增大。对相同应变量所需的差异应力则随温度上升而下降。但是,当温度>500℃时,相同应变量所需差异应力较300℃时显著增大,其屈服强度和变形模量在T≥500℃,σ≥300MPa时均因脱水明显增大。蒙脱石在高温高压下均为渐进失稳