剪切载荷扰动对断层摩擦影响的实验研究

利用双轴伺服控制加载装置,采用3块花岗闪长岩标本组成的含有2个滑动面的直剪结构,开展了摩擦滑动实验。实验中通过在剪切方向上叠加正弦波状的位移扰动,研究了剪应力扰动对断层粘滑失稳的影响。研究表明,在恒定的正应力和位移速率下,标本表现出较为规则的粘滑;当在剪切方向叠加位移扰动后,随扰动振幅的增加,粘滑发生时间与扰动的相关性增大,粘滑的应力降和时间间隔的分布趋于离散,其中扰动能产生明显影响的临界振幅大致为0.05MPa;粘滑应力降和时间间隔随扰动振幅增大而逐渐离散的现象在较高正应力下更为明显,而相同扰动振幅下粘滑失稳发生时间与扰动的相关性也随正应力增加而增大;扰动周期对摩擦性状的影响不明显。研究结果意味着,地震引起的同震剪应力的变化不仅会引起邻近断层上地震发生时间的变化,也可能引起地震强度的变化     

侧向应力扰动对断层摩擦影响的实验研究

利用双向伺服控制装置,对含有与最大主压应力σ1呈45°夹角的预切面的花岗闪长岩标本进行了摩擦实验,结果表明,在σ1方向位移速率恒定、侧向应力σ2恒定的条件下,粘滑间隔随滑动面上正应力的增加而增加,粘滑应力降也随滑动面上正应力的增加而呈线性增加。但当σ2叠加了高频小振幅的正弦波扰动时,这种相关性发生了明显的变化,应力降大小和粘滑间隔的离散度均显著提高,特别是应力降可能会大幅度增加。与σ1扰动的实验结果相比,σ2扰动对断层粘滑的影响更为显著,这主要归因于正应力变化使滑动面的非均匀性加剧     

速率-状态依赖摩擦定律引入连续-非连续方法的检验及断层倾角的影响

断层黏滑是一种摩擦失稳,能够诱发地震、矿震等诸多地质灾害.目前,断层黏滑(包括断层亚失稳)研究,主要集中在实验方面和基于连续方法或非连续方法的数值模拟方面.为了弥补连续方法和非连续方法各自的不足,一些兼具二者优势的连续-非连续方法应运而生.为了检验引入速率-状态依赖摩擦定律的自主开发的拉格朗日元与离散元耦合连续-非连续方法的正确性并探究断层倾角对断层黏滑的影响,首先,模拟了滑块-底板模型的滑动-保持-滑动实验;然后,模拟了双轴压缩岩样的断层倾角的影响,重点考察了断层黏滑过程中亚失稳阶段摩擦系数的演化规律.研究发现,随着断层倾角的增大,岩样上表面平均差应力的绝对值-时步数目曲线的锯齿形由规则向不规则变化;初次黏滑发生时的时步数目、平均应力降、平均黏滑周期和平均峰值应力均减小.当断层处于黏滑前阶段时,断层面各处的摩擦系数和剪应力相差较小.当断层进入亚失稳阶段后,断层面上摩擦系数的平均值下降速度加快,这可作为断层进入亚失稳阶段的特征之一.引入速率-状态依赖摩擦定律后的拉格朗日元与离散元耦合连续-非连续方法的断层黏滑结果能与现有结果（例如,断层黏滑实验结果）基本吻合,但更加丰富,这在一定程度上...     

应力扰动对断层摩擦声发射活动影响的实验研究

利用中尺度岩石摩擦实验开展了应力扰动对断层摩擦滑动过程中声发射活动影响的实验研究,据此讨论同震应力变化引起的小震活动特征及其预测意义.实验结果表明方波状应力扰动对粘滑失稳前的声发射活动有明显影响,即触发了一些声发射事件,使得粘滑发生前声发射活动增强并使出现的时间提前.这种影响随平均正应力的提高和扰动振幅的增大而增强,其...     

断层黏滑动态变形过程的实验研究

实验研究断层黏滑过程的变形演化,尤其是失稳黏滑瞬间的断层位移演化特征,对于了解地震从孕育到发生的全过程具有重要意义.本文基于数字散斑相关方法(digital speckle correlation method, DSCM),用三套图像采集系统(两套低速和一套高速图像采集系统)搭建了断层黏滑过程的多观测区域、多时间尺度的变形场测量系统,并用此系统对一种花岗岩双剪滑动模型的黏滑过程进行了实验研究.对间黏滑期和黏滑期断层位移演化特征进行深入分析的结果表明:间黏滑期断层位移演化体现出空间上的非均匀性和时间上的"趋同化"特征,断层滑动趋同化也许是断层错动匀阻化的一种宏观表现形式;断层黏滑动态过程持续时间非常短(本文300 mm断层黏滑过程持续时间约在1 ms量级),黏滑失稳前会出现预滑,预滑出现到黏滑失稳发生所经历的时间与黏滑失稳过程所用时间相差一个量级;断层的一次黏滑由若干个滑动速度不同的、小的失稳滑动组成,黏滑失稳过程中断层的滑动速度呈现出波动性,整个滑动过程中断层经历了多个高速滑动和低速滑动的交错.     

静态库仑破裂应力对断层地震失稳过程影响的模拟研究

基于速率—状态依赖性摩擦滑动定律,建立断层黏滑模型,采用阶跃形式的应力扰动加载于断层模型上,利用Runge-Kutta数值积分方法,主要分析了应力扰动值的正负、大小和加载时间t0对断层滑移时间的影响。结果发现,当库伦破裂应力为常数,不论是正应力起主导作用还是剪应力起主导作用,对后续断层的作用几乎一样。静态应力扰动作用下断层的成核周期会发生提前或者延后,具体表现为:当库伦应力为正时引起断层的成核时间提前,且提前量小于原有周期值;库伦应力为负时引起时间延迟,且延迟时间不受原有成核周期限制。库伦应力扰动的幅值越大,引起的滑移时间改变量越大。成核时间提前量与应力扰动的加载时间有关,在前期施加同样大小的应力扰动,时间提前量呈现随加载时间增加而增加的趋势。     

黏滑实验的震级评估和应力降分析

本文通过三种结构模型的黏滑地震模拟实验,利用高频速度连续观测系统获得了地震失稳过程的速度特征,讨论了最大位移量的选取方法,估算了实验室黏滑型地震的矩震级,探讨了黏滑类型、应力降大小与震级的关系.结果表明,黏滑型地震的应力降过程可能包含一次到多次高频振荡,对应若干次黏滑子事件.高频振荡的摆动幅度很大,包含有多种频率成分,峰值速度0.003~0.008 m·s^-1.初步估计黏滑型地震的震级范围为-4.4~-3级,断层构造面的差异对各种黏滑模型的地震震级分布有明显影响.总体来看应力降与地震震级没有明显相关性,决定地震震级的主要因素应当是震源尺度.     

平直断层黏滑过程热场演化及失稳部位识别的实验研究

实验室断层黏滑伴随有温度变化,温度不但与摩擦滑动有关,还与样本的应力状态相关。文中利用红外热像仪进行全场观测,研究平直断层黏滑不同阶段的热场演化。实验不仅观测到了峰值前后从应力积累转变为释放导致的温度由升转降的现象,还观测到了失稳后断层升温和块体降温的相反变化。更重要的是通过分析沿断层各个部位的温度随时间的变化,发现了识别失稳部位的温度前兆:失稳部位的温度从强偏离线性阶段开始,一直是相对高值,在亚失稳阶段升温速率突然增大,远高于其他部位。分离摩擦和应力的作用后,发现亚失稳阶段失稳部位的升温发生于围岩上而非断层带上,说明断层处于闭锁状态而相邻的围岩区域处于应力集中状态,推测满足这2个条件的部位可能是未来的失稳部位。此现象或许有助于野外发震位置的判断。     

断层滑动速率变化对滑动稳定性的影响

在与主压应力方向斜交的断层上,正应力与剪应力之间存在线性相关关系,以此为基础导出了小扰动条件下决定稳定性的临界刚度与滑动速率的关系。由于这一关系具有临界刚度随滑动速率增加而减小的特点,因此速率增加可能导致周期性粘滑向稳定滑动转化,而速率减小可能使本来稳定的滑动转化为周期性粘滑过程。在这种斜交断层中,速率增加虽然可能抑制周期性粘滑,但是稳滑时超过一定限度的速率增加会导致一次性不稳定滑动。三轴摩擦实验提供了关于粘滑与稳滑可相互转化的支持证据     

数值模拟静态应力扰动下的断层失稳:结果分析兼与Dieterich模型和Coulomb模型的对比

基于大量岩石力学实验,Dieterich和其他研究者(Dieterich,1978;Ruina,1983)首先提出了描述岩石摩擦过程的速率-状态摩擦定律(R-S摩擦定律).如今R-S摩擦定律已成为研究地震成核等地震演化机制的有效手段.Dieterich(1992,1994)最早提出了描述受静态剪应力扰动后断层失稳时间提前或推后的余震触发机制的解析模型.现在Dieterich模型已经成为解释余震随时间衰减规律的Omori定律等地震观测现象的有力工具.与之相对应,广泛使用的Coulomb应力失稳模型也可以给出断层受到静态剪应力扰动后,断层失稳时间的提前和推后量.Dieterich模型和Coulomb应力失稳模型基于不同的物理方法,所以在进行地震危险性评估时,二者均有各自的局限性.本文利用R-S摩擦定律控制的1-D弹簧-滑块模型,模拟计算了理论地震循环以及在不同静态剪切应力扰动下,失稳时间的提前和推后量的变化情况,然后将计算得到的时间提前和推后量分别与Dieterich模型和Coulomb模型的相应计算结果进行了定量化对比和差异性分析,并给出了相应的解释.数值模拟结果显示,对于R-S摩擦定律在参数不变的条件下,断层模型失稳时间的提前和推后量的大小强烈依赖于静态剪应力扰动的大小和作用时间,而且绝对值相同的正、负向静态剪应力扰动造成的失稳时间的提前和推后量的变化情况并不完全一致.在震后松弛/滑移阶段和闭锁阶段,时间提前和推后量是常数,且随静态剪应力扰动绝对值的增大而增大,两者的比值接近于1.0,这与Dieterich模型和Coulomb模型的结果是一致的,相应的差值小于两模型结果的10%.而在自加速阶段,模拟计算结果则存在与Dieterich模型和Coulomb模型结果不同的特征.首先,在自加速阶段模拟计算结果均偏离Coulomb模型,而且时间提前和推后量的比值小于1.0,相异于Coulomb模型的论断.不过当受到正向静态剪应力扰动后,Dieterich模型的结果和模拟计算结果是一致的,最大相差量不超过Dieterich模型结果的7%,可接近0.对于负向静态剪应力扰动,当其绝对值较小时,Dieterich模型的结果很接近模拟计算结果,相差量不超过该结果的14%.但对于绝对值较大的情况,模拟计算结果远大于Dieterich模型的结果,最大可达Dieterich模型结果的35倍,这是由于负向静态剪应力扰动后使得Ω=δ·θ/dc1的条件不再成立,进而使得Dieterich模型不再成立.总的来说,与模拟计算相比Dieterich模型可以很好地描述1-D断层受扰后失稳时间提前和推后量的变化情况,并且可以体现出正、负静态剪切应力扰动后失稳时间提前量和推后量变化的差异性,而Coulomb模型则不能完整地给出受到静态剪应力扰动后断层失稳时间提前或推后的估计值.     

Experimental Study on the Stick-slip Phenomenon of Intact Granite under Solid Confining Pressure

In this paper,compression tests of intact granite samples have been made in a triaxial testing machine with solid confining pressure.From the tests,the influences of confining pressure and loading rate(axial strain rate)on the deformation and fracture process of rock samples,on the stress drop and recurrence interval of stick-slip events,and on the geometric distribution of the main fracture have been studied.The experimental results show that the loading rate influences the stress drop and recurrence interval of stick-slip events greatly.At lower loading rates,the stress drop of stick-slip events is greater,their recurrence interval is longer and shows no regularity in distribution.When the loading rate goes higher,the stress drop will become smaller and the recurrence interval will tend to be constant and stick-slip events show a quasi-periodicity.At lower confining pressures and strain rates,the main fracture may evolve into 2 X-shaped conjugate shear faults; whereas at higher confining pressures and     

Cohesive zone length of metagabbro at supershear rupture velocity

We investigated the shear strain field ahead of a supershear rupture. The strain array data along the sliding fault surfaces were obtained during the large-scale biaxial friction experiments at the National Research Institute for Earth Science and Disaster Resilience. These friction experiments were done using a pair of meter-scale metagabbro rock specimens whose simulated fault area was 1.5 m?×?0.1 m. A 2.6-MPa normal stress was applied with loading velocity of 0.1 mm/s. Near-fault strain was measured by 32 two-component semiconductor strain gauges installed at an interval of 50 mm and 10 mm off the fault and recorded at an interval of 1 MHz. Many stick-slip events were observed in the experiments. We chose ten unilateral rupture events that propagated with supershear rupture velocity without preceding foreshocks. Focusing on the rupture front, stress concentration was observed and sharp stress drop occurred immediately inside the ruptured area. The temporal variation of strain array data is converted to the spatial variation of strain assuming a constant rupture velocity. We picked up the peak strain and zero-crossing strain locations to measure the cohesive zone length. By compiling the stick-slip event data, the cohesive zone length is about 50 mm although it scattered among the events. We could not see any systematic variation at the location but some dependence on the rupture velocity. The cohesive zone length decreases as the rupture velocity increases, especially larger than \( \sqrt{2} \) times the shear wave velocity. This feature is consistent with the theoretical prediction.     

Granular Controls on Periodicity of Stick-Slip Events: Kinematics and Force-Chains in an Experimental Fault

It is a long-standing question whether granular fault material such as gouge plays a major role in controlling fault dynamics such as seismicity and slip-periodicity. In both natural and experimental faults, granular materials resist shear and accommodate strain via interparticle friction, fracture toughness, fluid pressure, dilation, and interparticle rearrangements. Here, we isolate the effects of particle rearrangements on granular deformation through laboratory experiments. Within a sheared photoelastic granular aggregate at constant volume, we simultaneously visualize both particle-scale kinematics and interparticle forces, the latter taking the form of force-chains. We observe stick-slip deformation and associated force drops during an overall strengthening of the shear zone. This strengthening regime provides insight into granular rheology and conditions of stick-slip periodicity, and may be qualitatively analogous to slip that accompanies longer term interseismic strengthening of natural faults. Of particular note is the observation that increasing the packing density increases the stiffness of the granular aggregate and decreases the damping (increases time-scales) during slip events. At relatively loose packing density, the slip displacements during the events follow an approximately power-law distribution, as opposed to an exponential distribution at higher packing density. The system exhibits switching between quasi-periodic and aperiodic slip behavior at all packing densities. Higher packing densities favor quasi-periodic behavior, with a longer time interval between aperiodic events than between quasi-periodic events. This difference in the time-scale of aperiodic stick-slip deformation is reflected in both the kinematics of interparticle slip and the force-chain dynamics: all major force-chain reorganizations are associated with aperiodic events. Our experiments conceptually link observations of natural fault dynamics with current models for granular stick-slip dynamics. We find that the stick-slip dynamics are consistent with a driven harmonic oscillator model with damping provided by an effective viscosity, and that shear-transformation-zone, jamming, and crackling noise theories provide insight into the effective stiffness and patterns of shear localization during deformation.     

Experimental study on nucleation process of stick-slip instability on homogeneous and non-homogeneous faults

The nucleation process of stick-slip instability was analyzed based on the experimental measurements of strain and fault slip on homogeneous and non-homogeneous faults. The results show that the nucleation process of stick-slip on the homogeneous fault is of weak slip-weakening behavior under constant loading point velocity. The existence of a short “weak segment” on the fault makes slip-weakening phenomenon in nucleation process more obvious, while the existence of a long “weak segment” on the fault makes the nucleation process changed. The nucleation is characterized by accelerating slip in a local region and rapid increase of shear stress along the fault in this case, which is more coincident with the rate and state friction law. During the period when fault is locked, increasing of shear stress causes lateral elastic dilation near the fault, and the rebound of the dilation at the time of instability causes an instantaneous increase of normal stress in the fault plane, which is an important factor making fault be rapidly locked and its strength recovered.     

Experimental study on nucleation process of stick-slip instability on homogeneous and non-homogeneous faults

The nucleation process of stick-slip instability was analyzed based on the experimental measurements of strain and fault slip on homogeneous and non-homogeneous faults. The results show that the nucleation process of stick-slip on the homogeneous fault is of weak slip-weakening behavior under constant loading point velocity. The existence of a short "weak segment" on the fault makes slip-weakening phenomenon in nucleation process more obvious, while the existence of a long "weak segment" on the fault makes the nucleation process changed. The nucleation is characterized by accelerating slip in a local region and rapid increase of shear stress along the fault in this case, which is more coincident with the rate and state friction law. During the period when fault is locked, increasing of shear stress causes lateral elastic dilation near the fault, and the rebound of the dilation at the time of instability causes an instantaneous increase of normal stress in the fault plane, which is an important factor making fault be rapidly locked and its strength recovered.     

应力途径与岩石的摩擦滑动

用双剪法对济南辉长岩和点苍山大理岩进行了摩擦滑动实验.实验中的应力变化方式有两种.A 型实验:先使断层面上的正应力增加到一定值,然后保持正应力不变,并增加剪应力使断层发生粘滑;B 型实验:先使断层面上的正应力增加到一定的值,保持正应力不变,并增加剪应力到断层发生粘滑前的某一应力状态,再保持剪应力不变,减小正应力直到粘滑发生.实验表明,B 型实验中岩石的摩擦强度高于 A 型实验.A 型实验中粘滑发生前有声发射率增加的前兆,B 型实验中粘滑发生前看不到声发射率的明显增加.由实验得到一个启示,即闭锁断层的开锁可能采取两种形式:一种是冲开闭锁,即以剪应力的增加使断层发生错动;另一种是解开闭锁,即以正应力的减小使断层发生错动.断层的粘滑采取哪种形式,由断层带的应力变化途径决定.      

Period Doubling Bifurcation of Stress Drop for Stick-slip and Its Physical Implication

It is revealed in frictional experiments on medium-scale samples that period doubling bifurcation of stress drop for stick-slip occurs due to macroscopic heterogeneity of the sliding surface under conditions for typical stick-slip.The observed data show that the period doubling bifurcation of stress drop results from the alternate occurrence of strain release along the whole fault and along part of fault.This implies that complicated nonlinear behavior corresponds to clear physical implication in some cases.