逾渗模型的地震学含义

本文根据地震统计力学的结果从理论上讨论了逾渗模型的地震学含义,指出用这类几何相变模型研究地震破裂问题的处理方法不仅仅是一种唯象的类比,从其物理意义出发能够得到一些富有启发性的结果,并可在一定程度上明确逾渗模型应用于地震破裂和地震活动性研究的能力和限度。     

逾渗与岩石破裂的计算机模拟研究

用计算机模拟方法研究了岩石破裂的逾渗模型，给出了在微裂隙随机分布情况下破裂集团的分布图象、破裂集团的大小分布规律、总破裂集团数、集团平均大小、ｂ值、逾渗分维Ｄ及临界情形。所得结果与其他模型和实验基本一致，表明通渗模型是描述岩石破裂扩展演化过程的一种较合适的模型。还发现了岩石破裂过程存在的两个转折点，深入研究这两个转折点附近岩石的宏观性质，可为探索地震孕育演化过程的前兆性质提供依据。     

地震活动的逾渗模型及临界状态的研究

利用现代非线性物理理论及震源理论,结合地震活动的特点,建立了地震活动的逾渗模型．把一次大地震孕育发展的过程看做一次逾渗相变过程,应用重正化群方法处理了逾渗相变．把逾渗相变中的相关长度为无穷大作为重正化群变换中的不动点,在不动点下计算系统的临界性质,得到了逾渗概率指数、相关长度指数等临界指数．利用1975年海城地震以及1976年唐山地震前后的地震活动资料,对两次地震的逾渗相变过程进行了讨论．      

利用逾渗模型研究辽宁地区的地震活动

首先,我们利用现代非线性物理理论及震源理论建立了适合地震活动的逾渗模型。然后,我们利用这一模型,对辽宁地区１９７０年以来的地震活动进行了研究。通过对地震活动的逾渗相变过程中逾渗阈值附近的各种临界指数的计算,对破裂概率达到或超过逾渗阈值的子区域进行了讨论并对近期辽宁地区的地震活动趋势进行了探讨。     

用临界点理论讨论应变能加速释放现象和孕震区尺度

20世纪 80年代后期 ,地震的临界现象研究成为地震学界的热点之一。Hirata等 ( 1 987)通过大量实验和观测结果得出结论 :接近破裂的岩石与铁磁模型的二阶相变具有本质上的联系。岩石中的应力参数类似于铁磁相变中的温度参数 ,即低应力状态时 ,微裂纹随机产生且微裂纹之间关联程度较低 ;当应力达到岩石的破裂强度时 ,裂纹相互关联 ,裂纹大小呈幂率 (分形 )分布。根据临界点理论 ,地震孕育过程是一种临界现象 (Vere Jones ,1 977;Sornette ,etal.,1 990 ;1 995;Rundle ,etal.,1 999;Jaume ,etal.,1 999) ,但地壳并不总是处于临界状态。随着…     

岩石破裂时电磁辐射的机理研究

本文提出了岩石破裂时的电磁辐射是裂纹尖端电荷随着裂纹加速扩展运动所产生的假说.应用断裂力学方法推导了岩石破裂时初始裂纹长度与裂纹扩展加速度的关系,并计算了其速度和加速度值.根据破裂岩石的电子发射理论,解释了裂纹尖端带电荷的现象.利用岩石在单轴压缩致裂过程中记录到的近场电磁辐射的实验结果,计算了裂纹扩展时裂纹尖端的电荷量和远场电磁辐射强度.通过对电磁辐射波谱分析的研究,得到岩石破裂时电磁辐射频率上限的估计值.最后对岩石破裂时出现的声光电磁现象在理论上作了统一的定性的解释.     

具有割缝的大理岩试件破坏过程的有限元模拟

本文使用应变软化的弹塑性本构模型,用有限元方法对具有中心斜割缝的岩石试件在轴压下的破坏过程进行了数值模拟。得到了与实验观察相当一致的结果:在割线端部附近,首先发生张破裂,裂纹的扩张是逐渐地弯向试件的轴线方向,并变为稳定的。随着轴向压力增加,在张裂纹的相反方向上出现共轭的剪破裂。这些现象与割缝顶端附近材料的应变软化性质有关。说明所采用的有限元方法是研究岩石材料破裂过程的一种可行的方法。     

岩石破裂电磁辐射(EMR)现象实验研究

岩石破裂电磁辐射现象是客观存在的物理现象.随着电磁辐射观测技术在地震研究、冲击矿压预测等领域的应用,极大地推动了岩石破裂电磁辐射的实验研究.本文对岩石破裂电磁辐射的影响因素以及相伴生的现象,以及有关的物理解释进行了概括介绍.由于不同研究者使用实验设计、实验参数、实验条件的不同,使得观测和研究结果同样难以统一认识.不同的研究者根据各自的试验提出了不同的物理机制.同时对已发现现象的重复性、证实性研究岩石试验缺乏.严重匮乏利用数值模拟以及建立模型定量研究岩石破裂的电磁辐射.此外,岩样实验系统不同于实际的地震系统,进行模拟震源环境的实验研究,发展大尺度的标本和原岩现场实验的基础上,如何建立室内室外岩石实验与地震观测事实之间的联系是问题的关键.     

三维破裂及其在地震和断层研究中的应用（综述）

文中提出若干断层破裂和震源过程的重要问题,包括断层分布的形态、震源多重事件的非共面性、震源迁移和动力来源等,这些问题用目前二维力学模型无法回答,只有用三维模型才有可能。综述了三维岩石断裂力学的实验和Ｇｒｉｆｉｔｈ－Ｉｒｗｉｎ理论研究的进展情况,指出三维破裂研究既包括三维裂纹的破裂,也包括无初始裂纹的Ｈｅｒｔｚ接触引起的破裂。总结了岩石三维破裂的特征,并简述了三维破裂在震源过程和断层形成问题研究中的一些证据和研究前景,认为一些地震前兆机理问题有可能在三维模型中得到解答。同时也讨论了三维震源与断层模型简化为常用的二维模型的条件。     

岩石破裂电磁辐射频率与弹性参数的关系

为进一步研究岩石破裂电磁辐射特征,本文根据岩石破裂电磁辐射是由岩石破裂时产生带电粒子扰动引起的假说,通过断裂力学理论中的张开位移法计算岩石破裂过程中的裂纹宽度,由电磁辐射频率与破裂宽度之间的关系,研究电磁辐射频率与弹性参数之间的关系,并给出了它们之间的关系表达式.通过建立具有中心贯穿裂纹的无限大平板模型,根据破裂宽度计算了在该模型条件下几种岩石破裂过程中产生电磁辐射频率范围.理论模型计算出来的频率范围主要集中在实验观测的中高频段,并体现出频率随弹性参数的变化.     

震后地下岩层分形渗透率的时间演化规律研究

天然地震发生后,地震波及区域内的地下岩层渗透率常常会发生显著改变,其变化曲线显示出独有的特征,造成这一现象的机理较为复杂,传统渗流理论尚不能给出合理解释.针对这一问题,从震后渗透率变化规律入手,深入分析了地下岩层裂缝体系对渗透率的影响,给出了裂缝结构参数与渗透率之间的定量关系.结合岩层黏弹特性以及天然地震所产生的地下岩层体应变特征,基于裂缝体系分维度正比于外部应力的实验事实,将黏弹体应力松弛机制引入该体系,对裂缝分形渗透率模型进行了含时推广,建立起震后地下岩层渗透率的时间演化模型,理论预测曲线与实验曲线吻合较好.在此基础上提出‘分形裂缝渗透率松弛效应’这一全新概念.本研究为震控流体运移研究提供了新思路,对于揭示震后断层恢复机制,探讨断层活动与孕震的关联有一定的理论价值和现实意义.     

Research on percolation model and criticality of seismicity

IntroductionEarthquakepredictionisamainobjectiveintraditionalseismicitystUdy,whichistoattempttofindsomecriterionofprecursoryearthquakeactivitybycomparingdifferentpatternsofseismicityinhopesofpredictingoccurrenceofamajorshock.Theresultisoftendisappointing.Preearthquakeactivitiescandiffergreatlyforimpendingearthquake,althoughalltheruptureprocessesoflargeearthquakesareessentiallythesameasfarasweknowsofar.Asalreadydiscussedintheresultofresearchonseismicityevolution(Gu,Sun,1992),theself-enlargeme…     

一种基于逾渗模型的裂隙岩石渗透系数确定方法

针对裂隙岩体提出了一种基于双重逾渗模型的渗流系数分析方法。通过变参数研究,考察了岩体中渗流和孔压分布的不均匀;根据裂隙长度的不同将岩体分为孔隙控制渗流模式和裂隙控制渗流模式。这种模型不仅能够同时考虑孔隙和裂隙的作用,而且在模拟大规模裂隙网络时更加快捷简便。     

Scale Dependence of Hydraulic and Structural Parameters in the Crystalline Rock of the KTB

— Knowledge of rock properties controlling the fluid movement is a basic prerequisite to understand the dynamical processes and the temperature and stress regime of the upper crust. Fracture networks were investigated on different scales to obtain quantitative results of fracture geometry like fracture length, orientation and fracture frequencies. Due to the scale effect, these parameters differ in several orders of magnitude in dependence of the scale of investigation. On the microscopic scale, fluorescent thin sections from cores were analysed and permeability was estimated for 2-D hydraulic networks. On the macroscopic scale, fracture parameters were determined from images of structural borehole measurements. The vicinity of the drill site represents the megascopic scale, where seismic reflectors were assumed as active hydraulic structures for construction of a fracture network. Compiling the fracture densities from all investigated scales and taking into consideration only the networks above the percolation threshold, the fracture length distribution follows a power law with an exponent of ?1.9 ± 0.05. Besides the scale differences of the geometric parameters like fracture density and length and the hydraulic parameters like permeability, the connectivity of the networks seems to be a confining characteristic. This is quantitatively described by the percolation parameter and the mean number of intersections per fracture. When assuming a macroscopic hydraulic system at the percolation threshold for the KTB site, the macroscopic mean fracture length can be estimated to approximately 30 m. This stands in agreement with the hydraulic experiments on site.     

岩石裂隙电阻率特征研究

岩石的电阻率差是电阻率法的物理前提,利用电阻率法研究断层是比较有效的方法。利用断层破碎带与周围岩石的电阻率差异,跨断层做了大量的实验数据,通过对比和分析,得出了研究破碎带与周围岩石的电性差异,寻找变化规律,研究其变化特征。对今后断层探测具有重要价值,对防震减灾具有重要意义。     

Percolation and fracture

A statistical model of fracture, based on percolation theory, is presented which allows the quantitative evaluation of clustering of cracks in solids. Unlike models of branching processes which are more in accord with Griffith fracture, the concept of percolation lattices (finite and infinite) is used following from a physical model of multiple fracture.Some experimental results on acoustic emission, dilatancy and geophysical precursors of earthquakes can be correlated with the percolation fracture model. The model does not depend on the mechanism of crack formation, critical parameters being the number of elementary events (cracks), the dimensionality of the process and the coordination number for a network of cracks and, in finite systems, their specific size.Fracture prediction is possible from the number of elementary acts, cluster statistics and other characteristic parameters of the model. Possible applications of the percolation model for earthquake prediction are considered.     

Fractures: Finite-size scaling and multifractals

The distributions of contact area and void space in single fractures in granite rock have been determined experimentally by making metal casts of the void spaces between the fracture surfaces under normal loads. The resulting metal casts on 52 cm diameter core samples show a complex geometry for the flow paths through the fracture. This geometry is analyzed using finite-size scaling. The spanning probabilities and percolation probabilities of the metal casts are calculted as functions of observation scale. Under the highest stresses of 33 MPa and 85 MPa there is a significant size-dependence of the geometric flow properties for observation scales smaller than 2 mm. Based on this data, the macroscopic percolation properties of the extended fracture can be well represented by relatively small core samples, even under normal stresses larger than 33 MPa. The metal casts also have rich multifractal structure that changes with changing stress.     

Micro-computed tomography imaging and probabilistic modelling of rock fracture by freeze–thaw

A major problem in studies of rock fracture by frost is the paucity of direct observations in space and time of the initiation and growth of microcracks and their transition to macrocracks. Such observations are essential to understand the location, timing and controls of rock fracture by freeze–thaw. The aim of the present work is to image and elucidate the early stages of rock fracture by applying imaging and statistical methods to a frost-weathering experiment using intact specimens of a limestone (chalk) and sandstone. First, micro-computed tomography (μ-CT) is used to visualize rock fracture in three dimensions over the course of 20 freeze–thaw cycles and to estimate transverse strain using a pixel-based approach. Second, probabilistic correlation functions are applied to quantify the progressive expansion of the fracture phase and associated damage to rock specimens. The method of μ-CT is demonstrated for visualizing the growth and coalescence of microcracks and their transition to macrocracks. Fracture proceeded faster and to a greater extent in chalk relative to sandstone, and the macrocracks in chalk were mostly concentric and vertical. Both fracture development and positive transverse strain (dilation) accelerated after cycle 15, suggesting that a threshold has been exceeded, after which macrocracks were evident. Of three probabilistic correlation functions applied to the μ-CT results, the modified lineal-path function – which measures the continuous connectivity of the fracture phase in a specific direction – reveals that damage was more extensive in the chalk than the sandstone. It also allows a novel approach to define and quantify three zones of microcracking during freeze–thaw cycling of anisotropic rock: (1) the zone of inherent flaws; (2) the zone of active microcracking; and (3) the zone of weak influence during microcracking. The broader significance of this work is that it provides a new approach to investigate mechanistically how frost action damages rock. © 2019 John Wiley & Sons, Ltd.