岩石非均匀性对地震活动状态影响的数值模拟研究

地震的孕育、发生与震源位置及其岩石力学性质有着密切的联系,本文借助数值模拟方法研究了岩石均质度在岩样变形直至破裂过程中对声发射事件活动状态的影响。数值模拟结果表明,岩石非均匀性对岩样声发射活动状态的时间演化过程有着较大影响,所得结论进一步支持了分区研究强地震前兆异常的必要性。     

细观非均匀性对岩石破裂过程和微震序列类型影响的数值试验研究

运用岩石破裂过程分析RFPA2D系统，研究了岩石介质细观非均匀性对宏观力学行为的影响和微震序列特征. 通过对不同均质度系数m=1.1，1.5，2，3，5的5个样本进行破裂过程的模拟，发现均质度不同会产生不同地震序列类型，主要有：前震-主震-余震型、主震型和震群型. 此外，对5种不同均质度系数的岩石样本破裂过程的模拟表明，岩石介质的非均匀性不仅对岩样宏观强度和宏观变形非线性行为有显著的影响，而且也显著地影响试样破裂模式. 随着均质度系数的提高，主破裂呈现脆断模式. 同时介质的细观结构随机性，也对试样宏观破裂模式产生重要影响.     

由含断层岩石非均匀性产生的地震前兆的数值模拟研究

使用新开发岩石破裂过程分析软件(RFPA2D)，通过一系列模型实验，研究岩石中预制断层面几何特征和力学非均匀性对地震前兆产生的影响。模型使用5个具有不同均质度的岩石样本进行数值模拟研究。数值模拟结果表明，不同均质度岩石破坏在地壳中会产生不同的地震前兆现象。在一些区域，可以观测到明显的前兆，而在另一些地区却很难观测到明显的前兆现象。模拟结果与实验观测和自然界实际观测结果由很好的一致性。     

岩石原地应力的变化性

本文讨论了与不同尺度相关的岩石原地应力的变化性:构造区域尺度、工程场地尺度、洞室挖掘尺度、钻孔测量尺度以及微观尺度.造成这种应力变化性的因素有岩石非均匀性、岩石各向异性、不连续性以及自由面.本文介绍了关于岩石非均匀性导致应力变化的数值模拟.通过应力第一不变量的引入使应力随深度的变化变得明确.在锦屏Ⅱ号场地,钻孔中的岩石...     

地震序列障碍体模型的数值模拟试验研究

运用岩石破裂过程分析RFPA2D系统,研究了断层上含非均匀性障碍体对地震序列类型的影响。通过对断层障碍体不同均质度系数m=1.1、m=1.5、m=6.0这3个样本进行破裂过程的模拟,发现均质度不同会产生不同地震序列类型,这些序列类型主要是前震主震余震型、主震型和震群型。此外,对3种不同均质度的障碍体的岩石样本破裂过程的模拟表明,岩石介质的非均匀性不但对岩样宏观强度和宏观变形非线性行为有显著的影响,而且对试样破裂模式也有显著的影响。     

震源孕育模式的数值模拟研究

在充分考虑地质体材料力学性质非均匀性特点的基础上，运用岩石破裂失稳过程有限元分析新方法(RFPA)，以不存在明显孕震构造特征的包体模式为例，模拟研究了挤压边界条件下的震源孕育模式，包括断层的形成过程和地震活动特征，演示出孕震体由变形、破裂到宏观贯通的地震全过程以及它们的时空强基本规律．计算所得到的应力、变形和微震空间分布，形象地给出了变形局部化、震源迁移、膨胀或隆起，弹性回跳和X型共轭变形带等直观图象．      

岩石介质中多裂纹扩展相互作用及其贯通机制的数值模拟

运用岩石破裂过程分析RFPA^2D系统，通过对岩石试样中预置的一组右行右阶雁列式裂纹扩展过程的数值模拟，研究了非均匀岩石介中多裂纹扩展的相互作用模式及其贯通机制。数植模拟再现的受压混合型裂纹扩展过程中逐步演变的全场变形过程，以及与细观非均匀性有关的声发射和断续扩展模式的“岩桥”现象，清晰地揭示出多裂纹扩展的相互作用及其贯通机制。模拟结果说明，对于岩石这种地质介质而言，忽略其非均匀性影响，可能会掩盖岩石变形与破裂过程中的许多与非均匀性有关的特殊现象，包括声发射或微震模式、岩桥或雁行断裂等。     

用斜井钻孔崩落资料反演上地壳应力状态的遗传算法

用斜井钻孔崩落资料求取地壳应力状态是一个非线性反演问题。而遗传算法是解反演问题的有效方法之一。本文由斜井钻孔崩落的理论模型,用人工数据检验了遗传算法应用于此问题的有效性。对冀中坳陷内的饶阳凹陷和深县凹陷两个地区的６口油井的钻孔崩落数据进行了处理,用遗传算法反演了这两个凹陷的上地壳应力状态,与用非线性反演和枚举相结合的方法相比,大大减少了计算量,得到了令人满意的结果。     

当代钻孔地应力测量的主要问题

近半个世纪以来,钻孔法地应力测量中尚未解决的主要问题是:假定岩石在力学性质上各向同性;没有考虑钻孔效应;忽视了测量的时间效应;简化了岩石力学性质的多变性。由于这些问题的存在,使得主应力测值的误差可达100%,主应力方向的测量误差可达90°,还可以引起主应力性质的正负变换。要进行高水平的地应力测量,必须把测量建立在岩石方学性质各向异性的基础上,减少或避开钻孔效应的影响,考虑或避开测量的时间效应,避开岩石力学性质多变性的影响,分别测量各种地应力成份,进行定点长期连续观测。     

非均匀性对岩石介质中裂纹扩展模式的影响

运用岩石破裂过程分析ＲＦＰＡ２Ｄ系统,通过对岩石试样中预置的倾斜裂纹扩展过程的数值模拟,研究了材料非均匀性对岩石介质中裂纹扩展模式的影响．数值模拟再现了受压试样在裂纹扩展过程中逐步演变的应力场和应变场,以及与岩石非均匀性有关的声发射和断裂扩展模式的“岩桥”现象．模拟结果说明,岩石的非均匀性对含裂纹试样的变形、破裂过程及其破坏模式有很大的影响．     

Borehole Breakouts in Berea Sandstone Reveal a New Fracture Mechanism

— Vertical drilling experiments in high-porosity (22% and 25%) Berea sandstone subjected to critical true triaxial far-field stresses, in which σ _H (maximum horizontal stress) >σ _v (vertical stress) >σ _h (least horizontal stress), revealed a new and non-dilatant failure mechanism that results in thin and very long tabular borehole breakouts that have the appearance of fractures, and which counterintuitively develop orthogonally to σ _H . These breakouts are fundamentally different from those induced in crystalline rocks, as well as limestones and medium-porosity Berea sandstone. Breakouts in these rocks are typically dog-eared in shape, a result of dilatant multi-cracking tangential to the hole and subparallel to the maximum far-field horizontal stress σ _H , followed by progressive buckling and shearing of detached rock flakes created by the cracks. In the high-porosity sandstone a narrow layer of grains compacted normal to σ _H is observed just ahead of the breakout tip. This layer is nearly identical to “compaction bands” observed in the field. It is suggested that when a critical tangential stress concentration is reached along the σ _h spring line at the borehole wall, grain bonding breaks down and a compaction band is formed normal to σ _H . Debonded loose grains are expelled into the borehole, assisted by the circulating drilling fluid. As the breakout tip advances, the stress concentration ahead of it persists or may even increase, extending the compaction band, which in turn leads to breakout lengthening.     

根据钻孔崩落椭圆确定地壳应力方向

本文根据钻孔崩落椭圆是由水平地应力引起孔壁在最小水平主应力方向发生剪切破坏的理论,讨论了由崩落椭圆确定水平主应力方向问题.讨论了地层倾角和四臂井径测井的测量方法、资料处理以及识别崩落椭圆的原则,并列举出两个不同类型的实测例子.最后分析了河南濮阳地区的29个钻孔的地层倾角和四臂井径测井资料,得出该地区的平均崩落椭圆长轴方位是 N15E,由此确定的最大水平主应力方位是 N105E.      

根据钻孔崩落资料确定剑川地区应力场方向

本文论述了钻孔崩落的力学机制、产生环境及其与现今构造应力场的关系,介绍了超声波井下电视的测井原理、操作技术和钻孔崩落测井资料分析方法。根据一口800米深钻孔的超声波井下电视测井获得的崩落资料,确定剑川地震活动区最大水平主应力方向为N20°E。这与近两年来在该区采用水压致裂法测定的最大水平主压应力方向N15°E是十分一致的     

变形过程中岩石P波速度场的空间变化

在一次地震之前,在不同观测点测量岩石中弹性波速度,经常得到不同的结果.这一现象提示我们:岩石破坏前,其物理性质的变化在空间上的分布是不均匀的,破坏前兆的获得应该建立在对岩石性质的空间分布,即对物理场分析的基础上. 本实验观测了岩石样品在单轴压缩下,P波走时空间分布变化的全过程.实验表明:在岩石的破坏过程中,岩性的空间分布具有同步性变化的中长期前兆和差异性变化的短期前兆的特点.在岩石接近破坏时,岩性的变化表现出严重的不均匀性.岩石的整个破坏过程可以看成岩石的物性分布是由无序向有序的演化,即是一个熵减小的过程.      

Grain scale deformation in ultra-high-pressure metamorphic rocks—an indicator of rapid phase transformation

Conspicuous grain scale deformation is observed in some ultra-high-pressure (UHP) metamorphic rocks of the Dora Maira Massif, Western Alps, although no significant strain is discernible on the mesoscopic scale. In a jadeite–kyanite–quartz rock, some of the jadeite crystals reveal (100) deformation twins, indicating local differential stress levels above 0.3 GPa. Many kyanite crystals show marked kink or deformation bands, with a slip system (100)[001]. In contrast, the adjacent coarse-grained quartz matrix (grain size ca. 0.2 mm), which has formed from coesite during exhumation from >100 km depth, reveals a foam structure. The quartz grain boundary configuration is controlled by interfacial free energy, the grains are optically strain-free, and there is no crystallographic preferred orientation. Preservation of this foam microstructure, which indicates grain growth during low-stress annealing, precludes that deformation of the jadeite and kyanite crystals is a result of a late-stage low-temperature overprint. The orientation distribution of jadeite and kyanite with and without twins or deformation bands, respectively, has been investigated with a combination of universal stage and EBSD techniques. On the scale of a thin section, there is no preferred orientation of twinned jadeite and bent kyanite crystals and undeformed crystals, respectively. Thus, the orientation of the inferred local shortening direction is random. This precludes deformation driven by a homogeneous far field tectonic stress, but suggests an internally controlled stress field which is highly inhomogeneous on the scale of a few grain diameters. Laboratory experiments show that the coesite to quartz transformation proceeds within hours after decompression from 3.0 to 2.7 GPa at 800 °C. The microstructures of incompletely transformed samples indicate that the quartz growing at the expense of coesite undergoes crystal plastic deformation and recrystallizes with a very fine grain size during transformation. In this case, the deformation of quartz is attributed to the volumetric strain ΔV=+10% inherent in the coesite–quartz transformation, which causes a highly inhomogeneous stress field inside the sample related to the progress of the transformation. We propose that a similar process has taken place in the polyphase natural rock during exhumation, with the transient stresses causing mechanical twinning of jadeite and bending or kinking of kyanite. When the transformation had gone to completion, grain growth obliterated the microstructures of the quartz matrix, while the deformed jadeite and kyanite crystals preserved the record of inhomogeneous deformation at high temperatures. The peak differential stresses locally exceeded 0.3 GPa, which indicates very high strain rates and a correspondingly rapid transformation of coesite to quartz, comparable to the laboratory results.     

岩石应力状态改变引起岩石热状态改变的研究

岩石的应力状态发生改变是否能引起岩石的热状态发生改变，是一个值得研究的重要问题，我们在实验室对岩石试件进行实验，实验得出岩石的温度随岩石受到的压力增加而显著增加，在试件破裂前出现明显的破裂温度前兆；实验还发现岩石内部温度随压力变化的不均匀性，不同测温点的温度变化不同，其变化量可相差几度。     

Generation of electromotive force in igneous rocks subjected to non-uniform loading

When one end of an air-dry igneous rock block was uniaxially loaded in laboratory, there appeared an electromotive force that made electric currents flow from the stressed volume to the unstressed volume. Quartz-free rocks such as gabbro also generated this force, stronger than quartz-bearing rocks such as granite. This indicates that the piezoelectric effect of quartz and the electrokinetic effect of pore water do not make a large contribution toward generating the electromotive force. We focus on peroxy bond that is one of the abundant lattice defects in igneous rock-forming minerals. When mechanical loading deforms the lattice structure around this defect and breaks its bond, its energy levels change and act like an accepter. As an electron is trapped at this defect from a neighbor O^2- site, a positive hole is activated there. They attempt to diffuse toward the unstressed volume through the valence band and are simultaneously affected by the attractive electric force with the electrons trapped in peroxy bonds. This leads to a polarization in the stressed volume and the generation of electromotive force between the stressed and unstressed volumes. Similar electromotive force may be generated in the Earth's crust where inhomogeneous stress/strain is changing.     

A new approach to numerical simulation of source development of earthquake

ＡｎｅｗａｐｐｒｏａｃｈｔｏｎｕｍｅｒｉｃａｌｓｉｍｕｌａｔｉｏｎｏｆｓｏｕｒｃｅｄｅｖｅｌｏｐｍｅｎｔｏｆｅａｒｔｈｑｕａｋｅＣＨＵＮ－ＡＮＴＡＮＧ（唐春安）ＹＵ－ＦＡＮＧＦＵ（傅宇方）ＷＥＮＺＨＡＯ（赵文）ＣｅｎｔｅｒｆｏｒＲｏｃｋｂｕｒｓｔｓ...