Laboratory investigations on fault plane induced tensile cracks

Summary Tensile cracks induced by stress concentration around a fault plane in physical models under uniaxial load were analyzed. The results characterizing the decisive role of the fault plane inclination to the the stress direction are presented. Two stages of tensile crack life were determined, i.e. the first, seismoactive stage, accompanied by seismic energy release and the second aseismic one characterized by low velocity of crack propagation. Results obtained seem to be relevant to a better understanding of the character and regime of actual seismoactive faults.     

Experimental observations of elastic wave radiation characteristics from tensile cracks and pre-existing shear faults

Elastic waves were recorded from tensile cracks and prepared shear faults in the laboratory. The velocity of tensile crack propagation was measured. The duration of crack propagation was correlated with the signal pulse duration. Experiments with prepared shear faults showed that obstacles on the fault change the pulse form and the relation between wave amplitude (magnitude) and seismic moment.     

Propagation of surface waves in heterogeneous media containing a low velocity channel

Summary Propagation of surface wave in heterogeneous media with various laws of variation of elastic properties have been discussed previously by several authors. There the laws of variations were taken on the considerations that the solutions might be had in terms of known functions. Here the approximate solutions for polynomial law of variations of elastic properties have been obtained.     

含流体复杂孔隙介质地震波衰减与频散

含流体孔隙介质中地震波的速度频散和衰减在指导复杂储层含油气性识别领域具有重要意义.本文构建了包含微观挤喷流与介观层间流影响的跨尺度模型, 并使用求解介质等效模量的方式得到了模型中地震波的频散速度与衰减因子, 克服了前人在高频段计算结果出现异常值以及不同尺度衰减峰无法分离的缺陷.在该双尺度模型的基础上, 本文又综合考虑宏观尺度Biot流, 将三种地震波衰减理论耦合, 建立了相对统一的三尺度地震波衰减岩石物理模型.在Biot理论框架下, 分析了非均匀性流体、孔裂隙结构、微观挤喷流以及介观层间流对流体压力与弹性模量的影响, 得到了该三尺度模型中地震波的波动方程, 并求解得到了相应的地震波衰减与频散曲线, 分析了不同介质参数对衰减与频散曲线的影响.我们推导了在该模型上覆均匀各向同性介质情况下, 分界面处各类极性波的反射、透射系数特征方程, 并得到了随频率以及入射角变化的反射、透射系数三维曲面.

     

Propagation effects on radiation field pulses generated by cloud lightning flashes

As the electromagnetic fields propagate over finitely conducting ground, selective attenuation of the high frequencies takes place. As a result, the signatures of broad-band electromagnetic radiation fields generated by lightning flashes change as they propagate over such ground. In addition to being a function of the electrical parameters of the ground over which the electromagnetic fields propagate, these propagation effects depend on the height of their source above ground level. This makes the propagation effects on radiation fields from cloud flashes differ from those on the radiation fields generated by return strokes in ground flashes. In this paper the propagation effects on radiation field pulses of cloud flashes are illustrated and it is shown that these effects are not as severe as those of return strokes in ground flashes.     

Predicting the overall properties of composite materials with small-scale inclusions or cracks

This paper will summarise the present state of knowledge concerning the elastic and dissipative properties of composite materials in the long wavelength or static approximation. In this case the material, although containing numerous inclusions or cracks or other types of microstructure, can be regarded as a continuum. Established results are listed for the elastic parameters following a review of approximate and exact methods of their derivation.     

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.     

Approximate velocity formula over mobile sediment bed induced by velocity-skewed waves and current

A velocity formula is proposed for flow over a mobile sediment bed induced by velocity-skewed waves and current. The formula is obtained by a separation of waves and current velocities and requires seven free variables related to free stream velocity and sediment characteristics. The formula includes two parts:(1) a wave part consisting of the free stream velocity and defect function, which considers phase lead, wave boundary layer thickness, and mobile bed level, and(2) a current part, which ch...     

内日球子午面瞬态激波的传播特性

采用日球子午面内的二维三分量MHD模型,研究瞬态激波的传播特性,着重分析日球 电流片（HCS）、日球等离子体片（HPS）和低速流结构对激波传播的影响．结果表明,HCS 和HPS对激波传播几乎没有影响,而跨越HCS和HPS的低速流则显著改变激波的传播特性. 低 速流对激波的反射,导致激波扰动源一侧的激波速度加快、强度增强,低速流对激波透射的 阻碍作用导致激波扰动源异侧的激波滞后、强度减弱,但激波阵面的纬度跨度有所加宽．在 激波穿越过后,低速流区朝激波传播方向弯曲并受到骚扰,使得激波下游出现复杂的扰动结 构;对于激波扰动源同侧的激波下游,反射波与该处等离子体的相互作用同样会导致较为复 杂的扰动出现.     

Dilatancy and fracture induced velocity changes in rock and their relation to frictional sliding

Summary Laboratory room temperature triaxial friction tests on sawcut granite and serpentinite specimens suggest that stick-slip at high confining pressures is preceded by dilatancy in the intact rock adjacent to the shear surface. By using a fast-reacting servo-loading system in combination with a high resolution digital computer recording system it is possible to obtain a more realistic picture of the stick-slip mechanisms and the stress drop associated with unstable slip. Fracturing in granite under biaxial loading leads to a significant anisotropy in dilation andP-wave velocity of the rock. Velocity decreases remarkably in the directions of minor principal stresses with no indication for velocity recovery before macroscopic shear fracture development.The results suggest that dilatancy and velocity anomalies may precede crustal earthquakes under certain tectonic conditions.

---

Zusammenfassung Triaxiale Scherversuche an polierten Scherflächen in Granit- und Serpentinitproben (Normaltemperatur) lassen schließen, daß instabile Gleitvorgänge auf den Scherflächen bei sehr hohen Manteldrücken mit vorhergehenden Auflockerungen (Dialatanz) des intakten Gesteins in der Umgebung der Scherfläche verbunden sind. Durch die Verwendung eines reaktions-schnellen Servobelastungssystems in Verbindung mit einem hoch-auflösenden digitalen Aufzeichnungssystem konnte erstmals ein Einblick in den tatsächlichen Ablauf des instabilen Gleitprozesses gewonnen werden. Der Bruch in Granit bei biaxialer Belastung führt zu einer signifikanten Anisotropie der Auflockerung des Gesteinsgefüges und damit der Geschwindigkeit seismischer Wellen. Die Geschwindigkeit derP-Wellen nimmt in Richtung der beiden kleineren Hauptspannungen mit fortschreitender Deformation kontinuferlich ohne Anzeichen eines Geschwindigkeitsanstiegs vor der Entwicklung des makroskopischen Scherbruchs ab.Die Ergebnisse lassen den Schluß zu, daß Dilatanz und damit verbundene Geschwindigkeitsanomalien Erdbeben in der Kruste bei bestimmten tektonischen Bedingungen vorangehen können.

     

饱和储层砂岩中流体粘度引起的超声波速度频散实验研究(英文)

在实验室对5块储层砂岩进行了模拟地层压力条件下的超声波速度测试。砂岩样品采自WXS凹陷的W地层,覆盖了从低到高的孔隙度和渗透率范围。实验选用了卤水和4种不同密度油作为孔隙流体,结合温度变化,实现了对流体粘度引致的速度频散研究。对实验结果的分析表明:(1)对于高孔隙度和渗透率的样品,无论是哪种流体饱和,观察到的超声波速度测试值和零频率Gassmann预测值的差异较小(约2-3%),基本上可以用Biot模型解释;对于中等孔隙度和渗透率的样品,低粘度流体(<约3mP?S)的频散效应也可以用Biot模型得到合理解释;(2)对于低、中孔隙度和渗透率样品,当流体粘度增加时,喷射流机制起主导作用,导致严重的速度频散(可达8%)。对储层砂岩的微裂隙纵横比进行了估计并用于喷射流特征频率的计算,当高于该特征频率时,Gassmann理论的假设条件受到破坏,实验室测得的高频速度不能直接用于地震低频条件下的W地层砂岩的Gassmann流体替换研究。     

Propagation properties of guided wave in the anchorage structure of rock bolts

We investigated the properties of guided wave propagating in grouted rock bolts and the formation of the interface wave through theoretical analysis along with experimental and numerical simulations. Experimental and numerical simulations reveal that the wave propagating in anchorage structure is related to boundary conditions within the range of excitation wave frequencies. Waves with different frequencies have different propagation velocities and attenuation characteristics. The optimal excitation wave occurs in grouted rock bolts with minimized attenuation and maximized propagation distance, and the end reflection of grouted rock bolts can be observed clearly. Longitudinal wave propagating in rock bolts is very sensitive to anchorage strength. With the increase of anchorage strength, longitudinal wave gradually attenuates and eventually disappears. Subsequently, interface wave appears and the velocity of wave propagating in the grouted part becomes that of the interface wave. Based on these studies, ultrasonic guided wave was used to study the end reflection of embedded rock bolts with different anchorage strengths and bonding lengths. The relationships among anchorage strength, bonding length and attenuation coefficient K, as well as the means to inspect the bonding quality of the embedded rock bolts were also evaluated.     

Localization and characterization of cracks in clay‐rocks using frequency and time‐domain induced polarization

Induced polarization (IP) is a geophysical method that is potentially sensitive to the presence of cracks in porous rocks and therefore to damage. We performed time‐domain and frequency domain IP measurements at the Tournemire Underground Research Laboratory (URL, Aveyron, France) in areas where different types of cracks are observed. These cracks correspond to both tectonic fractures and new cracks associated with stress release and desiccation resulting from the excavation of a gallery. These measurements were performed both in eastern and northern galleries of the test site. The eastern gallery was excavated in 1996 while the northern gallery was excavated recently in 2008. This gives us the opportunity to study the electrical characteristics of the excavation damaged zone surrounding the galleries with respect to the age of the excavation. Longitudinal profiles were performed along the floor of the galleries with 48 Cu/CuSO₄ electrodes separated by a distance of 20 cm. Chargeability and resistivity were inverted using a Gauss‐Newton iterative approach assuming an isotropic heterogeneous clay‐rock material. The resulting IP tomograms show a correlation between high values of chargeability and the presence of calcite‐filled tectonic fractures. X‐ray analysis indicates that the presence of pyrite in these fractures is a potential source of the observed IP signals. The cracks associated with the mechanical damage of the formation exhibit low values of chargeability, on the same order of magnitude than the chargeability of the clay‐rock matrix and are therefore hardly observable. A smaller IP response associated with the presence of these cracks is observed in the older gallery and this observation is qualitatively related to the desaturation process associated with these cracks. In a specific area of one of the galleries, the presence of calcareous nodules is observed to be an important source of anomalous chargeability. This signature seems to be associated with the presence of pyrite.     

The mass transport velocity induced by free oscillations at a single frequency

Abstract

Second order effects due to the presence of a first order free oscillation at a single frequency in a variable depth rotating ocean are examined. It is found that the second order Lagrangian mean velocity (mass transport velocity) satisfies the linearized equations for unforced steady geostrophic motion. This implies that if the ocean basin is laterally bounded and contains no closed geostrophic contours, the second order Lagrangian mean velocity vanishes everywhere.     

The effects of sliding velocity on the frictional and physical properties of heated fault gouge

The frictional properties of a crushed granite gouge and of gouges rich in montmorillonite, illite, and serpentine minerals have been investigated at temperatures as high as 600°C, confining pressures as high as 2.5 kbar, a pore pressure of 30 bar, and sliding velocities of 4.8 and 4.8×10^–2 m/sec. The gouges showed nearly identical strength behaviors at the two sliding velocities; all four gouges, however, showed a greater tendency to stick-slip movement and somewhat higher stress drops in the experiments at 4.8×10^–2 m/sec. Varying the sliding velocity also had an effect on the mineral assemblages and deformation textures developed in the heated gouges. The principal mineralogical difference was that at 400°C and 1 kbar confining pressure a serpentine breakdown reaction occurred in the experiments at 4.8×10^–2 m/sec but not in those at 4.8 m/sec. The textures developed in the gouge layers were in part functions of the gouge type and the temperature, but changes in the sliding velocity affected, among other features, the degree of mineral deformation and the orientation of some fractures.     

套管井应力集中诱导井周波速各向异性的研究

针对在套管井中应用正交偶极声测井检测地层各向异性和确定异常构造应力的需要, 本文通过求解水平构造应力作用下套管井的应力场分布,应用声弹性理论说明应力集中对套管井井周弹性波速空间分布的影响,分析了波速空间分布对加套管后的正交偶极各向异性声测量的影响.井孔、套管、水泥环和地层系统的复杂性改变了原裸眼井情况地层中的应力场分布,使应力集中的范围明显缩小到井眼附近.对应不同方位径向偏振横波的交叉点向井孔附近移动.横波波速空间分布的方位极值规律发生变化,但纵波波速空间分布的方位极值规律不变,仍能提供最大远场构造应力施加的方向.     

涪陵地区井下页岩岩芯裂缝体密度与声学性质关系实验研究

本研究对涪陵地区井下产气的龙马溪组页岩岩芯,采用三轴压机压裂制造裂缝,用工业CT扫描压裂前后岩芯,应用图像识别技术统计出裂缝体密度,又用超声脉冲透射法测定样品破裂前后裂缝方向上的纵波、单偏振方向与裂缝不同夹角的横波,来研究裂缝对页岩岩芯声学性质的影响.实验结果表明：压裂后样品的纵波速度略微降低,只有含较多内部裂隙的150#样品纵波速度减小幅度明显.压裂前后样品的纵波波形差别不大,纵波主频随裂缝体密度呈下降趋势,即压裂后纵波频谱主频向低频端移动.压裂前横波速度随自身与裂隙方位角变化而变化,与0°和180°相比,在45°和135°时略微减小,在90°时速度降低幅度最为明显并且发生相位反转.典型样品的横波主频随偏振方向与裂缝夹角的增大而逐渐向低频移动;压裂后,横波频谱杂乱,出现多处局部峰值,速度和主频较压裂前更低,平均横波波速随裂缝体密度呈明显减小趋势.平均纵横波速比随裂缝密度呈近线性增加,表明其与裂缝体密度有较强相关性.     

General velocity formula of boundary layer above mobile sediment bed induced by asymmetric waves

Sediment movement in the wave boundary layer above a mobile sediment bed is complex.A velocity formula for the boundary layer is proposed for sheet flow induced by asymmetric waves above a mobile sediment bed.The formula consists of a free stream velocity and a defect function which contains a phase-lead,boundary layer thickness and mobile sediment bed.Phase-lag of sediment movement is considered in the formula for the mobile sediment bed.The formula needs six dependent variables about asymmetric wave and sediment characteristics.Asymmetry effects on parameters(orbital amplitude,roughness height,bed shear stress,and boundary layer thickness)are properly considered such that the formula can yield velocity differences among onshore,offshore,acceleration,and deceleration stages.The formula estimates the net boundary layer velocity resulting from the mobile sediment bed and asymmetric boundary layer thickness.In addition,a non-constant phase-lead also contributes to the net boundary layer velocity in asymmetric oscillatory sheet flow.Results of the formula are as good as that of a two-phase numerical model.Sheet flow transport induced by asymmetric waves,and the offshore net sediment transport rate with a large phase-lag under velocity-skewed waves,can be adequately estimated by the formula with a power sediment concentration function.