Sheath fold morphology in simple shear     

《Journal of Structural Geology》2013

Sheath folds are highly non-cylindrical structures often associated with shear zones. We investigate the formation of sheath folds around a weak inclusion acting as a slip surface in simple shear by means of an analytical model. We present results for different slip surface orientations and shapes. Cross-sections perpendicular to the shear direction through the sheath fold display closed contours, so called eye-structures. The aspect ratio of the outermost closed contour is strongly dependent on the initial slip surface configuration. The center of the eye-structure is subject to change in height with respect to the upper edge of the outermost closed contour for different cross-sections perpendicular to the shear direction. This results in a large variability in layer thickness across the sheath fold length, questioning the usefulness of eye-structures as shear sense indicators. The location of the center of the eye structure is largely invariant to the initial configurations of the slip surface as well as to strain. The values of the aspect ratios of the closed contours within the eye-pattern are dependent on the strain and the cross-section location. The ratio (R′) of the aspect ratios of the outermost closed contour (R_yz) and the innermost closed contour (R_y′z′) shows values above and below 1. R′ shows dependence on the slip surface shape and orientation but not on the number of involved contours. Using R′ measurements to deduce the bulk strain type may be erroneous.  相似文献   

薄覆盖层地区隐伏断层及其上断点探测的地震方法技术——以废黄河断层为例   总被引：8，自引：0，他引：8       下载免费PDF全文

顾勤平  康清清  许汉刚  刘建达  李大虎  聂碧波 《地球物理学报》2013,56(5):1609-1618

通过在同一条测线上应用三种不同地震勘探手段(共偏移距地震反射法、横波反射法与高分辨率折射法)联合反演的方法,获得了测线控制地段内废黄河断层的确切位置、上断点埋深以及速度分布图像.探测结果表明:在薄覆盖层地区的断裂调查中,上述三种技术手段的联合反演要比单独使用其中任何一种手段更加可靠,并能从不同角度查明断层的位置、性质及其特征,为钻孔联合剖面位置的布设和钻孔深度的设计提供地震学依据.经高精度钻孔联合地质剖面证实,三种地震勘探方法反演得到的主要地层界面和构造特征都与钻孔联合地质剖面吻合较好.试验表明了上述三种地震勘探方法在基岩面埋深较浅地区联合反演的可行性以及地震勘探与钻孔联合地质剖面相结合的工作方法的有效性.  相似文献   

Systematic changes in orientation of linear mylonitic fabrics: An example of strain partitioning during transpressional deformation in north Golpaygan,Sanandaj–Sirjan zone,Iran     

《Journal of Asian Earth Sciences》2014

Kilometer-scale, shallowly dipping, NW-striking top-to-the NE reverse and dextral strike-slip shear zones occur in metamorphic rocks of north Golpaygan. These metamorphic rocks are exposed at the NE margin of the central part of the Sanandaj–Sirjan zone in the hinterland of the Zagros orogen. NW-striking top-to-the NE normal shear zones were also found in a small part of the study area. Structural evidence of three deformation stages were found. Pre-mylonitization metamorphic mineral growth happened during D₁. The main mylonitization event was during the D₂ deformational event, following coaxial refolding, synchronous to retrograde metamorphism of amphibolite to greenschist facies in the Late Cretaceous–Paleocene, and before D₃ folding and related mylonitization. We documented the systematic changes in the orientations of D₂ linear fabrics especially stretching lineations and superimposition relations of structures. It is concluded that the dextral strike-slip and dip-slip shear zones were coeval kinematic domains of partitioned dextral transpression. The shallowly dipping reverse and strike-slip shear zones are compatible with partitioning in a very inclined transpressional model. Fabric relations reflect that the top-to-the NE normal shear zones were not produced during deformation partitioning of inclined dextral transpression. The Late Cretaceous–Paleocene strain partitioning was followed by later N–S shortening and NE-extension in the north Golpaygan area.  相似文献   

Shear behaviour of fractured rock as a function of size and shear displacement     

A.A. Giwelli  K. Sakaguchi  A. Gumati  K. Matsuki 《Geomechanics and Geoengineering》2014,9(4):253-264

This paper presents laboratory results regarding the shear behaviour of an artificial tensile fracture generated in granite. We used a direct shear rig to test fractures of different sizes (from 100 mm to 200 mm) under various shear displacements up to 20 mm and cyclic shear stresses with constant normal stress of 10 MPa. To determine the evolution of surface damage and aperture during shear, cyclic loading was performed at designated shear displacements. These changes in the surfaces topography were measured with a laser profilometer ‘non-contact surface profile measurement system’. In addition, changes were also measured directly by using pressure-sensitive film.

The results showed that the standard deviation (SD) of the initial aperture of the sheared fracture significantly increases with both shear displacement and size, which result in an increase in the non-linearity of the closure curve (since the matedness of the fracture surfaces decreases with shear displacement). Therefore, we concluded that shear dilation is not only governed by the surfaces sliding over each other, but is also strongly influenced by the non-linearity of closure with shear displacement. Furthermore, while the shear stiffness of the fracture during the initial stage decreases with fracture size, it increases with fracture size in the residual stage. This can be attributed to the fact that only small asperities with short wavelengths were mainly damaged by shearing. Moreover the result showed that the damaged zones enlarge and localise with shear displacement, and eventually tend to form perpendicular to the shear displacement.  相似文献   

倾斜裂缝地层qP波方位反射系数椭圆特征研究     

王顺昌  田景春  贾瀛  李春鹏  林小兵 《物探化探计算技术》2014,(4):452-457

倾斜定向排列裂缝地层可以等效为TI介质,根据TI介质弹性波反射透射方程,模拟了上覆各向同性泰勒岩/下伏含有倾斜裂缝的奥斯汀白垩岩模型qP波方位反射系数。通过将qP波方位反射系数拟合成椭圆,研究了裂缝密度、裂缝倾向、裂缝倾角与椭圆参数的关系。研究发现,随着裂缝密度增大椭圆扁率也在增大,裂缝倾向与椭圆中心点方位相差180°,裂缝倾角与椭圆中心点到坐标原点距离存在一定的对应关系。本研究可以为预测倾斜裂缝地层提供一定的理论支撑。  相似文献   

广西龙胜县柚子坪铅锌矿断裂构造控矿特征及成因探讨     

周宇  李刚  孔凡全  汤静如  黄伟纯 《云南地质》2014,(1):151-155

柚子坪铅锌矿的主要矿体是受F1断裂控制的脉状矿床,其单脉的成矿构造可分为剪切带型与破碎带型两种类型.破碎带型矿脉多呈不规则状,囊状,空间分布与断裂破碎带一致,矿化不均匀且品位低;剪切带型矿脉多呈透镜状,其成矿构造具有平行复脉、脉中脉及矿液压裂等特征,矿化较富集且品位高.工业矿体是由多个破碎带型或剪切型单脉组成的脉群.认为F1断层既是导矿构造,又是储矿构造,多期次的构造运动是形成上述构造特征的主要原因.  相似文献   

复式断陷边界控陷断层生长特征及油气地质意义——以松辽盆地长岭早白垩世复式断陷群东部为例     

王有功  吕延防  付广  孙永河  李鑫 《地质学报》2014,88(9)

在陆内裂陷盆地中,复式断陷的边界控陷断层具有分段生长的特征,通过古断距回剥技术利用最大断距相减法,对松辽盆地长岭早白垩世复式断陷群东部的5个断陷边界控陷断层形成演化历史进行恢复。得到各边界控陷断层形成均经历"孤立分段"—"软连接"—"硬连接"3个演化阶段,最终形成一条统一的边界控陷断层,即沿边界控陷断层走向多个次级断陷复合最终形成统一的断陷特点。但各个边界控陷断层分段生长演化历史具有差异性。这对复式断陷内油气聚集成藏具有十分重要的地质意义:边界控陷断层的分段生长控制复式断陷的复合时期,进而控制着不同时期有效烃源岩的分布范围;边界控陷断层分段生长的连接部位对火山岩与碎屑岩储层发育均有控制作用;各个次级断陷在复合过程中形成的古隆起往往是油气聚集的有利部位。  相似文献   

Development of quartz c-axis crossed/single girdles under simple-pure shear deformation: Results of visco-plastic self-consistent modeling     

《Journal of Structural Geology》2014

Quartz c-axis fabrics are widely used to determine the shear plane in ductile shear zones, based upon an assumption that the shear plane is perpendicular to both the central segment of quartz c-axis crossed girdle and single girdle. In this paper the development of quartz c-axis fabric under simple-pure shear deformation is simulated using the visco-plastic self-consistent (VPSC) model so as to re-examine this assumption. In the case of no or weak dynamic recrystallization, the simulated crossed girdles have a central segment perpendicular or nearly perpendicular to the maximum principal finite strain direction (X) and the XY finite strain plane, and at a variable angle relative to the imposed kinematic framework that is dependent on the modeled flow vorticity and finite strain. These crossed girdles have a symmetrical skeleton with respect to the finite strain axes, regardless of the bulk strain and the kinematic vorticity, and rotate in a way similar to the shear sense with increasing bulk strain ratio. The larger the vorticity number the more asymmetrical their legs tend to be. In the case of strong dynamic recrystallization and large bulk strain, under simple shear the crossed girdle switches into single girdles, sub-perpendicular to the shear plane, by losing the weak legs. The numerical results in our models do not confirm the above-mentioned assumption.  相似文献   

On the heat transfer coefficient between rock fracture walls and flowing fluid     

《Computers and Geotechnics》2014

Two analytical solutions are derived to model the heated flow-through experiments for granite fractures in the literature. The first model, which assumes an identical/continuous temperature between the bulk fluid and fracture surfaces, represents an upper bound solution of water temperature in rock fractures. The second model including the empirical parameter of heat transfer coefficient is used to calculate the average heat transfer coefficient based on the available experimental data. The obtained heat transfer coefficients are smaller than that from the thermal boundary layer theory for flat plates, but larger than the previous estimates. A power function is fitted to describe the relation between heat transfer coefficient and flow velocity. Both models show that water temperature increases non-linearly along fracture plane.  相似文献   

DEM–SPH simulation of rock blasting     

《Computers and Geotechnics》2014

A numerical model is proposed for the simulation of rock blasting. A bonded particle system is utilized to mimic the behavior of rock. The particles interact at the contact points through normal and shear springs to simulate rock elasticity. To withstand the deviatoric stresses, the particles are glued to each other. If the applied force exceeds the contact strength, local failure occurs and microcracks are developed in the synthetic rock. For simulation of gas flow, the smooth particle hydrodynamic method is implemented. The interaction of gas particles with the rock grains is assumed to follow a perfect plastic collision model in which the initial momentum of the colliding particles is preserved. A detailed examination of the interaction of gas with blast hole is investigated. It is shown that the proposed hybrid model is capable of simulating the induced shock waves in the gas together with wave propagation in the rock material. The model successfully mimics crack propagation in rock. In particular, the crushed zone around the borehole, radial cracks, and surface spalling are all captured successfully. The results of numerical analysis suggest that gas–rock interaction can, in fact, generate a few successive compressive waves in the rock specimen, causing further extension of radial cracks with time as the weaker secondary and tertiary waves interact with the crack tips.  相似文献