Spatial Characteristics and Controlling Factors of the Strike‐slip Fault Zones in the Northern Slope of Tazhong Uplift,Tarim Basin: Insight from 3D Seismic Data

The detailed characteristics of the Paleozoic strike-slip fault zones developed in the northern slope of Tazhong uplift are closely related to hydrocarbon explorations. In this study, five major strike-slip fault zones that cut through the Cambrian-Middle Devonian units are identified, by using 3D seismic data. Each of the strike-slip fault zones is characterized by two styles of deformation, namely deeper strike-slip faults and shallower en-echelon faults. By counting the reverse separation of the horizon along the deeper faults, activity intensity on the deeper strike-slip faults in the south is stronger than that on the northern ones. The angle between the strike of the shallower en-echelon normal faults and the principal displacement zone(PDZ) below them is likely to have a tendency to decrease slightly from the south to the north, which may indicate that activity intensity on the shallower southern en-echelon faults is stronger than that on the northern ones. Comparing the reverse separation along the deeper faults and the fault throw of the shallower faults, activity intensity of the Fault zone S1 is similar across different layers, while the activity intensity of the southern faults is larger than that of the northern ones. It is obvious that both the activity intensity of the same layer in different fault zones and different layers in the same fault zone have a macro characteristic in that the southern faults show stronger activity intensity than the northern ones. The Late Ordovician décollement layer developed in the Tazhong area and the peripheral tectonic events of the Tarim Basin have been considered two main factors in the differential deformation characteristics of the strike-slip fault zones in the northern slope of Tazhong uplift. They controlled the differences in the multi-level and multi-stage deformations of the strike-slip faults, respectively. In particular, peripheral tectonic events of the Tarim Basin were the dynamic source of the formatting and evolution of the strike-slip fault zones, and good candidates to accommodate the differential activity intensity of these faults.     

Spatio-temporal characteristics of acoustic emission during the deformation of rock samples with compressional and extensional en-echelon faults

Introduction By the experimental techniques of acoustic emission (AE) and surface strain observation, a lot of achievements on the study of deformation and fracture process of samples with en-echelon faults has been obtained (Bomblakis, 1973; LIU, et al, 1986; DU, et al, 1989; LI, et al, 1989; ZHANG, FANG, 1989; ZHANG, LI, 1989; MA, et al, 1995a, b; LI, et al, 2000). However, there still exist many problems. For example, most of discussion on the spatio-temporal evolution of microf…     

渤海湾盆地隐性断裂带识别及其地质意义

隐性断裂带是区域或局部应力场、基底断裂体系活动、潜山块体扭动影响下在沉积盆地盖层中产生的断裂趋势带, 它是断裂带的一种类型, 与显性断裂伴生于沉积盆地, 但由于其不具有显性断裂的固有特征, 隐蔽性强而常常被忽略.可以通过以下7个方面有效识别隐性断裂带: ①小型显性构造(小断层、小褶皱、断块)呈雁列式、断续状、错位对称式反映的大型隐性断裂带; ②基底断裂体系活动在沉积盆地盖层中产生的隐性断裂带; ③潜山、凹陷分布形成的线状、调节型或者侧列式隐性断裂带; ④砂体分布反映的隐性断裂带; ⑤油藏排列、分布、走向反映的隐性断裂带; ⑥相干体切片显示的隐性断裂带; ⑦断层叠覆端、末端、深大断裂分段活动等局部应力场变化形成的隐性断裂带.应用上述方法开展渤海湾盆地隐性断裂带识别研究, 综合国内外的调研结果, 建立了隐性断裂带的类型划分方案体系并阐述了不同级别构造单元中隐性断裂带的类型特征.研究表明, 隐性断裂带具有多方面的地质意义, 可以作为调节构造带调节盆地不均匀伸展活动, 分隔凹陷、隆起等构造单元; 控制盆地沉积相带发育分布, 影响断陷湖盆砂体的展布范围; 控制圈闭组合排列、改造输导体系, 形成串珠状、带状油气富集区; 深断裂活动触发地震的过程中会在地表形成隐性断裂带, 因此, 隐性断裂带的识别和分析具有现实意义.      

The Interrelationship of Micro-Meso and Macroscopic Structures on the Western Limb of the Hazara Kashmir Syntaxis, Pakistan

Detailed micro-meso to macroscopic structural analyses reveal two deformation phases in the western limb of the Hazara-Kashmir Syntaxis(HKS). Bulk top to NW shearing transformed initially symmetrical NNE-SSW trending meso to macroscopic folds from asymmetric to overturned ones without changing their trend. Sigmoidal en-echelon tension gashes developed during this deformation,that were oblique to bedding parallel worm burrows and bedding planes themselves. Strain analyses of deformed elliptical ooids using the R_f/φ method constrain the internal strain patterns of the NNE-SSW structures. The principal stretching axis(S_3) defined by deformed elliptical ooids is oriented N27°E at right angles to WNW-ESE shortening. The deformed elliptical ooids in sub-vertical bedding vertical planes contain ooids that plunge ~70° SE due to NW-directed tectonic transport. Finite strain ratios are1.45(R_(xy)) parallel to bedding plane and 1.46(R_(yz)) for the vertical plane. From these 2D strain values, we derive an oblate strain ellipsoidal in 3D using the Flinn and Hsu/Nadai techniques. Strains calculated from deformed elliptical ooids average-18.10% parallel to bedding and-18.47% in the vertical plane.However, a balanced cross-section through the study area indicates a minimum of~-28% shortening.Consequently, regional shortening was only partially accommodated by internal deformation.     

雁列式断层组合变形过程中的声发射活动特征

着重研究拉张或挤压型雁列式断层标本变形过程中声发射(简称AE，下同)的时空演化特征. 结果表明，预置构造对AE空间分布格局具有较强的控制作用，随着差应力的增加，AE首先在两个端点附近丛集，之后向两端点连线附近集中，出现明显的破裂局部化现象，较大事件还通常集中于某一端点附近反复发生. 前期微破裂丛集图象指示后期宏观破裂的扩展方向及扩展范围. 拉张和挤压型雁列区宏观破裂方向分别与轴向应力方向垂直和平行. 雁列式断层标本变形过程中，破裂前的弱化阶段相对较长、弱化过程明显. 微破裂事件累积频次指数增长可能是系统失稳前的典型征兆之一，而雁列区宏观破裂之后，AE数量逐渐减少、应变释放相对减弱. 摩擦滑动过程中，大的粘滑失稳前未见有AE活动前兆性的增强过程.雁列区的b值变化在失稳前显示趋势性降低——快速回升这一典型的变化过程，b值降低一般发生在差应力增强过程之中，并有可能延续至弱化阶段，而快速回升则一般发生在破裂失稳前的短时期内. 对比研究表明，构造差异所导致的b值差异远大于b值随差应力的增加而产生的变化量，而对同一构造标本，力学状态的改变会导致AE序列时序特征的急剧变化，较高的加载速率对应较高的应变能释放及明显的低b值. 先期破碎带由于较低的破坏强度，其对差应力的微小变化具有特殊敏感性，从而成为源、兆分离、窗口或敏感点效应等地震活动性前兆现象的一种可能的原因.      

雁列构造是走滑断层存在的充分判据?--来自平面砂箱模拟实验的启示

多年来 ,雁列构造被作为走滑作用的结果、并得到物理模拟实验模型的支持 ,通常作为走滑断层的判据加以运用。本文根据针对黄骅盆地所设计的曲折边界基底均匀伸展模型和针对焉耆盆地所设计的基底均匀收缩斜向挤压模型的砂箱实验结果 ,给出了雁列构造另外的成因解释。认为雁列构造的成因并非局限于基底走滑作用 ,基底均匀变形条件下的斜向伸展或斜向挤压作用均可形成雁列构造 ,因此雁列构造不能作为走滑断层存在的充分判据。     

Effect of fault jogs on frictional behavior: An experimental study

Studying the effect of geometrically irregular bodies on the mechanical behavior of fault activity is of significance in understanding the seismic activity along a fault zone. By using rock mechanics ex- periment with medium-scale samples, we have studied the effect of fault jogs, the most common irregularity along fault zones, on frictional behavior. The research indicates that extensional fault jog can be easily fractured because of its low strength and the fractured jog has no obvious resistance to fault sliding, and the micro-fractures occurring in the jog are indicative of stick-slip along the faults. The fault zone containing extensional jogs is characterized by velocity weakening and can be described by rate and state friction law. Compressional fault jog makes fault sliding more difficult because of its high fracturing strength, but the micro-fractures occurring in the tensile areas around fault ends at higher stress level can provide necessary condition for occurrence of stick-slip along the faults before the jog is fractured and thus act as precursors of fault instability. Compression jog can be taken as a stable indicator of fault segmentation until the jog is completely fractured and two faults are linked.     

Structure and deformational character of strike-slip fault zones

Strike-slip fault zones observed either in the field or in model experiments generally consist of several subparallel faults which make these zones complicated in geometry and kinematics. The geometry of a strike-slip fault or shear zone is dependent on arrangement (pinnate or en echelon), on step (left step or right step), and on the rank )smaller faults within larger faults) of the subparallel fault. The relations and interactions of these three factors create a variety of dynamic circumstances and tectonic settings within the strike-slip fault zones. These include pull-aparts in the release area between subparallel faults, push-ups in the jogs where the subparallel faults overlap, and pivotal movements, or rotation, of single faults along the whole fault zone. Each kind of tectonic setting is in itself characteristic, each setting consists of many subtypes, which are controlled chiefly by the geometric parameters of the subparallel faults. One of the most important phenomena revealed in the field work is two different kinds of evolution of strike-slip fault zones: one is the evolution of a zone with a tensile component, which is related to the growth of rock bridges, and the other, of one with a compressional component, which develops by the destruction of rock bridges. In this paper we discuss, on the basis of recent research on four strike-slip fault zones in China, the essential characteristics of strike-slip faults and the possible causes of the observed structural phenomena. Attention is focussed on the deformation, development, and distribution of horizontal displacements within strike-slip fault zones.     

大港歧口沿岸带前第三系构造体系探讨

大港歧口沿岸带位于太行山基底和鲁西基底接触的断裂带上--聊兰断裂北延段,沿海岸线呈NNE向展布.该带不仅是一个地理界线,而且是一个由基底断裂带控制的前第三系雁列褶皱带和第三系构造转换带.本文从分析区域构造背景入手,详细探讨了该带前第三系构造体系特征及其形成和演化过程.大港歧口沿岸带前第三系雁列褶皱带在平面上是由一系列NE向左阶排列的褶皱组成的左阶雁列构造,垂向上具有正花状断裂组合特征;是在印支期NEE向大型舒缓隆起的背景上,受燕山早期(晚三叠世到中侏罗世)深断裂的左旋压扭作用和燕山晚期的走滑作用形成,并在后期受到了喜马拉雅期伸展裂陷作用的强烈改造.     

塔中隆起NNE向走滑断裂特征及形成机制

为了确定塔中隆起NNE向走滑断裂特征及形成机制,利用构造要素相关性分析及构造解析方法,通过对二维和三维资料的解释,揭示了走滑断裂的构造变形特征,确定了走滑断裂的形成机制。NNE向走滑断裂在地震剖面上表现为压扭和张扭在垂向上叠加的特点,其形成演化主要经历了中奥陶世末压扭和晚志留世—中泥盆世张扭两个阶段。先存基底软弱带和塔里木板块周缘造山带的演化共同控制了这套走滑断裂的形成。中奥陶世末,塔里木板块南缘洋盆俯冲闭合产生的近南北向挤压应力斜向作用于NNE向的基底软弱带之上,导致断裂上部地层被撕裂产生走滑分量,从而形成了北东向的左旋走滑断裂系统,同时,来自塔里木板块西北缘的挤压应力垂向作用于走滑断裂上,导致NNE向走滑断裂发生压扭变形。晚志留世—中泥盆世,塔里木板块南缘的挤压应力继续斜向作用于NNE向走滑断裂之上导致其继续发生走滑变形,同时,来自塔里木盆地西北缘的NW向伸展应力垂向作用于走滑断裂上,导致NNE向走滑断裂发生张扭变形。