Analysis Method for Predicting Strain in Interior Beds and Sub-Resolution Faults from Area Balance Theory in Extensional Basins

Extensional basins include mainly grabens and half grabens displaced along a lower detachment. Based on area balance theory, there is a linear relationship between a height of regional and the lower detachment h on the outside of the basin and “lost area S“ from the regional in the basin. The pre-growth beds above lower detachment are of the same extensional displacement so that an “S-h diagram“ can be used to determine the depth to lower detachment and to calculate the total extensional displacement of the beds above the lower detachment. The extensional displacement is dominated by the heave of various scale normal faults. The displacement of obvious faults can be immediately figured out from the measured bed-length. The requisite extension calculated by area balance is the layer-parallel strain, which could be accommodated by displacement on sub-resolution faults. Accordingly, the layer-parallel strain can help us predict the magnitude and distribution of sub-resolution faults on the basis of analysis of the structural style and rheological behavior.     

用面积平衡原理预测伸展断陷盆地中岩层内部应变及亚分辨正断层的方法

大多数地堑和半地堑是由深度近水平的拆离正断层控制的。根据面积平衡原理,这些伸展断陷盆地岩层的区域基准面至拆离断层面高度（h）与其损失面积（S）呈线性比例。拆离断层之上的盆地基底岩层的水平伸展量相同,因此,用“S－h图解法”可以确定拆离断层深度,并能在此基础上计算出岩层的总水平伸展量。伸展盆地中的总水平伸展量主要是由不同尺度的正断层的水平离距体现出来的。可观测解释的断层的水平位移可以通过测量盆地宽度、岩层长度等直接得到。用剖面面积平衡方法可计算出盆地各岩层的平行岩层面的应变,其中相当部分是由在观测尺度上不能直接解释出来的“亚分辨正断层”的小尺度位移造成的。因此,在分析伸展断陷盆地的构造样式、岩层力学性质基础上,有可能对计算得到的平行岩层的伸展应变进行合理评估,进而可以定量地预测“亚分辨正断层”的密度和可能的分布部位。     

The geometry of planar domino-style normal faults above a dipping basal detachment

Geometrical analysis of planar domino-style normal faults rooted into a dipping basal detachment fault allows derivation of equations which relate: (1) horizontal extension within the upper plate; (2) dip of the detachment; (3) final fault dips; (4) rotation that faults and beds undergo; and (5) net slip on domino-style faults. Past geometrical models have focused on extremely idealized and non-unique geometries, in which domino-style faults are parallel and similar cut-off points are all at the same elevation after faulting. This corresponds to evenly spaced domino-style faults above a horizontal detachment. Considering non-parallel faults and dipping detachments introduces unique geometries, which allows calculation, for example, of permissible depth ranges to the detachment. Horizontal extension varies significantly: (1) with dip of the detachment; and (2) for synthetic and antithetic cases, in which the domino-style faults dip in the same or opposite direction, respectively, as the detachment. When other factors (e.g. rotation and fault dips) are held constant, horizontal extension greatly increases for moderate detachment dips and moderately decreases for antithetic detachment dips, as compared to the horizontal detachment case. This is important because the synthetic case has been widely reported.     

Relay structures in a Lower Permian basement-involved extension system,East Greenland

Extensional relay structures are described as offset listric faults having the same subhorizontal detachment in depth. The extension along one fault is transferred or relayed across a relay ramp defined between the tip-lines of the offset faults. The relay ramp interconnects the hangingwall and the footwall during deformation. An example of a crystalline basement-involved symmetrical relay system is described from the Lower Permian in the Karstryggen area, East Greenland.     

Reverse drag revisited: Why footwall deformation may be the key to inferring listric fault geometry

Although reverse drag, the down warping of hanging wall strata toward a normal fault, is widely accepted as an indicator of listric fault geometry, previous studies have shown that similar folding may form in response to slip on faults of finite vertical extent with listric or planar geometry. In this study we therefore seek more general criteria for inferring subsurface fault geometry from observations of near-surface deformation by directly comparing patterns of displacement, stress, and strain around planar and listric faults, as predicted by elastic boundary element models. In agreement with previous work, we find that models with finite planar, planar-detached, and listric-detached faults all develop hanging wall reverse-drag folds. All of these model geometries also predict a region of tension and elevated maximum Coulomb stress in the hanging wall suggesting that the distribution and orientation of near-surface joints and secondary faults may also be of limited utility in predicting subsurface fault geometry. The most notable difference between the three models, however, is the magnitude of footwall uplift. Footwall uplift decreases slightly with introduction of a detachment and more significantly with the addition of a listric fault shape. A parametric investigation of faults with constant slip ranging from nearly planar to strongly listric over depths from 1 to 15 km reveals that footwall fold width is sensitive to fault geometry while hanging wall fold width largely reflects fault depth. Application of a graphical approach based on these results as well as more complete inverse modeling illustrates how patterns of combined hanging wall and footwall deformation may be used to constrain subsurface fault geometry.     

南海北部珠江口盆地中段伸展构造模型及其动力学

位于南海北部大陆边缘上的珠江口盆地发育NNE向、NE向、NW向、近EW向等多组基底断裂,盆地结构复杂,并表现出明显的时空差异性。本文基于珠江口盆地中段地震资料解释的构造样式的变化推断地壳中存在一条向南缓倾斜、呈坡坪式形态的拆离断层,古近系构造属于这条拆离断层上盘的伸展构造系统。北部的西江凹陷属于拆离断层伸展构造系统的头部,凹陷边界正断层铲式断层面形态向深层延伸并收敛在拆离断层面上,凹陷表现为半地堑“断陷”样式;中部的番禺低隆起对应于拆离断层的低角度断坪部位,拆离断层上盘断块的伸展位移导致两侧的恩平组超覆在低隆起上;南部的白云凹陷位于拆离断层的深部断坡部位,充填的文昌组和恩平组表现为“断坳”或“坳断”样式;南部隆起位于拆离断层深部断坪部位,其上盘发育的分支断层控制着荔湾凹陷古近系、新近系的发育并使之表现为复杂的断陷断坳构造样式。该模型强调拆离断层上盘与下盘、不同地壳结构层均发生不同程度的伸展变形,且伸展变形方式、应变量等存在时空差异,而拆离断层正是不同构造单元、不同地壳构造层之间的调节性构造面。总体上,拆离断层上盘以脆性伸展构造变形为主,分支断层控制不同构造单元古近纪的构造演化,下盘则是以韧性伸展变形为主,并拖曳上盘发生不均一的伸展应变;西江凹陷的伸展应变量大于拆离断层下盘的伸展应变量,白云凹陷的伸展应变量则小于拆离断层下盘的伸展应变量。以西江凹陷北部边缘的NE向铲式正断层为头部的拆离断层控制了文昌组沉积,但在恩平组沉积期被近EW向高角度正断层切割破坏而被遗弃,拆离断层系统的头部由西江凹陷北部边缘迁移至番禺低隆起。盆地结构及断裂系统的时空差异性受盆地基底先存构造、地壳与岩石圈结构及伸展量等多方面因素的影响,但主要是对软流圈流动及岩石圈热结构变化的响应。用软流圈由北西向南东流动拖曳上覆岩石圈发生伸展变形的动力学模型能合理地解释珠江口盆地中段古近系构造的形成和演化。     

控制中国东部中-新生代盆地的铲形断裂构造

根据断裂延伸长度、切割深度、断裂的活动强度和断裂产生的前后序次及其对盆地的控制作用不同,分为基底断裂和同生断裂。 基底断裂控制着盆地或者盆地内二级构造单元的边界。同生断裂明显地控制了盆内的沉积作用,包括岩相、厚度变化等。 在中国东部中、新生代盆地形成和发展过程中,上述两类断裂不仅分布广,而且数量多。在形态特征上,一般断层面弯曲朝上,并随深度增加而变缓,都具有正滑性质,所以统称为铲形断裂。     

南海北部新生代盆地断裂系统及构造动力学影响因素

利用地震资料、油气勘探资料分析了南海北部大陆边缘珠江口-琼东南新生代盆地断裂系统的时空差异及动力学成因机制.珠江口-琼东南盆地古近系裂陷构造层以NE向、近EW向基底正断层构成的伸展断裂系统的几何学、运动学沿着盆地走向有明显变化,盆地内部隐伏的区域性和局部的NW向断裂及相关构造变形带构成伸展断裂系统之间的构造变换带.在空间上,区域性的云开、松涛-松南等NW向构造变换带以西为NE-NEE向正断层构成的"非拆离"伸展断层系,以东为NE向正断层、近EW向正断层(走滑正断层)复合而成的拆离伸展断层系.在时间上,古近纪裂陷作用可划分为早(文昌组沉积期)、中(恩平组/崖城组沉积期)、晚(珠海组/陵水组沉积期)3个有明显差异的裂陷期.裂陷早期,盆地西部以平面式正断层控制的简单地堑、半地堑为主,伸展量相对较小,东部则以铲式正断层控制的复式地堑、半地堑为主,伸展量相对大,断层向深部收敛在中地壳韧性层构成拆离的伸展断层系统.裂陷中期,琼东南盆地、珠江口盆地西部断裂具有继承性活动特点,珠江口盆地东部发育NWW-EW向伸展断层,并向深层切割早期浅层拆离断层,形成深层拆离伸展断层系统,而沿着云开构造变换带发育反转构造.裂陷晚期,琼东南盆地、珠江口盆地西部断裂具有活动性减弱特点,琼东南盆地东部发育NWW-EW向伸展断层,形成深层拆离伸展断层系统,而沿着琼中央构造变换带发育反转、走滑构造.珠江口-琼东南盆地不同区段断裂系统及其构造演化的差异性受盆地基底先存构造、地壳及岩石圈结构及伸展量等多方面因素的影响,拆离伸展断层系统与发育NWW向"贯穿"断裂的基底构造薄弱带、现今地壳局部减薄带相关,南海扩展由东而西的迁移诱导北部大陆边缘块体沿着先存NW向深大断裂发生走滑旋转是导致变换构造带两侧差异伸展的动力学原因,应力场及岩石圈热结构变化是引起拆离断层深度变化的重要因素.     

How normal faulting and sedimentation interact to produce listric fault profiles and stratigraphic wedges

In a series of scale-experiments, we generated listric normal faults by extending models composed of colored sand layers deposited at regular time intervals throughout deformation during syntectonic sedimentation. Progressive bulk extension along a single set of faults caused domino-type tilting of fault blocks. Underlying tilted faults propagated upwards, with constant dips into newly sedimented layers. Hence fault profiles become progressively more listric. Tilting of the free surface resulted in asymmetrical depressions and in fan-shaped deposits.Stepwise or continuous geometric models of domino-tilting and synchronous sedimentation yield the same structural and stratigraphic features as observed in the sand models. The continuous geometric model shows that a critical parameter governing fault curvature is the ratio R between rates of bulk strain and sedimentation.Both types of models reveal that synchronous sedimentation and bulk extension are capable by themselves of generating listric normal faults.     

Structural characteristics of the Suez rift margins

Field study of the Hadahid Block (the eastern margin of the central half-graben of the Suez rift) indicates two listric normal faults at its eastern and western boundaries, the rift-bounding fault and the Hadahid Fault, respectively. These faults were affected by two episodes of movement. The earlier movement (at the initial, Neogene rift opening) led to equal displacements on the two faults whereas the later movement (at the mid-Clysmic event, l7 Ma ago) caused the Hadahid Fault to bound the deep part of the central half-graben. A similar conclusion is also reached for the western margin of the southern half-graben of the rift (Esh El Mellaha and Zeit Blocks). The two listric faults bounding the margin blocks in these two oppositely tilted half-grabens (Hadahid and Esh El Mellaha Blocks) join at depth into a ramp-flat detachment. This geometry of the rift-bounding faults represents an intermediate stage in the evolution of rift basins. It is preceded by the early rifting stage where extension is less and oppositely tilted half-grabens are formed (e.g. the ancestral Red Sea-Gulf of Suez rift). Increased extension at later stages leads to the prevailance of one system of detachment instead of oppositely dipping detachments of adjacent half-grabens. The central and southern Red Sea have perhaps had this geometry before the onset of seafloor spreading.     

中国东部拉张区正断层的几何学和运动学特征与盆地动力学过程

中国东部拉张区变形期间发育的正断层,按其几何形态和运动学特征的差异,可确定为四种类型:1.非旋转平面状正断层;2.旋转平面状正断层;3.犁状正断层;4.低角度正断层或滑脱断层。它们及其组合控制着沉积盆地的外部轮廓、规模大小、沉积建造类型和内部变形以及油气构造的形成。本文综合分析了各类正断层特征及其演化过程,认为不同层次、不同尺度和不同类型正断层的发育过程,也是中国东部地壳拉伸变薄及沉积盆地的形成过程。     

Listric versus planar normal fault geometry: an example from the Eisenstadt-Sopron Basin (E Austria)

In a gravel pit at the eastern margin of the Eisenstadt-Sopron Basin, a satellite of Vienna Basin (Austria), Neogene sediments are exposed in the hanging wall of a major normal fault. The anticlinal structure and associated conjugated secondary normal faults were previously interpreted as a rollover anticline above a listric normal fault. The spatial orientation and distribution of sedimentary horizons and crosscutting faults were mapped in detail on a laser scan of the outcrop wall. Subsequently, in order to assess the 3D distribution and geometry of this fault system, a series of parallel ground penetrating radar (GPR) profiles were recorded behind the outcrop wall. Both outcrop and GPR data were compiled in a 3D structural model, providing the basis for a kinematic reconstruction of the fault plane using balanced cross-section techniques. However, the kinematic reconstruction results in a geologically meaningless normal fault cutting down- and up-section. Additionally, no evidence for a weak layer serving as ductile detachment horizon (i.e. salt or clay horizon) can be identified in stratigraphic profiles. Instead, the observed deflection of stratigraphic horizons may be caused by a displacement gradient along a planar master fault, with a maximum displacement in the fault centre, decreasing towards the fault tips. Accordingly, the observed deflection of markers in the hanging wall—and in a nearby location in the footwall of the normal fault—is interpreted as large-scale fault drag along a planar fault that records a displacement gradient, instead of a rollover anticline related to a listric fault.     

黄骅坳陷孔南地区新生代断裂特征及其与油气关系

黄骅坳陷孔南地区新生代盆地演化经历了断陷期、断坳期及坳陷期。盆地内部发育复杂断裂系统,根据断层活动特征可以分为沧东伸展断裂系统与徐西右旋走滑断裂系统。沧东断层剖面上具有铲式正断层特征,向深部滑脱,控制了孔南地区的构造变形;徐西断层可以看作是其上盘上的次级断层。在孔店组沉积期,沧东断层与徐西断层均表现出伸展正断层的特征,控制了其上盘孔店组沉积。在沙河街组三段沉积期,受基底断层右旋走滑影响,徐西断层及其上盘分支断层表现出右旋走滑特征。在伸展与走滑的共同作用下,在孔南地区中北部聚集了丰富的油气。     

东濮凹陷伸展连锁断层系统及其演化作用

东濮凹陷NNE向的主干基底断层向深部延伸与深层的拆离滑脱断层衔接在一起,与诱导出的调节断层以不同的方式连接,构成东濮凹陷的伸展连锁断层系统。东濮凹陷不同区段的连锁断层形态表现出不同的几何学和运动学特征。北区兰聊主断层面表现为相对较缓的平面式形态,伸展连锁断层系统总体上为多米诺式半地堑系。中区伸展连锁断层系统总体上表现为大型铲式正断层上盘的一个不对称的地堑。南区兰聊主断层面表现为坡坪式形态,断陷结构相对复杂。东濮凹陷伸展连锁断层系统的演化大体分为4期,不同区带伸展连锁断层系统演化模式不同,对古近系沉积和石油地质条件有较大的影响。     

黔东北燕山期构造变形特征及对华南"大塘坡式"锰矿勘查的影响——以普觉锰矿床犁式正断层为例

黔东北地区大地构造位置位于扬子板块西南部,自元古宙以来经历了多期次构造变形。不同期次的构造叠加对区内早期形成的沉积型矿产的埋藏和保存产生了重要影响。文章针对黔东北地区燕山期构造变形,采用中小尺度构造解析的方法开展露头尺度的构造样式、叠加关系剖析研究,同时,对研究区广泛发育的犁式正断层及其对南华纪"大塘坡式"锰矿的找矿勘查进行深入探讨。现有勘查成果认为犁式正断层为燕山早期—燕山晚期应力体制转换产物,该类断层倾角随深度增加而渐趋于缓,断距和断层错断区域伴随深度增加而加大,并伴生少量次级陡倾角分支断裂。冷水溪犁式断裂及其分支断裂将贵州松桃普觉超大型锰矿床体切割为多个独立单元,造成锰矿层不连续,且在矿区内形成了大小规模不等的断层错断区域。同时,由于冷水溪断层上盘下降,上盘锰矿体的埋藏深度增加,断层错断区域亦伴随深度加深而加大。对冷水溪犁式断层及其对锰矿体之间关系的分析,有利于深入研究整个黔湘渝地区"大塘坡式"锰矿的埋藏与保存特征,对助推区域上深部锰矿勘查,合理规避勘探风险具有重要的现实意义。     

丽水-椒江凹陷断裂构造运动学

丽水-椒江凹陷是晚白垩世以来发展起来的大陆边缘裂陷盆地.本文利用平衡剖面技术恢复计算了丽水-椒江凹陷不同构造部位各裂陷伸展期的盆地伸展量、伸展系数和伸展率.研究表明:研究区晚白垩世至古新世裂陷作用具有"幕式"渐进发展的特征,可划分为三个裂陷伸展期:早期(晚白垩世)的断陷主要由相对分散、独立的小断陷组成,控制半地堑凹陷的主断层主要以书斜式(domino-style)为主;中、晚期(古新世)的断陷由相互连通的半地堑凹陷组成,其主干断层以犁状(listric)或坡坪状(ramp-flat)正断层为特征.研究区不同构造部位其水平伸展率不同,表现为水平伸展量由南西向北东由大变小的特征,最大伸展期亦表现为由南西向北东变晚的规律.     

Analogue and numerical modeling of normal fault patterns produced due to slip along a detachment zone

In this paper, we investigate normal fault patterns produced by the sliding motion along a gently dipping normal fault by using analogue model tests and numerical modeling. The motivation for this study was offered by microseismic test data that indicate the existence of an active low-angle shear zone at a depth of 9–11 km in the extensional region of high seismic activity of the Gulf of Corinth (Greece). Both modeling techniques seem to support the hypothesis that the system of high-angle normal faults that are responsible for the final asymmetrical graben formation initiate at the tip of the active basal detachment nearest to the free surface. The normal faults propagate upwards with progressive sliding of the inclined basal plane, resulting in a first phase of symmetrical graben configuration that is delimited by a main synthetic fault and an antithetic fault forming a Rankine zone. Subsequent sliding on the inclined base induces a family of secondary antithetic normal faults, which are responsible for the asymmetry of the failure pattern and the diffusive character of deformation in that area. Shear deformation is more intense and localized along the synthetic normal fault than along the antithetic faults. Elaboration on the analogue test results has led to the phenomenological relations among four main parameters that describe the geometry of grabens, namely, (i) the width and (ii) the maximum subsidence of the graben, (iii) the dip angles of the conjugate normal faults, and (iv) the amount of sliding along the low-angle normal fault. However, analogue models do not produce the system of synthetic faults that is observed in the Gulf of Corinth. The effects of both friction angle variation along the detachment base and of the constitutive behavior of the model material on the configuration of the final structural pattern were also studied with a series of numerical continuum models. It was found that (a) the fault pattern of the Gulf of Corinth may be reproduced with either a strain-softening material with low elastic modulus or a constant strength material, and (b) two consecutive grabens, such as those of Gulfs of Corinth and Evia, may also be reproduced by an appropriate combination of variation of dip and frictional properties along the hypothesized detachment zone.     

Basement controls on fault development in the Penola Trough,Otway Basin,and implications for fault-bounded hydrocarbon traps

The Penola Trough is an intensely faulted northwest – southeast-trending half-graben structure. It is bound to the south by the major listric Hungerford/Kalangadoo Fault system. Several large prominent faults observed in the Penola Trough show offset of basement at depth. These basement-rooted faults have exerted significant controls on the geometry of smaller intra-rift faults throughout the entire structural history of the area. Faulting of the basement was initiated during the initial rift event of the Late Jurassic – Early Cretaceous. Faulting first propagated through a pre-existing basement fabric oblique to the north – south extension direction prevalent during this time. This resulted in the formation of the Hungerford/Kalangadoo and St George Faults with a northwest – southeast and north-northeast – south-southwest trend, respectively. A series of east – west-trending basement faults subsequently initiated perpendicular to the north – south extension direction as extensional strain increased in magnitude. Significant displacement along these basement-rooted faults throughout the initial rift event was associated with the formation of a complex set of intra-rift faults. These intra-rift faults exhibit a broadly east – west orientation consistent with the interpreted north – south extensional direction. However, this east – west orientation locally deviates to a more northwest – southeast direction near the oblique-trending St George Fault, attributed to stress perturbation effects. Many of the intra-rift faults die out prior to the end of the Early Cretaceous initial rift event while displacement on basement faults continued throughout. Faulting activity during the Late Cretaceous post-rift fault event was almost exclusively localised onto basement faults, despite a significant change in extension direction to northeast – southwest. A high-density, en échelon array of northwest – southeast-trending fault segments formed directly above the St George Fault and the large east – west-trending basement faults contemporaneously reactivated. Seismic variance data show that post-rift fault segments that are hard-linked to the St George Fault at depth have propagated through near-surface units. Non-basement-linked post-rift fault segments that lie away from the St George basement have not. This suggests that recent fault activity has continued to occur preferentially along basement faults up to relatively recent times, which has significant implications for fault seal integrity in the area. This is empirically validated by our structural analysis of fault-dependent hydrocarbon traps in the area, which shows that partially breached or breached hydrocarbon columns are associated with basement faults, whereas unbreached hydrocarbon columns are not.     

伸展边界方向对伸展盆地正断层走向的影响——来自平面砂箱实验的启示

五种不同边界几何条件的平面砂箱实验模型表明,一个方向的伸展变形可因伸展边界方向的变化形成不同走向的正断层,伸展裂陷盆地中不同走向的正断层并非一定代表不同方向区域构造应力作用、或多期构造变形的结果。伸展裂陷盆地正断层走向受伸展边界走向和构造伸展的方向共同控制,伸展边界的控制力随距离增大而逐渐衰减。伸展边界附近的断层走向主要受伸展边界方向控制,大致反映伸展边界方向。盆地内部断层走向主要受构造伸展方向控制(趋向于垂直构造伸展方向),主要反映构造伸展方向。盆地伸展边界方向的变化可以引起伸展裂陷盆地内部断层走向的转向。因铲式正断层上盘滚动变形产生的正断层,其走向平行于铲式边界断层的走向。     

The Gubbio normal fault (Central Italy): geometry, displacement distribution and tectonic evolution

Normal faults within orogenic belts can be pre-, syn- or post-orogenic features. We studied the Gubbio normal fault (central Italy), which is an example of a pre-orogenic fault reactivated in a post-orogenic stage. The Gubbio Fault is a 22-km-long fault bordering a Quaternary basin and part of an active faults system in the Umbria–Marche region (Central Italy). The interpretation of a set of seismic profiles enables us to reconstruct the fault geometry in detail and to measure displacement and throw distributions along the fault strike. Seismic data indicate that the Gubbio Fault represents an example of multiple reactivation: at least a portion of the fault was active in the Miocene and only a part of the total displacement was achieved in the Quaternary. The reconstruction of the fault geometry at depth shows that the fault is characterised by listric geometry. The fault is also characterised by a bend along strike and structure contours show that this geometry is maintained at depth. As the fault is commonly addressed as presently active, the maximum fault dimensions are correlated to the maximum expected earthquake, and the presence of the fault bend is discussed as a possible barrier to seismic ruptures propagation.