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1.
G. E. Exadaktylos I. Vardoulakis M. C. Stavropoulou P. Tsombos 《Tectonophysics》2003,376(1-2):117-134
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. 相似文献
2.
The NW-dipping Fiery Creek Fault System, located in the northern Mount Isa terrane, comprises numerous sub-parallel faults that record multiple episodes of Palaeo- to Mesoproterozoic movement. Hanging wall wedge-shaped stratal geometries and marked stratal thickness variation across the fault system indicate that the earliest movement occurred during episodic intracontinental extension (Mount Isa Rift Event; ca. 1710–1655 Ma). Reactivation of the fault system during regional shortening and basin inversion associated with the Mesoproterozoic Isan Orogeny (ca. 1590–1500 Ma) resulted in complex three-dimensional hanging wall geometries and highly variable strain in the hanging wall strata along the fault system. This has resulted in the development of discrete hanging wall deformation compartments, that are characterised by different structural styles. High strain compartments are characterised by relatively intense folding and the development of break-back thrusts, whereas low strain compartments are only weakly folded. Variations in hanging wall strain are attributed to selective reactivation of normal fault segments, controlled by the pre-inversion fault dip and lithological contrasts across the faults. Variation of the pre-inversion fault dip is interpreted to have been caused by episodic tilt-block rotation during crustal extension. Moderately dipping faults active early in the Mount Isa Rift Event show the greatest degree of reactivation, whereas younger and steeper normal faults have behaved as buttresses during inversion with strain focussed in zones of upright folding in the hanging wall. 相似文献
3.
AbstractPositive structural inversion involves the uplift of rocks on the hanging-walls of faults, by dip slip or oblique slip movements. Controlling factors include the strike and dip of the earlier normal faults, the type of normal faults — whether they were listric or rotated blocks, the time lapsed since extension and the amount of contraction relative to extension. Steeply dipping faults are difficult to invert by dip slip movements; they form buttresses to displacement on both cover detachments and on deeper level but gently inclined basement faults. The decrease in displacement on the hanging-walls of such steep buttresses leads to the generation of layer parallel shortening, gentle to tight folds — depending on the amount of contractional displacement, back-folds and back-thrust systems, and short-cut thrust geometries — where the contractional fault slices across the footwall of the earlier normal fault to enclose a “floating horse”. However, early steeply dipping normal faults readily form oblique to strike slip inversion structures and often tramline the subsequent shortening into particular directions.Examples are given from the strongly inverted structures of the western Alps and the weakly inverted structures of the Alpine foreland. Extensional faulting developed during the Triassic to Jurassic, during the initial opening of the central Atlantic, while the main phases of inversion date from the end Cretaceous when spreading began in the north Atlantic and there was a change of relative motion between Europe and Africa. During the mid-Tertiary well over 100 km of Alpine shortening took place; Alpine thrusts, often detached along, or close to, the basement-cover interface, stacking the late Jurassic to Cretaceous sediments of the post-extensional subsidence phase. These high level detachments were joined and breached by lower level faults in the basement which, in the external zones of the western Alps, generally reactivated and rotated the earlier east dipping half-graben bounding faults. The external massifs are essentially uplifted half-graben blocks. There was more reactivation and stacking of basement sheets in the eastern part of this external zone, where the faults had been rotated into more gentle dips above a shallower extensional detachment than on the steeper faults to the west.There is no direct relationship between the weaker inversion of the Alpine foreland and the major orogenic contraction of the western Alps; the inversion structures of southern Britain and the Channel were separated from the Alps by a zone of rifting from late Eocene to Miocene which affected the Rhone, Bresse and Rhine regions. Though they relate to the same plate movements which formed the Alps, the weaker inversion structures must have been generated by within plate stresses, or from those emanating from the Atlantic rather than the Tethyan margin. 相似文献
4.
Large earthquakes in strike-slip regimes commonly rupture fault segments that are oblique to each other in both strike and dip. This was the case during the 1999 Izmit earthquake, which mainly ruptured E–W-striking right-lateral faults but also ruptured the N60°E-striking Karadere fault at the eastern end of the main rupture. It will also likely be so for any future large fault rupture in the adjacent Sea of Marmara. Our aim here is to characterize the effects of regional stress direction, stress triggering due to rupture, and mechanical slip interaction on the composite rupture process. We examine the failure tendency and slip mechanism on secondary faults that are oblique in strike and dip to a vertical strike-slip fault or “master” fault. For a regional stress field well-oriented for slip on a vertical right-lateral strike-slip fault, we determine that oblique normal faulting is most favored on dipping faults with two different strikes, both of which are oriented clockwise from the strike-slip fault. The orientation closer in strike to the master fault is predicted to slip with right-lateral oblique normal slip, the other one with left-lateral oblique normal slip. The most favored secondary fault orientations depend on the effective coefficient of friction on the faults and the ratio of the vertical stress to the maximum horizontal stress. If the regional stress instead causes left-lateral slip on the vertical master fault, the most favored secondary faults would be oriented counterclockwise from the master fault. For secondary faults striking ±30° oblique to the master fault, right-lateral slip on the master fault brings both these secondary fault orientations closer to the Coulomb condition for shear failure with oblique right-lateral slip. For a secondary fault striking 30° counterclockwise, the predicted stress change and the component of reverse slip both increase for shallower-angle dips of the secondary fault. For a secondary fault striking 30° clockwise, the predicted stress change decreases but the predicted component of normal slip increases for shallower-angle dips of the secondary fault. When both the vertical master fault and the dipping secondary fault are allowed to slip, mechanical interaction produces sharp gradients or discontinuities in slip across their intersection lines. This can effectively constrain rupture to limited portions of larger faults, depending on the locations of fault intersections. Across the fault intersection line, predicted rakes can vary by >40° and the sense of lateral slip can reverse. Application of these results provides a potential explanation for why only a limited portion of the Karadere fault ruptured during the Izmit earthquake. Our results also suggest that the geometries of fault intersection within the Sea of Marmara favor composite rupture of multiple oblique fault segments. 相似文献
5.
综合运用地震剖面解释结果和构造编图成果,对东海西湖凹陷平湖斜坡带断裂系统按发育规模和形成期次进行分类,分析了断裂系统的平、剖面展布特征,采用古落差法和活动速率法研究了断裂运动学特征,结合区域应力场特征探讨了其成因机制。结果表明,平湖斜坡带断裂系统可划分为4个断裂带,由北至南依次为孔雀亭同向断裂带、武云亭反向断裂带、平湖同向断裂带和平南堑式断裂带。平湖斜坡带以发育多米诺、地堑、梳妆、正牵引等伸展构造样式为主,局部(如平湖同向断裂带)见微弱反转构造。断裂运动学特征研究表明,断裂活动高峰期具有分带性,平湖同向断裂带断层活动性最强,孔雀亭同向断裂带和武云亭反向断裂带次之,平南堑式断裂带最弱。平湖斜坡带断裂系统的发生、发展是应力集中与断层间相互影响共同作用的结果,是对东海陆架盆地构造演化过程的局部响应。 相似文献
6.
Experimental (clay) models of inversion structures 总被引：3，自引：0，他引：3
Experimental modeling is used to study the geometry and evolution of inversion structures. Two main types of inversion structures are analyzed:
1. (1) structures formed by fault-propagation folding; and
2. (2) structures formed by fault-bend folding on listric faults.
Fault-propagation inversion structures initially develop as broad drape folds with possible fault breakthrough during an early extensional phase. Syn-extensional strata deposited in the hanging wall typically thicken away from the fault. Compressional reactivation results in reversal of slip on the master and secondary faults, their rotation to shallower dips, and the development of a compressional fault-propagation fold. Key features of the fault-propagation fold are basinward thickening of syn-extensional units and resulting steep dips of the front limb of the structure. Fault-bend inversion structures initiate as rollover folds within extensional half-graben. Deformation is primarily localized along a system of antithetic faults. Syn-extensional strata typically thicken across the fault but also thin basinward away from the fault. During compression, the extensional rollover folds are folded into compressional fault-bend folds. Key features of this structure are thinning of syn-extensional units into the basin. Inversion of more symmetric graben results in a doubly-convex geometry of syn-extensional units. These observations of bed geometry and thickness provide predictive models for interpreting the geometries of inversion structures in areas of poor data quality. 相似文献
7.
Fault-propagation folds form an important trapping element in both onshore and offshore fold-thrust belts, and as such benefit from reliable interpretation. Building an accurate geologic interpretation of such structures requires palinspastic restorations, which are made more challenging by the interplay between folding and faulting. Trishear (Erslev, 1991; Allmendinger, 1998) is a useful tool to unravel this relationship kinematically, but is limited by a restriction to planar fault geometries, or at least planar fault segments. Here, new methods are presented for trishear along continuously curved reverse faults defining a flat–ramp transition. In these methods, rotation of the hanging wall above a curved fault is coupled to translation along a horizontal detachment. Including hanging wall rotation allows for investigation of structures with progressive backlimb rotation. Application of the new algorithms are shown for two fault-propagation fold structures: the Turner Valley Anticline in Southwestern Alberta, and the Alpha Structure in the Niger Delta. 相似文献
8.
为了研究含油气盆地中断裂对油气成藏与分布的控制作用,在断层侧向封闭机理及影响因素研究的基础上,对反向断裂下盘较顺向断裂上盘更易富集油气的机理进行了定量解释。结果表明,无论是反向断裂还是顺向断裂,均源于断层岩封闭油气,断层岩油气运移方向排替压力是影响其侧向封闭油气能力的主要因素。在断裂埋深、断裂倾角和地层岩性、地层倾角相同的条件下,理论上反向断裂断层岩泥质体积分数大于顺向断裂断层岩泥质体积分数,即反向断裂断层岩油气运移方向排替压力大于顺向断裂断层岩油气运移方向排替压力,反向断裂侧向封闭能力强于顺向断裂侧向封闭能力,造成反向断裂下盘较顺向断裂上盘更易富集油气。歧口凹陷板桥断裂下盘沙一段下部断层岩在反向条件和顺向条件下油气运移方向排替压力的实例研究结果表明,反向条件下较顺向条件下在油气运移方向有更高的排替压力,侧向封闭能力更强,更有利于油气在板桥断裂下盘沙一段储层中富集。 相似文献
9.
3D field data on mesoscale normal faults were collected to examine the geometries and growth of faults in multilayer systems. Observation and analysis of the fractures include the collection of geometric attributes such as fault dips and fault zone thicknesses, detailed mapping in cross-sections and plan views, and the construction of individual and cumulative displacement profiles. Fault zone growth is consistent with a “coherent model” and is strongly influenced by the multilayer system. In the limestone layers, faults grew in several steps, including opening and frictional sliding on 80° dipping segments. Faulting in clay layers was in the form of 40° dipping faults and sub-horizontal faults, the latter being mostly early features developed under the same extensional regime as normal faults and disturbing the fault architecture. The fault zone thickness increases with the limestone thickness and the presence of sub-horizontal faults in clay beds. Numerous connections occur in clay units. The moderate (≈0.08) and low (<0.03) mean displacement gradients in clays and in limestones respectively indicate that the vertical propagation of faults is inhibited in clay layers. Analysis of displacement along fault strike indicates that a 0.08 displacement gradient is associated with the horizontal propagation of fault segments in limestones. According to this value, the fault zones are much longer than expected. It is associated with ‘flat topped’ displacement profiles along some fault segments and connection between segments to form complex fault zones. 相似文献
10.
渤海湾盆地冀中坳陷中区中新生代复合伸展构造 总被引：24，自引：0，他引：24
通过对大量地震剖面的重新解释,并结合盆地的钻探资料及前人研究成果,揭示了冀中坳陷中区中新生代以来先后经历了：①燕山中晚期(J3-K1)与阜平变质核杂岩形成有关的热力伸展,变质核杂岩拱升隆起导致侧向伸展,太行山东缘拆离断层发育并在其下降盘形成同期断陷盆地(保定凹陷);②古近纪(E)区域应力伸展,太行山东缘断裂及其下降盘的保定凹陷具有明显的继承性,并有“早盛早衰”的特点。而中区东部边缘断裂及其控制的沉积洼槽主要发育于该阶段,断裂强烈活动时间相对晚,但持续时间较长;③古、新近纪之间(N／E)重力伸展,区域不均衡隆升导致饶阳凹陷南部发生大型重力滑覆构造,其运动轨迹类似昆虫前行时的“褶曲蠕动”,与经典的重力滑动构造模式有所不同。三期不同性质、不同类型的伸展作用有机相联,彼此影响,并进一步探讨了各类伸展构造的个性特征、形成演化及其盆山耦合的响应关系。 相似文献
11.
Basement-involved structures associated with reverse, vertical and normal faults commonly involve non-parallel shear within a triangular deformation (trishear) zone located on the front limbs of the structures. Deformation within the trishear zone is characterized by shear gradients and an associated decrease in the dips of the beds in stratigraphically higher units. Geometric models suggest that the layer-parallel strain within the trishear zone depends on the type of fault (normal, reverse, or vertical), the dip and throw of the fault, the dip of the anticlinal or synclinal axial surfaces, and the distance of any unit above the initial tip of the trishear zone, located at the basement-sediment contact. At any given location, reverse faults typically show increasing layer parallel shortening, followed by decreasing layer parallel shortening and a transition to extension, with increasing throw. The transition from contraction to extension occurs at lower values of throw for stratigraphically lower units and also for faults with smaller dips. Vertical and normal faults exhibit increasing layer-parallel extension of all units with increasing throw, with larger extension for stratigraphically lower units. Experimental models suggest that the trishear zone can expand with increasing fault throw. The strain within the trishear zones is accommodated largely by secondary faults, which are rotated with progressive deformation. The strain variations in the experiments closely mimic those predicted by the geometric models for reverse, vertical, and normal faults. 相似文献
12.
The ENE-tilted Mesta half-graben contains a 3-km-thick section of Priabonian (Late Eocene) to Oligocene sedimentary and volcanic rocks that rest unconformably on basement metamorphic rocks along its west side. Basal strata dip 50–60° E and dip at progressively lower angles upward, indicating synrotational deposition. The southern part of the half-graben contains nested volcanic caldera complexes, formed during the deposition of the middle part of the sedimentary sequence, which have been rotated by about half the total rotation of the sedimentary succession. The half-graben is bounded on the east by a fault that steepens from more deeply exposed structural levels in the south (8–18° W) to shallower exposed structural levels in the north (70° W) and together with the rotation of Paleogene strata during deposition indicate the Mesta half-graben is underlain by a listric detachment fault, the Mesta detachment. Subhorizontal Middle Miocene strata that unconformably overlie tilted Paleogene strata yield an upper age limit to the extension. West and northwest of the Mesta half-graben are many other NNW-trending NE-tilted Paleogene half-grabens which we suggest are part of an important extended area in SW Bulgaria and eastern Macedonia that lies above one or more west-dipping detachment faults and date the beginning of Aegean extension in the southern Balkan region as at least as old as Priabonian. The Mesta detachment is oblique to the trend of a contemporaneous Paleogene magmatic arc in the southern Balkans and the origin of the detachment is probably related to gravitationally induced spreading of thickened hot arc crust and Hellenic trench roll back. 相似文献
13.
U. Ring 《International Journal of Earth Sciences》1995,84(3):607-625
The results of a lithostratigraphic, tectonic and kinematic study of the Karoo deposits of northern Malawi are reported. The objective of the lithostratigraphic study is to correlate the deposits of the Karoo basins of northern Malawi with the well-known deposits of southern Tanzania, thus establishing a stratigraphic framework through which the timing of faulting can be constrained. The kinematic analysis of faulting constrains the opening direction for the Karoo graben in this area and provides basic data to discuss the Karoo graben development within the regional tectonic framework of south-eastern Africa. The studied adults are defined by moderately to steeply dipping cataclastic zones with a width of up to 15 m and are characterized by an array of slickensided fault surfaces with different orientations and slip directions. In this study, small faults (offset < 10 m) and meso-scale faults (offset > 10 m, but generally not exceeding 30–40 m) have been distinguished. Methods used to analyse the kinematic data include the ‘pressure tension’ (PT) method, which estimates the principal axes for the bulk brittle strain, and the internal rotation axis (IRA) method, which estimates the axis of bulk internal rotation and the overall sense of slip at the faults. A mass balance calculation reveals a volume increase of up to 16% during cataclastic deformation in the fault zones. The PT method shows an approximately east trending extension direction for faults that occur only in the latest Carboniferous (?) and Early Permian strata, whereas the fault kinematics from faults that cut middle Permian to Early Triassic rocks is characterized by a ESE to SE trending extension direction. The small faults yield essentially the same kinematic results as the meso-scale faults. In a transport-parallel cross-sectional view, the principal extension axes are at an acute angle of approximately 60° to the major fault planes. Given the moderate fault density, the relatively high angle between the orientation of the principal extension axis and the fault planes suggest only a moderate amount of horizontal extension across the Karoo graben of northern Malawi. Riedel structures in the fault zones formed within two conjugate sets of localized shear zones; slip on one set was top to the W/NW and, on the other, top to the E/SE. The two conjugate sets of Riedel structures have an acute angle about the regional shortening axes, implying that no pronounced rotation of the strain axes occurred. The internal rotation axes for the Riedel structures reveal a largely bimodal distribution and inferred weakly monoclinic to orthorhombic symmetry. Therefore the overall deformation during Karoo rifting in northern Malawi is interpreted to be close to a coaxial deformation with a limited amount of horizontal extension.[/p] 相似文献
14.
In metamorphic core complexes it is commonly unclear whether lower plate mylonites formed as the down-dip continuation of a detachment fault, or whether they represent a subhorizontal shear zone that was captured by a more steeply dipping detachment fault. Detailed microstructural, fabric, and strain data from mylonites in the Buckskin-Rawhide metamorphic core complex, west-central Arizona, constrain the structural development of the lower plate shear zone. Widespread exposures of ∼22–21 Ma granitoids of the Swansea Plutonic Suite enable us to separate Miocene strain coeval with core complex extension from older deformation. Mylonites across the lower plate consistently record top-to-the-NE-directed shear. Miocene quartz and feldspar deformation/recrystallization mechanisms indicate ∼450–500 °C mylonitization temperatures that were relatively uniform across a distance of ∼35 km in the extension direction. Quartz dynamically recrystallized grain sizes do not systematically vary in the extension direction. Strain recorded in the Swansea Plutonic Suite is also relatively uniform in the extension direction, which is incompatible with models in which lower plate mylonites form as the ductile root of a major detachment fault. Altogether these data suggest the mylonitic shear zone initiated with a ≤4° dip and was unroofed by a more steeply dipping detachment fault system. Lower plate mylonites in the Buckskin-Rawhide metamorphic core complex thus represent a captured subhorizontal shear zone rather than the down-dip continuation of a detachment fault. 相似文献
15.
This paper describes how a model of fixed-hinge, basement-involved, fault-propagation folds may be adapted to apply to thin-skinned thrust faults to generate footwall synclines. Fixed-hinge, fault-propagation folding assumes that the fold-axial surfaces diverge upwards, fold hinges are fixed in the rock, the fault propagated through the forelimb, thickness changes occur in the forelimb and the forelimb progressively rotates with increasing displacement on the underlying fault. The original model for fixed-hinge, fault-propagation folds was developed for the case of a planar fault in basement with a tip line that was at the interface between basement and the overlying sedimentary cover rocks. The two geometries applicable to thin-skinned thrusts are for the cases where a fixed-hinge fault-propagation fold develops above an initial bedding-parallel detachment, and an initial fault ramp of constant dip which flattens down-dip into a bedding-parallel detachment. 相似文献
16.
Roger Searle 《Tectonophysics》1984,101(3-4)
A long-range, sidescan sonar (GLORIA) survey of an approximately 100-km square area of the East Pacific Rise crest between 3°S and 4°S extends results obtained in the same area by Lonsdale (1977) using Deep-tow. The axial, linear volcano was found to be continuous over a distance of 75 km. The presence of major inward and outward facing fault scarps was confirmed, but the GLORIA data show several distinct differences between the two fault sets. The inward dipping faults are more numerous, more closely spaced, and longer than the outward dipping ones, and their dip-slopes backscatter sound more extensively than those of the outward dipping faults; moreover most of them appear to be formed within 2 km of the axis, whereas the majority of the outward dipping faults begin to develop between 5 and 8 km from the axis. These differences suggest that the two sets of faults have different origins. The horizontal pattern of inward dipping faults is similar to those observed on other mid-ocean rises at all spreading rates, though the lengths and separations of the scarps are slightly, and their throws considerably, less than on slower spreading rises. This common horizontal pattern suggests that inward dipping faults on all rises have a common mode of formation regardless of spreading rate. Horizontal tension is probably the dominant factor, but an additional mechanism is needed to explain the polarization of fault dips that occurs in the region 2–8 km from the axis. The similarity of major fault spacings on the East Pacific Rise to those on slower spreading rises suggests that faulting is invariant in space, rather than time, and that the lithosphere where these faults are formed (about 2 km from the spreading axis) has a similar, small thickness for all spreading rates. This is attributed to the regulating effect of hydrothermal circulation and plate cooling. 相似文献
17.
Middle Miocene graben development in Crete and its possible relation to large-scale detachment faults in the southern Aegean 总被引：1，自引：0，他引：1
The linkage between the development of south-facing Cretan graben and large-scale detachment faulting in the southern Aegean is unknown. Widespread Serravallian deposits in the Ierapetra graben of Crete supply constraints to Middle Miocene graben development in the southern Aegean. The Ierapetra graben, and by inference the Cretan graben in general, were hitherto believed to have formed as a result of sinistral transpression during N–S shortening. We argue that the formation of the Cretan graben is due to N–S extension. The south-dipping, N–S-extending Kritsa normal fault served as the master fault controlling graben development in the Ierapetra graben. The Kritsa normal fault is either an antithetic fault related to the top-N Cretan detachment or a synthetic fault associated with the top-S Ios detachment. The overall geometry and timing relationships lead us to favour a connection with the Ios detachment, which in turn implies a large-scale displacement on the Ios detachment. 相似文献
18.
The finite element program ELFEN is used to study the effect of basement fault dip on the evolution of shear band patterns in unconsolidated sand. The material properties and boundary conditions of the model were chosen to correspond to generic sandbox experiments.Model results reproduce the range of structural styles found in corresponding sandbox experiments. With a basement fault dip of 60° and lower, a graben structure is formed, composed of a synthetic shear band followed by one or more antithetic shear bands. With a basement fault dip of 70° and steeper, a reverse (precursor) shear band forms first, followed by a synthetic, normal shear band that accommodates all further displacement. The dip of the synthetic shear band is close to the basement fault dip. For basement fault dips between 60° and 70°, we observe a transition in localization patterns. An analysis of the stress fields and velocity vectors in the model explains the first-order aspects of the relationships observed.We consider the observed ‘precursor-dominated’ and ‘graben-dominated’ structural domains to be important components of normal fault systems in which the first order structural style and deformation patterns are only weakly dependent on the details of the rheology of the model materials and explore the interesting problem of the change in structural style from ‘precursor-dominated’ to ‘graben-dominated’ structural domains above a normal fault in basement. We find similar structural domains in sandbox experiments for the same set of boundary conditions but with slightly different material properties, suggesting that the modeled patterns are robust within these two structural domains, (i.e. will occur over a range of similar material properties and boundary conditions).The results of this study contribute to our ability to validate numerical models against experiments in order to finally better simulate natural systems. 相似文献
19.
The purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution. We pay particular attention to seismological and surface data from regions of present day active normal faulting, as the instantaneous three-dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static.Most normal faults are concave upward, or listric. This shape can be produced by geometric constraints, either because the faults reactivate curved thrusts, or because they must be curved to accommodate rotations. Another effect which will produce curved faults is the variation of rheology with depth: brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust. An important geometric feature of normal faulting is the uplift of the footwall. The amount of such uplift is related not only to the elastic properties of the lithosphere, but also to the throw and dip of the fault. A striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction. This behaviour arises because the faults cannot intersect: if they do, one must cease to be active. The rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed. Once a new fault cuts pre-existing faults the earlier faults become locked, and a new set of faults must propagate rapidly across the whole region involved. Many of these geometric constraints also apply to thrust faulting. 相似文献
20.
The internal sectors of the Orobic Alps (Northern Italy) are characterised by Alpine age regional shortening showing a transition, through time, from plastic to brittle deformation. Thrust faults cut Alpine ductile folds and are marked by cataclasites and, locally, by pseudotachylytes, suggesting that motion was accommodated by seismic frictional slip. In the Eastern Orobic Alps the thrusting initiated at depths deeper than 10 km (the emplacement depth of the Adamello pluton) and possibly continued at shallower depths. This demonstrates that thrust motion occurred between 10 km depth and the brittle-ductile transition, i.e., at mid-crustal depths. The Orobic Alps exhumed paleoseismic zone shows different geometries along strike. In the central sectors of the Orobic Alps, thrust faults, associated with pseudotachylytes, have average dips around 40° and show no pervasive veining. Much steeper thrusts (dips up to about 85°) occur in the eastern Orobic Alps. In this area, faults are not associated with pervasive veining, i.e., fluid circulation was relatively scarce. This suggests that faulting did not occur with supralithostatic fluid pressure conditions. These reverse faults are severely misoriented (far too steep) for fault reactivation in a sublithostatic fluid pressure regime. We suggest that thrust motion likely started when the faults were less steep and that the faults were progressively rotated up to the present day dips. Domino tilting is probably responsible for this subsequent fault steepening, as suggested by a decrease of the steepness of thrust faults from north to south and by systematic rotations of previous structures consistently with tilting of thrust blocks. When the faults became inclined beyond the fault lock-up angle, no further thrusting was accommodated along them. At later stages regional shortening was accommodated by newly formed lower angle shear planes (dipping around 30–40°), consistently with predictions from fault mechanics. 相似文献