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1.
The Tokai district in central Japan is located close to the convergent boundary between the Philippine Sea and Eurasian plates, and has experienced not only repeated large interplate earthquakes but also intense aseismic movement. In this paper, the spatial and temporal tectonic evolution of the Tokai district, particularly around the Omaezaki area, is discussed to assess whether the district has been and will be active or inactive. According to a geological survey, the horizontal crustal shortening strain can imply the hypothetical tectonic model that the area has been getting less active and the strain rate since the Neogene can be calculated as 12% and 2×10−6%/year, respectively. The present interseismic horizontal crustal strain and strain rate around the Omaezaki area are approximately 4×10−7% and 4×10−9%/year. By comparing these rates, the decrease since Neogene can imply the hypothetical tectonic model that the area has been getting less active influenced by the strain partitioning between the Suruga Trough and the Zenisu Thrust. 相似文献
2.
S. Mazzoli 《International Journal of Earth Sciences》1995,84(4):781-793
Analysis of strain in Jurassic argillites forming part of the folded and thrusted sedimentary succession of the Lagonegro basin (southern Italian Apennines) has been carried out using ellipsoid-shaped reduction spots as strain markers. Most of the determined finite strain ellipsoids are of oblate type and show a peculiar distribution of the maximum extension direction (X), with maxima either subparallel or subperpendicular to the local fold axes. Using the strain matrix method, two different deformation histories have been considered to assist the interpretation of the observed finite strain pattern. A first deformation history involved vertical compaction followed by horizontal shortening (occurring by a combination of true tectonic strain and volume loss), whereby all strain is coaxial and there is no change in the intermediate axis of the strain ellipsoid. By this type of deformation sequence, which produces a deformation path where total strain moves from the oblate to the prolate strain field and back to the oblate field, prolate strain ellipsoids can be generated and may be recorded where tectonic deformation has not been large enough to reverse pretectonic compaction. This type of deformation history may be of local importance within the study area (i.e. it may characterize some fold hinge regions) and, more generally, is probably of limited occurrence in deformed pelitic rocks. A second deformation sequence considered the superposition of pre-tectonic compaction and tectonic strain consisting of initial layer-parallel shortening followed by layer-parallel shear (related to flexural folding). Also in this instance, volume change during tectonic deformation and tectonic plane strain have been assumed. For geologically reasonable amounts of volume loss due to compaction and of initial layer-parallel shortening, this type of deformation history is capable of producing a deformation path entirely lying within the oblate strain field, but still characterized by a changeover, during deformation, of the maximum extension axis (X) from a position parallel to the fold axis to one perpendicular to it. This type of deformation sequence may explain the main strain features observed in the study area, where most of the measured finite strain ellipsoids, determined from the limb regions of flexural folds, display an oblate shape, irrespective of the orientation of their maximum extension direction (X) with respect to the local structural trends. More generally, this type of deformation history provides a mechanism to account for the predominance of oblate strains in deformed pelitic rocks. 相似文献
3.
Fry and Rf/ϕ strain methods constraints and fold transection mechanisms in the NW Iberian Variscides
Apúlia is a small Portuguese sector in NW of Central-Iberian Zone, that have been deformed in a non-coaxial sinistral transpressive regime during the first and main Variscan tectonic event (D1). This deformation give rise to a major NW–SE anticline, where the S1 N–S cleavage transect the inverted short NE limb; two and three-dimensional strains analysis have been done in the low metamorphic grade Ordovician quartzites of this limb using Fry and Rf/ϕ methods. The data show that most deformation was due to intergranular deformation mechanisms. The intragranular deformation leading to the distortion of strain markers and to cleavage was very incipient and a latter event in the D1 phase. The apparent plane strain ellipsoids (if no volume change is assumed) related to the intragranular mechanisms contrast with the more prolate strain ellipsoids related to the bulk deformation of Apúlia Quartzites. This constrictional bulk strain fabrics are characteristic of the sinistral transpressive regimes dominant in the northern sectors of the Central-Iberian Zone. 相似文献
4.
Shape fabric determinations in deformed grits, microconglomerates and conglomerates in the Landersfjord region of the Laksefjord Nappe, Finnmark, North Norway, have demonstrated the existence of prolate fabric ellipsoids. The correlation between shape fabric symmetry and the orientation of the principal fabric axes suggests that the fabrics are the result of a tectonic plane strain superimposed roughly coaxially on an initially oblate sedimentary fabric. A plot of the fabric ellipsoids on a three axis diagram allows the effect of the initial fabric to be removed, and the amount of strain to be determined. A contour map of the strain shows it to increase to the north and west. Models are proposed for the origin of the strain. 相似文献
5.
V.K. Gairola 《Tectonophysics》1977,41(4):291-319
Experiments have been carried out to study the orientation and values of the three principal extensions during folding, and to investigate the nature of the deformation paths of the strain ellipsoids at the fold hinges. Single layers embedded in a matrix were deformed by plane strain pure shear with the layers obliquely inclined to the axes of the bulk strain. The strains on the outer and inner arcs of the fold hinges were measured by means of grids on the layer surfaces. The orientation and values of three principal strains during folding depend on the layer orientation and the degree of deformation, and may be different on the outer and the inner arcs. The deformation paths in the outer arc are generally in the constriction field and those in the inner arc lie in the flattening field. The deformation paths have been computed by analyzing the manner by which components of layer shortening, tangential longitudinal strain and elongation parallel to the fold-hinge line combine to give the finite strain. 相似文献
6.
This paper shows a new continuous strain–stress map for Europe obtained from the direct inversion of earthquake focal mechanisms calculated from the centroid tensor method. A total of 1608 focal mechanisms have been selected with several quality criteria from different catalogues (CMT Harvard, ETH, Med-Net, I.G.N. and I.A.G.) from 1973 to the present day. Values for the maximum horizontal shortening direction and brittle strain–stress regime defined by the k′ ratio (ey/ez, horizontal maximum/vertical strain) have been calculated following in Europe and Pannonian Basin the slip model of tri-axial deformation. The individual results including Dey and the shape of the active brittle strain ellipsoid have been interpolated to a final 15′ regular grid taking into account the relationship between the tectonic horizontal strain–stress value and the vertical load. Both continuous strain regime and maximum horizontal shortening (Dey) maps show a good correlation with the primary tectonic forces generated along the plate boundaries, plate kinematics and also some local perturbations related with main crustal heterogeneities and topography, as well as significant spatial variations in integrated crustal strength. 相似文献
7.
The dependence of strength, ductility, and preferred orientation of polycrystalline anhydrite upon confining pressure (up to 5 kbar), temperature (up to 300° C), and strain (up to 30%) has been evaluated by compression tests.Strength and ductility increase at room temperature with increasing mantle pressure. Up to 1 kbar mantle pressure anhydrite is brittle and failure occurs by tension and shear fractures. Homogeneous flow between 1 and 3 kbar mantle pressure is mostly due to intercrystalline slip which is sensitive to pressure. Beyond the elastic limit the stress—strain curves are nearly horizontal. No preferred orientation develops. Between 3 and 4 kbar mantle pressure the intracrystalline mechanisms become noticeable. The stress—strain curves show weak strain hardening. The (210)-planes reveal a weak preferred orientation perpendicular to the axis of compression.With increasing temperature the strength decreases at low strains (< 5%). Intracrystalline mechanisms become more dominant, because the critical resolved shear stresses are lower with increasing temperature. At high strains (> 15%) both strength and ductility increase at higher temperatures. At even higher strains, strain hardening ceases once again and the stress—strain curves become nearly horizontal. From that point on preferred orientation is no longer increased. The stress—strain curves differ with the orientation of the specimen axis to the original fabric.
Zusammenfassung
In Stauchversuchen an polykristallinem Anhydrit wurde die Abhängigkeit der Festigkeit, der Verformbarkeit und der Gefügeregelung vom Manteldruck (bis 5 kbar), von der Temperatur (bis 300°C) und vom Verformungsgrad (bis 30%) untersucht.Festigkeit und Verformbarkeit nehmen bei Raumtemperatur mit steigenden Mantel-drucken zu. Bis etwa l kbar Manteldruck verhält sich der Anhydrit spröde und es treten Trenn und Verschiebungsbrüche auf. Die gleichmässige Fliessverformung bei Manteldrucken über 1 kbar erfolgt durch überwiegend interkristalline, manteldruckempfindliche Verformungsmechanismen. Die Spannungs—Verformungskurven verlaufen nach Überschreiten der elastischen Verformung nahezu horizontal. Eine Regelung tritt nicht ein. Ab 3 kbar bis 4 kbar Manteldruck beginnen sich intrakristalline Mechanismen bemerkbar zu machen. Die Spannungs—Verformungskurven weisen eine schwache Verfestigung auf. Durch die eintretende schwache Regelung stellt sich eine (210)-Ebene bevorzugt senkrecht zur Stauchachse ein.Mit steigender Temperatur bei sonst gleichen Bedingungen nimmt die Festigkeit bei geringen Verformungsgraden (< 5%) ab. Die Verformung erfolgt überwiegend durch intrakristalline Mechanismen, deren kritische Schubspannungen mit zunehmender Temperatur geringer werden. Die Spannungs—Verformungskurven steigen nach Überschreiten des elastischen Bereichs stärker an als zuvor. Es tritt mit zunehmender Temperatur eine stärkere Verfestigung und eine intensivere Einregelung von (210) senkrecht zur Stauchachse ein. Im Bereich hoher Verformungsgrade (> 15%) liegen die Festigkeiten bei höheren Temperaturen höher als bei niedrigen Temperaturen. Bei sehr hohen Verformungsgraden wird die Verfestigung so gross, dass interkristalline Mechanismen die intrakristallinen wieder ablösen. Die Spannungs—Verformungskurven werden wieder flacher und die Zunahme in der Regelung hört auf.Je nach der Orientierung der Stauchachse zum Ausgangsgefüge verlaufen die Spannungs—Verformungskurven unterschiedlich.Die Abhängigkeit der Verformungsmechanismen vom Manteldruck, Verformungsgrad und der Temperatur wird in einem dreidimensionalen Modell vorgestellt. 相似文献8.
The geometry of tectonic structures, attributed to the Neogene–Quaternary time interval, is described in the active setting of the Venezuelan Andes. Our methodology is based on the analysis of radar satellite and Digital Elevation Model imagery, complemented by structural fieldwork and the compilation of seismotectonic data to make a structural analysis on a regional scale. Radar images provide first class data for morphostructural analysis in areas of dense vegetation and frequent cloud covering, like the Venezuelan Andes. We focused our analysis in the Burbusay–Río Momboy and Boconó faults corner located in the central part of the belt.We have described three stages of deformation during the Neogene–Quaternary. The first one, Mio-Pliocene in age, is a NW–SE compression responsible for the uplift of the Venezuelan Andes. The second tectonic stage corresponds to a strike-slip regime of deformation marked by shearing along the Boconó, Burbusay and Valera faults, which separates two triangular wedges in the larger Trujillo block. This strike-slip faulting-dominated compressional-extensional tectonic regime allowed the Trujillo crustal block to move towards the NE. Wrenching has therefore started at some point between the Pliocene and the Quaternary. These two tectonic events are consistent with ongoing strain partitioning in the Venezuelan Andes. The third stage corresponds to extensional deformation limited to the Trujillo block and is still active today. Extension is associated with the motion of crustal blocks moving relative to each other, probably above the upper-lower crust boundary. Such extensional deformation can be understood considering that the crust extends and stretches at the same time as it moves towards the NE. The combination of both horizontal lateral motion and extension is characteristic of a tectonic escape process. The northeastward escape of the Trujillo block, which belongs to the larger North Andes block, occurs as a result of the combination of the NW–SE intracontinental convergence between the South-American plate and the Maracaibo block, and the presence to the north of the Caribbean oceanic plate considered as a free boundary. We have showed that the kinematics of the Caribbean plate offers not only a favorable environment, but may also be considered as the driving force of the tectonic escape of the North Andes block. 相似文献
9.
Strain analysis and vorticity of flow in the Northern Sardinian Variscan Belt: Recognition of a partitioned oblique deformation event 总被引：1，自引：0，他引：1
A field example of strain partitioning has been analysed along the Nurra–Asinara transect of the NW Sardinian Variscan chain (Italy). The section in the Nurra–Asinara area is in a continuous sequence of tectono-metamorphic complexes made of low- to high-grade metamorphic rocks affected by a polyphase tectonic history. The principal fabric of the area is controlled by a D2 progressive deformation phase in which the strain is partitioned into folds and shear zone domains. The D2 stretching lineation and shear sense show a clear change from south to north. The principal meso- and micro-structures, vorticity gauges and a quantitative kinematic analysis of local strain suggest that the D2 kinematic history could be envisaged as an oblique heterogeneous deformation similar to the transpressive systems described in ancient and modern settings elsewhere. Using a simple kinematic model we also propose that both a transpressive system followed by “thrusting” or a partitioned transpressive system could be responsible for the fabric distribution and strain accumulation described in the study transect. 相似文献
10.
淮南矿区深部地应力场特征研究 总被引：1，自引：0，他引：1
利用水压致裂法和套孔应力解除法对淮南矿区-500～-1 000 m深度范围内的12个矿井进行了地应力测量,取得了19个有效测点的数据。数据分析表明：（1）淮南矿区深部地应力场以水平应力为主,构造应力占绝对优势,属于典型的构造应力场类型;（2）地应力量级属高应力水平;（3）垂直主应力、最大及最小水平主应力随深度的增加均呈增大趋势;（4）侧压系数 随深度增大而减小,地应力场有从大地动应力场型向准静水压力场型过渡的趋势;（5）侧压比 的回归曲线分布于Hoek-Brown内外包线带内,且变化趋势与Hoek-Brown曲线相似,但与Hoek-Brown曲线相比,回归曲线 值偏小;（6）最大水平主应力与最小水平主应力的比值范围为1.12～2.02,其中68.42%的测点分布在1.67～2.02之间;（7）最大水平主应力方位为NEE－EW向。最后探讨了淮南矿区地应力与地质构造的关系,分析认为,矿区最大主应力方向与构造运动密切相关,矿区现今构造应力场最大主应力方位与实测最大水平主应力方位大致吻合。 相似文献
11.
One of the goals of using the Global Positioning System (GPS) and other geodetic survey techniques in tectonics has been to detect boundaries such as faults or shear zones between rigid or mildly deforming crustal masses. The calculation of infinitesimal strains and rotations with GPS data has been widely used to detect shear zones but it has been largely unsuccessful because infinitesimal strain and rotation, although useful in many other ways, is non-diagnostic of shear zones or faults. Our approach is to work with components of deformation, not strain, and to design specifically a diagnostic method of detecting shear zones. This paper introduces the first part of our method, the detection of two-dimensional, strike-shift shear zones (MODES-2D). The MODES-2D method has three elements: (1) determination of the orientation of a suspected strike-shift shear zone by analyzing components of a deformation tensor derived from a data set of displacements in an arbitrary coordinate system; (2) resolution of the deformation tensor into the coordinate system parallel and normal to the detected shear zone; and (3) exploration of the resolved data set for evidence for a belt of inhomogeneous deformation, which is an essential characteristic of a shear zone. The operation of MODES-2D is illustrated herein with a theoretical survey network across an ideal shear zone developed with a buried dislocation-fault and with a survey network afforded by the crossing of the Kaynaşlı viaduct by the 1999 Düzce–Bolu earthquake rupture in Turkey. 相似文献
12.
Transpression 总被引：2，自引：0，他引：2
Transpression is considered as a wrench or transcurrent shear accompanied by horizontal shortening across, and vertical lengthening along, the shear plane. A model for the strain in transpression is derived, from which the shape and orientation of the finite strain ellipsoid, and the stretch and rotation of lines can be determined. Shortening across the zone of transpression leads to oblate finite strain ellipsoids (k<1).By considering the superposition of small increments of strain various model deformation paths are computed. These are used to interpret the development of structures, such as en-échelon folds, in transpression zones. The incremental strain ellipsoid allows prediction of the orientation of the principal stresses and hence brittle structures within such zones. The model is also applied to bends and terminations of shear zones and used to interpret the observed patterns of folds and fractures in these. 相似文献
13.
Tang‐Tat Ng 《国际地质力学数值与分析法杂志》2009,33(4):511-527
The microscopic and macroscopic behaviors of assemblages of monodisperse ellipsoids with different particle shapes were studied using the discrete element method. Four samples were created with 1170 identical prolate ellipsoids. The samples were compressed isotropically to 100 kPa. Then triaxial compression tests were carried out to very large strains until the ultimate state was reached. This paper presents typical macroscopic result including stress–strain relationship and volumetric behavior. In addition, the fabric of the samples was examined at the initial state, at the peak shear strength state, and at the ultimate state. We studied the evolution of three vector‐typed micromechanical arguments with strain including the particle orientation, branch vector, and normal contact force. The normal contact force (micromechanical argument) was found to have a direct relationship with the principal stress ratio (macroscopic parameter). The angles between these vectors were also investigated. The maximum angle between vectors is related to particle shape. The results indicate that the distributions and the maximum values of these angles do not change with loading. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
14.
岩石磁化率椭球体的三个轴与应变椭球体的三个轴方向相平行,并具有一定的共构关系.变形岩石的磁组构参数P、T、F、L以及磁化率椭球体主张量方向等可以用来定量地表征岩石变形的性状及期次.本文通过实测和计算27个样品的磁组构参数,研究了博白-合浦断裂带的变形性状与期次,结果表明:博白-合浦断裂带大致经历了三期构造变形作用,不同时期具不同性质的构造变形.变形性状分别表现为韧性、韧-脆性及脆性变形,应变行为分别表现为平面、非平面和线性应变. 相似文献
15.
D. Legrand A. Calahorrano B. Guillier L. Rivera M. Ruiz D. Villagmez H. Yepes 《Tectonophysics》2002,344(1-2)
The phreatic activity and the subsequent dacitic dome growth in 1998–1999 at Guagua Pichincha volcano, Ecuador, were associated with two seismic swarms: one located in the northern part of Quito (population: 1,500,000) and another one, just below the active volcano, about 15–20 km SW from the first one. Quito swarm tectonic events have high frequencies (from 1 to 10–15 Hz). We registered more than 3200 events (among which 2354 events of 1.4≤ML≤4.2) between June 1998 and December 1999 at the −2- and −17-km depth. The volcanic events below the Guagua Pichincha caldera have high (from 1 to 10–15 Hz) and low (less than 3 Hz) frequencies. Approximately, 130,000 events were registered between September 1998 and December 1999 at the +2.4- and −3.5-km depth. Here, we study the stress tensors of these two swarms deduced from the polarities of P first motions and compare them to the regional stress tensor deduced from CMT Harvard focal mechanisms. The Quito swarm stress tensor is relatively close to the regional stress tensor (the σ1 axis was oriented N117°E close to the N102°E direction of the plate motion found by the GPS measurement, and σ3 is nearly vertical). The difference may be due to the action of the closely active Guagua Pichincha volcano. The Guagua Pichincha stress tensor is very different from the regional tectonic one. The σ1 axis of the volcano is oriented N214°E, almost perpendicular to the σ1 of the swarm of Quito and σ3 is almost horizontal. Even if these two tensors are different, they can be explained in a more general tectonic scheme. The almost horizontal direction of σ3 just below the volcano is compatible with an extensional horizontal direction that may be expected in the shallow extrados part of a compressional region and consistent with an opening of the top of the Guagua Pichincha volcano. The movement of the fluids (magma, gas and/or groundwater) produced by the closely active Guagua Pichincha volcano seems to have an influence in the acceleration of the generation of seismic events. 相似文献
16.
Striated and pitted pebbles provide scarce structures that preserve information on the stresses that their host rocks have undergone. This information can be obtained by the measurement of a large number of microfaults with striae and solution marks within a small rock volume. For non-rotational deformation, the statistical procedures for microfault analysis provide a valid tool for determining the overprinting of successive stress ellipsoids, including their axial ratios and the orientations of the main axes. The trends of compressions obtained from striae can be compared with the determinations from the pole of pebble solution pits. However, in complex tectonics settings, the solution pits of several deformation phases are mixed and only striae analysis allows overprinted paleostresses to be accurately distinguished. The analysis of several pebbles from the same outcrop, including five from moderately complex settings, allows determination of the homogeneity of the paleostresses at outcrop scale, the detection of redeposited pebbles, and supports the results of microtectonic analysis for large areas. Solution mark distributions on pebbles depend on the burial and tectonic stresses. Conglomerates from shallow levels, such as those from Quaternary fluvial terraces, only record horizontal compressional solution marks because the minimum vertical stress needed to develop these structures are not reached by burial.In the central Betic Cordillera, striated and pitted pebbles are composed of carbonate surrounded by a matrix containing siliciclastic elements. The study of several outcrops located across a transect of the Cordillera shows a change in the recent stress field. While conglomerates near the Internal–External zone boundary show extensional stresses that may be related to the uplift of the Cordillera since Tortonian times, the outcrops located in the External Zone and up to the mountain front indicate the existence of horizontal NW–SE and NE–SW compressions related to prolate ellipsoids. These two compression directions, which affect conglomerates up to the Quaternary in the same outcrop, may be produced by a local permutation of stress axes, which in general indicates NW–SE compression related to the Eurasia–Africa plate boundary convergence, but which locally may switch to an orthogonal compression. 相似文献
17.
Evaluating magnetic lineations (AMS) in deformed rocks 总被引：3，自引：0，他引：3
Magnetic lineation in rocks is given by a cluster of the principal axes of maximum susceptibility (Kmax) of the Anisotropy of Magnetic Susceptibility (AMS) tensor. In deformed rocks, magnetic lineations are generally considered to be the result of either bedding and cleavage intersection or they parallel the tectonic extension direction in high strain zones. Our AMS determinations, based on a variety of samples that were taken from mudstones, slates and schists from the Pyrenees and Appalachians, show that strain is not the only factor controlling the development of magnetic lineation. We find that the development and extent to which the magnetic lineation parallels the tectonic extension direction depends on both the original AMS tensor, which in turn depends on the lithology, and the deformation intensity. Rocks having a weak pre-deformational fabric will develop magnetic lineations that more readily will track the tectonic extension. 相似文献
18.
The implications of assuming isotropic elasto–plasticity to model the behaviour of soil under simple shear conditions are considered. For small strains, use of such a model implies the following three consequences: (1) strains and strain increments at any stage of shearing may be expressed as the sum of elastic and plastic components; (2) principal directions of stress and of plastic strain increment are collinear; (3) principal directions of stress increment and of elastic strain increment are collinear. These consequences are used in order to establish relationships between the stresses, stress increments and strains which develop in a simple shear test. No additional assumptions with regards the form of the yield function, the flow rule or the hardening function are required for this development. By defining the ratio of the plastic to the total shear strain increment on the horizontal plane (the plane of zero extension) as λ, it is possible to define the horizontal normal stress σx in terms of λ and other stresses and strains which are normally known during simple shear loading. As a result, all components of the stress tensor in the simple shear plane may be defined. Results of some direct simple shear tests on soft clay have been interpreted using the model and found to be generally consistent with some of the observations reported in the literature from tests in which boundary stresses were measured. 相似文献
19.
G. Herget 《Rock Mechanics and Rock Engineering》1974,6(1):53-64
SummaryGround Stress Determinations in Canada Stress determinations with the biaxial (Doorstopper) and the triaxial strain cell of the C. S. I. R., South Africa, are discussed and show that the triaxial cell is the more desirable instrument if good rock conditions exist. Vertical and average horizontal stresses in Canada are similar in magnitude to those from other parts of the earth's crust and show that vertical stresses are related to weight of overburden and average horizontal stresses increase in most of the cases with 0.407 kg/cm2 per metre of depth. More data are necessary to make any prediction for the average horizontal stress beyond a depth of 800 m.Stress determinations and a tectonic analysis show that the unravelling of the geological stress-strain history allows some prediction of principal stress directions, but the attached uncertainties due to gaps in documentation require proof by stress determinations.With 8 Figures 相似文献
20.
白鹤滩水电站是仅次于三峡水电站的第二大水电站,位于中国西南地区川滇菱形块体内的金沙江上。通常地壳应力状态是影响地下工程安全的重要地质因素,对地下硐室稳定性分析具有重要意义。在水电站右岸厂房建设过程中,为了水电站的长期安全运营,采用超声波井下电视录井测试系统对白鹤滩右岸厂房锚固洞内7处钻孔进行测试,基于钻孔崩落数据计算了现今白鹤滩右岸厂房区域上方工程岩体的主应力方向。研究结果表明:白鹤滩右岸厂房区域最大水平主应力（SH）方向为北北东—南南西方向,主要受到构造应力、自重应力、河流剥蚀作用以及岸坡卸荷作用的共同影响,属于局部构造应力场。 相似文献