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1.
《海洋地质与第四纪地质》2017,(2)
为确定南海西部的中—西沙地块是否存在前新生代地层与构造,对研究区内多道反射地震剖面资料进行了地层-构造解释,并结合围区钻井、拖网等岩石地层资料,在研究区北部发现了前新生代地层-构造变形形迹。运用回剥法、去断层恢复法和地质反序法对前新生代地层的构造变形进行了古恢复。结果表明,研究区的地层可划分为上、中、下三套构造层,其中属于前新生界的下构造层可见褶皱、逆冲等挤压构造样式,前新生代末期,其构造形态表现为一系列连续的宽缓褶皱,结合断层逆冲推覆方向可判断其主要挤压应力来自于东南方向,并推测该挤压作用与古南海的扩张有关。 相似文献
2.
土体在剪切变形过程中产生主应力方向的旋转时,主应变率方向与主应力方向之间存在着非共轴现象,然而,传统的弹塑性本构模型并不能考虑该现象的影响。通过在传统本构模型屈服面的切线方向增加一项非共轴塑性应变率,即可实现对非共轴现象的反映。利用有限元软件ABAQUS的材料子程序接口UMAT,通过显式积分算法和自动分步方法实现了非共轴模型在有限元分析中的应用。首先,对砂土的单剪试验进行数值模拟,预测了主应力方向和主应变率方向之间的关系,所得结论与试验结果较为吻合。然后,针对吸力桶与砂质地基间的相互作用问题进行弹塑性有限元计算,分析了土体主应力方向在剪切变形过程中的旋转规律,以及桶体的端部阻力、侧壁摩擦阻力和顶部阻力在变形过程中的变化规律。最后,检验了非共轴现象对地基承载力计算结果的影响。研究结果表明,所开发的非共轴模型对非共轴现象具有良好的预测能力。 相似文献
3.
谢丁吴世敏孙萍 《海洋地质与第四纪地质》2016,(3):91-102
利用樟木头及其邻区断层擦痕数据,采用"多重逆解法"反演该区晚中生代以来的构造应力场,为华南陆缘地区晚中生代以来构造演化过程的研究提供参考。通过5个野外断层擦痕测点观察与数据测量,采集了125组有效断层滑动数据,反演得到八种应力状态,进一步区分了晚中生代以来该区4个期次的构造应力场,即1NNW—SSE方向(254.9°~355.7°)的拉张应力体制;2ENE—WSW方向(64.9°)的拉张应力体制:3最大主应力优势方位为NE—SW向(约46.8°~59.9°)的走滑应力体制;4最大主应力优势方位NW—SE向(约329.5°~339.7°)的走滑应力体制。应力场的变化反映出控制该区不同时期的大地构造背景差异,即由早期的太平洋板块的俯冲带后撤、古太平洋俯冲方向的改变,之后的印度-澳大利亚板块与欧亚板块碰撞及印支块体顺时针旋转,最后,菲律宾海板块俯冲方向以及强度的变化。 相似文献
4.
为揭示马尼拉增生楔的形态结构并加深对其演化过程的理解,本文对横穿马尼拉俯冲带北段的几条典型地震剖面进行了深度偏移处理,得到叠前深度偏移剖面和深度-速度模型,并对马尼拉增生楔的形态结构及内部特征进行了精细解释,将马尼拉增生楔分为原始沉积段、褶皱变形段、逆冲推覆段和背逆冲段四个部分,分别代表增生楔演化的不同阶段。推断马尼拉增生楔下部存在由早期仰冲的菲律宾海板块的残留块体构成的弧前基盘,弧前基盘是控制马尼拉增生楔形成演化的关键构造。弧前基盘前端是拆离滑脱面突然降阶并在地震剖面上"隐没"的部位;弧前基盘向增生楔底部的不断挤入导致了逆冲脱序断层的渐次发育以及增生楔向弧前基盘之上的不断爬升,导致了增生楔上、下陆坡地貌的分化,并为褶皱变形段和逆冲推覆段的地层形变提供了主要的应力。 相似文献
5.
采用有限元方法模拟了扬子地区印支末期应力场的分布特征.根据模拟结果,对比已知断裂的展布方向,定量分析了扬子地区压应力及主应力方向的分布特征,并探讨了影响扬子地区印支末期构造特征的主要因素.据此得出以下研究结论:通过不断调整模型的边界条件发现,在印支末期,当华北地块为SE向挤压时,模型中压性应力场低值区的分布范围及主应力方向分别与扬子地区已知断裂密度及展布方向具有较好的对应关系. 相似文献
6.
海山等粗糙海底的俯冲对增生楔的结构、地貌、应力和地震灾害有着重要的影响。希库朗伊（Hikurangi）俯冲带位于新西兰北岛外海,希库朗伊高原向西正以40～47 mm/a的速率俯冲于澳大利亚板块之下。希库朗伊高原内部发育大量形态各异的海山,其俯冲造成希库朗伊北缘经历了严重的构造侵蚀。目前该区域的慢滑移事件有了很好的地震学和测地学约束,但对于希库朗伊北缘的构造侵蚀和构造应力体制如何演化以及对地震活动的影响仍然不清。本文基于离散元方法（DEM）数值模拟,结合地震反射剖面,探讨了海山俯冲对希库朗伊俯冲带北缘增生楔的形态、断裂结构、活动性、应变分配的影响。模拟结果显示海山的俯冲在其顶部形成一条巨型分支断层(mega-splay fault),吸收主要的缩短量并沿海底发生长距离、低角度逆冲推覆。随着俯冲的持续,海山前缘形成一个双重构造剪切带,而随着滑脱层的下移并向前扩展,最终形成前缘逆冲断裂体系。模拟证实海山俯冲提高了弧前增生楔内应力分布的非均质性,海山前缘最大剪切应力显著累积,而海山后缘则表现为一个稳定的应力影区。海山俯冲显著增加了希库朗伊俯冲带板间逆冲断层的几何粗糙度和物质非均质性,对微地震和... 相似文献
7.
在主应力方向的旋转过程中,主应力方向与塑性主应变增量方向之间存在着非共轴现象。基于屈服角点结构非共轴理论,建立了一种非共轴本构模型,通过有限元软件ABAQUS的二次开发子程序UMAT,将该模型运用到有限元数值计算中。首先,对中密砂单剪试验进行数值模拟,研究了非共轴现象及其对应力-应变关系的影响。然后,针对偏心荷载作用下条形浅基础荷载-变形特性进行数值分析,研究了非共轴现象对荷载-位移关系的影响。研究结果表明:非共轴模型计算得到的荷载增长速度滞后于共轴模型计算结果的增长速度;在地基变形的初期,非共轴现象比较明显,主应力方向的减小速度要滞后于塑性主应变增量方向的减小速度;随着地基沉降的增加,非共轴现象逐渐减弱;非共轴模型与共轴模型计算结果之间的差异在应变硬化情况下更加明显。 相似文献
8.
卷管式铺管法在海管铺设中的应用愈发广泛,在铺设作业中管道会发生几何非线性变形,导致出现复杂的力学性能变化。针对管道在上卷、退卷过程中的屈服变化过程,通过弹塑性理论进行分析,推导出管道退卷后残余轴向应力的解析解;随后利用有限元软件ABAQUS建立模型实例,对比解析解与有限元模型,两者的计算结果基本吻合。基于上述有限元模型,研究上卷时的张力和退卷时的后张力对椭圆度、截面轴向应力和剪切应力的影响,并进行敏感性分析。模拟结果表明张力和后张力变化会影响管道截面的变形程度,退卷后截面上残余的轴向应力远高于剪切应力,并且通过敏感性分析,得到了残余椭圆度、残余应力随张力和后张力变化的规律。研究可为卷管铺设过程中张力和后张力的选择提供参考和借鉴。 相似文献
9.
随着勘探开发程度的不断升高,西湖凹陷保俶斜坡带平北地区中上始新统平湖组构造―岩性复合油气藏显示出较大的勘探潜力。然而,该区构造―岩性复合油气藏勘探基础薄弱,加之构造、沉积条件复杂,砂体展布规律不清,阻碍了该区的勘探进程。本文基于三维地震及钻井等资料,从构造、层序及沉积3个方面对砂体分布的控制因素进行分析,认为构造古地貌及可容纳空间控制地层厚度及沉积体规模;同沉积断裂坡折带控制砂体的展布;体系域类型控制砂体的时空配置,沉积微相类型控制砂体的储集物性。综合分析控砂因素认为:断陷期的平下下段和平下上段是构造―岩性圈闭发育的主要层段,勘探方向为低位体系域控沉积断层下降盘的地势低洼汇砂区,而平中上段有利的岩性圈闭勘探区为三角洲前缘砂地比低或三角洲前端发育的潮汐砂脊带。 相似文献
10.
南海北部琼东南盆地中央峡谷成因新认识 总被引：3，自引：0，他引：3
通过对区域构造断裂体系和逐渐连片的高分辨率三维地震资料的精细解析,认识到琼东南盆地中央峡谷的形成机制除了与晚中新世区域构造变动、大规模海平面下降、充足物源供给以及凹槽型古地形特征等因素相关之外,还存在另外一个非常重要因素:峡谷底部早期隐伏断裂带的存在。研究表明:琼东南盆地中央坳陷带发育平行于陆架坡折的大规模深水峡谷,峡谷底部发育大型走滑断层以及走滑断层派生出一系列次级断层形成的地层破碎带,认识到峡谷的形成、规模以及展布方向均受断裂带影响;相应地峡谷的充填及演化亦是受物源、海平面变化、重力流作用等多种因素共同作用和相互叠加的过程。从而为研究经历了裂陷期和坳陷期盆地演化过程形成的大型峡谷提供了科学依据。 相似文献
11.
A discrete-element model is used to investigate the manner in which deformation and fault activity change in space and time during the development of a doubly vergent thrust wedge in the upper crust. Deformation is a result of shortening at a subduction slot in the base of the model, a configuration which produces a dynamic backstop within the cohesionless, frictional cover material. A series of experiments with differing basal (decollement) friction are performed. The distinct manners in which thrust wedges grow, and the variability of fault development and activity in space and time, are then examined. Both predicted large-scale wedge geometries and individual fault-fold structures are similar to those observed in sandbox models, and show the complex manner in which shortening is accommodated and localized during the development of the thrust wedge. When compared to a sandbox model with similar boundary conditions, model results are strikingly similar. In all cases, deformation initiates above the subduction slot with the formation of an axial zone; the wedge is then developed by displacement on a retro-wedge thrust and propagation of deformation into the pro-wedge region. Models with low coefficients of basal friction typically develop wide, shallow wedges with distributed, spaced deformation and rather symmetric, box-like structures; whereas those with high coefficients of basal friction develop narrower, steeper wedges, consisting of a series of stacked, pro-wedge thrust sheets, and a high-displacement retro-wedge thrust. In general, fault initiation and linkage is extremely complex in our models, with several smaller faults operating until linkage occurs to form a major through-going structure. Of particular interest is the observation that many of the faults do not develop at the basal decollement and propagate upwards through the cover but rather initiate at high levels in the cover and propagate/link downwards with other, deeper structures. Results also indicate the utility of the discrete-element approach in modelling large-displacement, complex deformation of geological materials. 相似文献
12.
Dominguez S. Lallemand S. Malavieille J. Schnürle P. 《Marine Geophysical Researches》1998,20(5):383-402
The Gagua Ridge, carried by the Philippine Sea Plate, is subducting obliquely beneath the southernmost Ryukyu Margin. Bathymetric swath-mapping, performed during the ACT survey (Active Collision in Taiwan), indicates that, due to the high obliquity of plate convergence, slip partitioning occurs within the Ryukyu accretionary wedge. A transcurrent fault, trending N95° E, is observed at the rear of the accretionary wedge. Evidence of right lateral motion along this shear zone, called the Yaeyama Fault, suggests that it accommodates part of the lateral component of the oblique convergence. The subduction of the ridge disturbs this tectonic setting and significantly deforms the Ryukyu Margin. The ridge strongly indents the front of the accretionary wedge and uplifts part of the forearc basin. In the frontal part of the margin, directly in the axis of the ridge, localized transpressive and transtensional structures can be observed superimposed on the uplifted accretionary complex. As shown by sandbox experiments, these N330° E to N30° E trending fractures result from the increasing compressional stress induced by the subduction of the ridge. Analog experiments have also shown that the reentrant associated with oblique ridge subduction exhibits a specific shape that can be correlated with the relative plate motion azimuth.These data, together with the study of the margin deformation, the uplift of the forearc basin and geodetic data, show that the subduction of the Gagua Ridge beneath the accretionary wedge occurs along an azimuth which is about 20° less oblique than the convergence between the PSP and the Ryukyu Arc. Taking into account the opening of the Okinawa backarc basin and partitioning at the rear of the accretionary wedge, convergence between the ridge and the overriding accretionary wedge appears to be close to N345° E and thus, occurs at a rate close to 9 cm yr–1. As a result, we estimate that a motion of 3.7 cm yr–1±0.7 cm should be absorbed along the transcurrent fault. Based on these assumptions, the plate tectonic reconstruction reveals that the subducted segment of the Gagua Ridge, associated with the observable margin deformations, could have started subducting less than 1 m.y. ago. 相似文献
13.
Yu-Ke Wang Yu-Feng Gao Yue Qiu Xiu-Qing Hu Ying Zhang 《Marine Georesources & Geotechnology》2016,34(5):493-502
The deformation behavior and shear strength of soft marine clays subjected to wave or traffic loads are different from that in triaxial loading due to the changes of major principal stress direction β and intermediate principal stress coefficient b. To investigate the anisotropy affected by β and b in natural soft marine clay, a series of drained tests were conducted by hollow cylinder apparatus. The principal stress direction relative to vertical direction were maintained constant under an increasing shear stress, with fixed intermediate principal stress coefficient b. The influence of the b and β on anisotropy of typically Wenzhou intact clay is discussed. It was found that octahedral stress–strain relationships expressed anisotropy with different b and β. The friction angle and deviator stress ratio with different b and β were presented to provide guidance for engineering projects in the coastal zone. 相似文献
14.
Naga fold thrust belt is an emerging destination for petroleum exploration in eastern India. It is a thin skinned FTB where new initiatives are being taken after a long gap of initial discoveries. In absence of sufficient drilling or quality seismic data in the southern part of the fold thrust belt, fluid pressure regimes remain largely speculative. Using the concept and the formulation for efficient coefficient of basal friction, we have revisited the method and concept of pressure-dependent Coulomb wedge theory for thin skinned thrust belts for deriving the fluid pressure ratio in Naga fold thrust belt. The efficient coefficient of basal friction on the decollement and the fluid ratio of Naga fold thrust belt are estimated to be 0.22 and 0.85 respectively. This indicates an overpressure situation in the wedge. This method of estimating basal friction and fluid pressure is more case-specific and can be obtained from the data of thrust initiation angle and thrust spacing. 相似文献
15.
Shusaku Goto Tomonobu Mizoguchi Ryo Kimura Masataka Kinoshita Makoto Yamano Hideki Hamamoto 《Marine Geophysical Researches》2012,33(3):269-283
We investigated the relationship between variations in the thermal conductivity of surface sediments and the topography in the Nankai subduction zone off Tokai, central Japan, the easternmost part of the Nankai subduction zone, which has an accretionary prism with varied topography. We analyzed sediment thermal conductivity data obtained from the trough floor and accretionary prism. Variations in the thermal conductivity of sediments were related to the topographic features formed by accretionary prism development. Thermal conductivities of 1.1?W/m?K were measured on the trough floor where thick terrigenous turbidites have been deposited. The thermal conductivity of Nankai Trough floor sediments decreases from northeast to southwest along the trough, probably because of the decreased grain size and/or changes in sediment mineral composition. High thermal conductivities (??1.0?W/m?K) were measured in fault scarps on the accretionary prism. A landward increase in these values on the prism may be explained by decreased porosity of the sediments attributable to tectonic deformation during accretionary prism development. At the base of the fault scarp of the frontal thrust, low thermal conductivities (<0.9?W/m?K) were measured, likely reflecting the high porosity of the talus deposits. Low thermal conductivity (0.9?W/m?K) was also measured in slope basins on the accretionary prism, likely also related to the high porosity of the sediments. Our results demonstrate that, for accurate heat flow measurement in an area of varied topography, the geothermal gradient and the thermal conductivity of the sediments must be measured within regions with similar topographic features. 相似文献
16.
A stress path with continuous rotation of the principal stress direction and continuous alteration of amplitude of deviatoric stress difference under the interaction of wave and earthquake loading was proposed based on the characteristics of the stress path under wave and earthquake loading, respectively. Using a GDS dynamic hollow cylinder apparatus, a series of cyclic triaxial-torsional coupling shear tests were performed on Nanjing saturated fine sand via the stress path mentioned previously under different relative densities, effective initial confining pressures, plastic fines contents, and loading frequencies to study the development of excess pore water pressure (EPWP) of saturated sand under the interaction of wave and earthquake loading. It was found that the development of EPWP follows the trend of fast-steady-mutative-drastic, which is different from that under the cyclic triaxial test or wave loading. The number of cycles causing initial liquefaction (NL) of saturated sand increases remarkably with relative densities. However, the relationships between NL and effective initial confining pressures, plastic fines content, or loading frequencies are more complex. 相似文献
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Brittle faulting-related shear heating is important in petroleum geosciences, tectonics and seismic studies. Temporal variation of shear heat related temperature rise for rotational and roto-translational faults are investigated in this work. For planar fault planes, devoid of gouge and any secondary faulting, temperature rise is proportional to the coefficient of friction, and rate of (angular) slip. Tectonically realistic physical parameters for rotational faults, especially prolonged faulting, can significantly increase temperature by shear heating at shallow crustal depth, capable of thermal maturity of hydrocarbons. 相似文献