Curvature of convergent boundaries     

M. I. Streltsov 《Island Arc》1997,6(3):234-243

Abstract It is well known that knowledge about convergent boundary geometry is crucial for global geodynamical reconstructions. At the same time, views related to the subject are controversial and speculative. For instance, island arcs, which are considered to be the most important convergent boundary structural elements, are thought to be either the parts of the small circles on the Earth's surface, or adjacent to each other as straight-line segments. Accordingly, one view says that island arcs are rectilinear rather than arched, and there are no reasons to consider their arched shape to be a rule. Is the island arc curvature invariant in time and space? General considerations, palaeomagnetic data and structural features such as strike-slip displacements of the opposite sign along the longitudinal faults on the island arc flanks, prompt the author to have a similar view to others, that is, that island arc curvature varies with time. It is worthy to note, nevertheless, that this statement could hardly be referred to as generally adopted, and it is not necessarily true. One can try to answer the second part of the question by means of mathematical statistics. Points of an island arc characterizing the geometry, such as volcanic centres or deep-trench axial line points, were led to the stereographical projection centre, where distortions are minimal. By the least squares method these points have been approximated with straight lines, circumferences and lines with variable curvature. Then by means of variance analysis the competing hypotheses have been compared. The results of the present study show that the curvature of the island arcs in the north-western Pacific varies with location. It is possible to search for relationships between island arc curvature as a measure of its bending, various physical parameters of island arc lithosphere and such recent island arc processes as volcanism, seismicity etc. Progress in this direction has already been made; namely a direct relationship between trench depth and island arc curvature has been established.  相似文献   

单层纵弯褶皱曲率指数与应力指数的关系探讨   总被引：1，自引：1，他引：1  

付永涛  曾佐勋 《地质科技情报》1997,16(1):108-112

褶皱含有岩石经历的变形和变形条件的信息。力学、数学、数值和实验分析显示，通过分析单层纵弯褶皱的形态可获得流变学信息。数值模拟表明褶皱的曲率指数ｋｉ对于应力指数ｎｌ有很好的依赖性，当波长厚度比λ／ｈ≥１０时，ｋｉ随着ｎｌ的增加而增加。基于数值模拟的结论，分析了北京西山板岩中石英脉肠状褶皱，获得了石英脉的应力指数大于１０的结果，并进而获得石英脉对板岩的粘度比在２４１～６６２之间。认为这种小构造的研究方法是一个新的获取岩石流变参数的可行途径  相似文献   

Patterns of rock fragment cover generated by tillage erosion   总被引：6，自引：0，他引：6  

Jean Poesen  Bas van Wesemael  Gerard Govers  Jos Martinez-Fernandez  Philippe Desmet  Karel Vandaele  Timothy Quine  Greet Degraer 《Geomorphology》1997,18(3-4)

Intensively cultivated areas in the upper part of the Guadalentin catchment (southeast Spain) show a systematic spatial pattern of surface rock fragment cover (R_c). The objective of this paper is to quantify and to explain this spatial rock fragment cover pattern. Therefore, a map of an intensively cultivated area of 5 km² was digitised, and for each pixel total topographic curvature was calculated. Next, rock fragment cover was determined photographically at 35 sites with a range of total slope curvatures. A linear relation between total curvature and rock fragment cover was found, except for narrow concavities. It was hypothesised that this pattern can be explained by a significant net downslope movement of rock fragments and fine earth by tillage. The displacement distances of rock fragments by tillage with a duckfoot chisel were measured by monitoring the displacement of tracers (painted rock fragments and aluminium cubes) on 5 sites having different slopes. The rare of tillage erosion for one tillage pass with a duckfoot chisel, expressed by the diffusion constant (k), equals 282 kg/m for up and downslope tillage and only 139 kg/m for contour tillage. Nomograms indicate that mean denudation rates in almond groves due to tillage erosion (3 to 5 tillage passes per year) can easily amount to 1.5–2.6 mm/year for contour tillage and up to 3.6–5.9 mm/year for up- and downslope tillage for a field, 50 m long and having a slope of 20%. These figures are at least one order of magnitude larger than reported denudation rates caused by water erosion in similar environments. Hence tillage erosion contributes significantly to land degradation. The downslope soil flux induced by tillage not only causes considerable denudation on topographic convexities (hill tops and spurs) and upper field boundaries but also an important sediment accumulation in topographic concavities (hollows and valley bottoms) and at lower field boundaries. Kinetic sieving (i.e. the upward migration of rock fragments) by the tines of the duckfoot chisel also concentrates the largest rock fragments in the topsoil in such a way that a rock fragment mulch develops in narrow valleys and at the foot of the slopes. These results clearly indicate that tillage erosion is the main process responsible for the observed rock fragment cover pattern in the study area. Since the study area is representative for many parts of southern Spain where almond groves have expanded since 1970, the results have a wider application. They show to what extent intensive tillage of steep slopes has contributed to the increase in soil degradation, to changes in hillslope morphology (i.e. strong denudation of convexities, development of lynchets and rapid infilling of narrow valley bottoms) and to the development of rock fragment cover patterns which control the spatial variability of the hydrological and water erosion response within such landscapes.  相似文献   

吐─哈盆地丘陵油田裂缝定量预测探讨     

童亨茂  钱祥麟 《高校地质学报》1995,(2)

裂缝油藏非常复杂和难以评价，本文从岩石脆性变形和递进变形的理论出发，从理论上指出了对裂缝发育程度进行定量预测的可能性，井尝试着在露头和岩芯裂缝资料的基础上，以脆性岩石的裂缝密度取决于岩石应变量为假设前提，通过构造曲率的定量分析、岩石弹性应变能的数值模拟计算，以及裂缝和断层的关系分析几方面相结合的方法，定量估算丘陵油田不同构造部位裂缝的发育程度。预测结果表明，丘陵油区裂缝发育程度总体有如下特征：裂缝密度总体西部相对较高，东部相对较低；中部较高，南北两侧较低。陵２４、２５井的预测结果和实际资料基本吻合。同时，对预测结果的可靠性作了初步评价。  相似文献   

基于DEM的地形曲率计算模型误差分析   总被引：2，自引：0，他引：2  

刘学军  王叶飞  曹志东  汤国安 《测绘科学》2006,31(5):50-53

地形曲率是地形表面几何形态和地学建模的基本变量之一。本文首先对曲率计算模型进行了归纳,然后通过数据独立的DEM误差分析方法和实际DEM的分析验证,对目前九种曲率计算的三类曲率计算模型进行了量化分析比较。研究结果表明,当DEM数据精度比较高时,高次曲面(四次曲面)能给出较高精度的曲率计算结果,而当DEM误差较大时,低次曲面(二次曲面)由于具有误差的平滑作用而能产生较高精度的曲率值。  相似文献   

钢筋混凝土不等肢异形柱轴压比限值的研究     

张新培  陈伟 《世界地震工程》2007,23(4):216-220

采用非线性全过程数值仿真算法确定不等肢T型、L型、十字型柱截面曲率延性比。再根据异形柱框架结构受地震作用时应具有的柱截面曲率延性水准确定不等肢T形、L形、十字形柱轴压比限值，为不等肢异形柱设计提供了必须的依据。  相似文献   

结合离散网格曲率和克里金的空间插值方法研究     

马志豪  王伟  孙黎明  汪淑平 《地理信息世界》2015,(3)

提出了一种结合离散网格曲率和克里金的空间插值方法,根据钻孔点数据构建初始Delaunay三角网,迭代计算三角网格点的高斯曲率,根据曲率的大小动态选择待插值点的位置,新点的高程值用克里金插值生成,完成三角网插值。在三维地质建模中实践证明,本方法在保证插值点精度的情况下,提升了曲面模型的光滑性,以较少的三角面片准确表达曲面模型的特征信息。  相似文献   

陕县申家窑矿区斜孔钻进及主要防斜措施          下载免费PDF全文

赵永利  时志兴  王春永  孟祥瑞 《探矿工程》2021,48(S1):106-110

河南省陕县申家窑-葫芦峪金矿区为国家森林保护区,在该区域内钻探施工,必须避开复杂地带及绿化区,进行绿色勘探、减少森林环境破坏,为此设计钻孔多为斜孔,但由于矿区地层遇层角大且含有大量软弱夹层,钻孔弯曲度不易控制,致使前期施工钻孔弯曲度超差而报废。本文以ZKS004钻孔为例,详细介绍了该矿区钻孔施工工艺、钻孔弯曲度的控制与预防及纠斜措施。  相似文献   

基于功率谱密度的评估岩石节理粗糙度新方法     

张传庆  郭宇航  徐金顺  刘宁  谢起明  崔国建  周辉 《岩土力学》2022,43(11):3135-3143

为进一步提高结构面粗糙特征描述的精确性和可靠性,更全面地体现出细微形貌的影响,将轮廓线凹凸起伏分解为幅值、倾角和曲率3个特征,分别代表轮廓线的高度变化、角度变化和弯曲程度变化。以Barton建议的10条标准轮廓线为例,计算其幅度、角度和弯曲度的特征曲线,获得了三者的分布规律。利用可表征微细观形貌的功率谱密度函数研究了3种特征曲线的频谱特征,然后从功率谱密度对数曲线中提取了可以描述形貌特征的分形参数D_j（斜率相关）和粗糙度参数A_j（截距相关）,在此基础上研究了D_j和A_j与节理粗糙度系数（joint roughness coefficient,简称JRC）的关系。同时,将该指标推广到了三维形貌的表征形式,并计算了大理岩剪切面的三维粗糙度。结果表明：新指标评估精确度高,可反映结构面各向异性特征,能有效表征结构面粗糙特征,对研究结构面剪切力学性质有重要意义。  相似文献   

一种基于局部曲率特征的点云精简算法     

麻卫峰  周兴华  徐文学  潘光江 《测绘工程》2015,(11)

平均曲率是分析三维表面的重要几何特征之一。根据平均曲率进行海量散乱点云数据的精简,首先通过空间包围盒法建立K邻域,然后对K邻域内的点拟合二次曲面计算平均曲率,最后以邻近区域内点的平均曲率中误差为阈值,结合点的精简概率判定点是否保留。通过与传统方法对比,证实了文中方法在保留特征点和压缩上具有较好的优势。  相似文献