Application of three numerical procedures to evaluation of earthquake-induced damages   总被引：1，自引：0，他引：1  

K. Sivathasan  X. S. Li  K. K. Muraleetharan  C. Yogachandran  K. Arulanandan 《Soil Dynamics and Earthquake Engineering》2000,20(5-8):325-339

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Indentation of a continent with a built-in thickness change: experiment and nature     

Dimitrios Sokoutis  Marco Bonini  Sergei Medvedev  Mario Boccaletti  Christopher J. Talbot  Hemin Koyi 《Tectonophysics》2000,320(3-4):243-270

Orogens oblique to the direction of plate convergence are currently attributed to obliquity between the margins of one or both of the sutured continents to their direction convergence. We use a single analogue experiment and natural examples to illustrate a potential additional factor: variations in strength of the indented continent at a high angle to the convergence direction. The wavelengths of structures in laterally shortened lithosphere depend on the strength of the most competent layers. Lateral variations in crustal thickness must therefore lead to structures oblique to any applied lateral compression.

An analogue experiment was performed to explore this phenomenon. A two-layer ‘indented continent’ was modelled by a brittle upper crust of sand above a lower crust of high-viscosity polymer floating on a single layer of low-viscosity syrup representing the mantle. The well-known strike-slip structures allowing lateral escape to distant weak boundaries were hindered by lateral boundaries in front of the indenter. This allowed us to focus on the effects of a thickness change built into the ‘indented continent’ along a zone parallel to the direction in which a vertical rigid wall advancing at a steady rate represented the indenter. Vertical escape led to an ‘orogenic belt’ oblique to the advancing wall; this obliquity influences subsequent lateral escape. Model scaling and interpretations are based on Extended Thin Sheet Approximation (ETSA) and standard theories of faulting.

Four sectors of the Alpine–Himalayan orogen (Iran, Tunisia, the Eastern Alps and the Himalaya) are oblique to the continental convergence direction, and we point to thickness changes at high angles to the suture that may account for this geometry. As crustal thicknesses north of oblique sectors of the Himalayas are not yet known, we speculate on them.

We infer from the main difference between our experiment and all our examples chosen from nature that vertical orogenic escape was oblique to our model suture but can be parallel to natural sutures.  相似文献   

Electron, muon, and hadron lateral distributions measured in air showers by the KASCADE experiment     

《Astroparticle Physics》2001,14(4):245-260

Measurements of electron, muon and hadron lateral distributions of extensive air showers as recorded in the Karlsruhe shower core and array detector experiment are presented. The data cover the energy range from 5×10¹⁴ eV up to almost 10¹⁷ eV and extend from the inner core region to distances of 200 m. The electron and muon distributions are corrected for mutual contaminations by taking into account the detector properties in the experiment. All distributions are well described by NKG functions. The scale radii describing the electron and hadron data best are 30 and 10 m, respectively. We discuss the correlation between the scale radii and the ‘age' parameter as well as their dependence on shower size, zenith angle, and particle energy threshold.  相似文献   

勒夫波群速度频散与太平洋地壳及上地幔三维构造   总被引：1，自引：0，他引：1       下载免费PDF全文

庄真  邓大量 《地球物理学报》1987,30(3):246-260

应用现代适配滤波频时分析技术对SRO/GDSN长周期面波记录进行处理,获得穿过太平洋盆地的117条波路径的勒夫波频散数据。我们用改进的分格频散反演方法,从混合路径频散数据中提取出对应于构成整个太平洋盆地的10°×10°分格的纯路径频散数据。所获得的18s到215s范围内的28个周期的太平洋勒夫波群速度的横向分布,揭示了速度随海底年龄的增大而逐渐增加的总趋势,以及其它变化细节。例如,对于同一等年龄线区而言,北太平洋及南太平洋的群速度要比中太平洋的低0.1-0.3km/s。在分格模型反演的基础上得出的深至300km的三维剪切波速度结构提供了太平洋盆地地壳及上地幔横向不均匀性的详尽的描述。  相似文献   

Basement control on oblique thrust sheet evolution: seismic imaging of the active deformation front of the Central Andes in Bolivia     

Ralph Hinsch  Charlotte M. Krawczyk  Christoph Gaedicke  Raul Giraudo  Daniel Demuro 《Tectonophysics》2002,355(1-4)

In the area of the Bolivian Orocline, we examine the deformation pattern associated with the active development of a new thrust sheet. A dense grid of reprocessed 2-D seismic lines from hydrocarbon exploration industry is interpreted and a 3-D simplified structural and kinematic model is deduced. In the Boomerang Hills, onlapping Paleozoic and foredeep sediments are detached from the underlying S-dipping basement. They are thrust northeastwards by less than 2 km. Two zones can be differentiated along the Andean deformation front: (1) a W–E to NW–SE striking frontal segment of predominantly orthogonal shortening, comprising a thrust and anticline system; (2) a WSW–ENE striking lateral zone of oblique shortening within a complex system of thin-skinned strike–slip faults and minor folds. The deformation front always follows a pronounced edge in the topography of the top basement surface close to the boundary of the Paleozoic basin. The observed deformation pattern indicates intensified strain partitioning caused by the interaction of contraction direction and basement topography, which provides a near oblique ramp for the onlapping wedge of sediments. The SW–NE thrusting direction is divided into orthogonal and tangential components. These are accommodated by convergent and strike–slip structures, respectively, which sole into a common detachment horizon. The structural evolution of the new thrust sheet in the Bolivian Orocline is primarily controlled by the paleorelief of the Brazilian Shield because: (1) the shape of the basement affects the taper of the thrust wedge and localizes the deformation front and (2) small asperities in/close to the top of the basement promote fault localization. The coincidence of a relatively high basement position and a structural high of the Eastern Cordillera leads to the conclusion that the shape of the Brazilian Shield also controls the structural evolution of the pronounced eastern border of the Bolivian Orocline.  相似文献   

用遗传算法确定三维横向不均匀介质中的近震震源位置   总被引：8，自引：0，他引：8       下载免费PDF全文

万永革  李清河  李鸿吉  丁志峰 《地震工程学报》1997,19(2):7-14

介绍了用遗传算法在三维横向不均匀介质中确定震源位置的研究思路并简述了三维横向不均匀介质中走时计算的基本原理，在遗传算法的迭代过程中，考虑到初始迭代阶段有较大的参数搜索空间而在最后迭代阶段有较小的参数空间，提出了遗传算法中变异概率随迭代次数下降的函数形式并对其进行了分析，结果表明，随迭代次数指数下降的变异概率使得算法收敛加快，而且反演得到的震源位置的各台站走时残差比原定震源位置的明显减小。  相似文献   

外侧性腰椎间盘突出和椎管狭窄的CT研究     

戴金汉  曾幼鲁 《CT理论与应用研究》1997,6(1):5-7

本文介绍１４例外侧性腰椎间盘突出和外则性椎管狭窄。普通放射学检查诊断结果常不满意。文章简述了椎管的正常解剖并了两种病症的发病原因和常见部位。特别指出ＣＴ和ＣＴＭ对此病的诊断正确率较高。  相似文献   

灌注桩桩土相互作用试验及有限元模拟研究   总被引：9，自引：4，他引：9  

赵法锁  俞剑勇  罗丽娟  卢全中  胡志平 《工程地质学报》2001,9(1):87-92

以灌注桩桩土相互作用的原位试验为基础, 结合西安土层结构、性质; 采用有限单元法对黄土地区的砼灌注桩桩土相互作用进行仿真模拟, 研究了桩土相互作用、荷载的传递规律、桩土相对位移与桩侧摩阻力的关系。通过桩载试验资料对比, 得出三维有限单元法的模拟结果与实测值相近, 该研究进一步揭示了桩土相互作用的实质, 为最优桩长的选取和单桩承载力的确定奠定了基础。  相似文献   

砂土液化诱发的地面侧移机理研究   总被引：4，自引：1，他引：4  

景立平  张荣祥 《地震工程与工程振动》1996,16(3):128-136

本文分析了砂土液化诱发的地面侧移的机理，提出了估计砂土液化诱发的地面侧移的一种新的方法。  相似文献   

Inversion of a transfer system into lateral ramps: An example from the South-Central Pyrenees (Spain)     

J. F. Flinch  J. M. Casas 《International Journal of Earth Sciences》1996,85(2):372-379

Field work in the South-Central Pyrenees suggests that omission contacts (i.e. younger over older rocks) occur at the base of the Cadí unit (Cadí thrust), and pass laterally into thrusts. This change occurs across tear faults which are present in the hangingwall of the Cadí thrust sheet and which controlled the deposition of Upper Cretaceous sediments (Adraén formation). Detailed mapping in the contact area between the Nogueres and Cadí units has shown that the actual thrust geometry in the study area is controlled by preexisting normal and transfer faults which developed in an already compressional context. Lateral ramps or tear faults develop depending on the angle between the pre-existing extensional transfer fault and the thrust transport direction.  相似文献