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排序方式: 共有172条查询结果,搜索用时 15 毫秒
1.
利用三维有限元模拟两层地球模型(包括弹性层和粘弹性层)介质的横向不均匀和断层错动的复杂性对震后地表位移场的影响,其数值结果包括弹性解和粘弹性解。结果表明,震后位移场的分布特征不仅与粘弹性层的流变特性有关,还与弹性层介质的剪切模量以及断层的同震错动有关。 相似文献
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根据中朝地台东北缘地区 (东经 1 1 7°0 0′— 1 2 6°0 0′ ,北纬 36°0 0′— 44°0 0′) 1 980— 1 997年的 380 0 0余条P波走时数据 ,利用正交投影法重建了该区地壳和上地幔的三维速度结构 .通过分析及同人工地震测深剖面的详细对比 ,证明了成像结果的可靠性 .结果表明 :中朝地台东北缘地区地壳上地幔介质存在显著的横向不均匀性 ,直至 1 2 0km深度处依然明显 ;地壳上部的速度图像清楚地反映了不同岩石单元的分布与该区不同性质的基岩分布基本吻合 ;从上、中地壳的速度图像中发现了研究区存在海城、朝阳、义县、丹东南、唐山等几个低速异常区(即速度逆反层区 ) ,其中海城、唐山、朝阳等地区的壳内低速层已由深地震测深资料所证实 ;研究区陆地发生的几次强震均发生于壳内低速层上方的高速脆性介质内 ,而渤海发生的强震 ,此现象不明显 ,但都发生于横向介质速度显著突变的位置 ;在地壳不同深度上发现了普兰店至山海关横跨渤海的北西向低速异常带 ;地震层析二维速度图像与深地震测深资料的对比表明 ,研究区利用地震层析成像技术 ,在一定条件下可以获得与人工地震测深相似的效果 相似文献
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不同电阻率测深方法对旁侧不均匀体的反映 总被引:2,自引:0,他引:2
利用三维有限元数值模拟,重点研究了旁侧三维不均匀体所产生的视电阻率的影响问题,展示了4种常规电阻率测深法在旁侧不均匀体上的异常分布特点;探讨了测深点正下方目标体异常与旁侧不均匀体异常的区别问题,指出旁侧不均匀体的影响是产生电阻率法假异常的主要原因之一. 相似文献
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Wide-angle seismic velocities in heterogeneous crust 总被引:5,自引:0,他引:5
Seismic velocities measured by wide-angle surveys are commonly used to constrain material composition in the deep crust. Therefore, it is important to understand how these velocities are affected by the presence of multiscale heterogeneities. The effects may be characterised by the scale of the heterogeneity relative to the dominant seismic wavelength (λ); what is clear is that heterogeneities of all scales and strengths bias wide-angle velocities to some degree. Waveform modelling was used to investigate the apparent wide-angle P -wave velocities of different heterogeneous lower crusts. A constant composition (50 per cent felsic and 50 per cent ultramafic) was formed into a variety of 1- and 2-D heterogeneous arrangements and the resulting wide-angle seismic velocity was estimated. Elastic, 1-D models produced the largest velocity shift relative to the true average velocity of the medium (which is the velocity of an isotropic mixture of the two components). Thick (width > λ) horizontal layers, as a result of Fermat's Principle, provided the largest increase in velocity; thin (width ≪λ) vertical layers produced the largest decrease in velocity. Acoustic 2-D algorithms were shown to be inadequate for modelling the kinematics of waves in bodies with multiscale heterogeneities. Elastic, 2-D modelling found velocity shifts (both positive and negative) that were of a smaller magnitude than those produced by 1-D models. The key to the magnitude of the velocity shift appears to be the connectivity of the fast (and/or slow) components. Thus, the models with the highest apparent levels of connectivity between the fast phases, the 1-D layers, produced the highest-magnitude velocity shifts. To understand the relationship between measured seismic velocities and petrology in the deep crust it is clear that high-resolution structural information (which describes such connectivity) must be included in any modelling. 相似文献
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Traveltime biases in random media and the S-wave discrepancy 总被引:4,自引:0,他引:4
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During several triaxial compression experiments on plastic hardening, softening, and failure properties of dense sand specimens, it was found on various stress paths that the size of the failure surface was not constant. Instead, it changed depending on the current state of hydrostatic pressure. This finding is in contrast to the standard opinion consisting of the fact that the failure surface remains constant, once it has been reached during an experiment or in situ. In general, the behaviour of cohesionless granular‐material‐like sand is somehow characterised in between fluid and solid, where the solid behaviour results from the angle of internal friction and the confining pressure. Although the friction angle is an intrinsic material property, the confining pressure varies with the boundary conditions, thus defining different solid properties like plastic hardening, softening, and also failure. Based on our findings, it was the goal of the present contribution to introduce an improved setting for the plastic strain hardening and softening behaviour including the newly found yield properties at the limit state. For the identification of the material parameters, a complete triaxial experimental analysis of the tested sand is given. The overall elasto‐plasticity concept is validated by numerical computations of several laboratory foundation‐ and slope‐failure experiments. The performance of the proposed approach is compared with the standard concept of a constant failure surface, where the corresponding yield surfaces are understood as contours of equivalent plastic work or plastic strain. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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T. K. De 《Pure and Applied Geophysics》1985,123(1):43-58
A method is proposed for the determination of the dispersion equation of Love waves propagating in a homogeneous layer lying over a laterally inhomogeneous half-space. The proposed method can be made to work only when the lateral inhomogeneities in the lower half-space are finite in nature so that their Fourier transforms are available. As an illustration the dispersion equation of Love waves is obtained for one of such media in which the shear-wave velocity and the rigidity in the lower half-space either increases or decreases along the direction of propagation of waves according as the parameter of heterogeneity is positive or negative. 相似文献