Seismic structure of the Helan–Liupan–Ordos western margin tectonic belt in North-Central China and its geodynamic implications     

《Journal of Asian Earth Sciences》2014

We study high-resolution three-dimensional P-wave velocity (Vp) tomography and anisotropic structure of the crust and uppermost mantle under the Helan–Liupan–Ordos western margin tectonic belt in North-Central China using 13,506 high-quality P-wave arrival times from 2666 local earthquakes recorded by 87 seismic stations during 1980–2008. Our results show that prominent low-velocity (low-V) anomalies exist widely in the lower crust beneath the study region and the low-V zones extend to the uppermost mantle in some local areas, suggesting that the lower crust contains higher-temperature materials and fluids. The major fault zones, especially the large boundary faults of major tectonic units, are located at the edge portion of the low-V anomalies or transition zones between the low-V and high-V anomalies in the upper crust, whereas low-V anomalies are revealed in the lower crust under most of the faults. Most of large historical earthquakes are located in the boundary zones where P-wave velocity changes drastically in a short distance. Beneath the source zones of most of the large historical earthquakes, prominent low-V anomalies are visible in the lower crust. Significant P-wave azimuthal anisotropy is revealed in the study region, and the pattern of anisotropy in the upper crust is consistent with the surface geologic features. In the lower crust and uppermost mantle, the predominant fast velocity direction (FVD) is NNE–SSW under the Yinchuan Graben and NWW–SEE or NW–SE beneath the Corridor transitional zone, Qilian Orogenic Belt and Western Qinling Orogenic Belt, and the FVD is NE–SW under the eastern Qilian Orogenic Belt. The anisotropy in the lower crust may be caused by the lattice-preferred orientation of minerals, which may reflect the lower-crustal ductile flow with varied directions. The present results shed new light on the seismotectonics and geodynamic processes of the Qinghai–Tibetan Plateau and its northeastern margin.  相似文献   

Study of the anisotropy of cosmic rays with <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript>≥5×10<Superscript>16</Superscript> eV using Yakutsk EAS array data     

A. V. Glushkov 《Astronomy Letters》2003,29(3):142-152

We present the results of a harmonic analysis of and search for clusters in the arrival directions of cosmic rays with energies E₀≥5×10¹⁶ eV and zenith angles ?≤53° detected at the Yakutsk extensive air shower (EAS) array from 1974 to 2002. We show that the phase of the first harmonic periodically varies greatly and takes on nonrandom values at a confidence level ≥4σ. These phases point to the Supergalactic plane (the Local supercluster of galaxies).  相似文献   

Fabric dilatancy and the plasticity modeling of granular media     

B. Muhunthan  N. Sasiharan 《国际地质力学数值与分析法杂志》2012,36(9):1181-1193

A novel conceptual model of the mechanics of sands is developed within an elastic–plastic framework. Central to this model is the realization that volume changes in anisotropic granular materials occur as a result of two fundamentally different mechanisms. The first is purely kinematic, dilative, and is the result of the changes in anisotropic fabric. There is also a second volume change in granular media that occurs as a direct response to changes in stress as in a standard elastic/plastic continuum. The inclusion of the two sources of volume change results in three important datum states. When subjected to isotropic strains, the resulting stress state in granular materials is not isotropic but lies upon the kinematic normal consolidation line. There exists a state at which the fabric‐induced volumetric strain rate becomes equal to the stress‐induced volumetric strain rate making the total plastic volumetric strain rate equal to zero. Granular response changes from contractive to dilative at this phase transformation line. The third datum state is the one in which the stress‐induced volumetric strain rate is zero. The sand, however, continues to dilate at this state with the difference between stress and dilation ratio a constant as predicted by Taylor's stress–dilatancy rule. These predictions are shown in accordance with experimental data from a series of drained tests and undrained on Ottawa sand. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Anisotropic Inhomogeneous Riemann S-Ellipsoids in Spheroidal Halos. I.     

M. G. Abrahamyan 《Astrophysics》2005,48(4):514-531

The classical Riemann S-ellipsoids are generalized to account for a Ferrers inhomogeneity in the mass distribution, a three-dimensional anisotropy of the velocity dispersions, and the gravitation of a spheroidal halo. The Ferrers inhomogeneity does not affect the equilibrium and stability conditions for the ellipsoids, but only changes the numerical coefficients in the equilibrium parameters. The anisotropy of the velocity dispersions changes both the equilibrium conditions and the criterion for stability of the ellipsoids, either extending or limiting the region in which the ellipsoids exist. A halo extends this region in all cases and stabilizes the ellipsoids. The observed of the velocity dispersions of stars in the neighborhood of the sun are obtained using the inhomgeneous model. __________ Translated from Astrofizika, Vol. 48, No. 4, pp. 613–632 (November 2005).  相似文献   

Overall properties of heterogeneous material   总被引：1，自引：0，他引：1  

J. A. Hudson 《Geophysical Journal International》1991,107(3):505-511

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Effects of applied stress on effective elastic anisotropy in cracked solids     

Evgenyi M. Chesnokov  Sergei V. Zatsepin 《Geophysical Journal International》1991,107(3):563-569

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Inverting shear-wave polarizations for anisotropy using three-component offset VSPs: synthetic seismograms   总被引：1，自引：0，他引：1  

Colin MacBeth 《Geophysical Journal International》1991,107(3):571-583

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层理性页岩力学参数对水力压裂裂缝形态的影响分析          下载免费PDF全文

胡光 《探矿工程》2022,49(2):97-103

岩石力学性质及地应力等地质力学参数是进行储层压裂改造的基础数据,影响着整个压裂设计的准确性。由于页岩层理发育及矿物组成的复杂性、页岩力学性质的横观各向同性,所以基于传统力学模型获取的压裂参数设计将丧失意义。以横向各向同性模型体现层理发育页岩储层的力学性质,通过简化的横纵弹性模量和泊松比可以较好地表达出页岩的横观各向同性,并总结了横观各向同性地应力解释方法。基于上述理论,应用商业化水力压裂数模软件对四川盆地某层理页岩储层进行了压裂设计,比较了基于横观各向同性模型与传统模型解释力学参数差异,非常规储层动静态力学参数转换,同时通过改变射孔位置研究了起裂点对裂缝形态的影响。研究发现,横观各向同性解释的杨氏模量、地应力要略高于传统方法,同时横观各向同性解释的地层地应力差较小,所以受不同射孔位置的变化对裂缝几何的形态影响要远远高于各向同性模型模拟的结果,特别是缝高变化更为明显。同时数据表明,在高应力区射孔将形成更为狭窄缝宽的水力裂缝,这会严重影响后续支撑剂的进入,以上结论将为提高页岩储层的压裂设计精确性给予重要帮助。  相似文献   

混合型缓冲材料砌块渗透性及其各向异性研究     

张虎元  王赵明  朱江鸿  周光平 《岩土力学》2022,43(3):573-581

缓冲材料砌块具备良好的防渗性能,是保证高放废物处置库封闭性的关键。缓冲材料砌块经单轴加载挤压成型,块体尺寸大,测试与评价其渗透性能的均匀性和各向异性,对缓冲屏障设计具有重要价值。研究制备不同干密度的混合型缓冲材料砌块,定向切割获得砌块内部不同位置、不同方向的小试样,开展刚性壁和柔性壁渗透试验,综合评价了混合型缓冲砌块不同方向的水力传导系数。研究结果表明：砌块干密度越大,砌块的水力传导系数越低。所有砌块的水力传导系数均处于10?10 cm/s数量级,沿砌块z、?、r方向的水力传导系数基本相等,表明砌块渗透性具有良好的均匀性和各向同性,且满足高放缓冲材料防渗要求。两种试验方法获得的渗透结果差异较小,柔性壁渗透条件下砌块产生10%～20%的体积膨胀,导致其水力传导系数略大于刚性壁下的平行试样。引入CT试验,分析了渗透前后砌块的微观特性变化。试验证实,在饱和渗透之后,以CT值显示的砌块密度分布趋于均匀,砌块内部存在的微裂隙愈合消失。  相似文献   

基于单三轴试验与直剪试验的层状软岩模拟     

潘文韬  杨文波  吴枋胤  何川  赵亮亮  姚人杰  傅舰锋 《岩土力学》2022,43(12):3437-3452

为探究模型试验中层状软岩模拟方法,依托九绵高速层状软岩隧道现场取样的室内试验结果,多次试验确定重晶石粉、石英砂、石膏粉、滑石粉和水的最优配比以模拟软岩基体,采用带孔薄膜模拟层理弱面的黏结作用,并通过直剪试验确定孔隙率,最后对不同层理角度与层理厚度的试样开展直剪与单、三轴试验以反映各向异性情况。结果表明：软岩基体模拟最优配比为0.55:0.15:0.07:0.06:0.17,重晶石粉对强度及破坏变形起决定作用,含量过低易压溃,含量过高产生上下贯通裂缝;采用30%孔洞率的薄膜模拟层理效果最佳;土样强度随层角呈U形变化,层厚减小（不小于2 cm）,强度减小。直剪试验中,45º层理剪切面朝层理方向倾斜,90º层理导致剪切面上下产生裂缝与碎裂,单三轴结果中,0º层理会产生小角度倾斜裂缝,45º层理产生垂直层理面的斜裂缝及二次破裂,90º层理产生顺层理的竖向劈裂;与现场结果对照后确定最优层厚为 3 cm,对层角与层厚的直剪与单三轴试验结果整体一致,揭示土样孔隙压密闭合−弹性−塑性胀裂破坏−徐变的过程。  相似文献