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我们收集了紫坪铺水库区域台网记录到的2004年8月16日至2008年5月12日汶川地震前发生在震中区及附近区域的486个小震震源机制资料,运用碎裂分析法对这些震源机制数据进行分析,获得了汶川地震前3年多时间内震源区应力水平随时间的演化过程.结果显示,强震发生前震源及附近区域约在2007年6月发生了应力突变,出现了2个应力异常高值区,其形成过程同时伴随着龙门山中央断裂的应力水平降低,最终强震发生在高应力区和低应力区之间的应力梯度带上.汶川地震前应力状态的演化过程,类似于实验研究中出现的非均匀断层失稳前的地震成核现象,符合地震成核的宏观表现.巴颜喀拉块体的南边界-鲜水河断裂的短基线测量也显示出,在同一时间段鲜水河断裂南段由左旋滑动转为异常的右旋错动,反映了汶川强震前整个巴颜喀拉块体有向东加速运动的异常过程. 相似文献
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Izvestiya, Atmospheric and Oceanic Physics - A method for determining the focal mechanisms of earthquakes using the S-wave polarization direction for weak close seismic events is developed based on... 相似文献
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Geotectonics - The results of using a technology for zoning hazardous faults developed at the Institute of Physics of the Earth based on natural stress data are presented. The source of these data... 相似文献
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Aboozar Garavand Yuri Pavlovich Stefanov Yuri Leonidovich Rebetsky Rustam Alfredovich Bakeev Artem Veniaminovich Myasnikov 《国际地质力学数值与分析法杂志》2020,44(6):823-850
In many wellbore stability analyses, the ability to forecast both the occurrence and extent of plastic deformation and failure hinges upon a fundamental understanding of deformation mode and failure mechanism in the reservoir rock. This study focuses on analyzing plastic zones, localized deformations, and failures around a borehole drilled overbalanced or underbalanced through a highly porous rock formation. Based on several laboratory experiments, porous rocks are prone to deform under both shear-induced dilation and shear-enhanced compaction mechanisms depending on the stress state. The shapes of the deformation and failure patterns around the borehole are shown, depending on the initial stress state and the local stress paths. The inquiry of the local stress paths in the near-wellbore zone facilitates the understanding of the reasons for different types of failure mechanisms, including the mixed-mode and the plastic deformation structures. The modification of the 2D plane strain condition by imitating third stress in the numerical scheme helps us bring the stress paths closer to the real state of loading conditions. Our modeling reveals that the transition from isotropic to anisotropic stress state is accompanied by an increase in the deviatoric part of effective shear tensor that leads to the development of inelastic deformation, degradation, and subsequent rock failure. Particular interest is devoted to the modeling of strain localization especially in compaction mode around a wellbore and computing the amount of stress concentration at the tips of dog-eared breakouts. Stress concentration can result in a change in irreversible deformation mode from dilatancy to compaction, elucidating the formation of the shear-enhanced compaction phenomenon at the failure tips in the direction of the minimum horizontal stress. 相似文献
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The formation structures of brittle destruction in a rock layer above an active strike-slip fault in the crystalline basement is studied. The problem is analyzed from the standpoint of loading history, when after the stage of pure gravitational loading, an additional strain state of uniform horizontal shear of both the layer and underlying basement develops, which is further followed by a vertically nonuniform shear caused by the activation of the deep fault. For the studied object, irreversible fracture deformations on macro- and microlevels arise as early as the initial stage of loading under the action of gravitational stresses. These deformations continue evolving on the megascopic level in the course of horizontal shearing that is quasi-uniform both along the depth and laterally. The final formation of the structural ensemble occurs after a long stage of horizontal displacement of the blocks of the crystalline basement—the stage of localized shear. The theoretical analysis of the evolution of the stress state and morphology of the failure structures established the presence of numerous fractures with the normal dip-slip components in the intermediate-depth part of the rock mass, which are formed at the stages of uniform and localized horizontal shearing. The fractures with a strike-slip component mainly arise in the upper and near-axial deep parts of the section. 相似文献
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Yu. L. Rebetsky 《Russian Journal of Pacific Geology》2009,3(5):477-490
The field of modern tectonic stresses was reconstructed for the Earth’s crust of the northwestern segment of the Pacific subduction
zones. For this purpose, we used the method of cataclastic analysis and data on the magnitude of the stresses released at
the source of the Simushir earthquake of 2006, which allowed us to determine both the orientation of the principal stress
axes and the magnitude of the stresses and to estimate the effective strength of rock masses. The effective cohesion was estimated
for this region of the Earth’s crust as 12 bar, and the maximum shear stresses are no higher than 300 bar. The analysis of
the reconstructed stress field in the zone of the preparation of the Simushir earthquake showed that this region was almost
free of domains with high stresses where brittle failure requires considerable energy inputs. The medium level of effective
pressure indicates that this region is most favorable for the development of a large-scale brittle failure. 相似文献
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A.S. Grigoryev I.M. Volovich A.V. Mikhailova Yu.L. Rebetsky Z.E. Shakhmuradova 《Journal of Geodynamics》1988,9(2-4)
The equilibrium of an infinite linearly viscous layer overlying a rigid basement which is separated into blocks by a narrow plane slit is considered. The state of stress in the layer is caused by slow translational motions of the basement blocks. This spatial problem is shown to separate into problems of plane and anti-plane strain; their solutions are constructed in analytic form. The theoretical study was accompanied by modelling experiments. The results are applied to a kinematic interpretation of recent movements in sediments. 相似文献
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We present the results of tectonophysical reconstruction of natural stresses of the Earth's crust in the Altai–Sayan mountain region using cataclastic analysis of fault slips and seismic data on the focal mechanisms of earthquakes. This method allows one to obtain the parameters of the total stress tensor by invoking additional data: generalized experimental data on the brittle fracture of rocks, seismic data on the released stress of strong earthquakes, and data on the topography and density of rocks. Results of the tectonophysical reconstruction of stresses showed significant inhomogeneity of the stress state, which is manifested not only in the variation of the strike and dip of the principal axes of the stress tensor, determining changes in the geodynamic regime of the Earth's crust, but also in the close location of the regions of high and low isotropic tectonic pressure in relation to the lithostatic pressure. The variance of the ratio of tectonic pressure to lithostatic pressure is in the range of 0.59–1.31, with an average value for the region close to unity. This paper discusses internal or external mechanisms capable of generating the stress field obtained by the tectonophysical reconstruction. 相似文献