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Within a geological massif in a stable geodynamical situation contacts on the grain boundaries in polycrystalline rocks at great depths are continuous and firm. The stress release of those rocks during drilling and excavation to the surface is accompanied by their disintegration (decompaction). The reason for the decompaction is generation of microcracks during stress release due to the difference between the elastic moduli of crystalline grains at their contacts. The mechanism of decompaction may occur not only in polymineral but in polycrystalline rocks as well. The method of decompaction evaluation of deep crystalline rocks under stress relief is presented. According to the calculations the initial manifestation of the decompaction effect in biotite gneisses will occur when they are extracted from the deep range of 0.8–1 km. The first microcracks arise on the grain borders between quartz–biotite and oligoclase–biotite. It is shown that the uplift of gneiss–granite varities of the rocks cut by the Kola superdeep borehole from depths exceeding 13–15 km will be possible in a form of separate mineral grains. Practical importance of the presented method is in an opportunity to evaluate the level of excavated decompaction. The method allow estimating the depth, from which the rock will be extracted only in a sludge form. 相似文献
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使用接收函数研究壳幔速度间断面和速度结构已是常用的技术,但介质各向异性或倾斜的莫霍(Moho)界面,都会造成接收函数波形的复杂性。本文利用远震P波接收函数计算台站下方的地壳各向异性,通过信噪比测试和谐波分析两种方法来验证各向异性结果的可靠性。通过甘肃地震台网的两个台站记录,讨论各向异性和倾斜界面对接收函数的影响,结果显示,台站BYT(白银)下方具有各向异性,而台站WYT(渭源)下方由于可能存在倾斜界面,得到的各向异性结果则有待进一步分析。为了更好地认识倾斜界面对各向异性计算结果的影响,采用合成理论地震图,计算接收函数,然后利用合成接收函数进行各向异性分析。结果表明,计算得到的快波方向不会受到倾斜界面的影响,但是时间延迟会受到影响。 相似文献
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使用二维粒子模拟（PIC）的方法研究了在电流片两侧具有不同温度或密度情况下的无碰撞磁场重联过程.在初始等离子体密度非对称的情况下,发现重联区等离子体流场结构、电磁场结构以及重联过程与对称情况下的结果有明显不同.通过对电流片两侧温度比取不同的参数Tm/Ts=1,2,5进行模拟(其中Tm和Ts分别代表磁层侧和磁鞘侧的温度),结果分析发现,(1)在密度非对称系统中,出流区电子沿着分离面出现一个整体的从高密度区向低密度区的流动,并围绕磁岛形成一个电流环;(2)在高温低密度一侧,在重联过程中,分离面两侧将出现很强的电荷分离并产生一个基本垂直于分离面的强度较大的电场Ez,其幅度和空间尺度与温度梯度近似地成线性正比和反比关系.在初始电流片两侧温度之比取Tm/Ts=5的情况下,Ez的幅度将达到0.71,其空间尺度与局地电子惯性长度de同一量级,这一结果与观测相吻合;(3)重联率随着温度梯度增大而下降. 相似文献
14.
许多水库大坝,特别是土、石坝,由于长年自然因素和人为破坏,普遍存在渗漏现象.为了维护水库的正常使用,对水库大坝的隐患进行检测,显得尤其重要.采用弹性波法中的垂直反射波法和瞬态面波法,利用坝基缺陷可能造成的反射波场和速度变化特征,给出了综合检测水库土、石坝基缺陷情况的方法技术.通过实践,验证了采用综合方法技术进行检测的有效性和实用性. 相似文献
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Jrme Gattacceca Pierre Rochette Matthieu Gounelle Matthias Van Ginneken 《Earth and Planetary Science Letters》2008,270(3-4):280-289
We investigate the petrofabric of crustal rocks from Mars and Vesta through the measurement of the anisotropy of the magnetic susceptibility (AMS) of achondrites. Previous data are integrated with new measurements to obtain a dataset that provide macroscopic information about the magnetic fabric of 41 meteorites of the howardite–eucrite–diogenite clan (HED, falls only) and 16 Martian meteorites. The interpretation takes into account the large contribution of paramagnetism to the magnetic susceptibility of these meteorites. We use a model that allows the computation of the anisotropy degree of the population of ferromagnetic grains and provides a quantitative proxy for the degree of shape preferential orientation of these grains in HED and Martian meteorites. The results also provide quantitative information about the shape of the magnetic fabric (prolate, oblate).In HED achondrites, the ductile FeNi grains are sensitive strain recorders and our magnetic fabric data provide the first quantitative insights to the strain history of the crustal rocks of Vesta. Most HED achondrites are breccias but display a strong and spatially coherent magnetic anisotropy, indicating that intense deformation of FeNi grains took place after brecciation. The average fabric of eucrites, howardites is oblate (i.e. the texture is foliated) whereas the fabric of diogenites is more neutral. The howardite results suggest the existence of an isotropic fraction of ferromagnetic minerals that can be ascribed to the presence of carbonaceous chondrite clasts that have preserved their original magnetic fabric. In this hypothesis, howardites have an intensity of petrofabric very similar to eucrites and diogenites. Thermal metamorphism (itself possibly impact-related) plus lithostatic compaction occurring after brecciation appears as the best candidate to explain the observed petrofabric in eucrites and diogenites, whereas compaction by hypervelocity impacts may be reponsible for the fabric of howardites.Martian meteorites may still possess their primary magmatic fabric. Among Martian meteorites, basaltic shergottites and nakhlites display an oblate fabric (foliated texture) with only limited variations among each group. Olivine–phyric shergottites have a neutral fabric that points to a different petrogenesis. Nakhlites have weaker fabric intensity than shergottites. The fabric intensity is comparable to what is classically observed in terrestrial volcanic and plutonic rocks. 相似文献
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