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地表点电流对地电阻率观测的影响 总被引:1,自引:0,他引:1
《国际地震动态》2015,(9)
<正>将地电阻率台站地下介质简化为水平层状均匀介质模型,以点电流模拟地表干扰电流源,针对对称四极观测装置,利用转换函数滤波器法计算电流大小、方位角、距离对地电阻率观测的影响。(1)计算方法。地电阻率采用对称四极观测装置,AB为供电电极,MN为测量电极,电极均位于地表,测区采用EW和NS两个相互垂直测向布极,中心点为O。选择理论对称四极装置的奥尼尔滤波器(O’Neill20),依据姚文斌(1989)利用转换函数滤波器法计算地电阻率表达式计算对称四极装置地电阻 相似文献
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地表与井下地电阻率观测数据分析 总被引:3,自引:0,他引:3
本文介绍了目前中国运行时间超过2年以上的4个同场地地表和井下地电阻率观测台站的基本情况, 通过分析观测曲线动态变化、 观测精度以及映震能力, 得到以下初步结果: ① 井下地电阻率观测对风、 降雨以及杂散电流干扰的抑制能力要优于地表观测; ② 井下地电阻率观测年变化与地表有较大的差别, 且井下观测大大削弱了年变化幅度; ③ 井下垂直方向地电阻率观测数据相对水平方向来说阶跃及突跳较频繁; ④ 天水、 河源、 海安台井下观测对其附近地震有一定的映震能力。 相似文献
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地铁建设对江宁地电台地电阻率观测造成较大影响,通过分析观测数据,比较了地表、井下观测受地铁等因素的干扰情况,并探讨了用影响系数来研究地表、井下观测的地表浅层干扰抑制能力,得到以下初步结果:①地铁试运行期间的干扰影响大于正式运营;②井下观测对供电电流更加敏感;③井下观测能够减轻地铁等的干扰,其地表浅层干扰抑制能力优于地表观测,可作为地电观测的重点发展方向之一。 相似文献
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地震地电阻率是观测中强地震孕震过程中微变形或微破裂变化的方法之一。近年来发展起来的小极距井下地电阻率观测,不仅能够抑制地表环境干扰,还能够缓解地表地电阻率占地面积大的困扰。基于北京地区延庆台、平谷台和通州台小极距井下地电阻率观测,通过与同场地地表地电阻率对比观测和数值模拟计算,分析了地表铁质干扰、季节变化、降水和潜水等因素对地电阻率观测的影响。结果显示,与同场地地表地电阻率相比,小极距井下地电阻率对地表自然环境因素的影响有较好的抑制能力,增强了观测效能。 相似文献
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<正>1研究背景近年来,随着城市化的快速发展,地电阻率观测表现出干扰种类多、幅度大等特点。为了有效抑制地表干扰,深井地电阻率观测技术开始在国内外得到应用并逐步发展。以往研究表明,地电阻率观测受台址条件、气温、降雨等因素的影响(钱家栋等,1998;张学民等,2009;张国苓等,2013),在地震前兆异常提取中有一定困难。深井电阻率观测试验表明,井下地电阻率观测能够有效抑制季节性降雨等产生的年变及地表干扰。 相似文献
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这篇文章给出了内蒙、甘肃、宁夏某些地区的大地电磁测深结果。这些结果显示出,在地震带内地壳和上地幔电导率分布的横向变化是很明显的,而在比较稳定的鄂尔多斯地台内电导卑分布的横向变化较小,地壳和上地幔的电导率结构比较简单。基于这些结果发现,上部地壳(10—15公里)低阻层在大震震中区较为发育,这可能与大震有关。我国西北地区已有的大地电磁测深结果显示出,莫霍面並不是一个清楚的电性分界面,而某些地区的地壳中部低阻层似乎与康拉界面相应,这就使得后者成为一个明显的电性分界面。 相似文献
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The computation of the electrical potential created by a source of direct current in a horizontally stratified earth is easy, and it is now a common practice to interpret, by manual or automatic procedures, the maps of apparent resistivity or of mise-à-la-masse surveys. The study of 3-D cases requires a computer cost too high for a general use, and the available techniques usually refer only to an anomalous body embedded in a stratified medium. In fact, it often happens that the surface of the ground cannot be regarded as a plane, an assumption which can cause large discrepancies between the observed and the calculated potentials. A first estimate of these discrepancies can be made by assuming that the earth's surface makes a dihedron and the underground consists either of one homogeneous medium or of several media whose plane interfaces pass through the edge of the ground surface dihedron. Although very schematic, this approximate model can provide a useful information on the effect of the relief. 相似文献
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2020年7月12日唐山古冶 MS5.1地震发生前,井下小极距地电阻率出现快速下降-折返的变化,变化形态、异常时长符合地电阻率孕震机理变化,但下降幅度远远小于地表大极距地电阻率孕震过程的变化幅度.因此,文章基于通州台地下电性结构和装置系统,采用数值分析方法,分析地表和井下小极距地电阻率的探测深度.结果表明,当底层电性变化区域介质电阻率发生某种减小时,通州台地表和井下小极距地电阻率装置系统地电阻率观测值会下降,下降的幅度随着深部介质电阻率变化区域上界面向上的扩展而增大.相比地表观测,井下小极距电阻率观测能更显著地接收到深部电阻率变化信号,对孕震有更强的反映能力. 相似文献
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When an electric current is introduced to the earth, it sets up a distribution of charges both on and beneath the earth's surface. These charges give rise to the anomalous potential measured in the d. c. resistivity experiment. We investigate different aspects of charge accumulation and its fundamental role in d. c. experiments. The basic equations and boundary conditions for the d. c. problem are first presented with emphasis on the terms involving accumulated charges which occur wherever there is a non-zero component of electric field parallel to the gradient of conductivity. In the case of a polarizable medium, the polarization charges are also present due to the applied electric field, yet they do not change the final field distribution. We investigate the precise role of the permittivity of the medium. The charge buildup alters the electric fields and causes the refraction of current lines; this results in the well-known phenomenon of current channelling. We demonstrate this by using charge density to derive the refraction formula at a boundary. An integral equation for charge density is presented for whole-space models where the upper half-space is treated as an in-homogeneity with zero conductivity. The integral equation provides a tool with which the charge accumulation can be examined quantitatively and employed in the practical forward modelling. With the aid of this equation, we investigate the effect of accumulated charges on the earth's surface and show the equivalence between the half-space and whole-space formulations of the problem. Two analytic examples are presented to illustrate the charge accumulation and its role in the d. c. problem. We investigate the relationship between the solution for the potential via the image method and via the charge density. We show that the essence of the image method solution to the potential problem is to derive a set of fictitious sources which produce the same potential as does the true charge distribution. It follows that the image method is viable only when the conductivity structure is such that the effect of the accumulated charge can be represented by a set of point images. As numerical examples, we evaluate quantitatively the charge density on the earth's surface that arises because of topography and the charge density on a buried conductive prism. By these means, we demonstrate the use of the boundary element technique and charge density in d. c. forward modelling problems. 相似文献
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地电阻率交流观测方法能够有效抑制测区杂散电流的干扰, 包括地铁、轻轨等城市轨道交通的干扰, 但是由供电线路与测量线路间磁场的相互作用所引起的电感性耦合效应会对观测结果产生一定的影响.为研究电感性耦合效应的特征, 本文建立了地电阻率交流观测的电感性耦合模型, 同时计算了供电线路与测量线路间的互感系数.在此基础上, 通过正演模拟分析供电信号频率、地电阻率值、供电线和测量线间距离以及平行长度等参数对电感性耦合效应的影响, 并将电感性耦合模型应用于台站实际观测数据的分析中, 验证模型的合理性.结果表明, 电感性耦合效应随供电信号频率、供电线与测量线平行长度的增大而增大, 随供电线与测量线间距离的增大而减小, 随地电阻率的变化存在峰值; 且模型预测的地电阻率值与台站实际观测值有较好的一致性.本文的研究结果为消除地电阻率交流观测值中的电感性耦合效应提供了理论依据和基本模型, 为地电阻率交流观测系统的设计和建设提供参考.
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Abstract Four geoelectrical soundings were measured with a combination of Schlumberger and azimuthal or equatorial dipole electrode arrays on a Carboniferous limestone basin of the Condroz area, Belgium. The measuring technique is briefly outlined as well as the interpretation procedure, which follows a closed-loop scheme with control of calculated model curves. Some general problems of interpretation of geoelectrical sounding curves are tackled, as far as they have a practical bearing on the treatment of Condroz soundings. The problem of determining the very high resistivity of limestone is approached through ARCHIE's formula, an empirical relation between the bulk rock resistivity, the porosity and the electrolyte resistivity. An evaluation of the latter two parameters, combined with electrical horizontal conductance measurements directly made on resistivity sounding curves, offers a possibility for fast determination of the total water storage in a limestone aquifer. Such storage determinations could be applied whenever an aquifer shows up as a conductive layer interbedded between two highly resistant layers (e.g. nonsaturated limestone and compact, non-fractured limestone). 相似文献
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自2018年12月起,因洛阳地震台测区内安装金属护栏,该台地电阻率出现异常变化。为正确评估此次影响,结合洛阳地震台电测深曲线、岩性资料建立了三维水平层状结构模型,利用有限元法计算了测区内金属护栏对洛阳地震台地电阻率观测的影响。同时,建立典型“H”型电性结构模型,分析了不同属性的金属导线对地电阻率观测的影响。结果显示:①金属护栏是洛阳地震台此次地电阻率年变异常的主要影响因素。当位于测区内影响系数为负的区域时,金属护栏引起地电阻率的趋势性上升;当位于影响系数为正的区域时,金属护栏引起地电阻率的趋势性下降。②不同属性的金属导线对地电阻率观测的影响不同。导线与测道夹角减小、导线长度增加、导线电阻率减小以及导线横截面积增加等均会导致干扰源对地电阻率年变影响作用增强。 相似文献