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1.
H. Fournier 《Surveys in Geophysics》1980,4(1-2):89-96
The technique of magnetotelluric sounding has been used for 25 years and a wealth of information has been obtained from regional studies. A table of results and an accompanying extensive bibliography was presented to the Murnau Workshop and this review discusses some aspects derived from the accumulated literature. In particular, the deep conducting layer (CCU) is considered. 相似文献
2.
为了避免形态滤波方法在大地电磁强干扰分离中的"过处理"、进一步保留大地电磁低频段的有用信息,提出基于信噪辨识的矿集区大地电磁噪声压制方法.首先,从信号处理的角度剖析矿集区典型强干扰与天然大地电磁微弱信号之间的定量辨识关系,利用形态分形维数和形态膨胀谱熵对大地电磁信号与强干扰进行信噪辨识.然后,结合形态滤波技术和阈值法,仅对辨识出明显不是天然大地电磁信号的异常波形进行噪声压制.最后,重构大地电磁有用信号,并对算法进行性能评价.仿真结果表明,形态分形维数和形态膨胀谱熵能较好地定量辨识大地电磁信号与强干扰,大地电磁信号中一些缓变化的低频信息得到了更为精细的保留;与形态滤波整体处理相比,本文所提方法获得的卡尼亚电阻率曲线更为光滑、连续,视电阻率值相对稳定,其结果更为真实地反映了测点本身所固有的大地电磁深部构造信息. 相似文献
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4.
Lamarque 《Geophysical Prospecting》1999,47(6):819-840
The great majority of data processing methods for magnetotelluric measurements are based on an average Fourier spectral analysis to estimate either the transfer function or the coherence function. This assumes that the time-series data are stationary. The aim of this paper is to present a preprocessing method able to extract the stationary and coherent part of the original signals. The practitioner can then apply the magnetotelluric method of his choice to these new data. This preliminary data sorting is done in four steps: (i) slow drifts are eliminated using a high-pass filter whose cut-off frequency is determined by an iterative procedure. Based on run tests, this procedure is also able to remove segments with non-independent samples in the time series; (ii) non-stationary segments are eliminated after band-pass filtering; (iii) non-coherent segments are eliminated before spectral analysis; (iv) the impedance tensor value is then retained, at a given frequency, only if the signals are coherent. This preprocessing method was tested on the simplest, but still used, magnetotelluric method which uses only two field components, and it was found that the average resistivity standard deviation decreased significantly from 14.6 Ωm without sorting to 8.6 Ωm after sorting. 相似文献
5.
The data of long-term electromagnetic monitoring are used for studying the dynamics of electric conductivity of the medium
and the electric field of the terrestrial sources. The electric conductivity of the medium is estimated from the magnetotelluric
transfer functions (impedance tensor and telluric tensor). The electric field of terrestrial sources is identified by filtering
the variations of the observed electric field of the Earth. The magnetotelluric parameters and the electric field of terrestrial
sources feature anomalous changes of supposedly earthquake-related origin. The anomalies associated with the same earthquake
are not simultaneous. It is shown that these anomalies are generated by processes occurring at different depths. The strong
earthquake is preceded by the appearance of surface anomalies several months before the event and accompanied by a deep coseismic
anomaly. The probable nature of the recognized anomalies is discussed. 相似文献
6.
The boundary-element method is used to model the 2D terrain effect on the magnetotelluric (MT) field. Firstly, the boundary-value problem of a 2D magnetotelluric field is transformed into an integral equation problem by using Green's theorem. Then the boundary-element method is used to solve the integral equation and to obtain the MT field and its normal derivative on the terrain. From these values, the apparent resistivity can be calculated. Compared with the finite-element method, the boundary-element method is simpler in element division and the initial data preparation. The configuration of a terrain divided by the boundary-element method is more consistent with the practical terrain. The method proposed in this paper can be run on a microcomputer, so that it can be used in the field. 相似文献
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作为全局非线性优化的新方法之一的遗传算法,近年来已从生物工程流行到大地电磁测深资料解释中.然而,大地电磁反演问题具有不适定性,解的非唯一性.通过结合求解不适定问题的Tikhonov正则化方法,本文采用实数编码遗传算法求解大地电磁二维反演问题.此算法在构建目标函数时引入正则化的思想,利用遗传算法求解最优化问题.常规的基于局部线性化的最优化反演方法易使解陷入局部极小值,而且严重的依赖初始模型的选择.与传统线性化的迭代反演方法相比,实数编码遗传算法能够克服传统方法的不足且能获得更好的反演结果.通过对大地电磁测深理论模型进行计算,结果表明:该算法具有收敛速度快、解的精度高和避免出现早熟等优点,可用于大地电磁资料解释. 相似文献
9.
祁连山东端冷龙岭隆起及其附近地区是青藏高原东北缘与阿拉善地块强烈相互挤压碰撞区域,也是历史地震活动极为强烈区域.为了揭示冷龙岭隆起及其附近区域的断裂深部延伸状况、强震孕育构造背景以及区域动力学特征等,我们在已有大地电磁数据的基础上,新近在冷龙岭隆起附近以及西南侧区域进行了数据采集,获得了一条自西南向北东穿过西秦岭地块、陇西盆地、祁连山冷龙岭隆起和阿拉善地块的长约460 km的大地电磁剖面(LJS-N)数据,并利用三维电磁反演成像技术对全剖面数据进行了反演,同时也对位于该剖面西侧约80 km外的一条大地电磁剖面(DKLB-M)数据进行了三维反演成像.2条电磁探测剖面结果均揭示了祁连—西海原断裂带展现为略向西南倾斜的大型超壳电性边界带,该断裂是祁连山东端冷龙岭隆起区域最重要的主边界断裂,其北东侧和西南侧地块的深部电性结构呈现出截然不同电阻率分布特征,其西南侧的南祁连地块、陇西盆地以及西秦岭地块在地壳尺度展示为埋深深浅不一的高-低-次高阻结构特点,而其北东侧古浪推覆体表现为西南深、东北浅“鼻烟壶”状较完整的高阻结构特征,再往北到阿拉善地块则呈现为高-低-次高水平三层结构样式.1927年M 8.0古浪、1954年M 7.0民勤和2016年M 6.4门源地震的震源都处于统一的高阻古浪推覆体之中.在青藏高原北东向挤压作用的控制下,祁连山东端冷龙岭隆起区域的祁连—西海原断裂、祁连山北缘断裂和红崖山—四道山断裂以叠瓦状向北北东向顺序推覆拓展到阿拉善地块,这种拓展作用是该区中强地震的动力来源. 相似文献
10.
本文将大地电磁场分解为一次场和二次场,应用交错网格有限差分法模拟计算大地电磁二次场,并引入各向异性最佳匹配层(PML)吸收边界条件作为二次场边界条件,实现了耦合PML吸收边界条件的三维大地电磁二次场有限差分正演模拟.为了确保正演的稳定性和效率,QMR求解器和磁感应矢量散度校正技术被用于PML吸收边界条件下系数矩阵的快速求解.三维模型正演响应表明,基于二次场的三维大地电磁有限差分算法具有较高的计算精度和可靠性.通过计算分析不同PML吸收因子条件的大地电磁正演结果,显示在适当的吸收因子下,PML吸收边界条件可较大幅度的减小外边界距离,从而有效的压缩模型求解空间,最终提高三维大地电磁正演模拟的效率. 相似文献
11.
V. V. Spichak 《Izvestiya Physics of the Solid Earth》2006,42(1):60-68
Various hypotheses of the geoelectric structure of the Transcaucasian region reflecting a priori geological and geophysical information and data from profile magnetotelluric (MT) soundings are analyzed. These hypotheses are used to construct simplified 3-D models of electrical conductivity differing in the patterns of the shallow and deep structure of the region. Numerical modeling of MT fields is performed. Comparative analysis of its results indicates that the most probable conductivity model consistent with the available data is a model involving a high-conductivity channel connecting the Black and Caspian seas. 相似文献
12.
采用规则六面体单元和并矢Green函数奇异积分等效积分技术,已有的大地电磁积分正演方法具有不能有效模拟地下复杂地质体和计算精度偏低的缺点.本文提出了一种新的三维大地电磁积分方程正演技术,即采用四面体单元、解析的并矢Green函数奇异积分表达式,达到既能模拟地下复杂异常体,又能有效提高已有积分方程法计算精度的目的.首先,采用四面体网格技术离散地下复杂异常体,获得四面体单元上的大地电磁积分方程.然后,利用针对四面体单元开发的新的奇异值积分的解析表达式,准确计算线性方程中的并矢Green函数的奇异积分,从而获得精确的线性方程.借助于PARDISO高性能并行直接求解器,实现了三维大地电磁问题的高精度求解.最后,基于国际标准3D-1模型和六棱柱模型,通过与其他方法结果的对比分析,验证了本文方法的正确性、处理高电导率对比度的能力(1000:1)和处理复杂模型的能力. 相似文献
13.
This paper reports the results of magnetotelluric sounding (MTS) in the area where the Bol’she-Bannyi hydrothermal springs are discharged. The MTS curves were inverted on the assumption of a twodimensional inhomogeneous model using longitudinal and transverse curves of apparent resistivity. It was found that the geoelectric section contains a nearly vertical anomaly of high electrical conductivity at depths of 5.5–8 km, which is the signature of a deep-seated fault. The resulting geoelectric section for the upper crust and data from regional magnetotelluric soundings were used as a basis for developing a conceptual deep model of the Bol’she-Bannyi hydrothermal system. We quote an approximate estimate of rock porosity. According to the model, deep fluids come from a crustal layer into the subvertical deep-seated fault then penetrate via fissures into the sedimentary–volcanogenic cover, and finally arrive at the ground surface in zones of high rock permeability. We provide a recommendation for drilling a deep well in order to determine the potential of the Bol’she-Bannyi hydrothermal field. 相似文献
14.
Synchronous annual variations in the geoelectric and geomagnetic field are studied on the basis of long-term electromagnetic monitoring. It is shown that the annual geoelectric variations have intraterrestrial origin and are not related to the annual geomagnetic variations. Temporal variations in the magnetotelluric impedance and magnetic tipper, which characterize the electrical conductivity of the geological environment, are analyzed. It is established that annual variations in the magnetotelluric impedance mainly describe the variations in the electrical conductivity of surface crustal layers and are less sensitive to the deep electrical conductivity of the Earth. The annual variations in the imaginary magnetic tipper at the periods of 1000–3000 s probably reflect the changes in conductivity of a deep transversal low-resistive zone (the fault). It is suggested that annual variations in the geoelectrical and geomagnetic fields, as well as in the electrical conductivity of the geological environment, arise as a response to the changes in the geodynamical processes caused by the revolution of the Earth around the Sun.
相似文献15.
快速且高精度的三维大地电磁法正反演是目前研究的热点.由于大地电磁法场源的平面波特性,以往的正演方法大多采用直接求解总场的方法,在边界强加二维边界条件.本文提出了一种基于二次场方法的三维大地电磁法正演算法,将平面波在层状背景模型中的响应作为场源项,得到二次场满足的偏微分方程,并利用交错网格有限差分法求取二次场.与其他学者的基于总场方法的结果的对比证明了本文采用方法的正确性.在基于二次场的正演算法基础上,实现了基于L-BFGS的三维反演方法,并对公开的数据集进行了反演.另外,针对大地电磁法的多频率观测特性,采用了基于MPI的分频并行策略对程序进行并行化,可达到接近线性的加速比. 相似文献
16.
Summary Methods of solving the inverse magnetotelluric problem are compared. Basic relations for Newton's method, the least-squares method and Marquardt's method are presented and the convergence properties of these methods are studied. The high effectiveness of Marquardt's method is demonstrated and its application to practical magnetotelluric data is discussed. 相似文献
17.
A formalism based upon the equal penetration depth stratification assumption is extended to a layered anisotropic medium, yielding a recursive algorithm for the computation of the magnetotelluric impedance tensor elements. The development of this new procedure requires an appropriate layer-discretization as well as an extension of the reflection coefficient definition for the anisotropic layered model.This method transfers the differential problem into an algebraic one, and is independent of the electric and magnetic field vectors. The technique is a recursive process which gives a rational matrix polynomial representation for the magnetotelluric impedance tensor.The procedure involves the use of second-order matrices, rather than the fourth-order ones normally used for such a case. Using this representation, a separation of the contribution of the model parameters from that of the frequency is achieved. Consequently the elements of the magnetotelluric impedance tensor are computed, for each frequency, using coefficients which are evaluated just once for a given model. 相似文献
18.
徐闻地区位于北部湾盆地向雷州半岛的延伸部分,具有较好的油气勘探前景.2003年至今,江苏油田在徐闻地区先后开展了重力、大地电磁测深、二维地震和三维地震,以及钻探、VSP和试油测试等油气勘探工作.徐闻地区存在比较特殊的地表与地下地质条件.工区跨越半岛陆上和浅海水域,浅表层多套火成岩覆盖(出露),深层构造破碎、地震反射成像困难.因此,开展了具有针对性的综合地球物理方法(重力、大地电磁测深和地震)研究与勘探实践,克服了单一地球物理方法的局限性,获得了较好的数据资料,减少了多解性并为该地区的油气发现奠定基础. 相似文献
19.
Vladimir Yu Semenov 《Acta Geophysica》2015,63(1):103-124
The first decade of 21st century is characterized by the appearance of new approaches to deep induction soundings. The theory of magnetovariation and magnetotelluric soundings was generalised or corrected. Spatial derivatives of response functions (induction arrows) were obtained for the ultra-long periods. New phenomena have been detected by this method: secular variations of the Earth’s apparent resistivity and the rapid changes of induction arrows over the last 50 years. The first one can be correlated with the number of earthquakes, and the second one–with geomagnetic jerks in Central Europe. The extensive studies of geoelectrical structure of the crust and mantle were realized in the frame of a series of international projects. New information about geoelectrical structures of the crust in Northern Europe and Ukraine was obtained by deep electromagnetic soundings involving controlled powerful sources. An influence of the crust magnetic permeability on the deep sounding results was confirmed. 相似文献
20.
Variations in horizontal and vertical components of the telluric field are studied within the range of periods from a few tens of seconds to diurnal and longer variations. Variations caused by an external ionospheric source are used for studying the geoelectric heterogeneity of the medium. For this purpose, an electric tipper is introduced by analogy with the geomagnetic field and its frequency response is examined. The magnetotelluric impedance is studied using data of remote geomagnetic observatories. According to the data of monitoring of the electric tipper and magnetotelluric impedance, anomalous effects are revealed that can be related to earthquakes with K ≥ 12. A method is developed for the extraction of electric field anomalies produced by intraterrestrial electric sources. 相似文献