大地电磁测深和电偶源频率电磁测深资料反演

在研究大地电磁响应函数频散关系的基础上,构制了一套滤波系数算法,以用于由一套视电阻率资料估算相应的阻抗相位.理论模型和实际大地电磁观测资料的数字试验表明,该法是行之有效的.由频散关系估算的相位值与观测的相位资料的比较,可用于检验观测资料是否满足频散关系.利用经频散关系校正的阻抗相位值,进行大地电磁阻抗的联合反演则可望获得更为可靠的结果.研究了观测频带相互衔接的电偶源频率电磁测深和大地电磁测深视电阻率的一维联合反演问题.对两个实测点两种电磁法的观测资料进行了联合反演试验,与钻井资料对比表明,所获得的电性分层参数是较为可信的.在补充了由频散关系获取的电偶源频率电磁相位资料后,对于两种电磁法的视电阻率————阻抗相位、阻抗实部视电阻率-阻抗虚部视电阻率进行了拟大地电磁反演,获得了相近的反演结果.      

大地电磁资料的灵敏度研究

本文研究了大地电磁资料对地球电性结构模型参数的灵敏度,它在反演解释中具有重要意义.通过研究均匀半空间中视电导率资料的灵敏度函数与计算分析实际观测资料的Fréchet导数和斜率表明,视电导率资料的灵敏度在地表最大,从地表向下呈指数衰减,频率愈高,电导率愈大,衰减也愈快.视电阻率资料和阻抗相位资料对高频、浅层和低阻层具有更高的灵敏度,几何参数的平均灵敏度高于电性参数的平均灵敏度,通常阻抗相位资料比视电阻率资料更灵敏.同时,根据阻抗实部定义的视电阻率与Kunetz定义的时间域大地电磁响应,反映地层电性差异的灵敏度最高. 文章还指出,在实际的反演解释中,如何正确有效地应用阻抗相位资料,提高分辨能力,仍是急待解决的问题.     

试论大地电磁测深法在地震前兆探索中的进一步应用

从大地电磁测深理论分析和实际资料数字试验出发,我们探讨了有关提高大地电磁测深法监测深部电性变化前兆效能的某些问题.研究结果表明,在所定义的几种大地电磁视电阻率中,尚未加以利用的阻抗实部视电阻率具有某些独特的优点,可能成为监测深部电性变化的一个较好的参数指标;应根据各记录道误差的分配,计算过程误差的传播和累加对不同大地电磁响应函数产生不同的影响,选择相对精度较高的参数作为主要监测参量;而识别深部电性变化的多参数综合判别方法应是基本的分析方法.实际观测到的反映地震前兆的某些大地电磁资料证实了上述论证.      

大地电磁视电阻率和阻抗相位资料的联合解释

本文叙述了大地电磁视电阻率和阻抗相位资料联合解释的原理与计算方法。通过具体算例的分析,表明该方法是正确有效的,而且在缩小多解性方面,要比单纯的视电阻率资料反演法或阻抗相位资料反演法优越     

一种利用频谱激电数据实部和虚部加权反演Cole-Cole模型参数的方法

频谱激电法(SIP)因具有多参数(Cole-Cole参数)解释异常的能力,一直受到电法工作者的关注.一些学者提出了用电场振幅和相位反演Cole-Cole参数的方法,但由于电场振幅和相位对不同Cole-Cole参数的敏感程度不同,往往导致有些Cole-Cole参数较难反演,特别是频率相关系数和时间常数.本文提出了利用视复电阻率的实部和虚部加权反演的方法.该方法采用视复电阻率实部和虚部联合反演的策略,并在反演不同Cole-Cole参数时对实部和虚部的目标函数进行不同的加权.模型试算结果表明:这种反演方法不仅可以很好的反演零频电阻率和极化率,还可以显著提高频率相关系数和时间常数的反演效果.     

基于交叉梯度耦合的大地电磁与地震走时资料三维联合反演

为了有效解决目前大地电磁和地震走时资料单方法反演结果一致性不好的问题,同时克服基于岩石不同物性参数间关系耦合约束联合反演的局限性,本文研究了基于交叉梯度耦合约束的大地电磁与地震走时资料的三维联合反演算法.以较为成熟的天然地震走时资料三维正反演和大地电磁三维正反演算法为基础,实现了具有共同的反演网格,以交叉梯度结构耦合约束,并能同时获得电阻率和速度模型的三维联合反演算法.分别利用单棱柱体模型和双棱柱体模型合成数据进行了联合反演试算.结果表明:无论是单棱柱体模型还是双棱柱体模型,联合反演结果比单独反演对异常体的空间形态都有更好的恢复,其中单棱柱体模型反演的异常体电阻率更接近于真实电阻率,双棱柱体模型的联合反演结果不仅消除了围岩的部分电阻率假异常,而且增强了对异常体深部速度结构特征的恢复程度.联合反演还能同时改善电阻率和速度反向变化异常体的单独反演结果,进一步证明交叉梯度耦合不依赖于岩石物性关系,而强调地下结构的相似性,具有更普遍的适用性.     

电偶源频率电磁测深视电阻率多参量联合反演效果检验

通过大量的数值模拟试验 ,对电偶源频率电磁测深 (FEMS)视电阻率多参量联合反演的效果进行了检验和对比 .结果表明 ,多参量联合反演具有较快的收敛速度和较高的拟合精度     

电偶源频率电磁测深视电阻率多参量联合反演效果检验

通过大量的数值模拟试验，对电偶源频率电磁测深（FEMS）视电阻率多参量联合反演的效果进行了检验和对比。结果表明，多参量联合反演具有较快的收敛速度和较高的拟合精度。     

电偶源频率电磁测深二维阻抗视电阻率计算的源效应校正法

研讨了频率域电磁法中不同源装置的大地电磁测深、线源频率电磁测深和偶极源频率电磁测深阻抗视电阻率的源效应影响特征。在唯象分析的基础上，提出了几种电磁测深法阻抗视电阻率的相互换算法──源效应校正法（大地电磁测深二维ＴＥ极化视电阻率和其它两种电磁法的赤道装置二维阻抗视电阻车）。模型试验表明，利用这一源效应校正法可以由大地电磁二维视电阻率近似地计算出线源频率电磁二维阻抗视电阻率。这一方法被尝试应用于由线源频率电磁二维阻抗视电阻率估算偶极源频率电磁二维阻抗视电阻率。     

MT方法中Basokur视电阻率定义的研究

电法勘探中不同的视电阻率定义可以带来不同的反演效果,好的视电阻率定义可以提高反演分辨率。传统的Cagniar视电阻率(1953)只是利用了波阻抗的模值,而Basokur 1994年提出的视电阻率利用波阻抗的实部和虚部。本文做了4个不同模型的Basokur视电阻率响应及反演,结果显示新的视电阻率对薄层有很好的反应,对常规模型也有不错的表现。     

THE DISPERSION RELATION, OF EARTH''S ELECTROMAGNETIC RESPONSE FUNCTIONS AND THE JOINT INVERSION OF DATA

On the basis of the dispersion relations of MT field, the necessity and applied prospects of the joint inversions using a pair of MT response functions which are correlative with the dispersion relations, are infered. A filter coefficient algorithm is made, with which the corresponding impedance phase data can be estimated using a set of apparent resistivities. The tests for the observed MT data show that when comparing the impedance phase estimated using the dispersion relation with the ob served phase, it can be checked whether the dispersion relation between observed apparent resistivity and phase data is satisfied or not, and that the use of the phase data corrected using the dispersion relation in the joint inversion is advantageous to obtain more confident results. It is shown that joint inversions are more advantageous than single parameter inversions, and that in the most case the joint inversion using the apparent resistivities of impedance real and imaginary parts is more advantageous than the jointinversion using the normal apparent resistivity and impedance phase. The existence of the dipersion relations between the ratio apparent resistivity and corresponding impedance phase of the orthogonal electric and magnetic field horizontal Components in the frequency EM sounding with horizontal electric dipole(FEMS) are discussed, the better effect of the joint inversion using the pair of EM response functions is obtained. The problems on the one-dimensional joint inversion for the MT and FEMS apparent resistivities, for which the observed frequency bands partly overlape each other, are studied. It is shown that this joint inversion is applicable and effective:the joint inversions of the practical data for two kinds of EM methods at two sites give the results well corresponding to the drilling data. The simulated MT inversions for the data of two kinds of EM methods are made, and more confident results also are obtained.     

The inversion of the data of magnetotelluric sounding and electromagnetic frequency sounding with horizontal electric dipole

On the basis of the dispersion relation of magnetotelluric response functions (MTRF), a filter coefficient algorithm has been made, with which the corresponding impedance phase data can be estimated using a set of apparent resistivity data. The tests of theoretical models and observed magnetotelluric (MT) data show that this algorithm is effective. Comparing the impedance phase estimated using dispersion relation with the observed phase, it can be checked whether the dispersion relation between the observed apparent resistivities and phase data was satisfied. The use of phase data corrected using the dispersion relation in the joint inversion for MT impedance is advantageous to obtain more reliable inversion results. The problems on the one-dimensional joint inversion for the (MT) apparent resistivity and the apparent resistivity of the frequency electromagnetic sounding (FEMS) with horizontal electric dipole, whose observed frequency bands are linked up each other, are studied. The observed data of two kinds of electromagnetic (EM) methods at two sites are used to inverse, the comparison with the drilling data show the results are more reliable. To supply the phase data of FEMS using the dispersion relation, for the apparent resistivity-phase data and impedance real part-imaginary part apparent resistivities of two kinds of EM methods the imitated MT joint inversions are made, and more similar results also are obtained. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 91–96, 1993. The projects sponsored by the Chinese Joint Seismological Science Foundation.     

用Occam法及广义逆法对兰州地区MT资料的一维反演解释

分别用Occam法和广义逆法对兰州地区MT资料进行了一维反演，两种反演结果可相互印证，使得解释结果更为可靠。并和相应资料的二维反演结果相一致。     

A field test of imaging properties of rotational invariants of the magnetotelluric impedance tensor

A part of the Békés Basin (an extensional sub‐basin of the Pannonian Basin, where the basement under thick Pannonian sediments is well known from deep boreholes and from seismic measurements, and where many magnetotelluric (MT) soundings have been carried out for frequencies ranging from 1 to 10^?3 Hz) was selected as a test area to assess the imaging performances of various apparent‐resistivity definitions computed with rotational invariants of either the real part of the complex impedance tensor, or its imaginary part, or both. A comparison (based on earlier 3D numerical studies) has been made between the magnetotelluric images obtained in this way and the depths to the high‐resistivity basement, as known from boreholes and seismic investigations. The correlation coefficient between the series of basement depth values at 39 MT sites and the apparent‐resistivity values was found to be stronger and high correlation appeared at a shorter period when it was computed with apparent resistivities based on the real tensor rather than with apparent resistivities based on the imaginary tensor. In the light of our studies, ρ_{Re Z} and the impedance phase seem to be more informative than any other combination of magnetotelluric interpretation parameters.     

Increased resolution of subsurface parameters from 1D magnetotelluric modeling

In electric and electromagnetic techniques, it is well known that the principle of equivalence poses a problem in the interpretation of subsurface layers. This means the inversion problem can provide the conductivity-thickness product more confidently than the individual parameters — conductivity and thickness — separately. The principle of equivalence corresponds to the middle layer in a three-layer earth structure. In order to resolve this problem, we have touched upon the different formulae of apparent resistivity proposed by earlier workers considering the real and imaginary parts of the impedance tensor and designed a new formula to compute apparent resistivity for different models. We observed that the application of our new formula for apparent resistivity using the combination of real and imaginary parts of the impedance has a better resolution as compared to earlier conventional formulae of apparent resistivity. These results have been demonstrated through both forward and inverse modeling schemes.     

电偶源频率电磁测深中磁场比值视电阻率与其相位间的频散关系及资料的联合反演

探讨了在电偶源频率电磁测深中利用磁场比值定义的视电阻率ρｚｙ的物理意义及与其相位间的频散关系,给出了在频散关系的基础上电视电阻率资料估算相位的方法,并证明所估算的相位与理论模型计算值是一致的研究了ρｚｙ与ψｚｙ联合反演问题,并研制出具有较好应用效果的实用化软件。     

A joint inversion algorithm to process geoelectric and surface wave seismic data. Part II: applications

Seismic and geoelectric methods are often used in the exploration of near-surface structures. Generally, these two methods give, independently of one other, a sufficiently exact model of the geological structure. However, sometimes the inversion of the seismic or geoelectric data fails. These failures can be avoided by combining various methods in one joint inversion which leads to much better parameter estimations of the near-surface underground than the independent inversions. In the companion paper (Part I: basic ideas), it was demonstrated theoretically that a joint inversion, using dispersive Rayleigh and Love waves in combination with the well-known methods of DC resistivity sounding, such as Schlumberger, radial dipole-dipole and pole-pole arrays, provides a better parameter estimation. Two applications are shown: a five layer structure in Borsod County, Hungary, and a three-layer structure in Thüringen, Germany. Layer thicknesses, wave velocities and resistivities are determined. Of course, the field data sets obtained from the ‘real world’ are not as complete and as good as the synthetic data sets in the theoretical Part I. In both applications, relative model distances, in percentages, serve as quality control factors for the different inversions; the lower the relative distance, the better the inversion result. In the Borsod field case, Love wave group slowness data and Schlumberger, radial dipole-dipole and pole-pole (i.e two-electrode) data sets are processed. The independent inversion performed using the Love wave data leads to a relative model distance of 155%. An independent Schlumberger inversion results in 41%, a joint geoelectric inversion of all data sets in 15%, a joint inversion of Love wave data and all geoelectric data sets in 15% and the robust joint inversion of Love wave data and the three geoelectric data sets in 10%. In the Thüringen field case, only Rayleigh wave group slowness data and Schlumberger data were available. The independent inversion using Rayleigh wave data results in a relative model distance of 19%. The independent inversion performed using Schlumberger data leads to 34%, the joint and robust joint inversion of Rayleigh wave and Schlumberger data gave results of 18% and 20%, respectively.     

华北地区上地幔及过渡带电性结构研究

采用远参考道和Robust技术,处理了华北地区14个地磁台站资料,得到了相干度超过0.8的地磁测深响应函数.并将其转换为大地电磁测深的响应函数,获取了105~107 s周期范围内的视电阻率和相位.应用ρ+理论对数据进行了一致性检验和反演,结果表明417km,850km深度附近可能存在电性间断面.同时采用基于一维最光滑模型的Occam反演方法得到了300~1000km范围的地幔电性结构,并与前人在其他地区的研究结果进行了对比.发现华北地区地幔过渡带的电导率在大兴安岭—太行山重力梯度带东西两侧表现不同,重力梯度带附近及西侧台站下方过渡带深度的电导率和北美的Tucson地区相当,而华北地区东部的电导率在地幔过渡带范围高出西侧约2~5倍,这很可能和太平洋板块的俯冲有关.     

Joint inversion of Rayleigh‐wave dispersion data and vertical electric sounding data: synthetic tests on characteristic sub‐surface models

In the traditional inversion of the Rayleigh dispersion curve, layer thickness, which is the second most sensitive parameter of modelling the Rayleigh dispersion curve, is usually assumed as correct and is used as fixed a priori information. Because the knowledge of the layer thickness is typically not precise, the use of such a priori information may result in the traditional Rayleigh dispersion curve inversions getting trapped in some local minima and may show results that are far from the real solution. In this study, we try to avoid this issue by using a joint inversion of the Rayleigh dispersion curve data with vertical electric sounding data, where we use the common‐layer thickness to couple the two methods. The key idea of the proposed joint inversion scheme is to combine methods in one joint Jacobian matrix and to invert for layer S‐wave velocity, resistivity, and layer thickness as an additional parameter, in contrast with a traditional Rayleigh dispersion curve inversion. The proposed joint inversion approach is tested with noise‐free and Gaussian noise data on six characteristic, synthetic sub‐surface models: a model with a typical dispersion; a low‐velocity, half‐space model; a model with particularly stiff and soft layers, respectively; and a model reproduced from the stiff and soft layers for different layer‐resistivity propagation. In the joint inversion process, the non‐linear damped least squares method is used together with the singular value decomposition approach to find a proper damping value for each iteration. The proposed joint inversion scheme tests many damping values, and it chooses the one that best approximates the observed data in the current iteration. The quality of the joint inversion is checked with the relative distance measure. In addition, a sensitivity analysis is performed for the typical dispersive sub‐surface model to illustrate the benefits of the proposed joint scheme. The results of synthetic models revealed that the combination of the Rayleigh dispersion curve and vertical electric sounding methods in a joint scheme allows to provide reliable sub‐surface models even in complex and challenging situations and without using any a priori information.     

大地电磁一维连续介质反演的曲线对比法

根据电磁波的传播特性，把视电阻率随周期变化的曲线转化为电阻率随深度变化的曲线，并以此作为初始反演的地电模型．通过初始地电模型得到的视电阻率曲线与真实模型的视电阻率曲线的对比，对初始地电模型的电阻率值进行校正．校正后的反演模型的视电阻率曲线与真实模型的视电阻曲线的拟合程度有所提高．然后如此反复进行多次校正，获得与真实模型更为接近的反演模型，反演的拟合误差一般小于ｌ％．模型试验和实际例子表明，该方法的拟合程度优于Ｂｏｓｔｉｃｋ法．