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强剩磁、强退磁改变了总磁化强度的大小和方向,给磁测资料解释带来困难.为此,本文利用二维井中磁测数据反演磁化强度矢量的二维分布.首先利用井中磁测的磁异常模量反演磁化强度大小的分布.然后,在已知磁化强度大小分布的前提下,拟合磁场分量,反演磁化强度方向的分布.其中,磁化强度大小和方向均用共轭梯度法求解,并通过预优矩阵改善磁化强度大小的反演效果.理论模拟说明,该方法能准确获得磁化强度矢量分布.磁化强度矢量反演结果包括感磁、剩磁及退磁的影响,这为研究强剩磁、高磁化率矿床提供了一种有效方法. 相似文献
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导了磁化强度矢量层析成像方程,并与磁化强度标量层析成像方程进行了对比. 使该矢量层析成像方程既适用于三维的也适用于二维,既适用于使用磁场垂直分量资料,也适用于使用磁场总强度资料. 本文采用改进的高斯-赛德尔迭代求解磁化强度矢量层析成像方程,在求解方程中引进了与深度有关的权系数. 并对二维模型开展了正反演研究. 当模型层数为二层,且每层51个柱体时,采用零初始模型就能获得较好的磁化强度垂直分量和水平分量反演结果,除了异常体边部外,磁化方向比较可靠. 当模型层数为五层,且每层51个柱体时,采用零初始模型不能得到较好结果,改用接近背景值的均匀初始模型,反演的磁化强度垂直分量和水平分量大致接近真实,但不能刻划某些细节. 相似文献
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TAPIO RUOTOISTENMÄKI 《Geophysical Prospecting》1993,41(4):413-433
Magnetic anomalies of complicated 3D sources can be calculated by using a combination of analytical and numerical integration. Two surfaces and the magnetization parameters (the amplitudes of the induced and remanent components and the direction cosines) of the source can be defined by arbitrary functions or by discrete data points in a plane. When combined with a polynomial magnetization function in the direction of the third axis, 3D magnetization distribution can also be modelled. The method gives very general equations for anomaly calculation. It can be used for direct modelling of sources interpreted by seismic or other methods and also for interactive interpretation with fast computers. It is possible to calculate anomalies of, for example, intrusives or folded sedimentary beds whose surfaces are functions of horizontal coordinates and which have polynomial magnetization variations in the vertical direction due to gravitational differentiation and arbitrarily varying magnetization in the horizontal direction due to regional metamorphosis. If the distribution of magnetization parameters in the vertical direction cannot be described satisfactorily by polynomials, models can be used whose surfaces are functions of the vertical coordinate and which can then have any arbitrary magnetization distribution in the vertical direction. 相似文献
5.
A new best estimate methodology is proposed and oriented towards the determination of parameters related to a magnetic field
anomaly produced by a simple geometric-shaped model or body such as a thin dike and horizontal cylinder. This approach is
mainly based on solving a system of algebraic linear equations for estimating the three model parameters, e.g., the depth
to the top (center) of the body (z), the index parameter or the effective magnetization angle (θ) and the amplitude coefficient or the effective magnetization intensity (k). The utility and validity of this method is demonstrated by analyzing two synthetic magnetic anomalies, using simulated
data generated from a known model with different random errors components and a known statistical distribution. This approach
was also examined and applied to two real field magnetic anomalies from the United States and Brazil. The agreement between
the results obtained by the proposed method and those obtained by other interpretation methods is good and comparable. Moreover,
the depth obtained by such an approach is found to be in high accordance with that obtained from drilling information. The
advantages of such a proposed method over other existing interpretative techniques are clarified, where it can be generalized
to be automatically applicable for interpreting other geological structures described by mathematical formulations. 相似文献
6.
《Physics of the Earth and Planetary Interiors》1992,70(3-4):194-200
Thermal remanent magnetization (TRM) and anhysteretic remanent magnetization (ARM) components were imposed on natural rock samples. The artificial laboratory components had different directions and the blocking temperature and/or coercivity spectra were overlapping. Two methods, principal component analysis (PCA) by Kirschvink and analytical modelling of demagnetization data (by Stupavsky and Symons, S&S) were used to resolve these components. The PCA technique calculated lines fitted to the demagnetization path with ASD = 10° (angular standard deviation), and the S&S method used four types of intensity decay curves for calculated components.
Both methods (PCA and S&S) resolved perfectly the one-component case. The two- or three-component case results strongly depended on spectra overlapping, and on the angles between component directions and magnetic minerals in samples. Principal component analysis gave more reliable results for separated spectra of TRM and thermally cleaned samples, whereas the S&S technique was more efficient for the case of strong spectra overlapping of ARM components and the alternative current field (AF) demagnetization method. Remarkable anisotropy of RM was observed which influences the results for the haematite-bearing samples. 相似文献
7.
A. B. Raevskii 《Izvestiya Physics of the Solid Earth》2008,44(7):548-554
An iterative algorithm is proposed for magnetic induction modulus inversion. The iterative process is based on a recurrence relation for the squared induction modulus, which can be represented at each iteration step by a system of linear algebraic equations for components of the magnetization vector. Formulas for the calculation of matrix elements of this system and the determination of the magnetization at the next iteration step are given. Model and practical examples illustrating the reconstruction of magnetization and anomalous field components are presented. 相似文献
8.
Natural sediments are a complex mixture of magnetic minerals with different origins and different geochemical history, each of which is called a magnetic component. Magnetic components practically never occur in isolated form, and their characterization using bulk magnetic measurements relies on the individuation of the systematic variation of some parameters within a large group of samples. These variations can be interpreted either as a mixing trend or as the result of natural processes, which affect the physical and chemical properties of the magnetic particles. An alternative approach is offered by the analysis of magnetization curves using model functions, which are supposed to represent the magnetic properties of individual components. The success of this approach relies on (1) the choice of model functions that can reproduce the natural properties of a component with sufficient accuracy by varying a minimum number of parameters and (2) on very precise and accurate measurements, which are necessary to overcome the extreme sensitivity of the method to noise. In this paper, the analysis of remanent magnetization curves proposed by Egli (2003) is applied to a large set of representative sediments from the most variable environments and to a set of artificial magnetite samples. Despite the variety of materials and natural processes involved in the formation of these sediments, seven groups of magnetic components with well-defined and consistent properties could be identified. It has been found that both lacustrine and marine sediments contain two magnetically distinct groups of magnetosomes, which react differently to changes of the redox potential. The effects of some natural processes, such as weathering, reductive dissolution and transport could be observed on the individual components. 相似文献
9.
We present a new method to estimate the direction of the magnetization vector of geological bodies based upon the correlation between the reduced-to-the-pole field for tentative values of the magnetization direction and the total magnitude anomaly, obtained by a transform of the measured magnetic field. The reduced-to-the-pole and the total magnitude anomaly are centred over the sources in the case of 2D anomalies or well-centred in the case of compact 3D sources and have similar patterns for the same source. The method has several important advantages over similar transform-correlation methods for estimation of the magnetization direction. It calculates only one transform for many tentative values of the magnetization direction. The method does not use derivatives of any order and relies on confident isolation of the target anomalies based on one of the compared transforms, the total magnitude anomaly. We studied the performance of the method on five 2.5D and compact 3D sources. We analysed possible inherent to the method errors, as well as errors due to interference from neighbouring sources. Finally, we estimated the magnetization-vector direction of the main sources causing the magnetic field in the Burgas region and the adjoining southeast Bulgarian Black Sea shelf. The sources in the Black Sea shelf show prevalently reverse magnetization, while the sources on land have normal or reverse magnetization. 相似文献
10.
Twenty six samples from seven hand specimens, collected from the station 6 boulder at the Apollo 17 landing site, were studied magnetically. The boulder is a breccia consisting of three lithologic units distinguished by their clast population. The direction of magnetization of samples from unit B which is almost devoid of large clasts cluster fairly well after alternating field demagnetization. Samples from unit C which is characterized by abundant large clasts up to 1 m in size do not contain a uniform direction of magnetization but the distribution is not random. Based on these data we propose that the natural remanent magnetization (NRM) in these breccias is the vector sum of two magnetizations, a pre-impact magnetization and a partial thermoremanence acquired during breccia formation. The relative contribution of the two components is controlled by the thermal history of the ejecta, which in turn is determined by its clast population. Depending on the clast population, the NRM can be a total thermoremanence, a partial thermoremanence plus a pre-impact magnetization, or a pre-impact magnetization. This model of thermal overprinting might be applicable to all lunar breccias of medium and higher metamorphic grade. 相似文献
11.
The inverse problem of magnetometry is solved for a horizontal layer. Model masses are magnetized nonuniformly. The magnetization vector is a function of two horizontal coordinates. The components of this vector are determined from data on the external magnetic field. 相似文献
12.
Jamaledin Baniamerian Shuang Liu Xiangyun Hu Maurizio Fedi Mahak Singh Chauhan Mahmoud Ahmed Abbas 《Geophysical Prospecting》2020,68(7):2320-2342
Inversion of magnetic data is complicated by the presence of remanent magnetization, and it provides limited information about the magnetic source because of the insufficiency of data and constraint information. We propose a Fourier domain transformation allowing the separation of magnetic anomalies into the components caused by induced and remanent magnetizations. The approach is based on the hypothesis that each isolated source is homogeneous with a uniform and specific Koenigsberger ratio. The distributions of susceptibility and remanent magnetization are subsequently recovered from the separated anomalies. Anomaly components, susceptibility distribution and distribution of the remanent and total magnetization vectors (direction and intensity) can be achieved through the processing of the anomaly components. The proposed method therefore provides a procedure to test the hypotheses about target source and magnetic field, by verifying these models based on available information or a priori information from geology. We test our methods using synthetic and real data acquired over the Zhangfushan iron-ore deposit and the Yeshan polymetallic deposit in eastern China. All the tests yield favourable results and the obtained models are helpful for the geological interpretation. 相似文献
13.
L.J. Srnka J.L. Hoyt J.V.S. Harvey J.E. McCoy 《Physics of the Earth and Planetary Interiors》1979,20(2-4):281-290
The source of the lunar magnetic anomaly associated with the Rima Sirsalis linear rille has been modelled using the vector field intensities due to arbitrary uniform magnetization in a rectangular prism. It is shown that in order to match the Apollo 16 subsatellite data, the lunar surface near the rille must have a vertical magnetization of 6–9 × 10−3 G if the anomaly is due to flux leakage from a gap in the crust with the dimensions of the rille. This is more than one order of magnitude larger than the magnetization of any lunar sample, but is comparable with the high magnetization recently deduced for the Reiner γ formation in Oceanus Procellarum. An alternative explanation is that Rima Sirsalis and its surroundings are the site of a vertical magnetization contrast of 10−5 – 10−4 G which is at least as wide as the rille and extends to a depth of tens of kilometers in the crust. A wider magnetic source reduces the required magnetization (or depth) proportionately, since to first order the field at high altitude is proportional to the magnetic dipole moment per unit length. 相似文献
14.
B.O. Ruud 《Studia Geophysica et Geodaetica》2006,50(3):479-498
The calculation of reflection and transmission coefficients of plane waves at a plane interface between two homogeneous anelastic
media may become ambiguous because it is not always obvious how to determine the sign of the vertical component of the slowness
vector of the scattered waves. For elastic media, the sign is determined by applying so-called radiation condition when the
slowness vector is complex-valued, but it has long been known that this approach does not work satisfactorily for anelastic
media. Other approaches have been suggested, e.g., by requiring that the reflection and transmission coefficients should vary
continuously with increasing incident angles, or by relating the sign to the direction of the energy flux. In the present
paper, it is shown that these approaches may give different results, and that the results can be inconsistent with the elastic
case even for weak attenuation. Instead, it is demonstrated that the ambiguity in the reflection coefficient can be resolved
by expressing the seismic response of a point source over an interface as a superposition of plane waves and their reflection
coefficients, and solving the resulting integral by the saddle point approximation. Although the saddle point itself (point
of stationary phase) does not provide new insight, the ambiguity is removed by considering the steepest descent path through
the point. Ray synthetic seismograms computed by this method compare well with synthetics computed by the reflectivity method,
which does not suffer from the above-mentioned ambiguity since the integration path is taken along the real axis.
This paper concentrates on the isotropic case, but it is discussed how the result may be extended to layered transversely
isotropic media. The suggested approach, derived for a point source and plane layers, does not directly apply to 2-D or 3-D
laterally inhomogeneous media, or to media of general anisotropy. A generalization of the result found is that the sign of
the vertical slowness components should be chosen according to the energy flux direction for subcritical incidence and according
to the radiation condition for supercritical incidence, even if this creates a discontinuity in the coefficients at the critical
incidence angle. Such a discontinuity is sometimes necessary to get results which are consistent with the elastic case. It
is discussed how the generalized result can be obtained by applying certain continuity criteria for the sub-and supercritical
angle intervals, but the validity of this approach for general models remains to be proved. 相似文献
15.
K. KUNARATNAM 《Geophysical Prospecting》1972,20(2):439-447
A method is presented for determining the lower surface of a two-dimensional body producing a magnetic anomaly when its upper surface and the intensity of magnetization are given. The magnetization vector is assumed to lie along a specified direction but the sense of magnetization may be different in different vertical sections of the body and may be regarded as unknown. The method is illustrated using the computed anomalies of some theoretical models. 相似文献
16.
The forward computation of the gravitational and magnetic fields due to a 3D body with an arbitrary boundary and continually varying density or magnetization is an important problem in gravitational and magnetic prospecting. In order to solve the inverse problem for the arbitrary components of the gravitational and magnetic anomalies due to an arbitrary 3D body under complex conditions, including an uneven observation surface, the existence of background anomalies and very little or no a priori information, we used a spherical coordinate system to systematically investigate forward methods for such anomalies and developed a series of universal spherical harmonic expansions of gravitational and magnetic fields. For the case of a 3D body with an arbitrary boundary and continually varying magnetization, we have also given the surface integral expressions for the common spherical harmonic coefficients in the expansion of the magnetic field due to the body, and a very precise numerical integral algorithm to calculate them. Thus a simple and effective method of solving the forward problem for magnetic fields due to 3D bodies of this kind has been found, and in this way a foundation is laid for solving the inverse problem of these magnetic fields. In addition, by replacing the parameters and unit vectors in the spherical harmonic expansion of a magnetic field by gravitational parameters and a downward unit vector, we have also derived a forward method for the gravitational field (similar to that for the magnetic case) of a 3D body with an arbitrary boundary and continually varying density. 相似文献
17.
Geomagnetism and Aeronomy - The method of path integrals is used to average the magnetic-induction equation written for the vector potential over the velocity field. This approach avoids the... 相似文献
18.
The remanent magnetization of igneous and sedimentary rocks, if not changed by heating or by alteration of magnetic minerals, keep the information about the intensity of that magnetic field in which initial magnetization took place.It has been determined that the dependence of anhysteretic remanent magnetization of such a rock on d.c. magnetic field permits us to find the paleointensity. A method of investigation of rock specimens by means of such remagnetization is suggested and applied to determining the paleointensity for a series of Permo-Triassic rocks. 相似文献
19.
Alternating field (a.f.) demagnetization has proved to be a very reliable technique for separating the magnetization components of rock samples. The method is subject to errors caused by either imperfection of the technique or by intrinsic properties of a rock. Recently, Stephenson [1,2] introduced the term gyroremanent magnetization (GRM) for a disturbing remanent magnetization that can be acquired by magnetic material during tumbling or stationary a.f. demagnetization. The implications for the routine a.f. demagnetization of anisotropic rock samples seemed to be very serious. Here, however, a method is presented on how to avoid the effect of GRM on results obtained from stationary a.f. demagnetization. 相似文献
20.
Accelerating the T‐matrix approach to seismic full‐waveform inversion by domain decomposition 
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下载免费PDF全文 A seismic variant of the distorted Born iterative inversion method, which is commonly used in electromagnetic and acoustic (medical) imaging, has been recently developed on the basis of the T‐matrix approach of multiple scattering theory. The distorted Born iterative method is consistent with the Gauss–Newton method, but its implementation is different, and there are potentially significant computational advantages of using the T‐matrix approach in this context. It has been shown that the computational cost associated with the updating of the background medium Green functions after each iteration can be reduced via the use of various linearisation or quasi‐linearisation techniques. However, these techniques for reducing the computational cost may not work well in the presence of strong contrasts. To deal with this, we have now developed a domain decomposition method, which allows one to decompose the seismic velocity model into an arbitrary number of heterogeneous domains that can be treated separately and in parallel. The new domain decomposition method is based on the concept of a scattering‐path matrix, which is well known in solid‐state physics. If the seismic model consists of different domains that are well separated (e.g., different reservoirs within a sedimentary basin), then the scattering‐path matrix formulation can be used to derive approximations that are sufficiently accurate but far more speedy and much less memory demanding because they ignore the interaction between different domains. However, we show here that one can also use the scattering‐path matrix formulation to calculate the overall T‐matrix for a large model exactly without any approximations at a computational cost that is significantly smaller than the cost associated with an exact formal matrix inversion solution. This is because we have derived exact analytical results for the special case of two interacting domains and combined them with Strassen's formulas for fast recursive matrix inversion. To illustrate the fact that we have accelerated the T‐matrix approach to full‐waveform inversion by domain decomposition, we perform a series of numerical experiments based on synthetic data associated with a complex salt model and a simpler two‐dimensional model that can be naturally decomposed into separate upper and lower domains. If the domain decomposition method is combined with an additional layer of multi‐scale regularisation (based on spatial smoothing of the sensitivity matrix and the data residual vector along the receiver line) beyond standard sequential frequency inversion, then one apparently can also obtain stable inversion results in the absence of ultra‐low frequencies and reduced computation times. 相似文献