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1.
It is preferable to use the three-dimensional (3D) magnetotelluric inversion, which provides volumetric geoelectric models, to handle the array input data. However, the soundings are frequently conducted on the single profiles or on the profiles that are considerably spaced apart from each other. We explore the possibilities of the 3D inversion of such data by the example of a three-layer model containing three local inhomogeneities. We previously showed that the simple processing of the data and their 1D or 2D inversion enable reconstructing the background cross section and locating all the three inhomogeneities. In the present paper, we use this information for constructing several versions of the starting model and carrying out the smoothing 3D inversion of the data. The experiments show that if the background cross section is incorporated into the starting model, the final model provided by the inversion closely reproduces the real distribution of all geoelectric parameters. At the same time, if the starting model that hosts the inhomogeneities has the form of a homogeneous half-space, the inversion is not able to reconstruct an adequate final model. 相似文献
2.
Magnetotelluric soundings are frequently carried out on a single profile or on profiles remote from each other. Interpretation
of the obtained data is difficult in the presence of spatially heterogeneous geoelectric structures. We evaluate its capabilities
on the basis of the synthetic data, that correspond to a geoelectric model, which consists of a three-layered section in the
background and three rectangular prisms, differently arranged relative to the profile. Using the simple methods of analysis
of magnetotelluric data, we succeeded in allocating all three heterogeneities over the area that surrounds the profile of
observations. As a result of the fast smoothed-structure 1D and 2D inversion of different components of data, taking into
account their specific features, the depths of the occurrence of anomalies and the order of the values of their electrical
resistivity were evaluated, and the background section was also reconstructed. On this basis, and, also, with the use of a
priori geological-geophysical information, the construction of a 3D model in a more or less broad band around the profile
and its correction with the aid of 3D data inversion are possible. 相似文献
3.
We present the results of long-term deep geoelectric studies using the JASC (Japan Sea Cable) submarine communication cable in the region of the Sea of Japan. In the 2D inversion of the amplitude and phase’s apparent resistivity curves and the frequency dependences of the tipper, we invoked the geological and geophysical information about the region and on-shore electromagnetic observations to fit the model to the observations. The resulting geoelectrical cross section of the region of the Sea of Japan along the JASC cable obtained in this way agrees well with the experimental data. The upper part of the section contains a conductive block beneath the bottom of the Central basin of the Sea of Japan at a depth of 10–40 km, a fault submerging below the continent in the marginal part and a deep fault in the continental region. In the lower portions of the cross section, the high-resistivity block interrupts the continuity of the horizontal conductive layers beneath the Yamato Uplift, and the conductive bottom part of the geoelectric cross section submerges under the continent. In the continental segment of the cross section, there is a large block with reduced electric resistivity, which is located between the conductive layers at a depth interval of 200–560 km. We analyze the characteristic features of the geoelectric cross section and the deep section imaged by seismic tomography in the region of the Sea of Japan. 相似文献
4.
The possibilities of reconstructing two-dimensional (2D) cross sections based on the data of the profile soundings by the transient electromagnetic method (TEM) with a single ungrounded loop are illustrated on three-dimensional (3D) models. The process of reconstruction includes three main steps: transformation of the responses in the depth dependence of resistivity ρ(h) measured along the profile, with their subsequent stitching into the 2D pseudo section; point-by-point one-dimensional (1D) inversion of the responses with the starting model constructed based on the transformations; and correction of the 2D cross section with the use of 2.5-dimensional (2.5D) block inversion. It is shown that single-loop TEM soundings allow studying the geological media within a local domain the lateral dimensions of which are commensurate with the depth of the investigation. The structure of the medium beyond this domain insignificantly affects the sounding results. This locality enables the TEM to reconstruct the geoelectrical structure of the medium from the 2D cross sections with the minimal distortions caused by the lack of information beyond the profile of the transient response measurements. 相似文献
5.
M. N. Berdichevsky N. S. Golubtsova Iv. M. Varentsov P. Yu. Pushkarev A. K. Rybin E. Yu. Sokolova 《Izvestiya Physics of the Solid Earth》2010,46(8):698-706
The paper presents the results of 2D inversion of deep magnetotelluric (MT) and magnetovariational (MV) soundings along the
Naryn Line. The method of partial (sequential) inversions is used. According to this method, at the first stage, magnetovariation
responses are used for the localization of deep anomalies of electrical conductivity, and then the magnetotelluric sounding
data are invoked to refine the structure of the host medium and the structural details in the upper part of the section. It
is shown that this approach enables one to estimate the informativeness of separate components of the electromagnetic field,
to reduce the distorting influence of the near-surface geoelectric inhomogeneities, and to increase the stability of the final
solution of the inverse problem. 相似文献
6.
M. S. Zhdanov V. I. Dmitriev A. V. Gribenko 《Izvestiya Physics of the Solid Earth》2010,46(8):655-669
The problem of quantitative three-dimensional interpretation of the magnetotelluric (MT) data ranks among the most difficult
problems in electromagnetic (EM) geophysics. Our paper presents a new rigorous numerical method for MT inversion, based on
the integral equations technique. An important feature of the proposed method is the calculation of the Frechet derivative
with the aid of a quasi-analytical approximation with an inhomogeneous background. This approach simplifies the algorithm
of inversion and requires only a single forward modeling on each iteration. We have also developed a method for a joint inversion
of MT and magnetovariational (MV) data. We show in the present paper that the joint inversion of MT impedances and the Wiese-Parkinson
vectors can automatically allow for the static shift in the observed data, which is caused by the geoelectric inhomogeneities
contained in the near-surface layer. 相似文献
7.
Electromagnetic methods are routinely applied to image the subsurface from shallow to regional structures. Individual electromagnetic methods differ in their sensitivities towards resistive and conductive structures and in their exploration depths. If a good balance between different electromagnetic data can be be found, joint 3D inversion of multiple electromagnetic datasets can result in significantly better resolution of subsurface structures than the individual inversions. We present a weighting algorithm to combine magnetotelluric, controlled source electromagnetic, and geoelectric data. Magnetotelluric data are generally more sensitive to regional conductive structures, whereas controlled source electromagnetic and geoelectric data are better suited to recover more shallow and resistive structures. Our new scheme is based on weighting individual components of the total data gradient after each model update. Norms of individual data residuals are used to assess how much of the total data gradient must be assigned to each method to achieve a balanced contribution of all datasets for the joint inverse model. Synthetic inversion tests demonstrate advantages of joint inversion in general and also the influence of the weighting. In our tests, the controlled source electromagnetic data gradients are larger than those of the magnetotelluric and geoelectric datasets. Consequently, direct joint inversion of controlled source electromagnetic, magnetotelluric, and geoelectric data results in models that are mostly dominated by structures required by the controlled source electromagnetic data. Applying the new adaptive weighting scheme results in an inversion model that fits the data better and resembles more the original model. We used the modular system electromagnetic as a framework to implement the new joint inversion and briefly describe the new modules for forward modelling and their interfaces to the modular system electromagnetic package. 相似文献
8.
Seismic envelope inversion: reduction of local minima and noise resistance 总被引：3，自引：0，他引：3 
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下载免费PDF全文 Waveform inversion met severe challenge in retrieving long‐wavelength background structure. We have proposed to use envelope inversion to recover the large‐scale component of the model. Using the large‐scale background recovered by envelope inversion as new starting model, we can get much better result than the conventional full waveform inversion. By comparing the configurations of the misfit functional between the envelope inversion and the conventional waveform inversion, we show that envelope inversion can greatly reduce the local minimum problem. The combination of envelope inversion and waveform inversion can deliver more faithful and accurate final result with almost no extra computation cost compared to the conventional full waveform inversion. We also tested the noise resistance ability of envelope inversion to Gaussian noise and seismic interference noise. The results showed that envelope inversion is insensitive to Gaussian noise and, to a certain extent, insensitive to seismic interference noise. This indicates the robustness of this method and its potential use for noisy data. 相似文献
9.
Many joint inversion schemes use 1D forward modelling in the integrated interpretation of various geophysical data. In extending the joint inversion approach to the investigation of 2D structures, the discretization of the model parameters and the appropriate choice of the forward‐modelling procedure play a very important role. In this paper, a hybrid seismic–geoelectric joint inversion method is proposed for the investigation of 2D near‐surface geological structures. The electric and seismic models are coupled together through the use of common boundaries between the adjacent layers. Assuming a 2D model composed of homogeneous layers with curved boundaries, a fast ray‐tracing algorithm is used for the calculation of refraction seismic traveltime data. In the geoelectric forward modelling, a locally 1D approximation is used. The boundary surfaces are written in the form of series expansion; the inversion algorithms are formulated for the expansion coefficients and the petrophysical parameters as unknowns. Two versions of the inversion method are proposed: in versions A and B, interval‐wise constant functions and Chebyshev polynomials are, respectively, used as basis functions of the series expansion. The versions are tested by means of synthetic and in situ measured data. The tests show that both methods are stable and accurate. 相似文献
10.
Mrta Kis 《Journal of Applied Geophysics》2002,50(4)
Horizontally layered (1D) earth models are often assumed as a model estimate for the interpretation of geophysical data measured along 2D geological structures. In this process, the individual data sets are usually inverted independently, and it is considered only in a later phase of interpretation that these local (1D) models have common characteristic features. Taking account of these common attributes, instead of the successive independent interpretations, the lateral variations of geometrical and petrophysical parameters can be efficiently determined for the whole 2D structure by applying a series expansion. Using global basis functions, two advantages can be achieved: (i) choosing an appropriate number of basis functions helps us to restrict the complexity of the model; (ii) the integration of all the data sets measured along the profile gives rise to the application of simultaneous or joint inversion methods. This results in a decrease of the number of independent unknowns, a higher stability during the inversion and a more accurate and reliable parameter estimation.In this paper, a joint inversion algorithm is presented using DC geoelectric apparent resistivities and refraction seismic travel times measured along various layouts above a 2D geological model. To describe lateral variations series, expansions are used, and furthermore, to improve the often used approximation of a (locally) 1D forward modelling, the integral mean value of the horizontally changing model parameters (calculated along an appropriately defined interval) is introduced. We call the inversion procedure that combines series expansions and the concept of integral mean Generalised Series Expansion (GSE) inversion. The method was developed and tested for both the simultaneous (integrating data sets of one method or methods on the same physical basis) and the joint inversion (where data sets of methods on different physical bases are joined together), using synthetic and field data sets. It is also demonstrated that the equivalence problem inherent in the independent inversion of DC geoelectric data can efficiently be resolved by the use of the joint GSE inversion method in the cases of conductive and resistive equivalent geological models. 相似文献
11.
We propose a system for the analysis of magnetotelluric (MT) data, which makes use of the invariant characteristics of the impedance tensor such as the maximum and minimum induction curves and the phase tensor. We examine the coefficients of the appearance and normalization of principal values of the impedance tensor. By the case study for Koryakiya, it is shown that the three-dimensional (3D) mathematical modeling and the Wiese-Parkinson vectors allow one to correct the results of one-dimensional (1D) and two-dimensional (2D) inversion of MT curves. Comparison between model and observed data based on the 1D inversion of MTS curves provides a pictorial view of the distortions of MT curves and their sensitivity to the parameters of a geological cross section. 相似文献
12.
The MTS data acquired in Kamchatka during the last 30 years have been analyzed and summarized. Our interpretation is based on curves oriented along and across Kamchatka. Longitudinal and transverse curves can be affected by local geoelectric inhomogeneities. These were suppressed by conformal averaging. A bimodal interpretation of average longitudinal and transverse curves yielded a deep geoelectric model, which can be adopted as a starting point to be subsequently refined by 3D numerical modeling. The model involves a crustal conductive layer extending along central Kamchatka. In the east of the peninsula this layer is connected with crustal transverse conductive zones as wide as 50 km. Those zones have extensions toward the Pacific Ocean. Major centers of present-day volcanism occur in the transverse zones. The upper mantle contains an asthenospheric conductive layer forming an uplift beneath the present-day volcanic belt of Kamchatka. 相似文献
13.
《Journal of Applied Geophysics》2011,75(4):167-174
A new target-oriented parameterization scheme, named the object-based model, is suggested to represent man-made or natural targets as regular shapes embedded in a two-dimensional resistivity background. The numerical values of the target parameters (size, depth, location and resistivity) are estimated in three steps consisting of conventional regularized inversion, exclusion of anomalous regions and delineation of target bodies. The method produces sharp edges and sharp variation in intrinsic resistivity between the targets and background.The number of target objects is decided by the visual inspection of the 2D resistivity section derived from the application of a conventional cell-based regularized inversion. The 2D background is also extracted from the same section. A genetic algorithm approach is used at the final stage to test a large number of distinct models. Each test model consists of the same number of objects buried in the 2D background. The size, depth, location and resistivity of the targets are estimated from a class of models generated by the application of biological rules. The derived images of buried bodies have sharp edges and can then be understood by engineers and archeologists. However, if the hypothesis about the ‘conceptual model’ is very different from the geometry of the subsurface, the proposed approach will not be able to produce satisfactory results. 相似文献
14.
Derecke Palmer 《Geophysical Prospecting》2010,58(4):561-575
The tau‐p inversion algorithm is widely employed to generate starting models with many computer programs that implement refraction tomography. However, this algorithm can frequently fail to detect even major lateral variations in seismic velocities, such as a 50 m wide shear zone, which is the subject of this study. By contrast, the shear zone is successfully defined with the inversion algorithms of the generalized reciprocal method. The shear zone is confirmed with a 2D analysis of the head wave amplitudes, a spectral analysis of the refraction convolution section and with numerous closely spaced orthogonal seismic profiles recorded for a later 3D refraction investigation. Further improvements in resolution, which facilitate the recognition of additional zones with moderate reductions in seismic velocity, are achieved with a novel application of the Hilbert transform to the refractor velocity analysis algorithm. However, the improved resolution also requires the use of a lower average vertical seismic velocity, which accommodates a velocity reversal in the weathering. The lower seismic velocity is derived with the generalized reciprocal method, whereas most refraction tomography programs assume vertical velocity gradients as the default. Although all of the tomograms are consistent with the traveltime data, the resolution of each tomogram is comparable only with that of the starting model. Therefore, it is essential to employ inversion algorithms that can generate detailed starting models, where detailed lateral resolution is the objective. Non‐uniqueness can often be readily resolved with head wave amplitudes, attribute processing of the refraction convolution section and additional seismic traverses, prior to the acquisition of any borehole data. It is concluded that, unless specific measures are taken to address non‐uniqueness, the production of a single refraction tomogram that fits the traveltime data to sufficient accuracy does not necessarily demonstrate that the result is either correct, or even the most probable. 相似文献
15.
A joint inversion algorithm to process geoelectric and surface wave seismic data. Part II: applications 总被引：1，自引：0，他引：1
R. Misiek A. Liebig A. Gyulai T. Ormos M. Dobroka & L. Dresen 《Geophysical Prospecting》1997,45(1):65-85
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. 相似文献
16.
The three-dimensional (3D) geoelectric model of the Kuznetsk-Alatau folded area is reconstructed by magnetotelluric inversion using 3D fitting. It is established that the zones of ore mineralization within the Batenevsky massif are confined to the subvertical faults characterized by the electric resistivity of 100–300 Ω m. Blocks with ρ ≈ 10−100 Ω m are identified at a depth below 10 km in the western part of the model. The blocks are located close to the areas marked by the increased thermal flux, reduced seismic velocities, and elevated Moho boundary. This is probably associated with the presence of the rift zone in this area.
相似文献17.
V. V. Belyavsky 《Izvestiya Physics of the Solid Earth》2007,43(3):237-244
Invariant amplitude curves of the phase tensor are shown to be applicable to the geoelectric model reconstruction in the lower part of the section even if its upper part includes geoelectric heterogeneities described by the tensor of galvanic distortions. The use of other types of invariant curves provides reliable constraints on the deep structure of the section only if the upper part of the section does not contain contrasting geoelectric heterogeneities. 相似文献
18.
近年来,海洋可控源电磁法(MCSEM)被引入油气勘探领域以降低勘探风险.在海洋环境中,受沉积因素所造成的电阻率各向异性的影响,地电模型往往会非常复杂.为更好地反映地下电性结构,本文实现了基于VTI各向异性介质的频率域海洋可控源电磁三维反演.其中,正演采用基于Yee氏交错网格的三维有限差分算法,所形成的离散线性系统通过大规模并行矩阵直接求解器(MUMPS)进行求解.反演采用基于不等式约束的有限内存BFGS(L-BFGS)算法.最后,利用VTI各向异性介质合成数据,分别进行了电阻率各向异性覆盖层和电阻率各向异性高阻层的三维反演,结果表明:(1)基于并行直接法的MCSEM非常适用于海洋电磁所特有的多场源问题;(2)针对各向异性覆盖层模型进行三维各向异性约束反演,提高了解的可靠性;(3)针对电阻率各向异性高阻层,Inline和broadside数据覆盖的反演结果对异常体位置有很好的反映. 相似文献
19.
Near-surface inhomogeneities can distort magnetotelluric (MT) data, thereby limiting interpretational accuracy. In the specific case of near-surface galvanic distortion the resulting frequency independent shift in apparent resistivity sounding curves can be most readily identified in data which are predominantly one-dimensional (1 D). We here consider data from a detailed grid survey which are thoroughly contaminated by parallel offsets. The data were collected over a limited portion of the basalt-covered Paraná basin in Brazil. The data appear largely 1 D over a three decade bandwidth down to a low frequency limit of about 0.1 Hz. A realistic conceptual model consists of a variable thin-sheet over a basin in which the layer parameters vary sufficiently slowly (laterally) that a 1 D interpretation of the static corrected data is valid down to some maximum depth (in this case basement). We consider the performance of three methods which attempt to remove static offsets and provide assessments of the configuration of the geoelectric units of the basin. The three methods consist of curve shifting, statistical/spatial averaging, and the application of parameter constraints. The unambiguous removal of static offsets undoubtedly requires one or more independent constraints at each measurement location. In the absence of such control the three methods are necessarily statistical and each must supply a constraint that has least conflict with the data characteristics. Simple spatial averaging of our data proves effective but the degree of success is generally not known. Parametric constraints, applied as uniform layer resistivities, allow phase-only (non-distorted) data inversion. Inverse models obtained from this approach are found to provide accurate estimates of the depth to the main resistivity interface, the base of the basalt cover, in the vicinity of a control well. 相似文献
20.
Interactive 3D forward modeling of total field surface and three-component borehole magnetic data for the Daye iron-ore deposit (Central China) 总被引：1，自引：0，他引：1
Yushan Yang Yuanyuan Li Tianyou Liu Yinglin Zhan Jie Feng 《Journal of Applied Geophysics》2011,75(2):254-263
The ground magnetic response of deep ore bodies in the Daye iron-ore deposit is relatively weak, and sometimes concealed by the strong magnetic background of shallower sources. Apart from the low-quality ground magnetic data, another critical problem for reconstructing the deep skarn-type ore bodies is developing a versatile inversion scheme that can simultaneously resolve 3D sources with arbitrary shapes. In this case, we resort to interactive 3D forward modeling solution with the joint use of two data sets-total field surface and three-component borehole magnetic data. Joint inversion of the two data sets is expected to help resolve the ambiguity associated with either data set and greatly reduces the nonuniqueness of the magnetic inversion. Such nonuniqueness is especially severe when a 3-D distribution of magnetic susceptibility, instead of a simple body, is sought from the inversion.In this paper, we calculate the magnetic field on the surface and in the borehole caused by 3D arbitrarily-shaped bodies with the triple integral method. The complex 3D magnetic sources having arbitrary shapes are constructed with cross-sections, termination points and facets in our visualization technology. We specify, interactively and in a user-friendly environment, the outline of the sources in terms of geometric elements and their magnetic parameters. The method automatically fits the observations within a prescribed precision. If dissatisfied, the user can redefine the model parameters and proceed to a new inversion. The method's ability to interpret a complicated 3D geologic environment is demonstrated on synthetic models and real data profiles in the Daye iron-ore deposit in central China. The interactive forward modeling results in all tests demonstrate a good correlation of estimated magnetic sources with corresponding known geologic features. 相似文献