共查询到20条相似文献，搜索用时 500 毫秒
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Tomographic Inversion In Reflection Seismology 总被引：7，自引：0，他引：7
P. R. Williamson 《Geophysical Journal International》1990,100(2):255-274
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Inversion for multiple parameter classes 总被引：2，自引：0，他引：2
Many geophysical data, such as the frequencies of the free oscillations of the Earth, depend on more than one type of model parameter. For inverse problems depending on multiple parameter classes, an iterative solution procedure is introduced in which each parameter class can be treated in the same way. This approach has considerable advantages where a large number of parameters are employed, but can still be useful for smaller systems.
The iteration by parameter class commences by solving for the direct dependence on a particular parameter class, and at subsequent iterations the cross-dependences between classes are introduced. The update affects only the right-hand side of the equations, and, because the same sets of equations have to be solved at each iteration, an efficient computational implementation can be made. The largest set of equations that has to be solved at a time corresponds to the number of variables in an individual parameter class rather than the full set of parameters, which confers substantial computational benefits for very large problems. 相似文献
The iteration by parameter class commences by solving for the direct dependence on a particular parameter class, and at subsequent iterations the cross-dependences between classes are introduced. The update affects only the right-hand side of the equations, and, because the same sets of equations have to be solved at each iteration, an efficient computational implementation can be made. The largest set of equations that has to be solved at a time corresponds to the number of variables in an individual parameter class rather than the full set of parameters, which confers substantial computational benefits for very large problems. 相似文献
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Summary. We examine the way in which measurements of velocity anisotropy can add to our understanding of upper mantle structure. Measurements of P -wave velocity anisotropy in a single plane contain very little direct information about the anisotropic structure. A promising technique is to fit the observed velocity variation with a mixture of an assumed anisotropic constituent and a proportion of isotropic material. Using this technique, mixtures of orthorhombic and transversely isotropic olivine are obtained, which are in excellent agreement with observed velocity variations in the Pacific. 相似文献
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Joint Inversion of Geophysical Data 总被引：6，自引：0，他引：6
《Geophysical Journal International》1975,42(3):977-991
Summary. By jointly inverting several different kinds of geophysical measurements at a site we avoid some of the ambiguity inherent in the individual methods. We show how this can be done for the combination of DC resistivity and magnetotelluric measurements on a layered medium by considering a simple 3-layer model. The combination resolves the resistivity of the thin resistive second layer, even though neither of the two methods can do so alone.
The method is then applied to field data from a shallow sedimentary basin. A blind zone occurs beneath a thick near-surface conductive shale. By a study of the eigenvalue structure of the model it can be seen that resolution in this zone would be slightly enhanced by higher frequency magnetotelluric data, but additional DC data at larger spacing would yield no improvement. 相似文献
The method is then applied to field data from a shallow sedimentary basin. A blind zone occurs beneath a thick near-surface conductive shale. By a study of the eigenvalue structure of the model it can be seen that resolution in this zone would be slightly enhanced by higher frequency magnetotelluric data, but additional DC data at larger spacing would yield no improvement. 相似文献
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Inversion of time domain three-dimensional electromagnetic data 总被引：7，自引：0，他引：7
Eldad Haber Douglas W. Oldenburg R. Shekhtman 《Geophysical Journal International》2007,171(2):550-564
We present a general formulation for inverting time domain electromagnetic data to recover a 3-D distribution of electrical conductivity. The forward problem is solved using finite volume methods in the spatial domain and an implicit method (Backward Euler) in the time domain. A modified Gauss–Newton strategy is employed to solve the inverse problem. The modifications include the use of a quasi-Newton method to generate a pre-conditioner for the perturbed system, and implementing an iterative Tikhonov approach in the solution to the inverse problem. In addition, we show how the size of the inverse problem can be reduced through a corrective source procedure. The same procedure can correct for discretization errors that inevidably arise. We also show how the inverse problem can be efficiently carried out even when the decay time for the conductor is significantly larger than the repetition time of the transmitter wave form. This requires a second processor to carry an additional forward modelling. Our inversion algorithm is general and is applicable for any electromagnetic field ( E , H , d B / dt ) measured in the air, on the ground, or in boreholes, and from an arbitrary grounded or ungrounded source. Three synthetic examples illustrate the basic functionality of the algorithm, and a result from a field example shows applicability in a larger-scale field example. 相似文献
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Inversion of gravity data using a binary formulation 总被引：1，自引：0，他引：1
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An inversion method is presented for the reconstruction of interface geometry between two or more crustal layers from teleseismic traveltime residuals. The method is applied to 2-D models consisting of continuous interfaces separating constant-velocity layers. The forward problem of determining ray paths and traveltimes between incident wave fronts below the structure and receivers located on the Earth's surface is solved by an efficient and robust shooting method. A conjugate gradient method is employed to solve the inverse problem of minimizing a least-squares type objective function based on the difference between observed and calculated traveltimes. Teleseismic data do not accurately constrain average vertical structure, so a priori information in the form of layer velocities and average layer thicknesses is required. Synthetic tests show that the method can be used to reconstruct interface geometry accurately, even in the presence of data noise. Tests also show that, if layer velocities and initial interface positions are poorly chosen, lateral structure is still recoverable. The inversion method was applied to previously published teleseismic data recorded by an in-line array of portable seismographs that traversed the northern margin of the Musgrave Block, central Australia. The solution based on interface parametrization is consistent with models given by other studies that used the same data but different methods, most notably the standard tomographic approach that inverts for velocity rather than interface structure. 相似文献
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Inversion of magnetometer array data by thin-sheet modelling 总被引：1，自引：0，他引：1
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Inversion for elastic parameters in weakly anisotropic media 总被引：1，自引：0，他引：1
Xuyao Zheng 《Geophysical Journal International》2004,159(3):1077-1089
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We have developed an inversion formuialion for velocity and attenuation structure using seismic attributes, including envelope amplitude, instantaneous frequency and arrival times of selected seismic phases. We refer to this approach as AFT inversion for amplitude, (instantaneous) frequency and time. Complex trace analysis is used to extract the different seismic attributes. The instantaneous frequency data are converted to t * using a matching procedure that approximately removes the effects of the source spectra. To invert for structure, ray-perturbation methods are used to compute the sensitivity of the seismic attributes to variations in the model. An iterative inversion procedure is then performed from smooth to less smooth models that progressively incorporates the shorter-wavelength components of the model. To illustrate the method, seismic attributes are extracted from seismic-refraction data of the Ouachita PASSCAL experiment and used to invert for shallow crustal velocity and attenuation structure. Although amplitude data are sensitive to model roughness, the inverted velocity and attenuation models were required by the data to maintain a relatively smooth character. The amplitude and t * data were needed, along with the traveltimes, at each step of the inversion in order to fit all the seismic attributes at the final iteration. 相似文献
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Thomas Forbriger 《Geophysical Journal International》2003,153(3):719-734
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