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Summary The dispersion of higher modes of surface waves over a region covered by an array of stations can be measured by applying a frequency-wavenumber transform to segments of the signals in these stations, centered at a number of group-velocities. Thus, at a fixed period, modes appear as separate maxima in a display of the power spectrum on a phase-velocity vs. group velocity plane.For regions of mild lateral heterogeneity, the main source of error is shown to be due to the inadequacy of the array-response. Numerical experiments with synthetic signals indicate that a precision of the order of 1% can be obtained with a realistic number of stations. Improvements should be obtained by averaging data obtained from different events. The danger of misidentification of modes can be reduced by iteratively removing the sidelobes from the mode-separation diagram. 相似文献
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Global P and PP traveltime tomography: rays versus waves 总被引：2，自引：1，他引：2
R. Montelli G. Nolet G. Masters F. A. Dahlen S.-H. Hung 《Geophysical Journal International》2004,158(2):637-654
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Ignace Loris Guust Nolet Ingrid Daubechies F. A. Dahlen 《Geophysical Journal International》2007,170(1):359-370
We propose the use of ℓ1 regularization in a wavelet basis for the solution of linearized seismic tomography problems A m = d , allowing for the possibility of sharp discontinuities superimposed on a smoothly varying background. An iterative method is used to find a sparse solution m that contains no more fine-scale structure than is necessary to fit the data d to within its assigned errors. 相似文献
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Finite-frequency tomography in a crustal environment: Application to the western part of the Gulf of Corinth 总被引：2，自引：0，他引：2
In this paper we investigate finite-frequency effects in crustal tomography. We developed an inversion procedure based on an exact numerical computation of the sensitivity kernels. In this approach we compute the 3D travel-time sensitivity kernels by using (1) graph theory and an additional bending to estimate accurately both rays and travel-times between source/receiver and diffraction points and (2) paraxial ray theory to estimate the amplitude along theses rays. We invert both the velocity and the hypocentre parameters, using these so-called banana-doughnut kernels and the LSQR iterative solver. We compare the ray-theoretical and the finite-frequency tomography to image the intermediate structures beneath the Gulf of Corinth (Greece), which has long been recognized as the most active continental rifting zone in the Mediterranean region. Our dataset consists of 451 local events with 9233 P- first-arrival times recorded in the western part of the Gulf (Aigion area) in the framework of the 3F-Corinth European project. Previous tomographic images showed a complex velocity crustal model and a low-dip surface that may accommodate the deformation. Accurate velocity models will help to better constrain the rifting process, which is still a subject of debate. The main results of this study show that finite-frequency tomography improves crustal tomographic images by providing better resolved images of the 3D complicated velocity structure. Because the kernels spread the information over a volume, finite-frequency tomography results in a sharpening of layer boundaries as we observed for the shallower part of the crust (down to 5 km depth) beneath the Gulf of Corinth. 相似文献
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Solving large linear inverse problems by projection 总被引：2，自引：0，他引：2
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Simultaneous inversion of seismic data 总被引：2，自引：0，他引：2
Guust Nolet 《Geophysical Journal International》1978,55(3):679-691
Summary. The resolving power of different data sets, consisting of surface-wave dispersion measurements and S travel times, are compared for a continental structure. The shear velocity in the low-velocity zone can be resolved in some detail with higher-mode phase-velocity data. Sufficient resolution for small density contrasts (0.03 g cm−3 ) until depths of ∼ 300 km can be reached if higher-mode group velocities are available as well, even at a precision as low as 0.10 km/s. At greater depths the density is not resolved, and here travel-time data are superior to higher modes in resolving the shear velocity. 相似文献
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