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Ponomarenko, A. V. (author), Kashtan, B. M. (author), Troyan, V. N. (author), Mulder, W.A. (author)Surface waves are often used to estimate a nearsurface shearvelocity profile. The inverse problem is solved for the locally onedimensional problem of a set of homogeneous horizontal elastic layers. The result is a set of shear velocities, one for each layer. To obtain a Pwave velocity profile, the Pguided waves should be included in the...journal article 2017
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Ponomarenko, A.V. (author), Kashtan, B.M. (author), Troyan, V.N. (author), Mulder, W.A. (author)We inverted seismic field data for a continuous, laterally invariant Pwave velocity profile. Instead of the usual approach that involves horizontal layers with piecewise constant densities and velocities, we consider models of one or two layers with a constant gradient of the squared slowness above a homogeneous halfspace. With a single layer...conference paper 2015
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Kazei, V.V. (author), Kashtan, B.M. (author), Troyan, V.N. (author), Mulder, W.A. (author)Low frequencies play a crucial role in the convergence of fullwaveform inversion to the correct model in most of its current implementations. However, the lower the frequencies, the bigger are the amplitudes of the surface waves, causing the inversion to be driven by the latter. If they are not blanked out or removed, this may lead to...conference paper 2015
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Anikiev, D.V. (author), Kashtan, B.M. (author), Mulder, W.A. (author), Troyan, V.N. (author)An elastic isotropic medium is described with three parameters. In seismic migration the perturbation of one elastic parameter affects the images of all the three, which means that these parameters are coupled. For an effective quantitative reconstruction of the true elastic medium reflectivity one can apply an iterative linearized migration...journal article 2014
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Shigapov, R. (author), Kashtan, B. (author), Droujinine, A. (author), Mulder, W.A. (author)We consider the problem of Q estimation from microseismic and from perforation shot data. Assuming that the source wavelet is not well known, we focused on the spectral ratio method and on sourceindependent viscoelastic full waveform inversion. We derived 3D nearfield approximations of monopole and dipole Green's tensors in a homogeneous...conference paper 2013
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Shigapov, R. (author), Kashtan, B. (author), Droujinine, A. (author), Mulder, W.A. (author)We consider the problem of anelastic full waveform inversion in a multilayered, isotropic viscoelastic medium from microseismic and crosshole perforation shots. Usually, the source wavelet is not well known, so we focus on Q estimation techniques that can handle this problem. We revisit the spectral ratio method (SRM) and discuss its domain of...journal article 2013
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Anikiev, D. (author), Kashtan, B. (author), Mulder, W.A. (author)Three model parameters as a function of position describe wave propagation in an isotropic elastic medium. Ideally, imaging of data for a point scatterer that consists of a perturbation in one of the elastic parameters should only provide a reconstruction of that perturbation, without crosstalk into the other parameters. This is not the case...journal article 2013
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Ponomarenko, A.V. (author), Kashtan, B.M. (author), Troyan, V.N. (author), Mulder, W.A. (author)Recently, we proposed an analytical approach to invert for a smoothly varying nearsurface Pwave velocity profile that has a squared slowness linearly decreasing with depth. The exact solution for such a velocity profile in the acoustic approximation can be expressed in terms of Airy functions and leads to a dispersion equation. The method was...conference paper 2013
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Kazei, V. (author), Kashtan, B.M. (author), Troyan, V.N. (author), Mulder, W.A. (author)Full waveform inversion suffers from local minima, due to a lack of low frequencies in the data. A reflector below the zone of interest may help in recovering the longwavelength components of a velocity perturbation, as demonstrated in a paper by Mora. Because smooth models are more popular as initial guesses for FWI, we consider the Born...conference paper 2013
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Ponomarenko, A.V. (author), Kashtan, B.M. (author), Troyan, V.N. (author), Mulder, W.A. (author)Surface waves can be used to obtain a nearsurface shear wave profile. The inverse problem is usually solved for the locally 1D problem of a set of homogeneous horizontal elastic layers. The output is a set of shear velocity values for each layer in the profile. Pwave velocity profile can be estimated if higher modes and Pguided waves are...conference paper 2013
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Kazei, V.V. (author), Kashtan, B.M. (author), Troyan, V.N. (author), Mulder, W.A. (author)It is generally believed that full waveform inversion needs very low frequencies in the data to avoid convergence to a local minimum, which would lead to an incorrect velocity model. Often, low frequencies are not present in the data. Then, a kinematically accurate initial model is required that contains the longwavelength structures that...conference paper 2013
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Kazei, V.V. (author), Ponomarenko, A.V. (author), Troyan, V.N. (author), Kashtan, B.M. (author), Mulder, W.A. (author)Full waveform inversion suffers from local minima, due to a lack of low frequencies in the data. A reflector below the zone of interest may, however, help in recovering the longwavelength components of a velocity perturbation, as demonstrated in a paper by Mora. With the Born approximation for the perturbation in a reference model consisting of...conference paper 2012