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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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Mulder, W.A. (author), Zhebel, E. (author), Minisini, S. (author)We analyse the timestepping stability for the 3D acoustic wave equation, discretized on tetrahedral meshes. Two types of methods are considered: masslumped continuous finite elements and the symmetric interiorpenalty discontinuous Galerkin method. Combining the spatial discretization with the leapfrog timestepping scheme, which is second...journal article 2013
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Mulder, W.A. (author)Migration velocity analysis with the constantdensity acoustic wave equation can be accomplished by the focusing of extended migration images, obtained by introducing a subsurface shift in the imaging condition. A reflector in a wrong velocity model will show up as a curve in the extended image. In the correct model, it should collapse to a...journal article 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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Bharadwaj, P. (author), Mulder, W.A. (author), Drijkoningen, G.G. (author)Leastsquares inversion of seismic reflection waveforms can reconstruct remarkably detailed models of the Earth’s subsurface. However, the cycleskipping associated with the highfrequency waveforms are responsible for spurious local minima in its objective function. Therefore, it is often difficult for descent methods to converge to the true...journal article 2013
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Zhebel, E. (author), Minisini, S. (author), Kononov, A. (author), Mulder, W.A. (author)With the rapid developments in parallel compute architectures, algorithms for seismic modeling and imaging need to be reconsidered in terms of parallelization. The aim of this paper is to compare scalability of seismic modeling algorithms: finite differences, continuous masslumped finite elements and discontinuous Galerkin finite elements. The...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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Mulder, W.A. (author)Masslumped continuous finite elements provide accurate solutions of the secondorder acoustic or elastic wave equation in complex geological settings, in particular in the presence of topography and large impedance contrasts. Elements of higher polynomial degree have better accuracy than those of lower degree but are also more costly. Here, the...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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Mulder, W.A. (author)Migration velocity analysis for the twoway wave equation based on focusing extended migration images at zero subsurface offset are sensitive to the presence of multiples. Even after thorough multiple suppression, remnant multiple energy can lead to conflicting events that will focus at different velocities, one for the primary and another for...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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Minisini, S. (author), Zhebel, E. (author), Kononov, A. (author), Mulder, W.A. (author)Modeling and imaging techniques for geophysics are extremely demanding in terms of computational resources. Seismic data attempt to resolve smaller scales and deeper targets in increasingly more complex geologic settings. Finite elements enable accurate simulation of timedependent wave propagation in heterogeneous media. They are more costly...journal article 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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Moghaddam, P.P. (author), Keers, H. (author), Herrmann, F.J. (author), Mulder, W.A. (author)Waveform inversion is the method of choice for determining a highly heterogeneous subsurface structure. However, conventional waveform inversion requires that the wavefield for each source is computed separately. This makes it very expensive for realistic 3D seismic surveys. Sourceencoding waveform inversion, in which the sources are modeled...journal article 2013
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Poor Moghaddam, P. (author), Mulder, W.A. (author)The classic leastsquares cost functional for full waveform inversion suffers from local minima due to loop skipping in the absence of low frequencies in the seismic data. Velocity model building based on subsurface spatial or temporal shifts may break down in the presence of multiples in the data. Cost functionals that translate this idea to...conference paper 2012
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Mulder, W.A. (author)Migration velocity analysis with the wave equation can be accomplished by focusing of extended migration images, obtained by introducing a subsurface offset or shift. A reflector in the wrong velocity model will show up as a curve in the extended image. In the correct model, it should collapse to a point. The usual approach to obtain a focused...conference paper 2012
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Mulder, W.A. (author)Since most of the easy hydrocarbon reservoirs have been found, accurate subsurface imaging for oil and gas exploration and production is crucial. Seismic data can provide a bandlimited reconstruction of impedance contrasts between different rock formations as well as a subsurface velocity model. Current compute power allows for the use of the...conference paper 2012
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Minisini, S. (author), Zhebel, E. (author), Kononov, A. (author), Mulder, W.A. (author)The spreading adoption of computationally intensive techniques such as Reverse Time Migration and Full Waveform Inversion increases the need of efficiently solving the threedimensional wave equation. Common finitedifference discretization schemes lose their accuracy and efficiency in complex geological settings with discontinuities in the...conference paper 2012
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Minisini, S. (author), Mulder, W.A. (author), Zhebel, E. (author), Kononov, A. (author)Abstract only.conference paper 2012