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Huiskes, M.J. (author), Plessix, RE (author), Mulder, W.A. (author)In land applications, topography variation may impact the imaging if not taken into account. With low-frequency and wide-aperture data, the long-to-intermediate wavelength components of the velocity model can be recovered by full-waveform inversion. Standard static corrections to handle the topography do not work satisfactorily on long-offset...conference paper 2017
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Kadu, Ajinkya (author), Mulder, W.A. (author), van Leeuwen, Tristan (author)Full-waveform inversion attempts to estimate a high-resolution model of the Earth by inverting all the seismic data. This procedure fails if the Earth model contains high-contrast bodies such as salt and if su ciently low frequencies are absent from the data. Salt bodies are important for hydrocarbon exploration because oil or gas reservoirs are...conference paper 2017
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Mulder, W.A. (author), Huiskes, M.J. (author)One approach to incorporate topography in seismic finite-difference codes is a local modification of the difference operators near the free surface. An earlier paper described an approach for modelling irregular boundaries in a constant-density acoustic finite-difference code, based on the second-order formulation of the wave equation that only...journal article 2017
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Shamasundar, R. (author), Mulder, W.A. (author)For seismic modelling, imaging and inversion, finite-difference methods are still the workhorse of the industry despite their inability to meet the increasing demand for improved accuracy in subsurface imaging. Finiteelement methods offer better accuracy but at a higher computational cost. A stress-velocity formulation with linear elements and...conference paper 2017
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Mulder, W.A. (author)Storage of the source wavefield during reverse-time migration and full-waveform inversion can be avoided by reconstructing that wavefield during reverse-time stepping along with the receiver wavefield. With absorbing boundary conditions, this requires the final states of the source wavefield and a strip of boundary values at all times. The width...conference paper 2017
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Bharadwaj, Pawan (author), Drijkoningen, G.G. (author), Mulder, W.A. (author), Thorbecke, J.W. (author), Neducza, Boriszlav (author), Jenneskens, R (author)In the near surface with unconsolidated soils, shear-wave properties can often be characterised better and with a higher resolution than compressional-wave properties. To enable imaging ahead of a tunnel-boring machine, we developed a seismic prediction system with a few shear-wave vibrators and horizontal receivers. The boring process is...journal article 2017
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Ishiyama, T. (author), Blacquière, G. (author), Verschuur, D.J. (author), Mulder, W.A. (author)Surface waves in seismic data are often dominant in a land or shallow-water environment. Separating them from primaries is of great importance either for removing them as noise for reservoir imaging and characterization or for extracting them as signal for near-surface characterization. However, their complex properties make the surface-wave...journal article 2016
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Bharadwaj, Pawan (author), Mulder, W.A. (author), Drijkoningen, G.G. (author)Least-squares inversion of seismic arrivals can provide remarkably detailed models of the Earth's subsurface. However, cycle skipping associated with these oscillatory arrivals is the main cause for local minima in the least-squares objective function. Therefore, it is often difficult for descent methods to converge to the solution without an...journal article 2016
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Huiskes, M.J. (author), Plessix, RE (author), Mulder, W.A. (author)We propose a finite-difference scheme for the simulation of seismic waves interacting with 3-D freesurface topography. The intended application is velocity model building by acoustic full-waveform inversion (FWI). The scheme follows an immersed boundary approach for wave equations in the firstorder stress-velocity formulation, discretized on a...conference paper 2016
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Geevers, Sjoerd (author), van der Vegt, Jaap (author), Mulder, W.A. (author)We present and analyse a Symmetric Interior Penalty Discontinuous Galerkin (SIPDG) method combined with an explicit hybrid Local Time Stepping (LTS) scheme for solving seismic wave problems in heterogeneous anisotropic elastic media. The discontinuous Galerkin method allows for local adjustment of the mesh size and approximation order, and can...abstract 2016
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Bharadwaj, Pawan (author), Drijkoningen, G.G. (author), Mulder, W.A. (author), Tscharner, Thomas (author), Jenneskens, Rob (author)The Earth’s properties, composition and structure ahead of a tunnel boring machine (TBM) should be mapped for hazard assessment during excavation. We study the use of seismic-exploration techniques for this purpose. We focus on a seismic system for soft soils, where shear waves are better and easier to interpret than compressional waves, as has...conference paper 2016
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Shamasundar, R. (author), Mulder, W.A. (author)The second-order formulation of the wave equation is often used for spectral-element discretizations. For some applications, however, a first-order formulation may be desirable. It can, in theory, provide much better accuracy in terms of numerical dispersion if the consistent mass matrix is used and the degree of the polynomial basis functions...conference paper 2016
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Shamasundara, R. (author), Mulder, W.A. (author)Finite-element discretizations of the acoustic wave equation in the time domain often employ mass lumping to avoid the cost of inverting a large sparse mass matrix. For the second-order formulation of the wave equation, mass lumping on Legendre–Gauss–Lobatto points does not harm the accuracy. Here, we consider a first-order formulation of the...journal article 2016
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Kadu, Ajinkya (author), van Leeuwen, Tristan (author), Mulder, W.A. (author)<br/>In seismic exploration, the delineation of large bodies with hard exterior contrasts but nearly constant interior properties is a challenge. Examples include salt diapirs, salt slabs, anhydrite or basalt layers. Salt geometries are of particular interest because they often have hydrocarbon reservoirs on their sides or underneath. This...conference paper 2016
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Mulder, W.A. (author), Shamasundara, R. (author)We consider isotropic elastic wave propagation with continuous mass-lumped finite elements on tetrahedra with explicit time stepping. These elements require higher-order polynomials in their interior to preserve accuracy after mass lumping and are only known up to degree 3. Global assembly of the symmetric stiffness matrix is a natural approach...journal article 2016
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Shamasundar, R. (author), Al-Khoury, R.I.N. (author), Mulder, W.A. (author)We investigated one-dimensional numerical dispersion curves and error behaviour of four finite-element schemes with polynomial basis functions: the standard elements with equidistant nodes, the Legendre-Gauss-Lobatto points, the Chebyshev-Gauss-Lobatto nodes without a weighting function and with. Mass lumping, required for efficiency reasons and...conference paper 2015
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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 P-wave 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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Pisupati, P.B. (author), Mulder, W.A. (author), Drijkoningen, G.G. (author), Reijnen, R. (author)In the near-surface with unconsolidated soils, shear properties can be well imaged, sometimes better than P-wave properties. To facilitate ground prediction ahead of a tunnel boring machine (TBM), active ‘surveys’ with shear-wave vibrators are carried out during boring. In such surveys, only a few shear-wave vibrators can be placed in front of...conference paper 2015
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Modave, A. (author), St-Cyr, A. (author), Warburton, T. (author), Mulder, W.A. (author)Improving both the accuracy and computational performance of simulation tools is a major challenge for seismic imaging, and generally requires specialized algorithms and computational implementations to make full use of modern hardware architectures. We present a computational strategy based on a highorder discontinuous Galerkin time-domain...conference paper 2015
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Pisupati, P.B. (author), Mulder, W.A. (author), Drijkoningen, G.G. (author)To overcome the local minima problem in FWI, we propose to use an auxiliary data-domain objective function during inversion. It reduces the data to a simpler form by squaring, followed by blurring to ensure that events that are too far apart can still interact during the inversion. As it effectively replaces seismic arrivals by bumps, we call it...conference paper 2015