Finite-difference modelling of wavefield constituents

The finite-difference method is among the most popular methods for modelling seismic wave propagation. Although the method has enjoyed huge success for its ability to produce full wavefield seismograms in complex models, it has one major limitation which is of critical importance for many modelling applications; to naturally output up- and downgoing and P- and S-wave constituents of synthesized seismograms. In this paper, we show how such wavefield constituents can be isolated in finite-difference-computed synthetics in complex models with high numerical precision by means of a simple algorithm. The description focuses on up- and downgoing and P- and S-wave separation of data generated using an isotropic elastic finite-difference modelling method. However, the same principles can also be applied to acoustic, electromagnetic and other wave equation

Exploring planets and asteroids with 6DoF sensors: Utopia and realism

A 6 degrees-of-freedom (6DoF) sensor, measuring three components of translational acceleration and three components of rotation rate, provides the full history of motion it is exposed to. In Earth sciences 6DoF sensors have shown great potential in exploring the interior of our planet and its seismic sources. In space sciences, apart from navigation, 6DoF sensors are, up to now, only rarely used to answer scientific questions. As a first step of establishing 6DoF motion sensing deeper into space sciences, this article describes novel scientific approaches based on 6DoF motion sensing with substantial potential for constraining the interior structure of planetary objects and asteroids. Therefore we estimate 6DoF-signal levels that originate from lander–surface interactions during landing and touchdown, from a body’s rotational dynamics as well as from seismic ground motions. We discuss these signals for an exemplary set of target bodies including Dimorphos, Phobos, Europa, the Earth’s Moon and Mars and compare those to self-noise levels of state-of-the-art sensors

A modified Lax-Wendroff correction for wave propagation in media described by Zener elements

ISSN:1365-246XISSN:0956-540

Source wavelet inversion for laterally-varying scaling errors using Marchenko focusing functions

ISSN:1029-7006ISSN:1607-796

A consistent implementation of point sources on finite-difference grids

We present a method to position point sources at arbitrary locations on finite-difference (FD) grids. We show that implementing point sources on single nodes can cause considerable errors when modelling with the FD method. In contrast, we propose to create a spatially distributed source (over multiple nodes) that nonetheless creates the desired point-source response. The spatial point source is formulated in the wavenumber domain and is based on the FD coefficients used for the wave propagation. Using this ‘FD-consistent source’ on 1-D and 2-D examples, we show that we can obtain superior fits to analytical solutions compared to single-node or sinc-function source implementations, and we show that sources can be offset to arbitrary locations from ‘on’ the grid to ‘off’ the grid, while resulting in solutions that are identical to within machine precisionISSN:0956-540XISSN:1365-246

Anisotropic elastic finite-difference modeling of sources and receivers on Lebedev grids

The Lebedev grid finite-difference (FD) method allows modeling of anisotropic elastic wave propagation. On Lebedev grids, erroneous point-source excitations can create spurious (non-physical) waves. The only known remedy for such artifacts in the literature is the Lisitsa-Vishnevsky method. This method uses a distributed array to create both point-sources and point-receivers on the FD grid. However, the Lisitsa-Vishnevsky method does not fully eliminate spurious artifacts. A novel approach is found in the FD-consistent point-source, which suppresses the spurious artifacts entirely. The method requires no array recording to create point-receivers. The advantage of this method over the Lisitsa-Vishnevsky method is demonstrated with two anisotropic modeling examples. © 2021 Society of Exploration Geophysicists.ISSN:0016-8033ISSN:1942-215

Correcting an acoustic wavefield for elastic effects

ISSN:0956-540XISSN:1365-246

Eliminating time dispersion from seismic wave modeling

We derive an expression for the error introduced by the second-order accurate temporal finitedifference (FD) operator, as present in the FD, pseudospectral and spectral element methods for seismic wave modeling applied to time-invariant media. The 'time-dispersion' error speeds up the signal as a function of frequency and time step only. Time dispersion is thus independent of the propagation path, medium or spatial modeling error.We derive two transforms to either add or remove time dispersion from synthetic seismograms after a simulation. The transforms are compared to previous related work and demonstrated on wave modeling in acoustic as well as elastic media. In addition, an application to imaging is shown. The transforms enable accurate computation of synthetic seismograms at reduced cost, benefitting modeling applications in both exploration and global seismology. The Author(s) 2017. Published by Oxford University Press. All rights reserved

Spatial wavefield gradient-based seismic wavefield separation

ISSN:0956-540XISSN:1365-246

Exact wavefield separation on an elastic-free surface with sharp corners

ISSN:1949-4645ISSN:1052-381