51 research outputs found
Damped wave-equation-based first-arrival traveltime tomography using the embedded boundary method
No full textFirst-arrival traveltime tomography (FATT) is used to delineate shallow velocity structures to identify static effects in oil exploration as well as to characterize the near surface for geotechnical purposes. Because FATT is generally used for land seismic data processing, it becomes necessary to consider irregular topography especially when performing wave-based tomography. However, the standard Cartesian finite-difference method cannot properly handle irregular topography. Hence, the embedded boundary method (EBM) is incorporated into the frequency-domain damped-wave equation in order to correctly describe irregular topography. The developed modeling algorithm is used to calculate first-arrival traveltimes and to perform FATT. The EBM-based modeling algorithm accurately describes the irregular surfaces of numerical velocity models on a regular mesh by exploiting the mirror image principle. The accuracy of the EBM-based traveltime calculation is validated by using two homogeneous velocity models with dipping and complex surfaces. The validation results demonstrate that the proposed algorithm is unaffected by the staircase approximation. The FATT is then applied to synthetic and real data to demonstrate the applicability of the developed algorithm to velocity models with complex topography. For the real data example, the inverted velocity model is used to apply static corrections. The processing results demonstrate an improvement in the continuity of seismic events, thus confirming the accuracy of the developed FATT method.11Nsciescopu
First-arrival traveltime inversion with embedded boundary method for irregular topography
No full textEquivalent source distribution for efficient 3‐D acoustic wave equation modeling in the Laplace domain
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Refraction traveltime tomography based on damped wave equation for irregular topographic model
No full textFirst-arrival traveltime tomography using limited-acquisition geometry in an irregular topography
No full textAdaptive preconditioning of full-waveform inversion based on structure-oriented smoothing filter
No full textPractical considerations in the implementation of time-domain acoustic full waveform inversion
No full textFull waveform inversion (FWI) plays a major role in the oil and gas industry as a state-of-the-art technique that produces quantitative subsurface structures with high-fidelity images. Various FWI studies have been conducted, and these suggest that FWI is a promising inversion method. Recently, many attempts have been made toward three-dimensional (3D) and four-dimensional FWI applications (which were difficult to perform in the past) because of the progress made in computer science and the growth of computer resources. To manage the very large data requirement of 3D problems, a time-domain FWI that is relatively efficient in terms of memory demands must be implemented. However, it could encounter practical issues, leading to failure in its convergence. In this paper, we introduce these practical issues and several alternative methods for mitigating them. The first issue is the bandpass filtering of the observed seismograms. We suggest that the frequency-domain filter based on a reference wavelet would be optimal in terms of both bandpass filtering and source wavelet estimation. The second issue is related to acoustic approximation. We show that a simple density model comprising only water and solid layers is a reasonable option to address seafloor reflectivity properly. The last issue is the accumulation of round-off errors due to the massive computation of the objective function. We demonstrate that a simple modification of the error calculation can resolve this round-off error problem. © 2021 Australian Society of Exploration Geophysicists.11Nsciescopu
Evaluation of Kirchhoff hyperbola in terms of partial derivative wavefield and virtual source
No full textThe Kirchhoff migration is computationally the most economic choice of migration currently available. From its beginning, the Kirchhoff migration has been developed and improved separately from wave-equation based migrations although they are founded on the same principle. In this paper, we reveal a link between the Kirchhoff depth migration and the wave-equation based migration such as reverse-time migration and least squares migration in terms of the partial derivative wavefield and the virtual source. The Kirchhoff prestack depth migration uses the partial derivative wavefield approximated by the Dirac delta function to migrate the seismic signals. Accordingly, the Kirchhoff hyperbola is defined as kinematic approximation of the partial derivative wavefield.This work was financially supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by Korea government (MOST) (No.R0A-2006-000-10291-0) and the Brain Korea 21 project of the Ministry of Education
La ville productrice de mal-être
No full textEn psychologie sociale, environnement et processus sociaux sont étroitement liés. Tout espace a une part d’influence sur la manière dont nous concevons les relations sociales. Il n’est pas rare de voir dans la littérature sud-coréenne contemporaine des exemples de dystopie urbaine, mais s’il y a une auteure qui fait de la ville un antagoniste récurrent de son œuvre, il s’agit de Pyun Hye-young. La ville de Pyun Hye-young est sale, délabrée, cruelle, répugnante : enfermés physiquement, ses personnages sont placés dans des situations extrêmes qui mettent en avant leur peur, leur solitude, et leur impuissance. Cette ville aux allures dystopiques est donc une occasion pour Pyun Hye-young de repenser les relations sociales et la santé psychique de ses personnages, comme elle en offre l’exemple dans son premier roman, Cendres et rouge.In social psychology, environment and social processes are intricately linked. Every space has a part of influence on the way we view social relationships. Urban dystopias are not a rare occurrence in South-Korean contemporary literature, but if there exists an author who makes of the city a recurring antagonist in her work, it is Pyun Hye-young. Pyun Hye-young’s city is dirty, ruined, cruel and disgusting: physically confined, her characters are placed in extreme situations which highlight their fear, their loneliness and their powerlessness. This dystopia-like city becomes a way for Pyun Hye-young to rethink human relationships and the mental health of her characters, as she offers an example through her first novel, Ashes and Red
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