Elastic versus acoustic inversion for marine surveys

Type
Article

Authors
Mora, Peter
Wu, Zedong

KAUST Department
Physical Science and Engineering (PSE) Division

Online Publication Date
2018-04-25

Print Publication Date
2018-07-01

Date
2018-04-25

Abstract
Full Wavefield Inversion (FWI) is a powerful and elegant approach for seismic imaging that is on the way to becoming the method of choice when processing exploration or global seismic data. In the case of processing marine survey data, one may be tempted to assume acoustic FWI is sufficient given that only pressure waves exist in the water layer. In this paper, we pose the question as to whether or not in theory – at least for a hard water bottom case – it should be possible to resolve the shear modulus or S-wave velocity in a marine setting using large offset data. We therefore conduct numerical experiments with idealized marine data calculated with the elastic wave equation. We study two cases, FWI of data due to a diffractor model, and FWI of data due to a fault model. We find that at least in idealized situation, elastic FWI of hard waterbottom data is capable of resolving between the two Lamé parameters λ and μ. Another numerical experiment with a soft waterbottom layer gives the same result. In contrast, acoustic FWI of the synthetic elastic data results in a single image of the first Lamé parameter λ which contains severe artefacts for diffraction data and noticable artefacts for layer reflection data. Based on these results, it would appear that at least, inversions of large offset marine data should be fully elastic rather than acoustic unless it has been demonstrated that for the specific case in question (offsets, model and water depth, practical issues such as soft sediment attenuation of shear waves or computational time), that an acoustic only inversion provides a reasonably good quality of image comparable to that of an elastic inversion. Further research with real data is required to determine the degree to which practical issues such as shear wave attenuation in soft sediments may affect this result.

Citation
Mora P, Wu Z (2018) Elastic versus acoustic inversion for marine surveys. Geophysical Journal International. Available: http://dx.doi.org/10.1093/gji/ggy166.

Acknowledgements
We would like to thank John Etgen for reading the manuscript and helpful suggestions which greatly improved the quality of the paper.We also thank the two reviewers (Milena Marjanovic and anonymous) and the editor (Rene-Edouard Plessix) whose helpful comments lead to many improvements of the paper.

Publisher
Oxford University Press (OUP)

Journal
Geophysical Journal International

DOI
10.1093/gji/ggy166

Additional Links
https://academic.oup.com/gji/advance-article/doi/10.1093/gji/ggy166/4985840

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