Analysis and algorithms for a regularized cauchy problem arising from a non-linear elliptic PDE for seismic velocity estimation

JOURNAL OF COMPUTATIONAL PHYSICS

卷:228

Article

Cameron, M. K.¹  Fomel, S. B.²  Sethian, J. A.³ 

[1] NYU, Courant Inst Math Sci, Dept Math, New York, NY 10012 USA

[2] Univ Texas Austin, Bur Econ Geol, Univ Stn, Austin, TX 78713 USA

[3] Univ Calif Berkeley, Dept Math, Berkeley, CA 94720 USA

关键词: Elliptic PDE;    Cauchy problem;    III-posed;    Seismic velocity;    Dix inversion;    Time migration;    Image rays;    Geometrical spreading;    Time coordinates;    Finite difference;    Error analysis;    Perturbation analysis;    Lax-Friedrics method;    Chebyshev spectral method;    Marmousi example;   

DOI  :  10.1016/j.jcp.2009.06.036

来源: Elsevier

【 摘 要 】

In the present work we derive and study a non-linear elliptic PDE coming from the problem of estimation of sound speed inside the Earth. The physical setting of the PDE allows us to pose only a Cauchy problem, and hence is ill-posed. However, we are still able to solve it numerically on a long enough time interval to be of practical use. We used two approaches. The first approach is a finite difference time-marching numerical scheme inspired by the Lax-Friedrichs method. The key features of this scheme is the Lax-Friedrichs averaging and the wide stencil in space. The second approach is a spectral Chebyshev method with truncated series. We show that our schemes work because of (i) the special input corresponding to a positive finite seismic velocity, (ii) special initial conditions corresponding to the image rays, (iii) the fact that our finite-difference scheme contains small error terms which damp the high harmonics; truncation of the Chebyshev series, and (iv) the need to compute the solution only for a short interval of time. We test our numerical schemes on a collection of analytic examples and demonstrate a dramatic improvement in accuracy in the estimation of the sound speed inside the Earth in comparison with the conventional Dix inversion. Our test on the Marmousi example confirms the effectiveness of the proposed approach. (C) 2009 Elsevier Inc. All rights reserved.

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