Modeling and inversion of PS-wave moveout asymmetry for tilted TI media: Part 1 - Horizontal TTI layer
IR@NIO: CSIR-National Institute Of Oceanography, Goa
View Archive Info| Field | Value | |
| Creator |
Dewangan, P.
Tsvankin, I. |
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| Date |
2007-04-13T07:19:42Z
2007-04-13T07:19:42Z 2006 |
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| Identifier |
Geophysics, vol.71(4), D107-D121pp.
http://drs.nio.org/drs/handle/2264/579 |
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| Description |
One of the distinctive features of mode-converted waves is their asymmetric moveout (i.e., the PS-wave traveltime in general is different if the source and receiver are interchanged) caused by lateral heterogeneity or elastic anisotropy. If the medium is anisotropic, the PS-wave moveout asymmetry contains valuable information for parameter estimation that cannot be obtained from pure reflection modes. The so-called PP + PS = SS method is generalized, which is designed to replace reflected PS modes in velocity analysis with pure (unconverted) SS-waves, by supplementing the output SS traces with the moveout-asymmetry attributes of PS-waves. The time-asymmetry attribute delta tPS is computed in the slowness domain as the difference between the paired traveltimes of the PS arrivals corresponding to ray parameters (horizontal slownesses) of equal magnitude but opposite sign. Another useful asymmetry attribute is the offset X sub(min) of the PS-wave traveltime minimum on a common-midpoint (CMP) gather. The effectiveness of the developed algorithm and the importance of including the asymmetry attributes of PS-waves in anisotropic velocity analysis for a horizontal transversely isotropic layer with a tilted symmetry axis (or TTI) medium are demonstrated. Simple analytic expressions for the moveout asymmetry PSV-waves, derived in the weak-anisotropy approximation, verified by anisotropic ray tracing. The attribute delta tPS is proportional to the anellipticity parameter eta and reaches its maximum when the symmetry axis deviates by 20 degrees-30 degrees from the vertical horizontal direction. All relevant parameters of a TTI layer can be estimated by nonlinear inversion of the NMO velocities and zero-offset traveltimes of PP- and SS-(SVSV) waves combined with the moveout-asymmetry attributes of the PSV-wave. The inversion of puremode (PP and SS) moveouts alone is nonunique, while the addition of the attributes delta tPS and X min yields stable parameter estimates from 2D data acquired in the vertical symmetry-axis plane. If the TTI model is formed by obliquely dipping fractures, the anisotropic parameters can be inverted further for the fracture orientation and compliances
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426969 bytes
application/pdf |
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| Language |
en
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| Publisher |
Society of Exploration Geophysicists
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| Rights |
©2006 Society of Exploration Geophysicists. All rights reserved. Authors and publishers may present or republish up to two figures or tables per SEG article or per SEG book without seeking written permission from SEG, provided that full acknowledgment of the source is provided in the new work. SEG considers this fair use. There are no fees associated with this permission. Authors who need documentation that SEG is extending this permission are encouraged to print this message and present it to their publishers. Those who require further documentation should contact the SEG publications director. SEG recommends that authors and publishers who intend to reuse SEG figures or tables also seek consent of the original work’s lead author, if possible. The member search on the SEG Web site might prove a helpful resource in locating these authors. Requests to use any portion of “Seismic Data Analysis: Processing, Inversion, and Interpretation of Seismic Data” should be directed to the SEG publications director.
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| Subject |
Mode-converted waves
Anisotropic velocity |
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| Title |
Modeling and inversion of PS-wave moveout asymmetry for tilted TI media: Part 1 - Horizontal TTI layer
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| Type |
Article
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