Error analysis of the converted wave deduced by equivalent velocity assumption
Wei Wang 1 Yun Wang 2 4 Junjie Yin 3 Xing Gao 11 The State Key Laboratory of Resources and Environmental Information System, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China.
2 Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China.
3 China United Coal Bed Methane Co., Ltd., Beijing, 100011, China.
4 Corresponding author. Email: yunwang@mail.iggcas.ac.cn
Exploration Geophysics 43(3) 162-170 https://doi.org/10.1071/EG11039
Submitted: 26 July 2011 Accepted: 17 March 2012 Published: 16 May 2012
Abstract
Based on the assumption of the equivalent velocity and offset, the converted wave travel-time equation, which has a double square root due to the asymmetric ray-path of the down-going P-wave and the up-coming S-wave, can be transformed into a single square root equation if the common scatterpoint (CSP) gathers are binned. This method simplifies the equation and decreases the errors of converted wave migration transferred by P-wave velocity error, compared to the equivalent offset method (EOM) migration proposed by Bancroft, Geiger and Foltinek . In this paper, the errors caused by the introduction of equivalent velocity for the PS-wave are analysed in detail. The discrete errors and effects introduced by discretization of the equivalent offset are presented, and finally the conditions for applying CSP gathers for PS-wave processing under the control of reasonable error limits are derived.
Key words: converted wave, EOM, equivalent offset, equivalent velocity, error analysis.
References
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