Normal moveout for long offset in isotropic media using the Padé approximation
Song Han-Jie1,2, Zhang Jin-Hai1, and Yao Zhen-Xing1
1. Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China.
2. University of Chinese Academy of Sciences, Beijing 100049, China.
Abstract：
The normal moveout correction is important to long-offset observations, especially deep layers. For isotropic media, the conventional two-term approximation of the normal moveout function assumes a small offset-to-depth ratio and thus fails at large offset-to-depth ratios. We approximate the long-offset moveout using the Padé approximation. This method is superior to typical methods and flattens the seismic gathers over a wide range of offsets in multilayered media. For a four-layer model, traditional methods show traveltime errors of about 5 ms for offset-to-depth ratio of 2 and greater than 10 ms for offset-to-depth ratio of 3; in contrast, the maximum traveltime error for the [3, 3]-order Padé approximation is no more than 5 ms at offset-to-depth ratio of 3. For the Cooper Basin model, the maximum offset-to-depth ratio for the [3, 3]-order Padé approximation is typically double of those in typical methods. The [7, 7]-order Padé approximation performs better than the [3, 3]-order Padé approximation.
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2016, Vol. 13 
