Aspects of seismic imaging using P-SV converted waves

David W.S. Eaton and Robert R. Stewart

ABSTRACT

Several aspects of processing P-SV data are more complex than the conventional P-wave processing case. In this study, four processes that pertain directly to the seismic imaging problem are examined: S1-S2 wave field separation, P-SV common conversion point (CCP) mapping, moveout correction and time migration. If a low-velocity near surface layer is present, fast and slow (split) shear waves recorded at the free surface can be separated prior to stack using a simple co-ordinate rotation. Current methods of CCP gathering for multifold P-SV data may result in excessive loss of spatial resolution. A new method is proposed to solve this problem by mapping each data sample to its correct conversion point position before stacking. Examples of this technique are provided using synthetic data. The coefficients of the power series expansion for the squared travehime for P-SV reflections are similar to the coefficients for the equivalent power series in the P-P case, and suggest that P-SV moveout is nearly hyperbolic. However, the hyperbolic moveout approximation is less accurate for P-SV events than P-P events. Finally, conventional time migration appears to produce valid results when applied to P-SV data after stack.

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