ABSTRACT

Conventional P-waves in seismic reflection studies fail to image beneath both the extrusive and intrusive basaltic rocks in sedimentary basins. But with the help of long offset seismic data acquisition by using large low-frequency sources, and special processing methods like prestack depth migration of converted waves, it is possible to image sub-basalt targets of interest. It is also difficult to deal properly with free-surface and interbed multiples in the near offset data, but by utilizing the converted waves in the post critical angle range, it is possible to image correctly the velocity structure and improve the sub-basalt imaging problem to certain extent. The conventional explanation for this imaging problem is that the basalts prevent penetration of seismic energy. In principle, the poor penetration of seismic energy is due to either by anelastic attenuation, which converts the seismic energy into heat, or by elastic back scattering. To deal with this problem, an attempt is made by emphasizing a numerical approach how to model the converted waves at long offsets and to image top and bottom basalts with synthetic examples in support of this study.

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