CONCLUSION

I evaluated the effect of different S-wave velocity contrasts at the BSR on seismic amplitudes by modeling synthetic CMP gather for different shear wave velocity contrasts. Increasing velocities display a pronounced increase of amplitudes with offset. Negative velocity contrasts show either near to constant AVO behavior or a slight decrease in amplitude with offset. This depends on the magnitude of the contrast itself. AVO analysis of these single modeled CMP gathers showed that even very small S-wave velocity contrasts of only $\pm$ 17 m/s can be distinguished in the case of ideal amplitudes. Simulating more realistic data by adding a random Gaussian noise to the data introduces significant variances in the seismic amplitudes. The resolution of the different models depends strongly on the data variance, and even a qualitative analysis to determine the sign of the Vs contrast (positive or negative) can be impossible. A subsequent 2-D seismic migration/inversion of a 2-D model suggests that even in the presence of noise, a reasonably good result can be obtained.

 

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Figure 9 P-impedance and S-impedance contrasts for noise-free data.

 

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Figure 10 P-impedance and S-impedance contrasts for noisy data.

 

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Figure 11 P*S impedance contrast maps for noise-free data (right panel) and noisy data (right panel).