Synthetic model

A simple synthetic was created with constant velocity of v_p=2000 and v_s=1000, and varying dips. Figure  shows on the left the reflectivity model, and on the middle and right panels, one single mode PP CMP gather and one converted mode PS CMP gather. The PP-CMP gather presents four reflection hyperbolas, all of them centered at zero-offset. The PS-CMP gather also presents the four reflection hyperbolas, corresponding to the same events as in the PP-CMP gather, however, they are not centered at zero-offset, as it is expected for the coverted-mode case. Also, the time axis for both synthetic data sets is different. The events on the PS CMP gather take longer to arrive, this is also a characteristic for the converted-mode case. The polarity flip is not included in this model, since it has been already discussed by Rosales and Rickett (2001b).

After wave-equation migration with the correct velocity model, the image is perfectly focused at zero subsurface offset, displayed on the left panel of Figure . Note, that both PP and PS sections, had the same SODCIG.

The middle and right panels of Figures  present the result of the transformation from SODCIGs into the single-mode ADCIG (center panel), and the the converted-mode ADCIG (right panel). It is possible to observe that the angle range (i.e. before the start of the artifacts due to the transformation in the Fourier domain) for the converted-mode ADCIG is longer than for the single-mode ADCIG, as it is expected, since the angle-information contains both the incidence and reflection angle information.

 

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Figure 7 Synthetic data. Left: reflectivity model. Right panels: One single-mode PP CMP gather, and one converted-mode PS CMP gather.

 

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Figure 8 Subset of the image after migration. Left: one SODCIG gather. Right panels: the single-mode PP transformation to ADCIG, and the converted-mode transformation to ADCIG.