Wavefront construction using waverays

Travel-times and amplitudes in the Marmousi model

marm80-time
Figure 9. Traveltime contours computed from the combined method, overlaid on a section of the Marmousi model. A frequency of 80 Hz is used.

marm10-time
Figure 10. As in the previous Figure, but for a frequency of 10 Hz.

marm80-ampl
Figure 11. Amplitude maps from the combined method at a frequency of 80 Hz.

marm10-ampl
Figure 12. As in the previous Figure, but for a frequency of 10 Hz.

Figures 9 to 12 display the results of a simulation that used the combined method. The underlying subsurface structure is the Marmousi model (Versteeg, 1993). A source was put at the surface, 5200 meters away from the left edge of the model, and the wavefronts were propagated until they crossed the boundaries of the model. Figure 9 shows the first-arrival traveltime contours calculated at a frequency of 80 Hz. Figure 10 shows the same experiment at a frequency of 10 Hz. Not much difference is apparent.

Figure 11 shows the amplitude estimates for the 80 Hz shot and Figure 12 shows the 10 Hz estimates. We see that more energy gets propagated down in the case of the low frequency, illuminating part of the high frequency shadow zones.

We have seen that the combined method accomplishes two important tasks, it can be used to compute first arrival traveltimes and amplitudes over any general velocity model and is it able to illuminate high frequency shadow zones.

For these experiments, the mesh of the model is re-sampled from the original model at 8 x 8 meters. The traveltime and amplitude outputs are placed in a mesh of 25 x 12.5 meters.

Wavefront construction using waverays