Nankai: Velocity Analysis, NMO, Stack, Migration
Below is the user area of iva.sh changed for the Nankai data. As stated in Section 10.4.2, we will do velocity analysis on every 25th CMP starting with CMP 933 (lines 13-16). We change the perc value to 95 (line 29), an accommodation for real data. Semblance values go from 1000 m/s (line 38) to 7000 m/s (nvs*dvs + fvs). CVS panels range from 1000 m/s to 6000 m/s (lines 41-44).
By looking at the Nankai stack, Figure 10.3 left, we know the water layer is approximately 6 seconds (two-way time) and we think there is not much reflection character below 7.8 seconds. The left side of Figure 11.1 is the velan of CMP 933. It appears that the time for picking events is restricted to between 6 seconds and 8 seconds.
Instead of making velocity picks in a narrow space on the screen, we window the file of CMPs: and use this as the input to iva.sh
We chose the full time (tmax=11) because on CMP 933 we see events around 9.5 seconds and we don't want to miss these and other potentially later events.
The result of using this new input file is shown on the right side of Figure 11.1. This makes better use of the screen.
Because we are not picking from zero time, we will have to modify the output pick file, adding zero time to the beginning of all the tnmo series and adding the water velocity to the beginning of all the vnmo