Figure 4. This plot
illustrates the magnitude of changes required of the raw sonic log (red
curve in left track) to tie fully to the seismic data (final sonic is
blue in left track). The drift between the edited sonic log and seismic
data is shown in blue in the right track (scaled from -20 to +20 ms).
The red dotted line indicates that we have two separate calibrations to
make. The break in drift slope occurs at a run splice, hence the need to
treat separate runs individually. The green curve in the right track
shows the final time errors in the tied synthetic seismogram (typically
less than 3 ms).