Figure 20. a) Synthetic seismogram of the Tedford #1 well generated with a time varying zero phase Butterworth filter and both the sonic and density logs. The Butterworth filter has the following characteristics: 20 Hz, 36 dB/octave slope - 60 Hz, 72 dB/octave slope down to 520 ms; 20 Hz, 36 dB/octave slope - 50 Hz, 72 dB/octave slope from 520 ms to the bottom. Both negative and positive polarity synthetics are shown with the sonic log. Correlation tops include ) WBSE (Wabaunsee Group), TPKA (Topeka Limestone), HBNR (Heebner Shale), LNSG (Lansing Group), KCTY (Kansas City Group), MRRW (top of Morrow clastic interval) and MISS (top of Mississippian limestone). b) Correlation of normal polarity synthetic with Line 3 (migrated section with reverse of field polarity and every other trace displayed). Well location indicated by thick, black vertical line.