Synthetic seismograms are constructed with Ricker wavelets of 30 Hz and 50 Hz dominant frequency to represent a gradually thinning bed with equal magnitude and opposite polarity reflection coefficients in a homogeneous medium. A tuning thickness of λ/4 is observed for the PP data and PS synthetic data. AVO intercept and gradient crossplot analysis for a slow velocity, less density thin layer are compared with a high velocity and high density layer. For a slow velocity thin layer above tuning thickness, the AVO crossplot results show a counter-clockwise rotation, indicating a negative correlation as the gradient decreases and the reflection coefficient magnitude increases. For the high velocity thin layer, a clockwise rotation occurs in the AVO crossplot as the bed thins; the gradient increases and the reflection coefficient magnitude decreases. Results below tuning thickness behave non-linearly and are less predictable.
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