# Dictionary:Fig D-12

FIG. D-12.
**Diffractions** generated by the termination of three horizontal reflectors. The diffraction curvature becomes smaller as depth increases. The diffractions under the reflector (the **backward branch**) have reversed polarity to the branches that extend beyond the reflection (**forward branch**). The crest of a diffraction curve locates the diffracting point and its curvature depends on the depth and the velocity above the diffracting point. Reflection amplitude decreases to one-half at the point where the reflection is tangent to the diffraction curve and the diffraction-curve amplitude is antisymmetric about this point of tangency. Amplitudes and waveshapes are continuous at the point of tangency. The diffraction curve is hyperbolic if the velocity above the diffracting point is constant. (Courtesy Chevron Oil Co.)