The Aki and Richards approximations to Zoeppritz's equations as well as approximations by Stewart, Smith and Gidlow, and Fatti et al. are employed to compute AVO-responses of two-layer models for AVO-Classes 1 through 4. These approximate responses are compared to exact Zoeppritz. A weak reflector and a strong reflector are considered for all AVO-Classes in order to test the small parameter change assumption. It is found that these approximations are not always close to exact Zoeppritz at small angles. Neither are these approximations always more accurate for weaker reflectors than they are for strong reflectors.
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