FORTHPIK
Flatten seismic events in CMP gathers with FORTHPIK. FORTHPIK performs automatic picking of anisotropic non-hyperbolic fourth-order NMO corrections. For layered media characterized by large vertical velocity gradients and/or velocity anisotropy, the moveout behavior of reflected events may deviate from the usually assumed hyperbolic formula when the offset to depth ratio exceeds 1.0. In order to "flatten" events in such media, it is necessary to specify deviations from the familiar hyperbolic moveout. FORTHPIK uses a 3-term anisotropic NMO correction to characterize these deviations from hyperbolic. The output from the program is the ETA parameter which is often referred to as the anellipticity. In simple models ETA is a measure of the amount of anisotropy present in the overburden.
GRVA
Improve your velocity model and get better NMO corrections with the GeoCenter Residual Velocity Analysis (GRVA) program. The GRVA program computes the AVO intercept and gradient (slope) traces from clean CMP gathers. The gradient (slope) is very sensitive to residual velocity errors. We use this sensitivity to develop a product indicator to minimize the error within the gradient. This product indicator is equal to IM(AB*) where B* is the conjugate of the analytic slope and A is the analytic intercept. The imaginary part of their joint correlation coefficient quantifies the gradient quadrature component and is proportional to the average of the fractional NMO velocity errors. The optimal NMO velocity is the one, which nulls this imaginary correlation.