Subsalt Velocity Analysis Using One-Way Wave Equation Based Poststack Modeling

Subsalt velocity analysis using prestack wave equation migration scans through perturbed velocity model is an accurate but expensive approach. To reduce turnaround time and computation cost, we investigated an alternative approach for subsalt velocity analysis. In this approach, we separate the prestack focusing step from the poststack modeling step. We first use the current best velocity model to perform one prestack migration to produce a subsalt image. We then use the subsalt image as a reflectivity model to perform upgoing one-way exploding reflector modeling to produce demigrated zero-offset seismic data. Using this demigrated data as input, we perform a scan of poststack wave equation migrations through perturbed subsalt velocity model. We demonstrate the necessity of demigrating only to the base of salt in order to avoid significant image degradation and we show the feasibility of this methodology using the 2D Sigsbee data set.