Wavefield tomography using RTM backscattering

Abstract

Reverse time migration (RTM) backscattering contains kinematic information that can be used to constrain velocity models. The backscattering results from the correlation between forward scattered and backscattered wavefields from sharp interfaces, i.e. sediment-salt interfaces. The synchronization between these wavefields depends on the velocity of the sediment section and the correct interpretation of the sharp boundary. Therefore, we can use these events along with reflection and diving waves to define a joint optimization problem for velocity model building. As in RTM images, in gradient computation the backscattering and diving information produces cross-talk. In order to avoid the cross-talk, we use a directional filter based on the Poynting vector which preserves the components of the wavefield that travel in the same direction. Using backscattered waves for constraining the velocity in the sediment section requires defining the top of salt in advance, which would imply a dynamic workflow for model building in salt environments where both sediment velocity and salt interface change iteratively during inversion.