Obtaining local reflectivity at two-way travel time by filtering acoustic reflection data

Abstract

A modified implementation of Marchenko redatuming leads to a filter that removes internal multiples from reflection data. It produces local reflectivity at two-way travel time. The method creates new primary reflections resulting from emitted events that eliminate internal multiples. We call these non-physical
primaries and their presence is a disadvantage. The advantage is that the filter is model free. We give the 3D filter and demonstrate with 1D arguments that starting the focusing wavefield with a unit impulse at zero time, while focusing below the bottom reflector, is the choice that leads to a model free implementation. The starting impulse generates the reflection data. Every later emitted pulse eliminates an internal multiple somewhere in the model and helps removing the transmission
amplitude effects in a physical primary. We show that
the amplitude of the non-physical primaries are a product of
three reflections, making them generally smaller than those of
the physical primaries. A 2D modeled shotgather at different
stages of filtering the data shows that the filter works well.