Slowness-Backazimuth Weighted Migration Method: A New Array Approach to a High-resolution Image

We have developed a new array method combining a conventional migration method with slowness- backazimuth deviations in the wavefield. All seismic traces are shifted based on the theoretical travel time of the scattered wave from grid points in a 3D volume. Observed slowness and backazimuth are calculated for each raypath and compared with theoretical values in order to estimate slowness and backazimuth deviations. Subsequently, stacked energy calculated by a conventional migration method is weighted by the slowness and backazimuth deviations to suppress any arrival energy whose slowness and backazimuth are inconsistent with the expected theoretical values. This approach was applied to two P wave data sets which comprise (1) underside reflections at the 410 km and 660 km mantle discontinuities and (2) D" reflections as well as their corresponding synthetic data sets. The results show that the weighting procedures dramatically increase the resolution of the migrated images and enable us to obtain well-constrained, focused images, making mantle discontinuities and D" reflections more distinct by reducing their surrounding energy.