Generating surface-offset common-image gathers with backward wavefield synthesis

Abstract

Surface-offset common-image gathers (CIGs) are an important data format for seismic velocity analysis. However, the reverse time migration (RTM) method, which is wavefield propagation based, does not directly produce surface-offset CIGs because it propagates waves from all the offsets together. Here, we propose the generation of surface-offset CIGs by synthesising the backward wavefields using the forward wavefields at locations where source and receiver locations overlap. This method produces surface-offset CIGs with high accuracy and low cost when compared to those generated by back-propagating each trace separately. We adopt non-negative least-squares filters for sparse linear deconvolution. The computational cost-effectiveness of the proposed method increases for higher dimensions, higher-order stencils, and more complicated wave equations. The proposed method works stably on a realistic towed-streamer acquisition system with moderate geometrical positioning errors between the locations of airguns and hydrophones.