Acoustic-elastic coupled least-squares reverse time migration in marine environment with rugged seabed interface

The severe rugged seabed interfaces bring great difficulties to seismic imaging in the marine environment. To accurately image submarine structures under the rugged seabed interface, an acoustic-elastic coupled curvilinear-coordinated least-squares reverse time migration (AE-CLSRTM) is proposed. This method is based on the coupled equation method, which uses the acoustic wave equations in seawater and the elastic wave equations in the underlying elastic medium. The pressure in the acoustic wave equations and the stresses in the elastic wave equations are transmitted steadily and continuously by using acoustic-elastic control equations at the seabed interface. To overcome the influence of the rugged seabed interface, the acoustic-elastic model is meshed into non-uniform curvilinear grids, and the corresponding mapping technique is used to transform the model with the rugged seabed interface to a horizontal one in the curvilinear coordinate system through the coordinate transformation. Based on the acoustic-elastic coupled equations in the curvilinear coordinate system, the acoustic-elastic coupled LSRTM algorithm in the rugged seafloor structure is realised. The numerical examples on a simple model and an actual area model show that the proposed LSRTM method can obtain the accurate imaging results of submarine structures in both P- and S-velocity components.