Least-squares reverse time migration in acoustic-elastic coupling media with irregular seabed interfaces
In the marine environment,seismic waves propagate through both acoustic and elastic wave media.In the seawater layer,seismic waves propagate in the form of longitudinal acoustic waves,while in the submarine tectonic layer,seismic waves propagate in the form of elastic waves with both longitudinal and transverse waves.A variety of interference waves exist at the seafloor interface.In this paper,the coupled acoustic-elastic equations applicable to the undulating seafloor interface are derived,aiming at eliminating the scattering and bypassing interference caused by the undulating seafloor interface,so as to realize the stable transmission and conversion between the acoustic and elastic wave fields.In order to solve the problem of false scattering noise generated by the undulating seafloor interface,this paper proposes a hierarchical veneer mesh dissecting strategy,which converts the undulating seafloor interface into a horizontal seafloor interface through coordinate transformation,and converts the veneer mesh in the physical domain into a rectangular mesh in the computational domain,so as to eliminate the influence of the undulating seafloor and the complex structure.The model test results show that the method can accurately simulate the wave field transfer in the undulating seafloor acoustic-elastic coupling medium and produce stable and clear waveforms.Compared with the traditional rectangular grid acoustic-elastic coupling and single elastic wave methods,the results of the least-squares inverse time offset imaging of the undulating seafloor acoustic-elastic coupling medium show a significant improvement in signal-to-noise ratio and resolution.
Irregular surfaceIrregular seabed interfaceAcoustic-elastic couplingBody-fitted gridsLeast-squares reverse time migration
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