Joint Acoustic and Decoupled-Elastic Least-Squares Reverse Time Migration for Simultaneously Using Water-Land Dual-Detector Data.

In marine seismic exploration, the ocean bottom cable (OBC) can receive both reflected P- and S-wave information from subseabed structures. Recently, a water-land dual-detector observation system has been developed to record acoustic pressure fields using water detectors and elastic displacement wave fields using land detectors. These water-land dual-detector datasets are commonly used to suppress multiples. However, the conventional elastic least-squares reverse time migration (LSRTM) based on single elastic wave equations cannot simultaneously utilize the ocean bottom dual-sensor (OBD) data. To solve the acoustic-elastic joint inverse problem by simultaneously using observed pressure and displacement records in the OBD data, we propose an OBD-data-based joint acoustic and decoupled-elastic LSRTM (JADE-LSRTM). This method constructs a new JADE misfit function, acoustic-elastic wave backward-adjoint operators and demigration operators in the curvilinear system, and gradient directions with respect to P- and S-wave velocity. In these acoustic-elastic-coupled wavefield propagation operators, acoustic equations are used to calculate forward-propagated and backward-propagated pressure wavefields in the seawater based on water detector datasets, while decoupled elastic equations are applied to produce the displacement wavefields in the underlying elastic medium, with a higher computational efficiency than the traditionally combining individual acoustic and decoupled-elastic wavefield operators. Compared to the conventional elastic LSRTM, the proposed method enables the use of acoustic data, which is crucial for OBD data. Two numerical examples demonstrate that the proposed curvilinear-coordinated JADE-LSRTM based on water-land dual-detector data can produce accurate images in P- and S-component with higher efficiency and accuracy.