Acoustic-elastic coupled equation for ocean bottom seismic data elastic reverse time migration

Abstract

Conventionally, multicomponent geophones used to record the elastic wavefields in the solid seabed are necessary for ocean bottom seismic (OBS) data elastic reverse time migration (RTM). Particle velocity components are usually injected directly as boundary conditions in the elastic-wave equation in the receiver-side wavefield extrapolation step, which causes artifacts in the resulting elastic images. We have deduced a first-order acoustic-elastic coupled equation (AECE) by substituting pressure fields into the elastic velocity-stress equation (EVSE). AECE has three advantages for OBS data over EVSE when performing elastic RTM. First, the new equation unifies wave propagation in acoustic and elastic media. Second, the new equation separates P-waves directly during wavefield propagation. Third, three approaches are identified when using the receiver-side multicomponent particle velocity records and pressure records in elastic RTM processing: (1) particle velocity components are set as boundary conditions in receiver-side vectorial extrapolation with the AECE, which is equal to the elastic RTM using the conventional EVSE; (2) the pressure component may also be used for receiver-side scalar extrapolation with the AECE, and with which we can accomplish PP and PS images using only the pressure records and suppress most of the artifacts in the PP image with vectorial extrapolation; and (3) ocean-bottom 4C data can be simultaneously used for elastic images with receiver-side tensorial extrapolation using the AECE. Thus, the AECE may be used for conventional elastic RTM, but it also offers the flexibility to obtain PP and PS images using only pressure records.

Analytic Acoustic–Elastic Coupled Equations and Their Application in Vector-Wave-Based Imaging of Ocean Bottom 4C Data

“…Appendix: Acoustic-Elastic Coupled Equations for Vectorial P/S Wave Decomposition Yu et al (2016) deduced the AECE in 3D isotropic media, and the equations of motion:…”

“…Snapshots in Fig. 4a show that using only particle velocity measurements in conventional receiver-side vectorial extrapolation caused three types of nonphysical events (nonphysical events 1, 2, and 3 indicated by black arrows), which have been introduced in detail by Yu et al (2016). Receiver-side tensorial extrapolation can help to suppress some nonphysical events (events 1 and 2) in Fig.…”

“…1). Yu et al (2016Yu et al ( , 2018 proposed to apply 4C data to the receiverside tensorial extrapolation with the AECEs, which can effectively suppress artifacts in migrated profiles.…”

Joint towed streamer and ocean-bottom-seismometer data multi-parameter full waveform inversion in acoustic-elastic coupled media

“…Currently, most FWI applications use only streamer data or OBS data, but few studies use both. We propose a joint acoustic-elastic coupled FWI (J-AEFWI) method that combines towed streamers and OBS data using the acoustic-elastic coupled equation (AECE), which can simultaneously record the pressure component, x, y, and z components in acoustic-elastic coupled media (Yu et al, 2016;Yu and Geng, 2019). The method can inject the residuals of the towed streamer data and the OBS data in time backward propagating to update P-wave and S-wave velocity models.…”

An efficient coupled acoustic-elastic local solver applied to phase inversion

“…This approach again limits the expensive solver to a small region, using a simplified solver for the remainder. Finally, Yu et al (2016) derive a coupled acoustic-elastic set of equations to aid elastic reverse time migration using ocean-bottom geophones.…”