Elastic Full-Waveform Inversion With Unconverted-Wave Adjoint Propagators

Elastic full-waveform inversion (EFWI) can restore high-resolution model parameters by minimizing the misfit function between the modeled and observed data. However, the coupling propagation of
$P$
- and
$S$
-waves will cause the crosstalk among elastic parameters and increase the nonlinearity of EFWI. The decoupled elastic wave equation can help EFWI to weaken the crosstalk effect, but it increases the computational cost of EFWI. In addition, the decomposition of the
$S$
-wave stress will produce artifacts. Hence, we have developed an EFWI approach with unconverted-wave adjoint propagators to recover the high-resolution model parameters. In the new EFWI, we use the unconverted-wave equation to construct the adjoint propagators without
$S$
-wave stress decomposition, which can reduce the artifacts. Since the unconverted-wave equation omits the cross term in the elastic wave equation, the computational cost of EFWI is reduced. Numerical examples have demonstrated that our EFWI can efficiently produce high-resolution models and reduce the computational cost of EFWI by about 30%.