Two-dimensional waveform inversion of multi-component data in acoustic-elastic coupled media

In order to account for the effects of elastic wave propagation in marine seismic data, we develop a waveform inversion algorithm for acoustic-elastic media based on a frequency-domain finite-element modelling technique. In our algorithm we minimize residuals using the conjugate gradient method, which back-propagates the errors using reverse time migration without directly computing the partial derivative wavefields. Unlike a purely acoustic or purely elastic inversion algorithm, the Green's function matrix for our acoustic-elastic algorithm is asymmetric. We are nonetheless able to achieve computational efficiency using modern numerical methods. Numerical examples show that our coupled inversion algorithm produces better velocity models than a purely acoustic inversion algorithm in a wide variety of cases, including both single- and multi-component data and low-cut filtered data. We also show that our algorithm performs at least equally well on real field data gathered in the Korean continental shelf.