Inversion starting with the simple stratified model: reconstructed velocity models with 2.5–5.0 Hz data using FWI (a) and LAWI (b), and subsequently reconstructed velocity models with 2.5–7.0 Hz data using FWI (c) and LAWI (d). The low-velocity anomaly reconstructed by FWI at the depth of 1.25 km is not as good as the one obtained with the tomographic starting model.