Three-dimensional simulation of Doppler signatures of acoustic–seismic coupling from moving marine sources

Moving marine sources radiate acoustic waves that couple into the solid Earth at the seafloor and produce Doppler-shifted seismic signals recorded by geophones and distributed acoustic sensing (DAS). Interpreting these signatures is complicated by multiphase coupling, interface waves, and sea-surface reverberations. We combine three-dimensional numerical simulations with nearshore DAS observations from Sanya, Hainan, to identify the mechanisms controlling Doppler signatures from moving marine acoustic sources. The simulations show that, under typical vessel-observation conditions, the dominant Doppler curve is controlled mainly by direct-path phases, including P waves, S waves, and evanescent waves, rather than by all coupled seismic phases. Interface-guided phases, including refracted P waves, leaky Rayleigh waves, and Scholte waves, become important only for specific source–seafloor configurations. Scholte-wave energy is strongly source-height dependent, increasing near the seafloor and decreasing rapidly with height, which suggests a potential indicator of near-bottom source activity. Strong sea-surface reflections generate higher-order multipath arrivals that transform a smooth Doppler ridge into a multibranched time–frequency structure. The Sanya DAS observations are well explained by the direct-path Doppler model, demonstrating the feasibility of passive vessel tracking using acoustic–seismic coupled signals.