Observation of forward-direct onshore and backscattered waves in water propagating in a wedge-shaped ocean.

To investigate low-frequency acoustic propagation in a wedge-shaped ocean, two ocean bottom seismometers (OBSs) were deployed on the seabed and a land-based seismometer (LS) was positioned near the coastline. A broadband acoustic source (airgun) generated signals at a standoff distance. The OBSs captured forward-direct waves and backscattered waves, while the LS detected shore-coupled forward-direct arrivals. Spectral element modeling revealed a frequency-dependent propagation mechanism: High-frequency components (>200 Hz) of the normal modes exhibited strong backscattering from the seabed slope, while low-frequency components (<200 Hz) of the first normal mode coupled into the seabed sediment and propagated onshore as geoacoustic waves.