Geoacoustic scattering from seafloor features in the ROSE area

A strong “refraction branch diffraction” has been observed on ocean bottom hydrophone data from the Rivera Ocean Seismic Experiment (ROSE). Modeling of the interaction between seismic/acoustic energy and the ocean bottom has shown that this arrival could be caused by scattering from common seafloor features. Seismic/acoustic wave propagation was computed for models of marine seismic refraction lines using a 2D heterogeneous formulation of the elastic wave equation. These models demonstrate that a significant amount of energy is diffracted from seafloor structures such as hills and valleys when both the direct water wave and the refracted compressional wave (traveling through the upper crust) are incident upon a structure. Since much of the diffracted energy travels through the crust, the diffracted arrivals appear on the refraction branch of the seismograms at large ranges. Energy partitioning at the seafloor of the two incident wave types produce both compressional (P) and shear (S) diffracted phases in the upper oceanic crust. The large models used also clearly demonstrate the existence of phases which are theoretically possible but rarely identified in marine seismic data such as the pseudo-Rayleigh wave and the P and S interference head waves.