Reflection and transmission of spherical waves at the seafloor interface

The investigation of wave properties at the seafloor interface is crucial for advancing seafloor observation technology, with broad applications in geophysical exploration, marine seismology, and related fields. Although plane-wave reflection and transmission phenomena at the seafloor interface have been intensively studied, the analogous behavior of spherical waves remains relatively unexplored. In view of this, we characterize the marine sediment as a porous solid medium using Biot’s theory, and derive reflection and transmission coefficients for both spherical and plane waves at the fluid/porous-solid interface. We systematically investigate the dependence of these spherical- and plane-wave coefficients on frequency, depth, porosity, and rock permeability. By modeling the marine sediment as an elastic transversely isotropic solid medium with a vertical axis of symmetry (VTI), we further derive the corresponding spherical- and plane-wave reflection and transmission coefficients at the fluid/VTI-solid interface. We subsequently investigate the effect of Thomsen anisotropy parameters (ε and δ) on the spherical- and plane-wave reflection and transmission coefficients. When sedimentary anisotropy is neglected, the framework further yields reflection and transmission coefficients for the fluid/isotropic-solid interface. Numerical analysis reveals significant differences between spherical and plane waves, highlighting the necessity to account for the substantial influence of the wavefront curvature on the reflected and transmitted waves at these seafloor interfaces.