On the possible role of gravity waves in the ocean in T-phase excitation by earthquakes

Abstract

Recent applications of a time-domain spectral-element method to obtain full-wave solutions of seismo-acoustic problems by Bottero et al. [J. Acoust. Soc. Am., 144, EL222–EL228 (2018)] and especially their investigation of T-phases in the Mediterranean [Bottero et al., J. Acoust. Soc. Am., 141, 4045 (2017)] challenge the existing understanding of the mechanisms of seismic energy conversion into T-waves, which propagate at the speed of sound in water. Motivated by these results, this paper aims to evaluate the contribution of scattering by hydrodynamic waves into T-phase generation. Ocean is modeled as a range-independent waveguide with superimposed volume inhomogeneities due to internal gravity waves and surface roughness due to wind waves and sea swell. Guided acoustic waves are excited by volume and surface scattering of ballistic body waves. The size of the effective source of T-waves and their amplitudes are calculated in the single scattering—multiple reflections approximation. Efficiency of the gravity wave-mediated conversion of seismic energy will be compared to that of the conversion that occurs on a seafloor slope.