T-phases excited by earthquakes propagate with low transmission loss along the ocean sound channel, and are characterized by long duration wavetrains, often having multiple peaks associated with bathymetric highs in the source region. Although T-waves were first identified almost fifty years ago, their activation has not been adequately explained. In this paper we show that, for continental margin earthquakes, realistic T-phase coda can be computed by expressing the acoustic energy in terms of several low order modes excited by point sources distributed uniformly over the seafloor. The conversion of seismic energy to acoustic energy is thus consistent with seafloor scattering. ¿ 1999 American Geophysical Union