Hydroacoustic waves generated by underwater earthquakes in the deep ocean are observed at very long ranges (hundreds and thousands of kilometers) from the place of their generation. This implies that they propagate in the underwater sound channel (USC) without any reflections from the bottom. However, the direct trapping of the acoustic waves is impossible. A physical mechanism of the trapping of waves owing to their scattering from a rough sea surface is investigated. To solve this issue an energetic approach is used. For low frequencies, in the ``single scattering---multiple reflection'' approximation an expression for the spectral density of the sound intensity is obtained. For numerical calculations a piston model of the earthquake and a ``bilinear'' model of the USC are used. It is shown that the largest contribution to the sound intensity is given by a weakly divergent bundle of rays. Calculated sound-pressure spectral levels significantly exceed that of the dynamic ambient noise in the ocean for typical values of parameters of the problem. The total acoustic power trapped by the USC is estimated.