ИСТИНА

This study is focused on tsunami generation mechanism due to nonlinear energy transfer from high-frequency (acoustic) oscillations of water layer to low-frequency gravitational surface waves. The acoustic oscillations are considered as a result of seismic bottom motions. Mathematical description of the nonlinear tsunami generation mechanism is based on the nonlinear 2D Euler equations. It is assumed that fluid velocity, density and pressure can be expressed as a sum of variable (fast) and time averaged (slow) terms. The fast components are calculated as a linear response of water layer to bottom motions. Averaging the Euler equations in time we obtain equations to describe the time-averaged flow (surface gravitational waves). The nonlinearity of the Euler equations introduces additional terms in the time-averaged flow equations which can be interpreted as external mass force and distributed mass source. The time-averaged flow equations are solved within framework of the linear shallow water theory. The amplitude and energy of the surface gravitational wave generated by the nonlinear mechanism are estimated as a function of bottom motion parameters and bottom topography. It is shown that this mechanism can provide a noticeable contribution to tsunami amplitude.