ИСТИНА

Mathematical models of tsunami waves commonly use incompressible fluid theory. We had earlier shown that water compressibility plays significant role during tsunami generation by bottom displacements whereas tsunami propagation and run-up can be described in the framework of incompressible fluid theory. The behavior of a real compressible ocean differs from that of an incompressible one mostly by the formation of elastic oscillations of water layer with the dominating period 4H/c, where H is ocean depth; c is sound velocity in water. Until recently, such oscillations have not been registered in-situ. In 2003 JAMSTEC successfully recorded bottom pressure variations in source area of tsunamigenic Tokachi-Oki earthquake. Analysis of these data results in coincidence of the main maximum of the pressure variations spectrum and the minimal normal frequency of the elastic oscillations of water layer. Contribution in tsunami amplitude due to nonlinear energy transfer from high-frequency (elastic) oscillations of water layer to low-frequency gravitational surface waves is estimated.