ИСТИНА

In description of tsunami generation the following traditional assumptions are made. An earthquake instantly causes permanent deformations of the ocean bottom. The displacement of the bottom is simultaneously accompanied by formation at the water surface of a perturbation (initial elevation), the shape of which is fully similar to the vertical permanent deformations of the bottom. The initial elevation, thus obtained, is then applied as the initial condition in resolving the problem of tsunami propagation. The initial field of flow velocities is assumed to be zero. Imperfectness of such a traditional approach is due to at least two reasons. First, even if the ocean bottom is horizontal, and the bottom deformations are instantaneous, the displacement of the water surface and the vertical residual bottom deformation will not be equal to each other: the displacement of the water surface will be smoother. Thus, “fine spatial structure” of bottom displacement is not manifested on the water surface. Second, in the case of a sloping (non-horizontal) bottom the horizontal deformation components can also contribute significantly the displacement of the water surface. A logical development of the traditional approach, we suggest, consist in calculation of the initial elevation from the solution of the 3D problem taking into account all three components of the bottom deformation vector and the distribution of depths in the vicinity of the source. We suggest considering this problem in the framework of classical linear potential wave theory. If the bottom deformation process turns out to be long, then the initial conditions must include, besides the initial elevation, the initial distribution of flow velocities. In case of instantaneous deformation, the evolutionary problem can be reduced to a more simple static problem. The developed method is applied for calculation of initial elevation in the source of Central Kuril Islands tsunamis on November 15, 2006 and on January 13, 2007.