  The main reason for the generation of tsunamis is the deformation of the
bottom of the ocean caused by an underwater earthquake. Usually, only the
vertical bottom motion is taken into account while the horizontal co-seismic
displacements are neglected in the absence of landslides. In the present study
we propose a methodology based on the well-known Okada solution to reconstruct
in more details all components of the bottom coseismic displacements. Then, the
sea-bed motion is coupled with a three-dimensional weakly nonlinear water wave
solver which allows us to simulate a tsunami wave generation. We pay special
attention to the evolution of kinetic and potential energies of the resulting
wave while the contribution of the horizontal displacements into wave energy
balance is also quantified. Such contribution of horizontal displacements to
the tsunami generation has not been discussed before, and it is different from
the existing approaches. The methods proposed in this study are illustrated on
the July 17, 2006 Java tsunami and some more recent events.
