  By using the Hugoniot curve in detonics as a Riemann invariant of a
velocity-pressure model, we get a conservative hyperbolic system similar to the
Euler equations. The only differences are the larger value of the adiabatic
constant (= 8.678 instead of 1.4 for gas dynamics) and the mass density
replaced by a strain density depending on the pressure. The model is not
homogeneous since it involves a gravity and a friction term. After the seismic
wave reaches up the bottom of the ocean, one gets a pressure wave propagating
toward the surface, which is made of a frontal shock wave followed by a regular
decreasing profile. Since this regular profile propagates faster than the
frontal shock waves, the amplitude of the pressure wave is strongly reduced
when reaching the surface. Only in the case of a strong earth tremor the
residual pressure wave is still sufficient to generate a water elevation with a
sufficient wavelengths enable to propagate as a SaintVenant water wave and to
become a tsunami when reaching the shore. We describe the construction of the
model and the computation of the wave profile and discuss about the formation
or not of a wave.
