The exitation of gravity waves by both point and finite dimensioned line sources was considered in the flat elastic-gravitational model. The excitation functions were analyzed in terms of normal mode formalism in a far-field approximation of the surface wave.

A line source was modeled by a set of point sources, uniformly distributed along a fault and moving along it with a constant velocity. A detailed analysis of the double-couple mechanism shows that a line source with a vertical dip-slip motion generates more intensive gravity waves than one with a strike-slip motion. The calculation of theoretical marigrams for gravity waves demonstrates that the amplitude of a wave generated by a line source is larger than that for a point source of the same seismic moment.

A numerical experiment reveals that the rigidity of the rock and the source duration both exert a strong influence on the amplitude of the gravity waves generated by an underwater earthquake. A slow rupture with velocity 1-2 km/s occurring in low rigidity rock generates a more intensive gravity wave. It is suggested that the use of the more realistic finite dimensioned line source is appropriate to model "tsunami-earthquake" events.