Excitation of surface waves by a finite seismic source: The case of gravity waves in the liquid layer-elastic half-space

The excitation of gravity waves by both point and finite dimensioned line s ources was considered in the flat elastic-gravitational model. The excitati on 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 anal ysis of the double-couple mechanism shows that a line source with a vertica l dip-slip motion generates more intensive gravity waves than one with a st rike-slip motion. The calculation of theoretical marigrams for gravity wave s demonstrates that the amplitude of a wave generated by a line source is l arger 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 wav es generated by an underwater earthquake. A slow rupture with velocity 1-2 km/s occurring in low: rigidity rock generates a more intensive gravity wav e. It is suggested that the use of the more realistic finite dimensioned li ne source is appropriate to model "tsunami-earthquake" events.