Abstract
The excitation 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.
Highlights
In this paper we present an analytical model for investigation of the excitation and propa gation process of special type of a surface waves the gravity wave
A number of hypothesis have been proposed to ex plain anomalously large excitation of long period gravity waves, among them the source rupture times of unusually long duration (Kanamori 1972), non-double couple sources such as submarine landslides (Hasegawa and Kanamori 1987), an underestimation of the actual seis mic moment from surface waves due to shallow source depth and fault angle (Ward 1982), and shallow faulting within sediments accompanied by a change in fault orientation during the rupture (Fukao 1979; Okal 1988)
The source depth was 45 km corresponding to the midpoint of a line source
Summary
In this paper we present an analytical model for investigation of the excitation and propa gation process of special type of a surface waves the gravity wave. The problem of generation and propagation of gravity waves requires an in-depth theoretical investigation, most studies in this direction are largely concen trated on the numerical modeling of the propagation of tsunamis excited by particular events, for instance, Nicaragua 1992 (Imamura and Shuto 1993), Peru 1996 (Heinrich et al 1998), Papua New Guinea 1998 ( Tanioka 1999) and others. In these studies the real bathymetry are used for numerical computations ofwaveform. The present paper, while based on the newest findings of Bilek and Lay (1999), is an attempt to change somewhat at the standard point of view on the problem of excitation of gravity waves by seismic sources, thereby filling a long-standing gap in this domain
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