Amplification of gravity and Rayleigh waves in a layered water-soil model

The coupled seismic to gravitational surface wave fields are analyzed in a liquid layer lying on the gravitating elastic, low-rigidity half-space. Sol ution is obtained within the framework of the normal mode formalism applied to the flat ocean-solid Earth model. From the theory of propagation of cou pled surface waves (Rayleigh and Love) in layered media, we find the indivi dual multipliers that determine the surface wave spectrum over the entire f requency range. Spectra of excitation functions are investigated for dip-sl ip point source in the half-space. Main results can be summarized as follow s. When the half-space is filled with sediments, dip-slip excitation functi ons of gravity and Rayleigh waves are one order of magnitude larger than fo r the half-space composed of hard rocks. including gravity in the elastic m edium essentially changes the character of gravity wave spectrum, leading t o an appearance of the third maximum. At the deepening of the source amplit ude of this maximum increases. Theoretical marigrams show that including gr avity in the half-space also increases period of the gravity wave excited b y deep sources by a factor of two, up to 10 minutes. At the same time, pres ence of gravity force in the half-space has no effect an the spectrum of th e Rayleigh wave.