Type : oral.

COEXISTENCE OF ELASTIC WAVES AND GRAVITY WAVES IN SOFT SEDIMENTS.

Raul Esquivel+, Department of Physics and Astronomy, Ohio University, Athens Ohio 45701. (raul@fenix.ifisicacu.unam.mx).

Based on a linear viscoelastic model, we study the coexistence and transition of gravity waves and surface elastic waves in a half space of unconsolidated sediment. The dispersion relation and surface response functions of the system are calculated as a function of wave period and rigidity of the system. The dispersion relation for this case shows two branches. One corresponds to a Rayleigh wave for short wave periods and evolves into a leaky surface wave as the period increases. The second branch corresponds to a gravity wave that shows a linear dependence of phase velocity with period. The vertical surface response function has two distinct peaks. One corresponds to the Rayleigh wave and the second peak is a gravity related mode whose amplitude is strongly dependent on the wave period and soil rigidity.

The case of gravity effects on Lg-modes in stratified systems is also studied. In this case gravity effects are more relevant at large wave periods, and an increase in phase velocity of the elastic waves is observed.

+ On leave from Instituto de Fisica, Universidad Nacional Autonoma de Mexico.