Numerical study on wave propagation in a low-rigidity elastic medium considering the effects of gravity

•We discuss the effects of vertical gravity force on wave propagation in a low-rigidity medium.•Gravity terms are introduced into the 2D linear FEM for the simulations.•The fastest phase propagating from a surface point source can be transformed into a gravity wave.•The fastest phase is identified as a leaking Rayleigh wave.•The other phases should not have the feature of a gravity wave.

We discuss the effects of vertical gravity force on wave propagation when a material is intermediate between solid and fluid, especially we focus on what kinds of phase are generated and how it propagates on the surface. We introduce gravity terms into the 2D linear finite element method in order to account for the contribution from the gravity. Numerical simulations are conducted for a half-space model and a two-layered, single horizontal layer overlain on a half-space, model. Both models are compared between the results including and excluding the viscosity. The fastest phase propagating from a surface point source, a leaking Rayleigh wave for usual elastic material, is transformed into an interesting phase including some common features to the gravity wave when the gravity effect becomes significant. The viscosity does not affect the fastest phases, whereas it affects other latter phases appearing only for the two-layered model.