Seismic Metamaterials for Rayleigh waves attenuation: analytical and numerical survey on the effect of soil stratification.

Locally resonant materials and periodic media have been recently proposed as a mean to control and redirect elastic waves at different length scale. In particular, at geophysical scale, large resonant/periodic structures have been used as an innovative solution to attenuate the propagation of seismic waves. Previous studies have shown the possibility of attenuating surface ground motions by deflecting seismic Rayleigh waves into soil bulk. This surface to bulk wave conversion has been proved in the case of homogenous soil. Here we investigate how the surface to bulk wave conversion is influenced by inhomogeneous depth dependent soil properties. Analytical and numerical evaluation have been developed in time and frequency domain to determine the efficiency of soil-resonators interaction in inhomogeneous layered media to be used as comparison with experimental results obtained from an experimental setup built at ETH. Furthermore, results from the inhomogeneous case have been compared with the homogenous soil case, to exploit effectiveness and limitation of wave conversion phenomenon. It has been shown that the soil with depth dependent profile strongly influence wave motion. In fact, no effective wave conversion is present in this case, due to stiffer properties of the soil with depth that force the wave to reconvert its direction to the surface.