Partially Embedded Gradient Metabarrier: Broadband Shielding from Seismic Rayleigh Waves at Ultralow Frequencies

A partially embedded gradient metabarrier (PEGM) for seismic Rayleigh waves was designed and studied using the finite-element method (FEM). Investigations on the partially embedded periodic metabarrier (PEPM) were carried out first, and relations between band gaps (BGs) and some sensitive parameters were examined in detail. A PEGM and piecewise PEGM were then designed and discussed based on these investigations. It was found that BGs at ultralow frequencies can be obtained by the PEPM and effectively tuned by the geometrical parameters, especially the embedded depth. The PEGM broadens the frequency attenuation zone significantly, and the piecewise PEGM further extends the zone to cover the main frequency range of seismic waves from 1 to 20 Hz. Surface wave with tens of meters wavelength can be successfully controlled by the designed meter-scaled metabarrier. Simulations of the transmission spectra of El Centro and Taft waves showed that the piecewise PEGM exhibits high efficiency of earthquake shielding.