  Seismic metamaterials (SMs) are expected to assist or replace traditional
isolation systems owing to their strong attenuation of seismic waves. In this
paper, a one-dimensional inverted T-shaped SM (1D ITSM) with an ultra-wide
first bandgap (FBG) is proposed. The complex band structures are calculated to
analyze the wave characteristics of the surface waves in the SMs. We find that
the FBG of the 1D ITSM is composed of two parts; part 1 with surface evanescent
waves and part 2 with no surface modes. Similar results are found in the
complex band structure of the FBG of the SM consisting of periodically arranged
pillars and substrate. The propagation of seismic surface waves in the 1D ITSM
is different in these two frequency ranges of the FBG. In part 1, the seismic
surface waves are significantly attenuated in the 1D ITSM, while in part 2, the
surface waves are converted into bulk waves. Finally, the ultra-wide FBG is
verified by using a kind of the two-dimensional ITSM in large-scale field
experiments.
