光子晶体、声子晶体和声学超材料在调控波和波衰减等领域产生了深远影响。它们并不是自然界中新发现的材料，而是根据不同需求设计的复合结构，通常利用布拉格散射或局域共振机理来达到调控声波/弹性波能带结构的目的。和光子晶体不同，声子晶体和声学超材料感兴趣的工作区域在较低频区域，因此获得低频且大范围的禁带是该领域的研究重点，并逐渐拓展到频率低、波长长的地震波的隔震减灾防控上。本文从纳米光子和地震波超材料的联系出发，从固体物理的视角分析了地震超材料的城市群、自然森林超材料等，并将新型人工地震超材料在分布区域、禁带机制、实验方式三个方面进行分类并比较论述。另外，本文展望了现阶段地震超材料研究的一些局限性以及面临的挑战。

In the recent three decades, the breath-taking discoveries of phononic crystals in conjunction with research advances in acoustic metamaterials have far-reaching implications in many science and engineering branches. These new discoveries can be traced to the fundamentals of wave manipulation and wave attenuation, etc., within a very wide frequency spectrum from ultrahigh electromagnetic wave frequency to very low seismic frequency ranges. Inspired by electromagnetic and photonic crystals, these newly designed artificial structures are able to control acoustic/elastic waves at relevantly low frequency ranges. In periodic systems, Bloch waves are formed by reflection, refraction and scattering of De Broglie, electromagnetic/light and acoustic/elastic waves. These waves contain marvelous band structures which allow transmission or lead to attenuation, that correspond to frequency domains of passbands and stopbands, respectively. There exist many studies that materialize the idea of designing metadevices at will by utilizing wave band behaviors. Generally, the mechanism for forming stopbands contains two parts, i.e., Bragg scattering and local resonance, that can also be used to identify phononic crystals and acoustic metamaterials. Especially, a Bragg scattering type metamaterial prohibits waves with wavelength of the same order as the lattice constant from propagating through the structure. It results in a large-scale structural dimension for a low frequency bandgap. Comparatively, local resonance type metamaterials allow the generation of bandgaps at low frequency ranges with relatively small dimensions as their properties rely primarily on the local resonance.

The study of seismic wave propagation in civil engineering has been reinvigorated due to the new, exciting concept of seismic metamaterials. The spectacular designs provide new approaches to control seismic surface (Rayleigh and Love) and bulk (pressure and shear) waves for civil and structural engineers. This review traces the state-of-the-art developments of seismic metamaterials and establishes a link between photonic crystals at nano/micro scale and seismic metamaterials at macro scale. We present a survey of more recent developments in seismic metamaterials in terms of geometry, physics (i.e., the mechanism for forming stopbands) and experimental approaches which range from natural sources to artificial structures. A variety of mathematical and physics tools can be extended from photonic crystals to seismic megastructures, such as effective media theory, Brillouin zone, reciprocal space, rainbow trapping, etc. The development of finite element methods provides the possibility to simulate and analyze these complex artificial designs numerically. A school of forest trees as natural seismic metamaterials is a focal point in this review, which enables attenuation of seismic waves using natural resources and also inspires the discovery of seismic metasurfaces. For artificial structures, designs are generally made based on locations (i.e., metabarriers and metafoundations) or mechanisms (i.e., Bragg scattering and local resonance mechanism). Some metamaterial-like transformed urbanism or cities are also verified to work as seismic shielding or cloaking. Further, similar to experimental methods in other disciplines, scale model experiments and full-scale experiments have been explored to validate the efficiency of seismic metamaterials in wave attenuation. Although research in phononic crystals is moving towards extreme frontiers, metastructures working at low frequencies with stability, high bearing capacity, high ductility, wide bandgap and efficient attenuation zones remain substantial challenges. Besides soil-structure interactions, the combination of various components of seismic waves, ground conditions, soil properties, effects of groundwater table, structural nonlinearity or other ineluctable factors is yet to be fully considered. Ultimately, the emergence of seismic metamaterials broadens the horizons for seismic isolation and seismic vibration control. This review will help future researchers witness the continuous development of seismic metamaterial and comprehend the current challenges in this promising, potential and exciting research.