以地震超材料設計為考量之震波傳遞行為模擬與探討

Abstract

超材料之發展最早起源於電磁波與光學領域，其利用超材料內單元晶格之特殊性質，以達到控制波傳之目的。透過自身所反映出之負的材料參數，其可突破一般自然界中所看不到的物理性質。而地震超材料亦為一新興外部隔減震技術，其概念繼承原先超材料技術所展現出之效果，藉由設置於待保護區域周圍之方式，同時獲得大面積保護效果與不影響原建物之兩項優點。經過分析單元晶格之頻散曲線，其可以由帶隙得知超材料之濾波範圍。為了使帶隙與地震主頻率 (<10Hz) 重合，局部共振所帶來之亞波長特性經常被用作於縮小單元晶格尺寸之手段。隨著此領域對於超材料的設計日漸完善，帶隙範圍逐漸能夠覆蓋地震發生時之震波頻率，而對於超材料之減震效益分析，過去的研究通常採取將其放置於均質土壤之方式來進行純體波與表面波的波傳衰減測試。本研究將從地震波傳之角度切入，探討地震超材料於真實震波下之反應。藉由引入地球速度模型與淺層速度模型之地質數據，其即可獲得地震波於岩層中傳遞所需之介質資訊，並由埋入式波源之輸入來達成地震波場模擬之環境建置。此外，本研究也將探討地震超材料之各種擺置對於波傳衰減之影響，提供一個地震超材料發展之新思路與啟發。

The development of metamaterials initially originated in electromagnetics and op tics, where their specially designed unit cells were used to control wave propagation. By exhibiting negative material parameters, they reveal physical properties that are otherwise unattainable. Seismic metamaterials, as an emerging wave attenuation technology, inherit the core concept of conventional metamaterials and achieve two advantages, including wide-area protection and avoiding direct alterations to existing structures by surrounding the area to be protected. By analyzing the dispersion curves of unit cells, one can iden tify the frequency band gaps that define the filtering range of metamaterials. To align the band gap with the dominant frequency of seismic waves (below 10 Hz), the subwavelength characteristics induced by local resonance are often utilized to reduce the unit cell size. As the design of seismic metamaterials has become increasingly refined, the resulting band gaps are now more capable of covering the frequency range of seismic events. In most prior studies, the effectiveness of seismic metamaterials in wave attenuation was evaluated using homogeneous soil models, focusing on the reduction of body and surface wave propagation. In this study, we approach it from the perspective of seismic wave propagation to investigate the performance of seismic metamaterials under realistic ground motion. By introducing geological parameters from global and shallow velocity models, we acquire essential material properties for wave propagation in the simulation. A buried source is employed to construct a seismic wavefield simulation environment. Furthermore, this study explores the influence of various metamaterial configurations on wave attenuation, offering new insights for the development of seismic metamaterials.