針對台灣西部平原進行微地動陣列量測及高密度微地動測量，分別求得其淺層剪力波速度構造及場址特性，建立一個包含淺部速度構造之完整三維速度模型，進行震波模擬。 七個大型微地動陣列量測求得深度三公里內淺部S波速度構造，無論在淺部或深部之速度和分層皆能反應真實地層狀態，由近地表極低速之鬆軟土層，隨著深度漸增，並出現數個顯著速度介面。深部地層之介面深度與速度可與震測所描繪之上新統和中新統層面相對應，其深度變化受北港高區影響，顯示西部平原之淺部S波速度變化主要仍受地層構造控制。微地動單站頻譜比法研究顯示，平原中心區域1.0至2.0 Hz之地層共振主頻是西部平原最為顯著之場址放大區域。在平原東側接近麓山帶的區域，則是高主頻或無場址放大之岩盤特性。平原西側沿海區域由於深厚且速度漸變之沖積層，使其單站頻譜比變化平緩且起伏不大，而部份測點近地表薄層的高頻放大，導致高低頻交錯的主頻分佈。此外，本研究建立一基因赫氏法，利用地層SH波理論轉換函數擬合微地動單站頻譜比來推估淺層速度構造，並以越南河內地區微地動研究進行測試，證實此方法可完整並正確描繪河內地區之基盤深度變化；但西部平原之場址特性變化導致基因赫氏法實行上的困難。 TAIGER陸地人工震源炸測實驗在西部平原之炸點，在近地表低速地層激發顯著的表面波能量；利用微地動陣列淺部一維模型波數積分法合成其波形，可產生類似觀測波形之慢速短週期表面波。本研究在台灣tomography之三維速度模型上加入地表VS30、更新統、上新統和中新統頂部介面深度變化，利用平行化三維PSM/FDM方法對1993年嘉義大埔及1998年嘉義瑞里地震作震波模擬；以此三個淺部主要速度介面形貌所建立的完整三維模型，可重建地震波在西部平原傳播之波形特性變化與表面波生成，而此淺部速度構造造成台灣西部平原內地震波複雜的長時間振盪。 The shallow S-wave velocity structures and site effect of the western plain of Taiwan were respectively estimated by the microtremor array measurements and dense station measurements. The complete 3D velocity model was constructed with the shallow structures to simulate the seismic wave propagation in the western plain. Seven microtremor arrays estimated the S-wave velocity structures from the surface to a depth of 3 km. The velocities at near-surface were very slow and increased gradually. And several interfaces with substantial S-wave velocity variations were found. The depths of the last two main interfaces in deeper part corresponded to the tops of the Pliocene and upper Miocene formations, respectively. Further, the average S-wave velocities of the Plio-Pleistocene, Pliocene, and Miocene formations were estimated in this study. The existence of the Peikang Basement High affects the features of these two interfaces and the shallow structures of the western plain. The H/V ratios of microtremor apparently amplify in the frequency range 1.0~2.0Hz in the center of western plain. The eastern part of western plain showed the higher predominant frequencies or the non-amplified effect of rock site. But, the area along the coast exhibits the mixed predominant frequency because the velocity variations of deep alluvium are gradual with some local thin structures in surface. Based on that the H/V ratios confirme with the theoretic SH wave transfer functions, the GA-Haskell method was developed to simulate H/V ratios and estimate shallow velocity structures. The capability of this method was tested and confirmed in the microtremor research of Hanoi region, Vietnam. The shape of basement and velocity structures in Hanoi region were figured out by the GA-Haskell method. Unfortunately, the complex site effect of the western plain is not suitable for the analyses of GA-Haskell method. The active sources of TAIGER in western plain excited the strong surface waves in the low velocity layers of near-surface. And the slow surface waves can be simulated based on the shallow velocity model estimated by the microtremor array. The three main interfaces indicated by the microtremor array and Vs30 were combined with the 3D tomography velocity structure to constructe the complete 3D velocity model of the western plain. Finally, the parallel 3D PSM/FDM method were used to simulate the seismic waveforms of 1993 Tapu and 1998 Rueyli earthquakes. The observed waveforms of the western plain were reproduced by the simulations. The characters of seismic wave propragation and the surface waves were simulated based on the complete 3D velocity model. The shallow S-wave velocity model generates the longer and more complex seismic waveform in the western plain of Taiwan.
