近年於台灣發生的2016年美濃地震與2018年花蓮地震，雖屬中型規模地震，但因震源產生的破裂方向性造成明顯速度脈衝，加上近地表土層場址效應的影響，均使近斷層地區記錄到異常強烈的地震動，以致嚴重建物毀損與生命損失。本研究利用中央氣象局建置的地表—井下強震觀測網，針對這兩起地震進行近地表強震場址分析以及破裂方向性探討，利用大地工程常用的等效線性一維地盤反應分析方法，進一步考量場址條件與邊界效應差異對地震動分析可能產生的影響，將井下觀測紀錄模擬至場址效應影響甚微的自由面岩盤條件參考站，以進行更詳細的場址效應分析探討，場址分析結果顯示各測站於近地表地區之短週期平均反應譜比均落於1至1.8倍之間。 本研究亦利用自由面岩盤條件參考站的模擬紀錄進行破裂方向性探討，反應譜比結果顯示美濃地震在新化地區的長週期訊號有明顯的放大，衰減分析亦顯示長週期訊號（1秒以上）於斷層距30公里內於東西向有平均9倍左右的放大，而短週期訊號則東西向強烈非線性效應無明顯放大，南北向最高約4倍的放大，說明了破裂方向性於美濃地震在長週期訊號的貢獻，進行破裂方向性衰減分析之結果亦顯示了長週期訊號受到破裂方向性強烈放大的特性。 而在近斷層的新化地區與花蓮市區之地表與井下觀測紀錄的速度脈衝的週期有顯著差異，地表速度脈衝訊號之週期較短，而井下速度脈衝訊號之週期較長，而地表脈衝週期可對應到該測站受到土壤非線性效應影響而低移的振動主頻，此現象顯示近地表土層特性可能會影響由震源產生的速度脈衝訊號的能量，但這樣的特性仍需進一步探索。 ;Although 2016 Meinong and 2018 Hualien earthquake were classified as moderate magnitude earthquakes, near fault regions still recorded anomalously strong motions because of the velocity pulses generated by rupture dirctivity and the subsurface site characteristic. This study aims to carry out the site effect and the rupture directivity analysis of Meinong and Hualien earthquakes by data from Surface-Downhole Seismic Network which constructed by CWB. We utilize one-dimensional equivalent linear approach in this study. In order to analyse site effects during strong motion events more carefully, we further consider free surface effect of the borehole stations, then simulate strong motions from borehole observed records to the free-surface reference bedrock stations. The results of the site analysis show the overall average response spectra ratio are about 1 to 1.8. . This study conducts the rupture directivity analysis based on the simulated records of reference bedrock stations. Results show a great amplification in HsinHua at long period signal (above 1 Hz). Attenuation analysis also shows the similar result, which indicates the amplification at long period signal of the forward direction is about 9 times compared with the backward direction within 30 km. The amplification at short period signal shows implicit amplification due to the soil nonlinearity on E-W component, and shows maximum 4 times amplification on N-S component. These results show the contribution of the rupture directivity at long period band during Meinong earthquake. According the velocity pulse identification results of the observations in HsinHua and Hualien, we find that the pulse period difference between boreholes and surface records. Furthermore, the pulse periods of the surface records correspond well with the dominant frequency of the site. This phenomenon indicates that the site characteristic of station may affect the period of velocity pulses which generate by the source. It is necessary that we should explore carefully.
