地形效應對地震反應之影響

The Topographic Effects on the Seismic Response Caused by Earthquake

洪誌偉(Chih-Wei Hung)

指導教授 ： 林美聆

國立臺灣大學/工學院/土木工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202000510

摘要

臺灣位在歐亞大陸板塊與菲律賓海板塊的交界處，使得本島地形相當陡峭且地質環境破碎。歷史上有許多的案例皆指出，不規則的地形會對地震震波造成放大效應，可能是導致破壞的主因之一，尤其是在坡度較陡的邊坡或山頂位置其地表運動相對平地而言較為強烈。
為了瞭解現地地形的起伏程度，本研究透過計算地形粗糙度指數(Topographic Ruggedness Index, TRI)將地表地形起伏量化，並利用9x9、15x15與19x19網格大小進行分析，找出與地形相對應的TRI。接著利用二維現地模型及簡化模型進行數值模擬，分析震波在受到地形效應時於地表之反應情況，最後再將數值模擬結果與TRI及地表地形進行比對。
模擬的結果顯示，地形放大比率的分佈和震波的主要波長有關，放大比率波峰與波峰的距離約為一倍波長，主要的放大區域在一倍波長的距離內，當地表地形改變時則會對放大比率的分佈造成影響，山峰地形與局部地形之間的複合作用，會使地表產生更大的振動反應，而地表的振動反應除了受到該點地形影響外，也與土層的厚度有關。
由TRI與現地高程剖面之間的比對結果，本研究最終使用15x15網格計算的TRI與地形放大比率進行比對，對於大範圍的地形起伏，地形粗糙度指數與放大比率的比對結果較差，然而在局部地形有明顯變動的區域，兩者的行為表現較為一致。

關鍵字

地形起伏 ； 地震波 ； 地形粗糙度指數 ； 地形放大效應 ； FLAC

並列摘要

Taiwan is located at the junction of the Philippine Sea Plate and the Eurasia Plate with resulted steep terrains and the fragmented geological environment. Many cases have showed that the irregular terrain will amplify the seismic wave, which may be one of the main reasons for landslide hazard, especially on steep slopes or hilltops where the ground motion is more intense than the even terrain.
In order to understand the terrain relief variation, the study quantified the surface topography by calculating the topographic ruggedness index (TRI) with the 9x9, 15x15 and 19x19 grid sizes and identified the TRI corresponding to the actual terrain. Then, the study adopted the FLAC 2D numerical model to analyze the seismic responses affected by the topographic effects. Finally, the simulated results were compared with TRI.
The simulation results show that the distribution of topographic amplification ratio is related to the dominant wavelength of the seismic wave, the amplification ratio wave crest is about one wavelength apart from the wave crest with amplified area mainly within one wavelength. When the surface topography changed, the distribution of the amplification ratio would be affected. The interaction between the ridge terrain and local terrain will cause stronger seismic response on the surface. The vibrations of surface were not only affected by the terrain relief, but also related to the soil thickness.
Based on the comparison results between the TRI and in-situ topographic profile, the study adopted the 15x15 grid sizes to calculate the TRI and compared it with topographic amplification ratio. For the large-scale of terrain relief, the comparison results of topographic ruggedness index and amplification were poor, while in the area with significant variated local terrain, the two behavior are relatively consistent.

並列關鍵字

terrain relief ； seismic wave ； topographic ruggedness index ； topographic amplification ； FLAC

參考文獻

鄒銘徽(2011)，振動台模型相似律及滑移行為分析，國立台灣大學土木工程研究所碩士論文。

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陳俊甫(2015)，地形對地表放大效應之影響，國立台灣大學土木工程研究所碩士論文。

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