台灣東北部外海地震之三維強地動模擬; Simulations of Strong Ground Motion: Case Study of Taiwan NE-Offshore Earthquake

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Title:	台灣東北部外海地震之三維強地動模擬;Simulations of Strong Ground Motion: Case Study of Taiwan NE-Offshore Earthquake
Authors:	邱翊維;Yi-Wei Chiu
Contributors:	地球物理研究所
Keywords:	有限差分法;震源輻射效應;路徑效應;三維波傳;source radiation effect;path effect;finite difference;3D wave propagation
Date:	2005-07-01
Issue Date:	2009-09-22 09:55:25 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	北台灣為主要都市以及人口集中區域。要能夠降低外海地震所造成的災害，對於地震波產生與傳播特性需要有更深入的瞭解，其中又以強地動的研究最為迫切，本研究目的藉由有限差分法的三維強地動模擬運算，檢視路徑上以及不同的震源機制對北台灣強地動值的分佈與波傳行為的影響，希望推估出對北台灣最可能形成危害的外海地震類型及可能的形成因素。首先透過以331外海地震為例，震源機制採用BATS(Broadband Array In Taiwan For Seismology)所求得之震源機制解進行三維強地動與地震波傳遞的順推模擬，並藉由假設四個不同的地震深度15、30、45、60公里來檢視波傳過程並分析複雜的三維非均質路徑效應，以及局部地下速度構造對強地動震幅加乘的影響，來了解路徑效應對強地動值的貢獻程度。接著參考可能的背景震源機制，再引入可能震源機制及不同的震源位置後，分析受近場效應較強的宜蘭和遠場效應較強的台北、新竹、台中這幾個都會區的強地動影響程度，進ㄧ步的深入探討除了路徑上以及震源輻射的影響，並藉此歸納出最有可能對台灣造成危害的外海地震型態。研究結果指出東部外海331位置的淺層地震，無場址效應下，其傳播路徑上的聚焦效應以及與震波能量匯聚亦可在台北盆地造成強地動值增大，新竹區域底下的淺部低速碗狀構造，震波能量傳遞至此聚焦並陷入震盪形成表面波與強地動值的增大。震源往西的傳播過程中，中央山脈底部的低速構造與淺部局部高速區造成地震波能量傳播至台中遭受大幅損失不易形成災害。震源輻射與路徑效應下，歸納出外海走向-滑移型態的淺部15公里震源易造成台中、新竹、台北、宜蘭有較大地動值，而在A點(331震央位置)與B點(宜蘭台北交界)震央位置的逆衝型地震只對於台北影響較大。 For reducing the hazard caused of off-shore earthquakes, producing and the characteristic of propagation need deeper understanding to the seismic wave. Among some related studying, the research of the strong earthquake is the most urgent. Under three-dimension wave propagation based on finite-difference method. The research purpose is to understand the influence on spreading of strong ground motion and the behavior of wave propagation on the north Taiwan by inspecting on the path and different focal-mechanism. We hope to estimate out the earthquake type and possible forming factor endangered to north Taiwan most possibly. From 331 offshore-earthquake as an example at first, the focal- mechanism adapt BATS then calculated the three-dimension strong ground motion forward simulation. For studying the path effects contribution to the strong ground motion, we inspect wave propagation process and the local underground structure caused of the influence to the strong ground motion. Then we consulted the possible background focal-mechanism. After introducing the possible focal-mechanism and different source location, we analyzed the influence degree of strong ground motion to these cities of the Yilan that near effects is stronger and far effects in Taipei, Hsinchu, Taichung. Then we could conclude that the offshore-earthquake type cause danger to Taiwan most possibly. The result of study points out that the shallow layer of earthquake at 331 epicenter position, the focusing effect and assembling with seismic waves energy can also cause the strong ground motion to increase in the basin of Taipei, even no site-effect. The local low-speed structure like bowl form under the area of Hsinchu. When seismic wave energy pass through there, the clear focusing effect and energy trapped, further then surfer wave generated. By the reason, it increased strong earthquake value. In addition, in the spread process from source to the west, because of low velocity structure and local shallow high-velocity are under the central mountain range. So cause seismic wave energy loss quickly, it is difficult to make the calamity loss to Taichung. Under path effect and source radiation effects, we can conclude that apt to cause Taichung, Hsinchu, Taibei, Yilan have large strong ground motion value, when offshore-earthquake is strike-slip type and at the depth of shallow 15 kilometer. But A and B epicenter location only against to Taipei, when source type is thrust.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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