| Summary: | 碩士 === 國立中央大學 === 地球物理研究所 === 93 === 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.
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