A Study on Strong Ground Motion Site Effects of the Ilan Plain Based on Response Spectrum

• Main Authors: Chen, Kwen-Chien, 陳坤杰
• Other Authors: Tsai Yi-Ben
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/29468571471553024297

碩士 === 國立中央大學 === 地球物理學系 === 85 === The strong ground motion data recorded by the Taiwan Strong Motion Instrumentation Program (TSMIP) were used to analyze the site effect of Ilan Plain in terms of response spectrum. The data consist of all available horizontal accelerograms of 21 earthquakes with magnitudes between 4.8 and 6.6 from January, 1994 to August, 1996. After investigating the characteristics of the response spectrum shape of Ilan plain, regardingthe effects of normalizing parameter, classification of the site effects, and the relationship between site effects and local site geology, we obtain following conclusions：(1) The normalized response spectrum shape was used to study the strong motion site effects of Ilan Plain. The results showed that when the focal depth change from deep to shallow and the epicenter distance from near to far, the dominant frequency of the normalized response spectrum shape shift from high to low. (2) The site effect and dominant frequency of Ilan Plain depend on the thickness of the shallow alluvial layers, the distribution of the three major rivers of the Ilan Plain , and the lateral finiteness of the surface layers. (3) Sites Class 1 were located at the areas having larger thickness of the shallow alluvial layers, the dominant frequency can be found between 0.33 to 1 Hz. The distribution of sites Class 2 are along the three existing major rivers of the Ilan Plain. Sites Class 3 were located at the transition zone from the hill areato the alluvial valley, the dominant frequency can be found between 1 to 3 Hz. Sites Class 4 were located near the mountains having dominant frequency larger than 5 Hz. (4) The two normalizing parameters, PGA and MSA, were found to be positively correlated. Since the MSA represents the water- level average of a response spectrum over the entire frequency band, the correlation means that the level of the entire response spectrum is also proportional to the PGA. This means that a large PGA will elevate the entire response spectrum , confirming the practice that the maximum peaks in time histories may be used for defining seismic ground motion.(5) The peak of site response relative to the whole Ilan plain shift to increasing frequency as the sites moves toward the Plain edge. After reaching 5 Hz, the strong motion station near the mountain edge will have ground motion behavior quite like rock sites.