| Summary: | 碩士 === 國立中央大學 === 地球物理研究所 === 99 === The Jiasian earthquake occurred at 8:18:53 A.M. on March 4th, 2010 and it was a large earthquake with magnitude ML=6.4 and focal depth 22.6 km. occurred on land in Taiwan. It also caused many structures damage, soil liquefaction, and a high speed rail car derailed.
The factors affect the ground motions are quite complex. The main factors are source, path, and local site effects. In this study, the data from the Jiasian earthquake and the weak motion data from 1993~2009 are analyzed by using the single station spectral ratio method (Nakamura, 1989) to study the site effect in southwestern Taiwan.
From the dominant frequency contour map and the H/V Ratio maps of different frequency bands show that at the coast plain the dominant frequencies are about 0.3~2 Hz; at the plain, hill, and the area near mountain the dominant frequencies are about 2~4 Hz; at the mountain areas the dominant frequencies are greater than 4. And the higher stories school buildings are damaged at the high H/V Ratio area of low frequency bands, in contrast, the lower stories school buildings are damaged at the high H/V Ratio area of higher frequency bands. So, structure design should avoid the structure frequency around the same with the local dominant frequency; or need to consider the local dominant frequency in the seismic design of structure.
Compared the dominant frequency distribution observed from Jiasian earthquake, weak motion, and microtremor data in the study area, it would understand that the weak motion results are averaged response from many earthquakes. The result of Jiasian earthquake was a signal event so it might present the certain of layers. It was the reason of the differencet between the dominant frequency of Jiasian earthquake and weak motion for some stations. And the microtremor response can be used to infer the response of shallow layer when the earthquake happened.
Finally, the event of high speed rail car derail was discussed. Assumed the earthquake warning system also installed on the all of strong motion stations it would increase much more time to brake the trains and decrease the probability of derail. After observed the waveform from Jiasian earthquake, it might infer that the reason of high speed rail car derail were due to the surface wave generation.
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