HR: 0830h
AN: S51E-0097    [PDF]
TI: Ground Motion Characteristic in the Kaohsiung Area, Taiwan
AU: * Chiang, H
EM: gemini@s319m.gep.ncu.edu.tw
AF: Institute of Geophysics, National Central University, Chung-Li, 320 Taiwan
AU: Wen, K
EM: wenkl@s319m.gep.ncu.edu.tw
AF: Institute of Geophysics, National Central University, Chung-Li, 320 Taiwan
AU: Chang, T
EM: taoming@s319m.gep.ncu.edu.tw
AF: Dept. of Information Management, Hsing Wu College, Lin-Kou, 244 Taiwan
AB: Kaohsiung city is the most important harbor in Taiwan. Recently, there are many high-rise buildings and public transportation system are under construction in this area. Therefore, it is very important to know the surface geological conditions for many practical reasons especially after the strikes of 1999 Chi-Chi, Taiwan earthquake. The Central Geological Survey had spent four years to bore more than 50 wells. And now, it is very clear to know the basement depth is changing from 120 to 40 meters for the western and eastern part of the Kaohsiung city. The harbor and commercial area locate at the western part of this area, and the eastern part is small hill area. To serve the purpose of earthquake hazard mitigation, it would be better to understand the soil amplification effect of the Kaohsiung city. We then conducted a research to study the site effects of the Kaohsiung city, which includes analyze the acceleration seismogram data of TSMIP (Taiwan Strong Motion Instrumentation Program) network and two newly installed borehole seismometer arrays, and perform very dense microtremor measurements in the study area. Most microtremor measurements were done during the midnight to reduce artifacts. After carefully selection, we pick 233 records and use the H/V ratio method to get information of soil amplification. From the result, we found it correlated to the basement depth very well. For the purpose of the earthquake resistant design, earthquake engineers must consider the site response at a specific period. For example, the structure period of a ten-flour building is at about 1 second. If the input ground motion is dominate at 1 Hz, then the building will has a resonant effect. Therefore, in this study, we select 10 frequencies (0.3, 0.5, 0.7, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0 Hz) to plot out the contour map for understanding the frequency responses in this area. For the 0.5 Hz, the contours show that main amplification effects occurred at the southern part of Kaohsiung area. With the frequency increasing to 2.0 Hz, the main amplification area move from the harbor and the southern part of Kaohsiung area to the hill area, which locates at the eastern part of Kaohsiung area. For the higher frequency (3.0 Hz), there are no obvious high contour areas. We pick the dominant frequency of each record and plot out the contour map. At the harbor and city area, the dominant frequency is about 0.5 ~ 0.9 Hz, and the northeastern part is about 1.3 ~ 1.7 Hz. We found that the basement structure can explain the contour very well. Yet, the H/V dominated frequency distribution map reveals more detail features.
DE: 1734 Seismology
SC: Seismology [S]
MN: 2003 Fall Meeting