台灣北部震波耗散及場址效應之分離

• Main Author: 林金泉
• Other Authors: 王乾盈
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/76500111788014829151

碩士 === 國立中央大學 === 地球物理研究所 === 87 === A ten-station linear seismic array across the Northern Taiwan provides us a good opportunity to study the seismic wave propagation in this area. The data set consists of 60 earthquakes and are capable to estimatie good Q values when waves pass the array station by station. The obtained Q values are lower than those found previously. It means that a high wave attenuation may exist in the northern Taiwan which may not be negleted when considering the attenuation law for strong motion study . Using this new Q value, we attempt to correct the propagation effect and then to separate the source and site effects within the data set of TSMIP. Stable source spectrum are extracted, which have clear ω0、ω-2 and ω-3 dependence. On the contrary, the site response spectrum are much more complex. Four different types of site responses with low, middle, high and even spectrum are found which shows good correlation with the local geology. High site responses are restricted in the basin area, except the Taichung basin which reacts as at rock sites. We obtain the following conclusions from in this study: 1) Q value of S wave in the northern part of Taiwan is: Qs= 77.6˙f 1.6724 0.4Hz≦f≦1.4Hz Qs= 133.7˙f 0.090 1.4Hz≦f≦2.0Hz Qs= 86.7˙f 0.6931 2.0Hz≦f≦20.0Hz (2) Using well-distribution stations we can obtain good Q value and then obtain more perfect source spectrum and better site responses after proceeding parameter separation method。 (3) After these spectrum separation studies, we can obtain the site responses in the northern Taiwan as follows: (a) The site effect in the Taipei basin is found to have low frequency amplification at the area where the thickness of Sungshan Formation is over 40 meters. The middle frequency amplification area is along the boundaries, and the high frequency amplification is at the northwestern basin edge. It is interesting to find that no special amplification at any frequency along the major streams . (b) The site effect in the Ilan plain generally can be devided into the west and the east parts along a boundary 10 km west of Ilan to Lotung. The eastern part amplifies the ground motion appreciably and the western sites are more like rock sites. (c) The site effect in the northwestern Taiwan can be devided into several parts. The site effect have middle or high frequency amplification in the Western Foothills and Hsueshan Range and have high frequency amplification in the southern part of Changhua plain. The site effect have low frequency amplification in the Taichung basin and Taoyuan terrace. The site effect have no special amplification at any frequency at some stations of Hsinchu and Holi。 (4) The distribution of PGA magnification and site responses in the high frequency (10Hz) is in good agreement. PGA magnification can represent approximately site responses at high frequency. (5) The attenuation formula of peak ground acceleration corrected after PGA magnification in the northern Taiwan is: Y=0.0301e1.1997M(R+0.1580e0.7191M)-1.7304