Azimuth-Dependent Site Amplification

隨方位變化的場址放大效應

邱宏智(Hung-Chie Chiu) ； 黃蕙珠(Huey-Chu Huang)

《Terrestrial, Atmospheric and Oceanic Sciences》 3卷1期 (1992/03) Pp. 21-37

摘要

本研究使用SMART-1強震儀陣列中的兩個測站所收錄的地震記錄探討場址放大效應隨震央方位的變化情形。本文共選用了十五個地震，乃因它們同時啓動E01土層測站和E02岩盤測站的強震儀。首先，我們將E01和E02的記錄分別截取一段包含直接S波的波線，並求其傅氏振幅譜，然後再求E01對E02之頻譜比。由於岩盤測站受場址效應的影響較小，因此頻譜比可將大部份的震源及波傳路徑效應消除，而呈現E01的場址放大效應。
為了比較不同震央距及方位角對放大效應的影響，我們將這些地震分成十組，使同一組之地震具有相近的震央距及反方位角，分析這些地震之結果顯示：不同組資料有不同之放大效應，而各組間並無明顯的系統性差異。至於同一組的地震，預期應有相似的頻譜比，但所得的結果卻只有部份組之部份頻段存在相似性，而這些異常現象可歸因於近震源及非線性放大兩種效應所致。

並列摘要

The strong motion accelerograms recorded at two stations of SMART-1 array have been analyzed to investigate azimuth-dependent site amplification. Fifteen earthquakes which triggered both accelerographs at rock site E02 and soil site E01 were selected for this study. We measure the spectral ratio of E01 to E02 in a window which includes direct S waves. Since ground motions at the rock site are less modified by the site effects and E02 and E01 are only 2 km apart, the spectral ratio of the soil site to the rock site will cancel most of source and raypath effects and reflect the site amplification of the soil site.
These earthquakes are divided into 10 groups. The earthquakes in the same group have similar epicentral distance and backazimuth. Our studies show that different groups have different spectral ratios and no systematic changes have been found among the groups. In the same group, all earthquakes were expected to have the similar spectral ratio. However, similar spectral ratios were only found in some groups over some limited frequency ranges. These discrepancies are interpreted as the results of near-source and non-linear effects.