台灣垂直陣列地盤反應之研究

Site Response at the Vertical Arrays in the Taiwan Surface-Downhole Monitoring Network

姚竣介(Chun-Chieh Yao)

指導教授 ： 郭安妮

國立臺灣大學/工學院/土木工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU202003764

摘要

為了改善地震監測的品質，中央氣象局在台灣建立了地表井下監測網，其中包含了大約50個垂直陣列測站。垂直陣列是由一對分別安裝在地表與井下的地震儀所組成，且可以提供穩定的地震訊號供有關場址效應之研究使用。在本研究中會探討所選擇的垂直陣列測站之經驗和理論的地盤反應。具體來說會使用一維頻率域擬線性的分析方法分別計算經驗與理論的轉移函數(Transfer function)與地表反應(Response spectra)。結果顯示某些垂直陣列的場址並不具有一維波傳的特徵。另一方面，比較地表與井下的水平垂直頻譜比(HVSR)後，結果顯示地表與井下頻譜比的值大部分都分布在1左右。最後，利用垂直陣列資料所計算出高頻衰減參數κ來求取修改過後之小應變阻尼剖面圖，並以此重新求取理論之地盤反應。但是，新求取之理論地盤反應與原本預測之地盤反應不盡相同。

關鍵字

場址效應 ； 垂直陣列 ； 高頻衰減參數

並列摘要

To promote the quality of ground motion monitoring, the Central Weather Bureau of Taiwan has constructed the Surface-Downhole Monitoring Network, which consists of approximately 50 vertical arrays. Vertical array has a pair of sensors installed at surface and downhole, which can provide valuable information for the study of local site effect. In this study, empirical and theoretical site response at selected vertical arrays in the Surface-Downhole Monitoring Network is explored. More specifically, the transfer functions and surface response spectra are evaluated empirically and theoretically (using one-dimensional frequency domain equivalent-linear analyses). The results indicate that some of the vertical arrays do not exhibit one-dimensional wave propagation characteristics. On the other hand, the surface and downhole horizontal-to-vertical spectral ratios (HVSR) are compared. The results reveal that the value of ratios are about 1, which is no difference at surface and at depth. Lastly, spectral decay parameter κ is evaluated based on surface and downhole recordings to obtain the modified small-strain damping profiles for the vertical arrays. The theoretical site response is re-evaluated using these updated profiles, however, it is found that the improvement in the predicted response is not distinct.

並列關鍵字

Site Response ； Vertical Array ； Spectral Decay Parameter

參考文獻

Afshari K., Stewart J. (2017), “Implications of California vertical array data for the analysis of site response with 1D geotechnical modeling”. UCLA: Civil and Environmental Engineering.

Anderson J.G. (1991), “A preliminary descriptive model for the distance dependence of the spectral decay parameter in Southern California”. Bull. Seismol. Soc. Am., 81, 1969-1993.

Anderson J.G., Hough S.E. (1984), “A model for the shape of the Fourier amplitude spectrum of acceleration at high frequencies”. Bull. Seismol. Soc. Am., 74, 1969-1993.

Campbell K.W. (2009), “Estimates of shear-wave Q and κ0 for unconsolidated and semiconsolidated sediments in Eastern North America”. Bull. Seismol. Soc. Am., 99, 2365-2392.

Darendeli M.B. (2001), “Development of a new family of normalized modulus reduction and material damping”, PhD Dissertation, University of Texas at Austin, Texas, USA.