以2016美濃地震的垂直陣列與自由場地動紀錄探討台灣場址效應之特色

A Study of Site Effect from the 2016 Meinong Earthquake by Using Vertical Array and Free-Field Recordings in Taiwan

吳俊毅(Chun-Yi Wu)

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(2017年)

https://doi.org/10.6342/NTU201704136

摘要

台灣位於地震頻繁的歐亞板塊及太平洋海板塊交界之東亞島弧地震帶上，因此在進行各項結構設計時，需慎重考慮及評估工址受到地震影響時的地盤反應對設計結構物之影響，以利耐震設計時，能使結構物發揮足夠的韌性，而不致破壞。
在地震工程中，影響地動的因素相當複雜，主要可以分成三項:包括地震規模、震源深度和斷層破裂過程及形式的震源效應(source effect)、地震波傳遞的路徑效應(path effect)、地震波因局部地質土壤材料組成特性、土層剪力波速構造、場址附近之地形變化所引起之場址效應(site effect)等。
常用來預測地震強度的方法有理論地盤反應分析(Ground Response Analysis)，以及地動預估衰減式(Ground Motion Prediction Equations,GMPEs)，其中GMPE主要概念為以一數學式描述特定地震規模的地震事件中，特定區域地表受震之地動反應情形。
在本研究中，以2016年2月6日所發生芮氏規模6.6 (Mw = 6.4)之全台有感的美濃地震(the 2016 Meinong earthquake)為例，分析自由場強地動觀測網(free-field)及井下陣列觀測網(vertical-array)所記錄到之地震加速度歷時紀錄，計算並畫出PSA反應譜比值(spectral ratio)以及傳遞函數(transfer function)作為量化場址放大效應 (Amplification)的參數，並針對不同地質情形(geology)、至剪力波速達1公里/秒以上地層之深度(Z1.0) 、地表下30 公尺內土層之平均剪力波速(Vs30)作測站分類(site classification)，比較區域性土壤性質相同的測站所得場址效應放大因子，且以四個不同的地動預估衰減式探討並比較這些GMPE在美濃地震事件中對於強地動值預測之合適性。

關鍵字

地動預估式 ； 地震強度參數 ； 場址效應 ； 地盤反應分析 ； 美濃地震

並列摘要

Ground motion prediction equations (GMPEs), which are empirical models derived from past earthquake recordings, are often used to estimate ground motion intensity measure at a site. The site term in a GMPE can predict the site effect on ground motion. On the other hand, site effect can also be evaluated using ground response analyses if detailed sediment properties (e.g. shear wave velocity profile and stress-strain behavior) are available. Site amplification/deamplification can be expressed in terms of the ratio between the response spectra at surface and at downhole location, as well as transfer function.
In this study, using the ground motions recorded during the 2016 Meinong earthquake at the free field stations and vertical arrays operated by the Central Weather Bureau of Taiwan, the ground motion amplification (or deamplification) characteristics due to local site effect are evaluated. For free field ground motions, the source and path effects are removed by subtracting the general source and path terms (from a Taiwan-specifc GMPE) from the data, Then the trend of the remainders is identified and compared to the site terms from various GMPEs. For vertical arrays, the empirical transfer functions and amplification factors (ratio of intensity measure at surface to the same intensity measure at downhole location) are evaluated. The trends of these quantities are identified and compared to the theoretical values.

並列關鍵字

GMPE ； Site Effect ； Meinong Earthquake ； Amplification factor ； ground response analysis

參考文獻

陳泊鈞, (2016), 總應力與有效應力地動分析法偏差評估之研究-以臺灣垂直陣列為例, 國立台灣大學土木工程學研究所碩士論文

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