利用傅立葉轉換預測指南宮之地震動

Using the Fourier Transform to Predict the Ground Motion in Jr-Nan Temple

林東慶(Dung-Ching Lin)

指導教授 ： 陳慧慈

國立中央大學/工學院/土木工程學系/碩士(2006年)

摘要

如何能預測一個適合特定場址的地震動以進行構造物的耐震評估或特定區域的地震風險評估，乃成為近年工程地震學研究的主要課題。本研究首先將台北市指南宮測站規模大於5的地震動歷時，依據地震震央的位置分成四區，以離散傅立葉轉換，求得傅氏譜和群延遲時間，再以合適的機率密度函數來模擬，經由回歸分析求得所選取分布曲線的參數與地震規模間的關係，未來只要給定某一地區之地震規模就可經由離散傅立葉反轉換預測地震動。
就指南宮測站而言，研究結果顯示（1）傅氏譜可以利用對數常態分布的機率密度函數曲線來模擬。（2）將頻率分成十個區間後，每個區間的群延遲時間可以用常態分布的機率密度函數來模擬。（3）測站的地震歷時的震央來自某一個區域越多時，則可以越準確的預測由該區域所產生的地震動。（4）擁有相同數目的震央時，對於來自震央分布的範圍較大地震而言，地震動預測的結果將越不理想。

關鍵字

地震動預測 ； 傅立葉轉換 ； 群延遲時間

並列摘要

In recent years, a topic of considerable research interest in the engineering seismology is to predict a suitable ground motion for seismic evaluation of a structure or earthquake risk assessment of a designated site.
This study uses the discrete Fourier transform method to predict seismic ground motion of a recording site. The accelerograms at the recording site are divided into four sites according to which the location of epicenter, and for each site the suitable distributions of probability density function are selected to model Fourier spectrum and group delay time with the associated parameters being regressed as function of earthquake magnitude. Thus, with the given magnitude, predicted accelerograms can be generated using the inverse Fourier transform.
The earthquake records with magnitudes equal to or greater than 5.0 from the Jr-Nan Temple Station in Taipei are selected for this study. For the Jr-Nan Temple Station, the following conclusions can be drawn：（1）the Fourier spectrum of records can be modeled as a lognormal probability density function；（2）separated frequency range into ten intervals group delay time of records can be modeled as a normal probability density function in each interval；（3）if more records with the epicenters located within small region are available, the accuracy of the predicted motion originated from that region can be enhanced；（4）if two regions have the same numbers of epicenter, the accuracy of the predicted ground motion originated from the region with epicenters spread over a small area will be better.

並列關鍵字

group delay time ； predicted ground motion ； Fourier transform

參考文獻

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