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  • 學位論文

小波轉換在強震記錄解析的應用

Applications of Wavelet Transform on The Analysis of Strong-Motion Data

指導教授 : 羅俊雄
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摘要


工址地質與土壤條件對於地表反應和震害的影響,在耐震設計方面扮演重要的角色。從台北盆地的強震紀錄的反應譜中,經常可以在週期2至3秒間發現不尋常的高峰。雖然有關工址效應的研究為數甚多,可是鮮少提及此一不尋常高峰的成因及其影響。本項研究旨在利用小波轉換從測站強震記錄中解析其可能成因。透過小波轉換技術可以將各站水平向加速度記錄分解成對應各種不同頻率的分量。若將某特定頻率的兩個水平分量會製成加速度軌跡,即可觀察此一測站在特定頻率的運動方向及強度。本項研究利用一項新定義指標以及適當參考測站的選取,可以從三個重要地震事件分析中,分離出台北盆地的共同低頻振動訊號。將所有測站的加速度軌跡繪製於盆地地圖上,可供研判盆地低頻效應的成因。經研判此一低頻效應發生範圍在0.2至0.5 Hz.之間,應該是盆地土層共振效應所致。本項研究發現低頻效應發生時,較大的地表振動大多發生在盆地西側最深處和盆地中央地區。當頻率在0.6至1 Hz.之間時,較大的地表振動發生在盆地東側邊緣。經由原始加速度記錄和低頻訊號的反應譜作比較,可以證明此項低頻訊號就是反應譜中不尋常高峰發生的原因。本項研究也利用小波轉換從近斷層加速度記錄分析估計測站的永久變位,該項結果與衛星定位資料比對,顯示兩者非常符合。

並列摘要


The influence of local site geological and soil condition on the intensity of ground shaking and earthquake damage has been known for years, which plays an important role in earthquake-resistant design and must be accounted for on a site-by-site basis. From the response spectra of the recordings in the Taipei basin, unusual spectral ordinates can be found in the range of period between 2 – 3 second and such ground motion would be very harmful to tall buildings. Although many efforts work on the site effects of Taipei basin and derive many important results, however, the origins of the unusual response spectra have been rarely discussed. This study tries to find the origins which result in unusual spectral ordinates in the recordings of the soil sites. Through the application of Wavelet Packet Transform (WPT), the complicated acceleration trace of a record can be decomposed into many components with very narrow frequency band. By the adequate time window and comprising the strong shaking stage signals of the E-W and N-S component, we can derive a very simple decomposed acceleration trace (DAT) with a distinct shaking direction and maximum amplitude. Through the new defined index CEI, the common low-frequency components corresponding to the low-frequency basin effects of the soil sites can be found. The 3rd (fc=0.244 Hz.) to 5th (fc=0.439 Hz.) decomposed ground motions are identified to be the main components due to the basin effects. From the figure associates the Taipei basin map with the DATs of all soil sites, we can observe the response of the Taipei basin at a certain period of shaking. The low-frequency strong shakings usually occur at those sites at the central and the western deepest area of the basin. The systematic behaviors of soil sites including horizontal oscillations and rotations seem to be due to the resonance of the basin sediment. Because of the lack of phase information in the DATs and results obtained from limited recordings of limited events, the oscillations and rotations due to resonance of the sediment is still a speculation. More studies are needed to verify. The amplifications of those sites at the east and south edge of the basin are found to be small in these three low-frequency components. For higher frequency bands (0.6 – 1 Hz.), the large amplifications can be found at the central area and the east edge of the basin. By the comparison of the SAs of the original and the extracted ground motions, we can find that the SAs in the range of period 2 – 5 second are comparable with each other. This approach can extract the low-frequency ground motions from a record effectively, and can be helpful to the improvement of design spectrum corresponding to the Taipei basin in the future. This study also proposes a three-phase approach includes the calculation of constant-level coda trace, which helps to estimate residual ground displacement. The obtained permanent displacement values are strongly consistent with the values obtained by GPS measurements.

參考文獻


[1] Kobayashi, H., K. Seo and S. Midorikawa, 1986, “Estimated strong ground motion in Mexico city”, The Mexico Earthquake Factors involved and lessons learned, ASCE, pp. 55-69
[4] Safak, E., 1997, “Models and Methods to Characterize Site Amplification from a Pair of Records”, Earthquake spectra, Vol.13, No.1, pp. 97-129
[5] Boatwright, J., L. C. Seekins, and C. S. Mueller, 1991, “Ground Motion Amplification in Marina”, Bulletin of the Seismological Society of America, Vol. 81, pp. 1117-1131
[8] Shoji Y., and M. Kamiyama, 2002, “Estimation of Local Site Effects by A Generalized Inversion Scheme Using Observed Records of Small-Titan”, Soil Dynamics and Earthquake Engineering, 22, pp. 855-864
[11] Yamazaki, F., and Mehedi A. Ansary, 1997, “Horizontal-to-vertical Spectrum Ratio of Earthquake Ground Motion for Site Characterization”, Earthquake Engineering and Structural Dynamics, Vol. 26, 671-689

被引用紀錄


秦正宇(2016)。小波轉換於風力發電機葉片診斷之應用〔碩士論文,國立臺灣大學〕。華藝線上圖書館。https://doi.org/10.6342%2fNTU201601551

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