圖書典藏及影音數位平台

本委託計畫旨在定期保養和維護設置於天花湖水庫計畫壩址處之3部強震儀，使之維持正常運轉功能，而持續收錄地震資料；並就所收錄之地震資料加以分析，做為大壩工程設計之依據。

1、Preface The purpose of this project is to routinely maintain the three strong-motion seismographs located around dam site in Touwu Township, Miaoli County, and to keep them in good operational condition for recording earthquake ground motion. The recorded ground motions are analyzed for the reference of dam design. The annual report includes the process of routinely maintaince and result of data analysis. The items of this project are： (1)Strong motion seismometer maintenance and observation (2)Seismic data analysis (3)Preliminary analysis of resonance frequency (4)Patrol and report of regular for personnel (5)Report writing 2、Strong-motion seismometer maintenance and observation Three strong-motion seismographs are built around the dam site, west (S01), south (S02) and north (S03) of dam for processing strong motion observation. During the execution time, routine maintenance were carried out on January 28, February 13, March 13, April 28, May 28, June 30, July 23, August 18, September 16, October 30, Nov. 10, December 1 in 2015. 3、Seismic data analysis (1)Strong motion observation result In this year 2015, there are 94 strong-motion data recorded by S01, 90 strong-motion data recorded by S02 and 87 strong-motion data recorded by S03. S01, S02 and S03 collect 271 strong-motion data totally which triggered by 95 seismic events. The maximum and minimum magnitude is 6.7ML (NO. 942) and 1.95M_L (NO.972) respectively. The minimum epicenter distance is 8.76km (NO.972). The maximum peak ground acceleration is 12.11gal (NO. 974) which epicenter distance is 171.19km, magnitude is 6.4M_L. (2)Acceleration, velocity, and displacement time histories After down load from seismographs, the acceleration ground motion are processed by integral and low pass filter, then the velocity and displacement time histories are estimated. (3)Fourier amplitude spectrum Inorder to estimate the frequency content of strong ground motion, the acceleration time histories has been transformed into frequency domain by FFT, and the amplitude spectrum are obtained. (4)Response spectra Consider the single degree of freedom system (SDOF), the response spectrum are calculated for the damping ratio of 0％、0.5％、1％、2％、5％ and 10％ (Nigam and Jennings, 1986). The response spectrum turn into tripartite logarithmic plot. Represent the PSD PSV and PSA with cycle relation. (5) Attenuation law of peak ground acceleration Earthquake energy radiates from the source and attenuates during the propagation due to geometrical spreading and physical absorption of media between source and recording site. Attenuation law of peak ground acceleration (PGA) describes the relationship among earthquake magnitude, distance between source and site, and PGA. This project adopts the empirically attenuation relationship formula from NCREE (2011) and Wen (2014). Compare the PGA predicted by attenuation formula with that observated by these three seismographs, we can findout that, on average the strong-motion intensity observed by seismographs are underestimated by the prediction of these two empirical formulas. 4、Preliminary analysis of the resonance frequency The strong motion intensity is affected by seismic source (source effect), propagate path (path effect)and site condition near the seismograph (site effect), in which, the preliminary analysis of site effect is target of this project. When seismic waves propagating to the seismographs, the amplification of amplitude of motion in frequency domain would be controlled by the geology structures under the field. The resonance frequency and vibration characteristics of specific site is worthy of understanding especially in dam design. We used HVSR method as well as seismic data recorded in this project to assess the resonance frequency and vibration characteristics, the preliminary results shows that, the fundamental frequency of S01, S02 and S03 are 1~3Hz, 3.5Hz and 1~3Hz, respectively.