結合等效線性場址修正之隨機式地動模擬; Stochastic Ground Motion Simulation with Site Correction Using Equivalent-Linear Method

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题名:	結合等效線性場址修正之隨機式地動模擬;Stochastic Ground Motion Simulation with Site Correction Using Equivalent-Linear Method
作者:	薩伏丁;Saifuddin
贡献者:	地球科學學系
关键词:	隨機式點震源方法;等效線性方法;TAP086;五股井下地震儀陣列;stochastic point-source method, equivalent-linear method, TAP086, Wuku downhole array
日期:	2013-07-22
上传时间:	2013-08-22 11:43:49 (UTC+8)
出版者:	國立中央大學
摘要:	在地震災損評估研究上，工程師最方便的方法就是利用最大地表加速度（PGA）衰減關係式。本研究結合了隨機式點震源模擬（Boore, 2003）以及等效線性方法（Idriss & Sun, 1992）進行地動之模擬，並與衰減關係式之計算結果作比較。進行隨機式地動模擬所需之基本地震參數，則由前人之研究取得（Sokolov et al., 2006 2009）。本研究先直接模擬台北盆地邊緣之岩盤站（TAP086測站）以及靠近五股井下地震儀陣列之沖積層站，岩盤站所得之結果尚能接受，但沖積層站之結果則有所低估。所以接下來使用模擬所得之岩盤站和沖積層站之波形記錄，利用等效線性方法進行下一步的場址修正。由前人之研究可以得到五股井下地震儀陣列之剪力波速剖面（Wen et al., 1995 Wang et al., 2004）以及土壤地質剖面（Su et al., 1997），將這些參數整理後代入，並以上一步驟所得到的岩盤站波形當成盆地下方入射波形，以等效線性方法計算井下地震儀陣列在不同深度以及地表之波形。此入射波形也可置放在不同的深度（30公尺，工程基盤和地質基盤）入射，則得到不同之場址修正結果。以五股井下地震儀陣列為例，等效性方法能有效的修正地表最大加速度值以及傅氏振幅譜，可降低預估PGA的誤差率（σlnErr）以及DSPD值，DSPD值是用來表示兩頻譜間差異之一種計算方式。且將入射波形從較深之位置入射，σlnErr會較低。與利用衰減關係式計算之結果作比較，本研究方法預估之岩盤站（TAP086）與沖積層站（五股井下地震儀陣列）結果皆較佳。本研究也將同一套流程對松山菸場井下地震儀陣列進行地動模擬，從30公尺入射之結果，σlnErr與DSPD值並無太大改變，但是從工程基盤和地質基盤入射之結果，σlnErr與DSPD值則有變大，此一現象或許跟松山菸場井下地震儀陣列之場址條件有關。如不考慮此一現象，從工程基盤和地質基盤入射，五股與松山菸場之結果皆可以得到類似之場址修正。這現象可能由於松山層顯著地控制著此場址之土層放大效應造成。 Attenuation relationship of peak ground acceleration is widely employed by engineers in seismic hazard estimation studies. This study was conducted by combining stochastic point-source (Boore, 2003) and equivalent-linear (Idriss & Sun, 1992) methods to simulate ground motion, and compared the results of attenuation relationship. Seismic parameters for stochastic method were selected based on previous studies (Sokolov et al., 2006 2009). The stochastic method was performed to obtain simulated waveforms at a rock site (TAP086 station) near of Wuku downhole and a soil site (Wuku downhole). It showed decent results at rock site, while underestimated results at soil site. Simulated waveforms at rock- and soil-sites locations were used as outcrop input motions for site correction. Site correction was performed using equivalent-linear method. Shear wave velocity profile (Wen et al., 1995 Wang et al., 2004), geological soil profile of Wuku downhole (Su et al., 1997) and input motions were required for equivalent-linear method to obtain simulated waveforms at soil surface of Wuku downhole array. Site correction was performed using outcrop input motions at different depths (30 m, engineering and geological bedrocks). Comparison of peak ground acceleration (PGA) observation against simulation was presented in log and linear scales while degree of spectrum difference (DSPD) was only in log scale. In general, equivalent-linear method could assist to correct simulated PGA and Fourier amplitude spectrum (FAS) at Wuku downhole either using simulated waveform at rock or soil-site locations. It was showed by reducing value of error in PGA comparison in log scale (σ_lnErr) and linear scale excluding input motion using simulated waveform of rock site at geological bedrock in linear scale and reducing slightly value of DSPD. For input motion in Wuku downhole, we found tendency that the deeper of input motion, the lower σ_lnErr value. Comparison of our simulation results to attenuation relationship, we found that our results were slightly better at TAP086 and Wuku downhole. We also applied stochastic point source and equivalent-linear methods to Sungshan downhole site. Stochastic point-source already yielded decent PGAs at surface of Sungshan downhole, site correction was also performed at different depths of input motions (30 m, engineering, and geological bedrocks). Site correction at 30 m did not alter value of σ_lnErr and DSPD, while engineering and geological bedrocks enlarged the value of σ_lnErr and DSPD. These phenomena might be occurred due to site condition of Sungshang downhole. Regardless of the results from Sungshan downhole were not decent as Wuku downhole, we found that engineering and geological bedrocks obtained similar site correction as Wuku downhole. These phenomena might be occurred because significant amplification was controlled by top layer of engineering bedrock which is Sungshang Formation.
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