在地震災損評估研究上，地動預估為廣為接受的手段，其中高頻地動模擬為一重要之方式。本研究所使用之地震動模擬方法，嘗試結合隨機式模擬及一維等效線性方法來進行。隨機式地動模擬技術為以符合地震學的物理假設方式，有效地考慮震源、路徑及場址效應，在前人研究多證明此方法可以合理評估頻譜表現及預估PGA。同時，考量地震波傳遞時，不同的場址條件將顯著影響地震波之特性，因此當進行地動模擬方法時，場址效應都應加以考慮進行修正，尤其隨著高強度地震動發生時，近地表的鬆軟土層有可能會產生非線性效應，對地震動的影響非常大，因此土壤非線性分析則須納入考量，常用之方式為於頻率域進行的等效線性法計算。 本研究為考量高頻及可能之土壤非線性效應，即利用兩種模擬技術優點的結合來進行地動預估，選用羅東大比例尺地震儀陣列 (LSST) 的地表及井下地震記錄為例，根據前人詳細調查之速度模型、土層構造，進行一維等效線性模擬於高震度時的非線性效應。以第一階段隨機式點震源模擬地震波至蘭陽平原鄰近LSST陣列的岩盤站ILA031，其模擬加速度記錄視為等效線性法的輸入波，經第二階段計算獲得LSST陣列土層表面的模擬波形以進行場址修正。經由經驗轉換函數進行場址修正後之隨機式點震源模擬於參考岩盤站模擬結果顯示，其頻率域及PGA表現皆與觀測記錄相符合，其誤差計算結果於DSPD值及PGA之誤差率 (σ_lnErr ) 皆有效降低其模擬誤差。最後，本研究之結果顯示若使用適當的土壤剖面、剪力模數及阻尼比設定，透過兩階段隨機式模擬加上等效線性法之計算皆可以有效地預估觀測值，對於土壤受高強度震動之土壤非線性效應，其於較高頻訊號之壓抑放大現象亦能模擬呈現與觀測頻譜之相符趨勢，此模擬方法對於未來可能發生之大地震可有效進行相關之地動評估工作。 ;Ground motion prediction has been widely accepted in seismic hazard studies, and high frequency ground motion simulation is quite important for engineering seismology in recent years. Ground motion simulations were conducted by combining stochastic method and one-dimensional equivalent-linear method in this study. Stochastic ground motion simulation technique can effectively consider the source, path and site effect, which depends on physical-based seismological knowledge from previous studies. Meanwhile, considering the site effect will efficiently affect different characteristics of the propagation of earthquake motions for different site conditions. It’s important to consider such effect for site correction in all kinds of the simulation method. The soil nonlinearity may be observed at soft soil sites, especially in high-intensity ground motion. Frequency domain equivalent linear analysis is one of the most common approaches for one-dimensional site response analysis. Thus, numerical modeling of site response is used to carry out the soil nonlinearity problem by the equivalent-linear method in this study. This study used the combination of the advantages of the two simulation techniques to estimate the high frequency ground motion accompanying with possible soil nonlinearity. Firstly, seismic data investigated velocity profile and soil dynamic parameters from the Large Scale Seismic Test (LSST) downhole array in Lotung, Taiwan were checked with one-dimensional simulations. Then, the first stage stochastic ground motion simulation was performed and verified to obtain simulated accelerograms at a rock site ILA031 near LSST in Yi-lan plain. The second stage, these accelerograms were regarded as the input motions for equivalent-linear method to obtain simulated accelerograms at soil surface of LSST array. The ILA031 station results after the site correction of empirical transfer function during stochastic point-source simulation in the first stage, the FAS and PGA prediction are well approximation to the observation records that the DSPD and the PGA error showed the obviously improved. Finally, if the suitable soil profile, shear modulus, and damping ratio could be effectively calculated by two stages of simulation technique including equivalent-linear method when comparing to the reality. The results showed the de-amplification comparing to the reality, results also show the overall good approximation. The proposed simulation method could help to evaluate future possible large earthquakes.
