在地質營力的作用下，地殼抬升與侵蝕造成地形起伏，隨著地形越陡峭，剝蝕率也逐漸增加，直到抬升速率與剝蝕率達平衡，此時的地形即為臨界穩定地形。而剝蝕作用主要有三類，分別為風化、山崩及侵蝕。山崩為構造活動劇烈之地區主要的剝蝕作用，又山崩的發生與岩體強度密不可分，因此有許多探討地形與岩體強度關係之研究。除了岩體強度外，地震力亦是影響邊坡穩定的外在因素，故地形起伏也一定程度記錄了地震的影響。因此，研究區域選擇於已呈臨界穩定地形的臺灣中部，透過野外調查與室內實驗估計岩體強度，假設垂直地震力係數為水平的1/2進行邊坡穩定分析，逆分析具代表性之岩坡於臨界穩定下可承受之地震力係數。結果顯示研究區可能承受之最大水平地震力係數為0.50~0.61，考慮邊坡擬靜力地震力係數之平均值一般為尖峰地震力係數之1/2，此一範圍大於大部分與測試區同屬斷層上盤之集集地震強震記錄（水平地震力係數0.105~0.625），符合本研究逆分析結果應為該研究區曾承受之地震力係數的上限，顯示由岩體強度、坡度與坡高反算岩坡曾承受之地震力係數具可行性。若考慮本案例參數的不確定性，逆分析結果可產生±65%的變化。另外，透過參數敏感度分析，發現地質強度指標（GSI）對於地震力係數逆分析之敏感度最高，孔隙水壓比（Ru）居次，單壓強度（UCS）與岩性係數（mi）相對較不敏感。The maximum stable relief is defined as the balance of topography which the denudation rates equal to uplift rates. In active orogen, the denudation rate is highly correlated to with landslides. For non-structural controlled landslide, rock mass strength is a key factor dominating the slope stability. Therefore, there is a close linkage between rock mass strength and relief in active orogen region. Furthermore, seismic forces also play an important role in slope stability. In this study, we selected a stable relief region located in central Taiwan. The rock mass strength of representative rock slopes was estimated from field investigations and laboratory experiments. Subsequently, we back calculated the upper bound of seismic coefficient through slope stability analysis. Results show that the seismic coefficients（0.50~0.61）are greater than most of the strong motion records （seismic coefficient 0.105~0.625）on the hanging wall near the research area during the Chi-Chi earthquake. The results show the seismic coefficients are upper bound of the study area which indicates that the back calculated seismic coefficients are reasonable. The results also show ±65% deviation if the uncertainty of all parameters is considered. According to parameter study, the GSI is the most sensitive parameter influencing the back calculate results of seismic coefficient.
