三角剪切模式(Trishear model)是用於解釋斷層與褶皺關係之運動學模式，在模式中影響褶皺形貌變化重要參數為斷層破裂距離和斷層滑移量之比值(P/S)。然而，三角剪切模式為運動學分析模式，因此P/S值之力學意義並不清楚。為了解P/S之力學意義，本研究以有限差分程式FLAC模擬斷層擴展褶皺(Fault-propagation fold)之地層變形過程，分析使用之彈性模式考慮斷層前緣初始深度、上覆地層彈性常數，而彈塑性模式考慮上覆地層與基盤間之摩擦性質對地層變形之影響。至於力學模型中P/S值乃利用位移-距離法(Displacement/Distance Method)加以計算，同時將變形反饋至三角剪切模式進行逆分析，以驗證位移-距離法於FLAC分析剖面之適用性。本研究採用位移-距離法獲得之結果充分反應累積剪應變增量之分佈，經將褶皺變形帶依變形特性分為三段後，本研究得以合理解釋並計算斷層擴展褶皺三角剪切模式中之P/S值。根據FLAC斷層擴展褶皺模擬及利用位移-距離法分析變形剖面之P/S值變化，結果顯示P/S值變化趨勢於斷層錯動過程中符合斷層成長模式(Fault-growth model)。除此之外，斷層前緣初始深度越深、上覆地層與基盤間之摩擦角越大則P/S值越大，其中尤以斷層前緣初始深度影響P/S值最為顯著，而上覆地層彈性常數對P/S值之影響則不明顯。 Trishear model is a kinematic model. It is used to simulate the geometry of fault-related fold. The ratio of fault-propagation to slip (P/S) is one of the important parameters of Trishear model which effects geometry of fold. However, the mechanical significance of P/S of Trishear model is unclear. This study used finite difference analysis software “FLAC” to simulate fault-propagation fold. The influence of initial depth of fault tip, elastic modulus of cover material and basement-cover contact strength on the P/S is investigated. In mechanical model, the P/S of deformed section is evaluated using Displacement-Distance Method. Backward analysis using Trishear model confirm that Displacement-Distance Method is suitable for determining the P/S value of deformed section import from FLAC analysis. P/S can be evaluated and explained reasonable by divide folded zone into three areas according to the deformed characteristics. The relation between the determined P/S and different slip of deformed section can be explained by Fault-growth model. Furthermore, P/S increase with increasing depth of fault tip and resistance to slip along basement-cover contact. On the other hand, the influence of elastic modulus on P/S is unobvious.
