胡植慶2006-07-252018-06-282006-07-252018-06-282002http://ntur.lib.ntu.edu.tw//handle/246246/11804利用三維數值模式分析研究脆性變形中 常見之主應力軸交換的現象，在野外量測斷層 滑移及地震斷層機制解中常可從逆推的主應 力軸方向，觀測到上述之主應力軸交換之現 象。本研究之主要目的在於利用三維數值模式 建立主應力軸交換的力學模式，至於因間冰期 所產生之彈性回跳所造成之主應力軸交換則不在本研究範疇內。不管遠場的應力狀態，由因岩體流變性質 的改變造成應力值的改變足以更改局部的構 造應力分布而造成主應力軸交換，此主應力軸 交換並不是單純肇因於方向上的改變，而大部 分是肇因於主應力值的變化。此結果與自然界 之觀察頗為一致。雖然因應力軸方向的改變所 造成的主應力軸交換亦存在，但應力值的改變 卻是造成主應力σ1-σ2 或σ2-σ3 軸交換的主要因 素，此結果與脆性構造變形的觀察相吻合。值 得注意的是本研究的結果是在邊界條件中間 主應力值等於最大主應力值及最小主應力值和之平均（Φ值等於0.5 ）下完成。一般而言，較低的Φ值較易造成σ2/σ3 軸交換，而較高的Φ值較易造成σ1/σ2 軸交換。以地質的特性而言，主應力軸交換的主要 因素在於脆性變形的異質性（如在斷層密部的 地塹變形帶中存在著較剛性的塊體）或是斷層 及斷裂作用所造成的力學性質的非均向性（如 岩體中平行斷層走向比其他方向更剛性），我 們的研究明確顯示力學性質的非均向性易於 造成主應力軸交換。因在自然界中變形帶常隨 著時間及空間而演變，因此主應力軸交換的現象非常普遍。Using 3-D distinct-element modeling, we explore a variety of simulations to characterize the stress permutations observed in brittle tectonics. Stress inversions of fault slip data or earthquake focal mechanisms often reveal such permutations. The main aim of our study is to produce mechanically consistent 3-D models that account in a simple way for switches between principal stress axes σ1-σ2 or σ2-σ3. Other phenomena, such as those related to elastic rebound, are beyond the scope of this work. It appears that the stress changes induced by variations in rheology are large enough to modify the local tectonic behavior and produce permutations of principal stress axes, despite the simplicity of far-field boundary conditions. Rather than simple directional changes, which exist but are limited, the relative variations in principal stress values are the major cause of permutations σ1-σ2 and σ2-σ3. This is in good agreement with observations in nature, where despite permutations the orientations of axes often remain tightly clustered. Note that the most demonstrative experiments were done with a ratio Φ of 0.5, implying that σ2 is the arithmetic mean between σ1 and σ3 (low Φ ratios favor σ2/σ3 permutations, whereas high Φ ratios favor σ1/σ2 ones). In terms of geological significance, we conclude that the major causes of stress permutations are the heterogeneity of the brittle deformation (e.g., intact rock massifs between heavily faulted grabens of deformation zones)and the anisotropy of the mechanical properties that results from the fracturing and faulting (that is, a rock more resistant in the direction parallel to faults than in other directions). Our modeling effectively revealed that anisotropy in rock properties favor stress permutations. Of major importance seems to be the existence of relatively resistant zones at the tips of deformed ones, acting as channels where stress concentrates and switches occur. Because in nature such zones move in time and space, it is not surprising that stress permutations are so pervasive. In our modeling experiments, we explored a variety of compressional, extensional and strike-slip tectonic situations involving stress permutations.application/pdf196609 bytesapplication/pdfzh-TW國立臺灣大學地質科學系暨研究所數值模式脆性變形應力軸交換3-D numerical modelingbrittle tectonicsstress permutationsreporthttp://ntur.lib.ntu.edu.tw/bitstream/246246/11804/1/902116M002035.pdf