蘭陽平原以南山麓地區斷層擦痕之古應力分析研究
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2015
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蘭陽平原以南的山麓地區由早期的造山擠壓轉變為現今以西北-東南向拉張為主的應力場，顯示其地體構造上相對較為複雜，因此本研究主要目的在於了解蘭陽平原以南的山麓地區的脆性構造特性與應力場演化史。透過觀察清水溪、寒溪與南方澳野外露頭之構造特性，量測地表斷層擦痕並利用擦痕截切關係進行分期，以獲得各期脆性構造特性與順序以及相對應的斷層擦痕資料。
斷層擦痕數據使用MIM程式與T-Tecto3.0軟體進行古應力反演，解算各區域不同期的獨立應力場，藉由擦痕的截切關係與交差比對應力場後，可將全部區域之應力場分為五期。N+1期為東北-西南向拉張的正斷層應力場；N+2期為東北-西南向拉張，西北-東南向擠壓之走向滑移應力場；N+3期為為西北-東南向拉張，東北¬西南向擠壓之走向滑移應力場；N+4期為西北-東南向拉張的正斷層應力場；N+5期為西北-東南向拉張，東北¬西南向擠壓之走向滑移應力場。
本研究的N+1期之正斷層在比較山脈的同造山伸張模式後推測最早期的正斷層可能為受重力作用造成的山脈塌陷。利用本研究的五期應力場之最小主應力軸方向比對區域內的主軸應變率後，發現N+3期至N+5期應力場與GPS主軸應變率比較有一致的趨勢，這代表N+3~N+5期應力場較趨近於現今所觀測到的結果且應力場於空間分布有旋轉的現象。
In southern foothills area of the Ilan Plain, stress field changes from the compression of mountain building to NW-SE extension of the Okinawa trough, indicating tectonics is relatively complex. The aim of this study is to understand the characteristics of brittle structures and the evolution of stress field in south foothills of Ilan Plain. By observing the structure characteristics, measuring fault slip data and classifying the different stages via cross-cutting relationship in the Chingshuixi, Hanxi and Nanangao outcrops, aspects of brittle structures, development sequence and corresponding fault slip can be established. This study used the Multiple Inversion Method and T-Tecto 3.0 program for stress inversion analysis of fault slip data to gather the independent stress fields of different phases. Based on cross-cutting relation and comparison with stress fields, 5 phases of stress field can be classified. N+1 phase is characterized as normal faulting stress field with the northeast-southwest extension. N+2 phase is consisted of strike-slip faulting stress regime with northeast-southwest extension and northwest-southeast compression. N+3 phase is strike-slip faulting stress regime with northwest-southeast extension and southwest-northeast compression. N+4 phase is characterized as normal faulting stress regime with northwest - southeast extension. N+5 is considered as strike-slip faulting stress regime with northwest-southeast extension and northeast-southwest compression. Comparing the aspects of N+1normal faulting with the characterization of synorogenic extension model, it is speculated that the earliest normal faulting may be caused by mountains extension due to the gravity influence. Correlating the horizontal minimum stress orientations of 5-phase stress regimes to the principal strain rate calculated from GSP data, stress field between N+3 and N+5 is more consistent with strain rate pattern. The results suggest stress field of N+3-N+5 phases is more closed the current stress state. Also, the stress field has spatial rotation phenomena.
In southern foothills area of the Ilan Plain, stress field changes from the compression of mountain building to NW-SE extension of the Okinawa trough, indicating tectonics is relatively complex. The aim of this study is to understand the characteristics of brittle structures and the evolution of stress field in south foothills of Ilan Plain. By observing the structure characteristics, measuring fault slip data and classifying the different stages via cross-cutting relationship in the Chingshuixi, Hanxi and Nanangao outcrops, aspects of brittle structures, development sequence and corresponding fault slip can be established. This study used the Multiple Inversion Method and T-Tecto 3.0 program for stress inversion analysis of fault slip data to gather the independent stress fields of different phases. Based on cross-cutting relation and comparison with stress fields, 5 phases of stress field can be classified. N+1 phase is characterized as normal faulting stress field with the northeast-southwest extension. N+2 phase is consisted of strike-slip faulting stress regime with northeast-southwest extension and northwest-southeast compression. N+3 phase is strike-slip faulting stress regime with northwest-southeast extension and southwest-northeast compression. N+4 phase is characterized as normal faulting stress regime with northwest - southeast extension. N+5 is considered as strike-slip faulting stress regime with northwest-southeast extension and northeast-southwest compression. Comparing the aspects of N+1normal faulting with the characterization of synorogenic extension model, it is speculated that the earliest normal faulting may be caused by mountains extension due to the gravity influence. Correlating the horizontal minimum stress orientations of 5-phase stress regimes to the principal strain rate calculated from GSP data, stress field between N+3 and N+5 is more consistent with strain rate pattern. The results suggest stress field of N+3-N+5 phases is more closed the current stress state. Also, the stress field has spatial rotation phenomena.
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蘭陽平原, 斷層擦痕, 古應力分析, Ilan plain, fault slip, paleostress analysis