ctive tectonics in the hanging wall area of Sanyi fault: from Chentoushan to Cholan area, Central Taiwain

大安溪北岸枕頭山至卓蘭一帶河階地形發達，附近也有多條活動構造，可見此區域構造運動活躍。此區域位於三義斷層與車籠埔斷層（九二一地震斷層）兩條主要構造之間，此外，這兩條主要斷層之間仍存在有其他活動構造—如枕頭山斷層與內灣背斜。本研究分析地表地形方面主要利用40公尺DEM（Digital Elevation Model）作為基礎，配合五千分之一航空照片與野外調查，根據地形面分析，大安溪北岸階地主要分為兩大群：群組一為紅土化階地；群組二為未紅土化階地。 在群組一階地群主要有枕頭山斷層線崖可被判釋出，而在過去研究將該斷層視為1935年屯子腳地震斷層往北延伸，本研究經由地形分析與野外觀察，認為枕頭山斷層是一條逆衝為主的斷層，與右移的屯子腳地震斷層有所差異；在地下震測剖面亦顯示屯子腳地震斷層源於三義斷層下盤深處之ㄧ條正斷層，斷層面向西北傾，反之，枕頭山斷層為三義斷層上盤一分支斷層，斷層面向東南傾，因此兩條斷層無論是斷層面幾合型貌、運動特性、以及構造層位皆大為不同，只是在平面上看似線性關係。 此外，本研究利用河流剖面與震測剖面結合，可以模擬地下構造與地形演育之間的動力學模型。研究顯示在群組一階地面形成之後，三義斷層與枕頭山斷層分別位移300公尺與116公尺。而群組二階地，由航照判釋可判釋出在921地震之前曾受構造活動而變形，但確切的初始活動年代則須進一步作定年研究才可釐清。據構造演化推演結果，此區域內西半部紅土階地演育與主要受三義斷層與枕頭山斷層所主導，東半部未紅土化階地則受內灣背斜及內灣向斜所影響。In the area between Chentoushan and Cholan, Central Taiwan, a series of river terraces have been developed along the northern bank of the Taan River. There are several previously proposed active structures in this area, including the Sanyi fault, Chelungpu fault i.e., (1999 Chi-Chi earthquake fault), and Chentoushan fault. By using DEM（Digital Elevation Model), aerial photographs, and field investigations, these terraces are remapped and then categorized into two groups: lateritic group and non-lateritic group to the west and east respectively. The result of detailed mapping suggests that the Chentoushan fault (CTSF) is thrust dominant rather than strike slip dominant with a fault line scarp of 70 m in height, entirely different from that of the 1935 Tuntzuchiao fault (TTCF) which is dextral strike-slip fault with a fault scarp of only 3 m. From seismic profile, a pre-existing normal fault is considered as the subsurface extension of TTCF. On the other hand, the CTSF is a branch fault, generated from the deeper part of the Sanyi fault. Based on this three-dimensional relationship and kinematic analysis, the above-mentioned two faults are not the same fault as suggested before, but only similarly oriented on the ground surface.ntegrating geomorphic feature mapping and structural profile constructed from published seismic profiles, a kinematic model of the Sanyi fault and Chentoushan fault is presented in this study. From our modeling result, the slip of Sanyi fault has reached 300 m after the formation of the terrace Lt1. Based on the riser offset of the terraces, fault slip of 116 m can be derived along Chentoushan fault. According to aerial photo analysis, the non-lateritic terraces have been tilted by Neiwan anticline and Neiwan syscline prior to the Chi-Chi earthquake; however, age data are needed in the future study to define the ages of the terraces. On the other hand, the western lateritic terraces are deformed by Sanyi and Chentoushan faults.摘要 Ⅲbstract Ⅳ一章 緒論 1.1研究動機 1.2 研究目的 3.3研究區域概況 3.4大地構造架構 5.5區域地質 5.6地表地質相關研究 6.6.1 三義斷層 6.6.2枕頭山斷層 8.6.3 1999集集地震斷層（埤豐橋以東至卓蘭地區） 11二章 研究方法 13.1研究架構 13.1地表地形分析 14.1.1構造地形判釋 14.1.2數值高程模型與航空照片 16.1.3 階地投影 18.2 地下構造分析 18.2.1震測剖面 18.2.2構造回復 18三章 研究結果 20.1 地形面分析 20.2構造地形判釋 21.2.1枕頭山線型與野外調查結果 21.2.2下太平到西坪沿線與野外調查 29.2.3 卓蘭至內灣階地群分析與野外調查 32.3 階地投影與震測剖面資料結合 34.3.1剖面回覆 40四章 討論 44.1 枕頭山斷層 44.2 枕頭山斷層與屯子腳地震斷層之間的關聯性 45.3 枕頭山地區之地質製圖 47.4 主要構造演化過程 49.5 新構造活動與河階地形之發育 51.6 三義斷層長期滑移速率 55五章 結論 57考文獻 5