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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/5418

    Title: 九二一地震車籠埔斷層震測研究
    Authors: 陳璿臣;Hsuan-Chung Chen
    Contributors: 地球物理研究所
    Keywords: 車籠埔斷層;薄皮逆衝
    Date: 2002-01-15
    Issue Date: 2009-09-22 09:53:37 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 1999年九二一集集地震是臺灣陸上百年來最大的地震,地震規模為7.3,震源深度8公里。此次地震觸動車籠埔斷層,引起地表強烈破裂,斷層總長度為90公里,主要為逆衝斷層,斷層面向東傾斜20—50度。該斷層引發之地表垂直錯動量由南往北增加,從0.6公尺到7公尺,但在大坑以北加入左移成分,地表量到的水平位移最大到達9.6公尺,規模驚人。車籠埔斷層主要沿著地形崖界分布,近乎南北走向,但在豐原以北轉為朝東,過石岡再轉北,連過二溪以迄卓蘭為止。地質上,車籠埔斷層緊跟隨著錦水頁岩層分布,係為沿地層層面滑動之斷層。本研究以薄皮逆衝理論來解釋此次地震行為,認為錦水頁岩是一個滑脫面,車籠埔斷層即沿此一阻力不大之滑脫面上衝。為探討薄皮逆衝引發斷層帶構造變化,本研究在斷層附近,以50條以上之測線進行詳細的震測調查,得到結論如下: (1) 地表岩層走向和傾角與車籠埔斷層面之地下形貌頗吻合,且破裂線和地層走向大致平行或呈一低交角的關係。 (2) 斷層上盤,錦水頁岩及其上覆地層受到擾動破裂,而位於下盤的頭嵙山層,近乎水平進入錦水頁岩層之下而未受到擾動,此為薄皮逆衝的特性。 (3) 斷層面在接近地表傾角時較大,而在深部時漸趨和緩。 (4) 斷層在錦水頁岩層內錯動,引發與地層夾45度角之破裂,以及拌生的逆衝彎曲上昇,造成地表破裂。 (5) 斷層面大部份為沖積層所覆蓋,斷層逆衝時抬起厚沖積層,形成複雜的地表破裂。 (6) 當斷層面接近地表以圓鍬形變化時,所產生之地表變形帶較為寬廣,其上的沖積層亦被扭曲旋轉,破裂較為複雜且嚴重。 (7) 地表破裂在斷層北段較為嚴重,而在南段錯動量較小,此在震測剖面中亦可觀察到,北段上盤之地層受到擾動變形且破裂多,地面抬升及破裂是由與錦水頁岩層夾45度角的破裂向上延伸至地表所造成,其角度可達60度至80度。南段則單純屬於錦水頁岩直接逆衝至沖積層之上造成地面隆起,但抬升量不大。 (8) 大甲溪南岸整個錦水頁岩層最接近地表,致使斷層錯動破裂大量出露。但緊接著大甲溪下方又有一下凹,使得斷層行為甫變,造成東彎現象。 The 1999 Chi-Chi earthquake (Mw=7.6) occurred in center Taiwan marks the island’s largest inland seismic event in the twentieth century. It triggered an existing active fault, the Chelungpu fault. The fault was a reverse type dipping 20-50 degrees to the east and extending north-south about 90 km . The observed vertical displacements increased from the south (0.6m) to the north (7m), and the maximum horizontal displacement was 9.6m. Most of fault segments were characterized by pure thrust with minor lateral slip, but the left-lateral component of slip increased in the northern part near Shihkang. The Chelungpu fault developed along the topographic scarp running mosty in the north-south direction. However, it bended toward the northeast near Fengyuan and Shihkang, crossed the Ta-anhsi and the Tachiahsi rivers, finally stopped at the town of Cholan. In geology, the Chelungpu fault was a bed-plane fault sliding along a sedimentary layer, the Chinshui shale. The purpose of this study is to detect the underground structure in the vicinity of the Chelungpu fault by the shallow seismic reflection method. The obtained seismic sections enable us to examine the detailed faulting mechanism along the fault. The following conclusions are obtained: 1)The structures in the study area are surprisingly simple, with layers dipping regularly to the east. They are controlled by the background structural fold systems. 2)The up-dip movement of the Chelungpu fault along the Chinshui shale layer has lifted the structures above it, and at certain weak places the fractures cut through the beds with a 45o angle and thus make a 60o-70o dip, in relation to the surface. These fractures caused the ground to buckle and break. 3)The fault surface within the Chinshui shale has a dipping angle of 20o -50o to the east and 10o to the south. Some up and down undulation of this surface may exist. 4)The abnormal behavior of the fault at the northern tip can be explained as a result of the fault surface shape changes there. The structural variation of layers directed the thin-skinned thrust faulting. 5)The shallow reflection seismic method can be useful to study large-scale structures, if applied along with appropriate geologic theories.
    Appears in Collections:[地球物理研究所] 博碩士論文

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