以反射震測法研究九芎坑斷層及其附近構造; Investigating the Chiuhsiungkeng Fault and Nearby Structures by the Seismic Reflection Method

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題名:	以反射震測法研究九芎坑斷層及其附近構造;Investigating the Chiuhsiungkeng Fault and Nearby Structures by the Seismic Reflection Method
作者:	翁子偉;Zi-Wei Oung
貢獻者:	地球物理研究所
關鍵詞:	梅山斷層;九芎坑斷層;反射震測;Chiuhsiungkeng fault;reflection seismic;Meishan fault
日期:	2005-04-15
上傳時間:	2009-09-22 09:55:19 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	鑑於九二一集集大地震為台灣帶來百年最慘重的災情，圍繞北港基盤高區的半環狀孕震帶需要密切關注。九芎坑斷層位於此區的逆衝斷層帶前緣，伴隨著地殼變動，具明顯的逆衝斷層形態，亦與梅山地震斷層(M=7.1)相交，可能誘發在人口密集地區之地震，屬於較為敏感重要的地震潛能區。本研究利用淺層反射震測法調查九芎坑斷層，經配合深部震測剖面、地形及地表地質，探討九芎坑斷層地下構造，及其與鄰近構造間的關係。研究結果發現九芎坑斷層特性如下: 1. 九芎坑斷層僅介於古坑斷層及竹崎斷層之間，受地下南北向斷坡及斷坪構造之影響，斷層錯動量由北往南遞減，而斷層傾角由北往南漸增，依據不同特質可分為北段(古坑至大湖口)、中段(梅山至南勢坑)及南段(南勢坑至竹崎)。 2. 北段為層間斷層，傾角30度，將卓蘭層滑移約4公里至出露地表。該段斷層滑動逆衝之形態與車籠埔斷層相當。 3. 中段進入小梅背斜構造區，斷層切穿地層以33度角逆衝向上，滑距約銳減為400公尺，斷層下盤為小梅背斜之東翼，內偶見梅山斷層橫移錯動之痕跡。 4. 南段地層漸趨於水平，斷層以36度角從中穿過，錯動量只剩90公尺以內。斷層下盤之地層明顯受壓而扭曲，造成溪湖向斜及J背斜，協助吸收板塊運動作用力，使得九芎坑斷層受壓舒緩而停止於牛稠溪，不再繼續往南發展。 5. 位於大湖口溪之「梅山古脊」及三疊溪之「中軸線」為分段之邊界，此為北傾面上之斷坡轉折或構造高區，發生明顯的分段作用，使得斷層錯動行為由北而南持續改變，形成「重北輕南」之極具特色的九芎坑斷層。 Recently due to the threat of faulting as occurred in the 1999 Chi-Chi earthquake (MW=7.6), the active fault studies on the Taiwan island have been largely emphasized. The Chiuhsiungkeng fault is located in the seismogenic zone along the east margin of the Peikang High. The 1906 Meishan earthquake fault (M=7.1) happened here. High earthquake potential in this populated region has always been a great issue. In this study, we used the shallow reflection seismic method to investigate the Chiuhsiungkeng fault and its nearby structures. The following conclusions are obtained : (1) The Chiuhsiungkeng fault is flanked by two tear faults: the Gukeng fault at the north and the Chuchi fault at the south. The fault offsets gradually reduce toward the south, and on the contrary, the fault dip-angles increase. This 15km fault can be divided into three parts: the northern part (Gukeng-Tahuko), the middle part (Meishan-Nansukeng), and the southern part (Nansukeng-Chuchi). (2) At the northern part, it is a bedding-parallel fault with a dip-angle of 30 degrees. The Cholan Formation on the hanging wall may have slipped for about 4.5 km and exposed at the surface by the fault. (3) At the middle part, the fault cuts structural layers with an angle of 33 degrees, and the slippage distance decreases rapidly to about 400m. A Meishan range is proposed as a barrier to interfere the fault slippage from the north to the south. (4) At the southern part, the fault becomes a small facture penetrating flat layers with an angle of 36 degrees. The fault offsets are reduced to being smaller than 50m. The fault could be terminated by the Chuchi tear fault at its southern end. (5) The Meishan range and the Central line are two significant ramps developing in the big northward dipping slope. They play the key roles which control the fault behaviors to be in a ‘heavy-slipping north and slight-moving south’ pattern of the Chiuhsiungkeng fault.
顯示於類別:	[地球物理研究所] 博碩士論文

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