以反射震測法研究六甲斷層及其附近構造

木屐寮斷層及六甲斷層都在台灣西南部的嘉南地震帶內，南北接續，位置恰好在平原與麓山帶交界處，屬於外麓山帶西緣中、最南端的斷層，地形上有明顯的北北東走向之線形，從八掌溪以南延伸至曾文溪以北。斷層東側有系列西傾之地層，但在地表上缺乏明顯的地層錯動證據。雖然此二南北接續的斷層之間有所轉折，但就地形面來看，木屐寮斷層與六甲斷層相似，斷層兩側均呈現相當明顯的高低落差，斷層附近出露的地層特性也都相同，同時研究區域之布蓋重力圖顯示木屐寮-六甲斷層之東側，等重力線密集增加，代表有構造急遽上升，更重要的，木屐寮斷層與六甲斷層皆呈現線性排列，其間雖有些微轉折，但地下構造變化均勻，因此，應可視為相同斷層之二分段。木屐寮-六甲斷層分別受關子嶺背斜、牛山背斜影響，形成地層彎拱上抬及垂直軸面擠壓特性。本研究利用反射震測仔細測繪六甲斷層的地下構造形貌，從密集分布的測線剖面，發現該斷層具有牛山背斜西翼的向斜軸之軸面擠壓的特性，兩側地層顯現彎曲上抬，但看不出有明顯的錯移斷距，在牛山背斜彎拱愈大處，其西側之六甲斷層軸部彎曲就愈劇烈，造成「褶皺調適的軸部破壞」。六甲斷層西側與東側地層傾角的差異，在在顯示出斷層面上持續受到擠壓與彎曲之應力，而東側之地層變形更是高度應力累積之結果，具有發展成活動斷層之可能性。從地層彎曲度，可將六甲斷層分為南北二分段，愈往南構造越趨和緩，終至消失，其斷層活動性也相對減小。雖然未發現六甲斷層錯動的證據，但整體地層壓縮彎曲的程度，已具有活動構造之特徵，六甲斷層之活動性不宜低估。

關鍵字

六甲斷層；反射震測法；牛山背斜

並列摘要

The Liuchia fault lies along the western border of the southwestern Taiwan’s foothill. The fault lines up with the Muchiliao fault and can be combined as the Muchiliao-Liuchia fault. Both faults are ranked as ‘suspected’ faults in the Central Geologic Survey’s active fault list. This research uses the seismic reflection method to study the Liuchia fault including the location and the configuration of the fault. The possible mechanism of the fault evolution is also under investigation. The Liuchia fault is formed as a result of the tectonic pushing developed with the Newshan anticline. The Newshan anticline is the main structural rise of the area and the Liuchia fault is just at the bending axis of its western wing. Basing on bending levels of the structural layers on both sides, the fault can be divided into the northern and southern parts. At the northern part, the fault suffers greater distortions, but does not have obvious fault breakages. At the southern part, the layer bending becomes gentle and finally ceases the development at the southern end. Although obvious fault offsets are not found, the structure layers have been bent up to 80 degrees. It proves that the fault behaves as an ‘active’ structure, and its potential to become an active fault should not be under-estimated.

並列關鍵字

Liuchia fault ； Newshan anticline ； Seismic Reflection Method

參考文獻

陳郁文，2006. 以反射震測法研究處口斷層及其附近構造，陀利中央大學地球物理研究所碩士論文，台灣中壢，76頁。

王宏霖，2006. 以反射震震測法研究木屐寮斷層及其附近構造，國立中央大學地球物理研究所碩士論文，台灣中壢，118頁

Baker, G. S. , D.W. Steeples., C.S., M. P. and R.P. (2001) Near-surface imaging using coincident seismic and GPR data. Geophys. Res. Lett. , 28, NO.4, PAGES 627-630.

Hung, J.H. , Wiltschko D.V., Lin H.C., Hickmman J.B., Fang O., and Bock Y., 1999. Structure and Motion of the Southwestern Taiwan Fold and Thrust Belt . TAO, 10, 543-568.

Luigi, I. and Aldo Z. (2003) High-resolution seismic tomography across the 1980 (Ms 6.9) southern Italy earthquake fault scarp. Geophys. Res. Lett. , 30, NO.10,1494, doi:10.1029/2003GL017077.

國際替代計量

以反射震測法研究六甲斷層及其附近構造

未授權

主題瀏覽