瑞穗断层长期滑移速率.DOC

瑞穗斷層長期滑移速率 本研究於先前開挖之安定橋1號與2號槽溝南側再開挖3號槽溝，本槽溝位址較先前開挖的地勢為低，因此有利於挖掘出更老的地震事件。(圖1)槽溝中地層以礫石為主，含有透鏡狀砂泥層，為沖積扇河道與沙洲的環境(圖2、3)。剖面中一共出現三個斷層面，F3斷層位態為N24°E、20-35°E，截切G1礫石層而被O耕作土覆蓋，南牆SG3垂直錯移量可達約28公分，推斷此為最近的一次事件(1951年地震)。F2斷層位態N24°E、24-30°E ，截切SG1砂礫層而被G2礫石層覆蓋，南牆SG1垂直錯移量可達約40公分。F1斷層僅於南牆出現，位於F3斷層上盤，位態N24°E、25°E，切穿SG1砂礫層，斷層兩側SG3砂礫層的垂直錯移量約為75公分。根據構造回復的結果所估算的斷層垂直變動量，F3斷層約為45公分，F2斷層約為52公分，而F1斷層約76公分。根據地層的年代，F1與F2斷層所造成的古地震時間應晚於550-630年前，而最近一次的斷層活動F3應為1951年地震事件所造成。 圖1、安定橋3號槽溝位置圖。 圖2、安定橋3號槽溝北牆剖面。 圖3、安定橋3號槽溝南牆剖面。  Long-term slip rate of Juisui fault This study we trench the Anting bridge no. 3 site in the more south area of the fault scarp that we trenched the no. 1 and no. 2 trenches. This site is lower in relief and it has the advantage of trenching the older paleoseismic events.(figure.1) The sedimentary units in this trench profile is mainly constituted by gravel, and sometimes contains lenticular sand/mud layers. It characterizes the channel and bar environment of alluvial fan system.(figure.2, 3) There are 3 faults in the profile. Attitude of F3 fault is N24°E, 20-35°E, and it cuts through G1 gravel bed and is overlay by O soil. The vertical displacement estimated from the SG3 unit is about 28 cm, and we infer this event as the recent one (1951 coseismic event). F2 fault strikes in N24°E, dips 24-30° to the east, and it cuts through SG1 unit and is overlay by G2 unit. The vertical displacement estimated from the SG1 unit is about 40 cm. F1 fault cutting through the hanging wall of F3 only present in the south wall. Its attitude is N24°E, 25°E, and it cuts through SG1 unit. The vertical displacement estimated from the SG3 unit is about 75 cm. Estimating the coseismic vertical displacement by restoration of deformed bed, we give the value for each event is: F3 is about 45 cm, F2 is about 52 cm, and F1 is about 76 cm. Based on the dated age of the sedimentary unit, we suggest the timing of F1 and F2 events are later than 550-630 yr BP. And the latest event caused by F3 is 1951 cose