本文選題：龍泉山斷裂帶　切入點：構造特征　出處：《成都理工大學》2015年碩士論文

【摘要】：2008年汶川地之后,四川盆地中活動性斷裂的研究及地震危害性評價引起了廣泛關注。而龍泉山斷裂帶距離成都市區(qū)不足20km,所經地區(qū)經濟發(fā)達,人口稠密,是重要的農業(yè)和工業(yè)基地,因此其活動性評價尤為重要。龍泉山斷裂帶位于四川盆地西部,南起樂山,北至中江縣,是成都市區(qū)內的一條活動性斷裂帶。區(qū)域上屬于揚子板塊,是次級構造單元川西盆地與川中隆起的界線,總體走向呈NE20°~30°,總長大于230km。龍泉山斷裂帶主要由分布于龍泉山背斜東西兩翼的東坡斷裂和西坡斷裂組成。其中西坡斷裂由一系列傾向南東的逆沖斷層組成,龍泉山背斜發(fā)育在龍泉山西緣逆斷裂帶的上盤,呈西陡東緩的斷裂擴展背斜展布;東坡斷裂為傾向北西逆沖斷裂,形成了與龍門山構造帶向反的構造格局。通過對龍泉山斷裂帶的地表地形調查可知龍泉山斷裂帶整體呈西邊陡而東邊緩,且西坡斷裂的規(guī)模和斷距都明顯大于東坡斷裂,由此認為西坡斷裂是致使龍泉山背斜形成的主干斷裂,而東坡斷裂則是規(guī)模較大的反向斷層。且西坡斷裂局部具有晚更新世弱活動性,曾經發(fā)生過ML=5.5級左右的地震;東坡斷裂活動性較弱,未發(fā)現(xiàn)可以證明第四紀以來活動性的地貌。通過對龍泉山斷裂帶的地震剖面解釋發(fā)現(xiàn)龍泉山斷裂帶向上突破地表,向下斷距逐漸減小,傾角變緩,直至消失于雷口坡組膏鹽層中。且深部構造反映的褶皺形態(tài)表明,龍泉山背斜是受深部滑脫面控制的脫頂構造,龍泉山背斜形成與龍泉山斷裂有密切的成因聯(lián)系。雖然前人對龍泉山斷裂帶做了大量研究,但是對于龍泉山斷裂帶的形成機制還沒有達成統(tǒng)一認識。構造物理模擬實驗是研究地質構造形成機制與演化的重要手段,由此本文通過構造物理模擬實驗發(fā)現(xiàn)龍泉山斷裂帶與龍門山構造帶應屬于同一個構造系統(tǒng)。龍泉山斷裂帶是其構造前緣部分,與由龍門山推覆帶傳遞過來的推擠力息息相關。實驗結果顯示龍泉山斷裂帶已經過了活動最強烈的成長期,進入了相對穩(wěn)定的定型期,與龍門山構造帶相比較,龍泉山斷裂帶的變形程度和斷裂活動性都遠遠低于龍門山構造帶,由此推測龍泉山斷裂帶不太可能發(fā)生ML=6級以上強震。龍泉山及周邊地震活動的空間分布不均勻,斷裂活動對龍泉山斷裂周邊的地震孕發(fā)具有一定的控制作用。歷史上研究區(qū)曾多次中小地震,但破壞性地震僅發(fā)生一次,表明龍泉山斷裂是具有發(fā)生中強地震能力的地震構造。然而在龍泉山斷裂帶地表處形成了斷裂傳播褶皺,使得斷裂的滑動量大部分由傳播褶皺吸收[1],發(fā)生大地震的可能性很小,結合構造模擬實驗結果認為潛在地震能力在5.5級左右。但該斷裂帶為一區(qū)域性斷裂,做為新構造單元劃分的邊界之一,并且也具備發(fā)生中強地震的構造條件,所以認為其最大發(fā)震能力不超過6.5級。
[Abstract]:After Wenchuan in 2008, the study of active faults in Sichuan Basin and the evaluation of earthquake hazard have aroused widespread concern. The Longquanshan fault zone is less than 20km from Chengdu, and the region is economically developed and densely populated. The Longquanshan fault zone is located in the western part of the Sichuan basin, with Leshan in the south and Zhongjiang County in the north. It is an active fault zone in Chengdu. It belongs to the Yangtze plate. Is the boundary between the West Sichuan Basin and the Central Sichuan uplift. The overall strike is NE20 擄30 擄and the total length is more than 230 km. The Longquanshan fault zone is mainly composed of the east slope faults and the west slope faults distributed on the east and west flanks of the Longquanshan anticline, in which the west slope faults consist of a series of thrust faults inclined to the south and east. The Longquanshan anticline developed on the upper side of the reverse fault zone in the Shanxi margin of Longquan, where the spreading anticline is distributed in the west, steepness and east, the east slope fault is inclined to the north west thrust fault, the east slope is inclined to the north west thrust fault, Through the investigation of the surface topography of the Longquanshan fault zone, it can be seen that the Longquanshan fault zone is steep in the west and gentle in the east, and the scale and distance of the fault in the west slope are obviously larger than those in the east slope. It is concluded that the Xipo fault is the main fault causing the Longquanshan anticline to form, while the Dongpo fault is a large-scale reverse fault. The Xipo fault has a weak activity in the late Pleistocene and has occurred earthquakes with magnitude ML=5.5 or so. The activity of the Dongpo fault is weak, and no geomorphology can be found to prove the activity since Quaternary. Through the seismic profile interpretation of the Longquanshan fault zone, it is found that the Longquanshan fault zone breaks through the surface upward, the downward fault distance decreases gradually, and the dip angle becomes slower. The fold pattern reflected by the deep structure indicates that the Longquanshan anticline is a topping structure controlled by the deep slip surface. The formation of Longquanshan anticline is closely related to the Longquanshan fault. However, the formation mechanism of the Longquanshan fault zone has not yet reached a unified understanding. The tectonic physical simulation experiment is an important means to study the formation mechanism and evolution of geological structures. It is found in this paper that the Longquanshan fault zone belongs to the same structural system as the Longmenshan tectonic belt, and the Longquanshan fault zone is the leading part of the structure. The experimental results show that the Longquanshan fault zone has passed through the strongest active growth period and entered a relatively stable period, compared with the Longmenshan tectonic belt. The deformation degree and fault activity of the Longquanshan fault zone are far lower than that of the Longmenshan tectonic belt, so it is inferred that strong earthquakes of magnitude ML=6 are unlikely to occur in the Longquanshan fault zone. The spatial distribution of seismic activities in Longquanshan and its surrounding areas is not uniform. The fault activity has a certain controlling effect on the occurrence of earthquakes around the Longquanshan fault. In the history of the study area, there were many small and medium earthquakes, but only one destructive earthquake occurred. It shows that Longquanshan fault is an earthquake structure with moderate earthquake potential. However, the fault propagation fold is formed on the surface of Longquanshan fault zone, which makes the slip of fault absorbed mostly by propagating fold [1], and the possibility of large earthquake is very small. Combined with the result of structural simulation experiment, the potential seismic capacity is about 5.5. However, the fault zone is a regional fault, which is one of the boundaries of the new tectonic units, and also has the structural conditions for the occurrence of moderate strong earthquakes. Therefore, its maximum earthquake generating capacity is not more than 6.5 magnitude.
【學位授予單位】：成都理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：P315.2

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