龍門山斷裂帶南段階地變形定量研究
發(fā)布時(shí)間：2019-06-10 10:54
【摘要】：2008年龍門山斷裂帶中段突發(fā)汶川Ms8.0級大地震,時(shí)隔5年后的2013年4月20日在同一條斷裂帶的南段再次發(fā)生蘆山Ms7.0級強(qiáng)烈地震,震源相距85km。本次地震沒有產(chǎn)生連續(xù)的地表破裂帶,其發(fā)震構(gòu)造不明確。龍門山斷裂帶南段第四系沉積差,晚第四紀(jì)構(gòu)造活動(dòng)性資料零星,結(jié)論也存在差異。本文通過遙感解譯、野外地質(zhì)調(diào)查、對河流階地進(jìn)行差分GPS精確測量及詳細(xì)的研究,建立了龍門山南段隴東鎮(zhèn)至蘆山盆地鳳禾鄉(xiāng)的河流階地位相圖,通過構(gòu)造-氣候旋回估計(jì)了河流階地的廢棄年齡,并結(jié)合石油物探資料和流動(dòng)地震臺站CCP成像結(jié)果、蘆山地震余震精定位結(jié)果以及1:20萬區(qū)域地質(zhì)調(diào)查報(bào)告等多種資料,研究了龍門山斷裂帶南段的構(gòu)造活動(dòng)性,取得如下認(rèn)識:1)青衣江寶興縣隴東鎮(zhèn)至蘆山縣鳳禾鄉(xiāng)段主要發(fā)育6級河流階地,T1階地主要為堆積階地,階地結(jié)構(gòu)完整;T2-T6級階地為殘留的基座階地,河流相堆積層缺失或殘存,但基座保留較完整,上覆第四系沉積物,前緣往往基座出露。依據(jù)構(gòu)造-氣候旋回方法,推測T1至T6階地的廢棄年齡分別約8-15ka、20-27ka、50-57ka、95-105ka、130-140ka、750-770ka,建立了晚第四紀(jì)以來的地貌時(shí)間標(biāo)尺。2)晚更新世以來鹽井-五龍斷裂的逆沖活動(dòng)速率約0.7mm/a。構(gòu)造類比可知,龍門山斷裂帶南段的鹽井-五龍斷裂與龍門山斷裂帶中北段的中央斷裂結(jié)構(gòu)類似,雖然活動(dòng)性弱,但具有發(fā)生特大地震的潛能。3)大川-雙石斷裂的活動(dòng)未造成T2階地的基座發(fā)生垂直斷錯(cuò),其在T6階地形成以來也無明顯的垂向活動(dòng),未造成其上盤的中央塊體掀斜變形。4)龍門山斷裂帶南段山前背形山晚更新世以來平均縮短速率約0.015mm/a。5)蘆山地震區(qū)域構(gòu)造環(huán)境是包括大川-雙石斷裂、底板逆沖斷層、蘆山主發(fā)震斷層和蘆山反沖斷層之間的沖起構(gòu)造組成的構(gòu)造體系。主發(fā)震斷層為大川-雙石斷裂前緣的蘆山主發(fā)震斷層和蘆山反沖斷層。用GPS觀測到的本次蘆山地震的垂直斷裂的最大水平位移代表每次地震龍門山山前背形的水平縮短量,則蘆山地震的復(fù)發(fā)間隔約2000-2600a。蘆山地震的發(fā)震特點(diǎn)是震級小,頻率高。6)盡管蘆山地震和汶川地震的震源相距僅85km,時(shí)隔僅5年,汶川地震的發(fā)震斷層為中央斷裂和前山斷裂,而蘆山地震的發(fā)震斷層與龍門山南段前緣褶皺相關(guān),兩次地震為相互獨(dú)立的地震事件,因?yàn)椴辉谙嗤臄嗔焉?所以不具有相互填補(bǔ)的關(guān)系。因此,龍門山斷裂帶南段未來仍有大震危險(xiǎn)性,該區(qū)的大震發(fā)震構(gòu)造可能是以逆沖性質(zhì)為主的鹽井-五龍斷裂。南段的應(yīng)力釋放方式,也可能以龍門山山前一些規(guī)模相對較小的次級斷裂釋放,如本次蘆山地震的發(fā)震斷裂。
[Abstract]:In 2008, a Wenchuan Ms8.0 earthquake broke out in the middle part of the Longmenshan fault zone, and a strong earthquake of magnitude Ms7.0 occurred again in the southern section of the same fault zone on April 20, 2013, five years later, with a focal distance of 85 km. There is no continuous surface rupture zone in this earthquake, and its seismogenic structure is not clear. The Quaternary sedimentary data in the southern segment of Longmenshan fault zone are poor, and the late Quaternary tectonic activity data are sporadic, and the conclusions are also different. In this paper, by means of remote sensing interpretation and field geological survey, the differential GPS accurate measurement and detailed study of river terraces are carried out, and the phase diagram of river rank from Longdong Town in the southern section of Longmen Mountain to Fenghe Township in Lushan Basin is established. The abandoned age of river terraces is estimated by tectonic-climatic cycles, combined with petroleum geophysical data and CCP imaging results of mobile seismic stations, fine location results of aftershocks of Lushan earthquake and 1: 200000 regional geological survey report. The tectonic activity of the southern section of Longmenshan fault zone is studied, and the following understandings are obtained: 1) from Longdong Town to Fenghe Township Section of Baoxing County, Qingyi River, there are mainly 6 grade river terraces, T1 terraces are mainly accumulation terraces, and the terraces structure is complete; The T2-T6 terrace is a residual pedestal terraces, and the fluvial accumulation layer is missing or residual, but the pedestal is preserved completely, the Quaternary sediments are overlying, and the front edge is often exposed. According to the tectonic-climatic cycle method, it is inferred that the abandoned ages of terraces T1 to T6 are about 8: 15ka, 20 / 27ka, 50 / 57ka, 95 / 105 ka, 130 / 140ka and 750 / 770ka, respectively. The geomorphological time scale since the late Quaternary has been established. 2) the thrust activity rate of the Yanchi-Wulong fault since the late Pleistocene is about 0.7 mm / a. The structural analogy shows that the Yanchi-Wulong fault in the southern section of the Longmenshan fault zone is similar to the central fault structure in the central and northern segment of the Longmenshan fault zone, although the activity is weak. However, it has the potential to occur a large earthquake. 3) the activity of the Dachuan-Shuangshi fault does not cause the vertical fault of the base of the T2 terraces, and there is no obvious vertical activity since the formation of the T6 terraces. There is no oblique deformation of the central block in the upper plate. 4) the average shortening rate of the Piedmont back mountain in the southern segment of the Longmenshan fault zone since the late Pleistocene is about 0.015mm/a.5) the regional tectonic environment of the Lushan earthquake includes the Dachuan-bimolith fault. The structural system composed of bottom plate thrust fault, Lushan main seismic fault and Lushan recoil fault. The main seismic faults are Lushan main seismic fault and Lushan recoil fault at the leading edge of Dachuan-Shuangshi fault. The maximum horizontal displacement of the vertical fault of the Lushan earthquake observed by GPS represents the horizontal shortening of the front shape of Longmen Mountain in each earthquake, then the recurrence interval of the Lushan earthquake is about 2000 脳 2600a. The earthquake of Lushan earthquake is characterized by small magnitude and high frequency. 6) although the source distance between the Lushan earthquake and the Wenchuan earthquake is only 85km and the interval is only five years, the seismic fault of the Wenchuan earthquake is the central fault and the Qianshan fault. The seismic fault of Lushan earthquake is related to the front fold of the southern segment of Longmenshan section. The two earthquakes are independent seismic events, because they are not on the same fault, so they do not have the relationship of filling each other. Therefore, there is still the risk of large earthquakes in the southern section of Longmenshan fault zone in the future, and the seismic structure in this area may be the Yanchi-Wulong fault, which is dominated by thrust. The mode of stress release in the southern section may also be the release of some relatively small secondary faults in front of Longmen Mountain, such as the seismic fault of the Lushan earthquake.
【學(xué)位授予單位】：中國地震局地震預(yù)測研究所
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P315.2
本文編號：2496412
[Abstract]:In 2008, a Wenchuan Ms8.0 earthquake broke out in the middle part of the Longmenshan fault zone, and a strong earthquake of magnitude Ms7.0 occurred again in the southern section of the same fault zone on April 20, 2013, five years later, with a focal distance of 85 km. There is no continuous surface rupture zone in this earthquake, and its seismogenic structure is not clear. The Quaternary sedimentary data in the southern segment of Longmenshan fault zone are poor, and the late Quaternary tectonic activity data are sporadic, and the conclusions are also different. In this paper, by means of remote sensing interpretation and field geological survey, the differential GPS accurate measurement and detailed study of river terraces are carried out, and the phase diagram of river rank from Longdong Town in the southern section of Longmen Mountain to Fenghe Township in Lushan Basin is established. The abandoned age of river terraces is estimated by tectonic-climatic cycles, combined with petroleum geophysical data and CCP imaging results of mobile seismic stations, fine location results of aftershocks of Lushan earthquake and 1: 200000 regional geological survey report. The tectonic activity of the southern section of Longmenshan fault zone is studied, and the following understandings are obtained: 1) from Longdong Town to Fenghe Township Section of Baoxing County, Qingyi River, there are mainly 6 grade river terraces, T1 terraces are mainly accumulation terraces, and the terraces structure is complete; The T2-T6 terrace is a residual pedestal terraces, and the fluvial accumulation layer is missing or residual, but the pedestal is preserved completely, the Quaternary sediments are overlying, and the front edge is often exposed. According to the tectonic-climatic cycle method, it is inferred that the abandoned ages of terraces T1 to T6 are about 8: 15ka, 20 / 27ka, 50 / 57ka, 95 / 105 ka, 130 / 140ka and 750 / 770ka, respectively. The geomorphological time scale since the late Quaternary has been established. 2) the thrust activity rate of the Yanchi-Wulong fault since the late Pleistocene is about 0.7 mm / a. The structural analogy shows that the Yanchi-Wulong fault in the southern section of the Longmenshan fault zone is similar to the central fault structure in the central and northern segment of the Longmenshan fault zone, although the activity is weak. However, it has the potential to occur a large earthquake. 3) the activity of the Dachuan-Shuangshi fault does not cause the vertical fault of the base of the T2 terraces, and there is no obvious vertical activity since the formation of the T6 terraces. There is no oblique deformation of the central block in the upper plate. 4) the average shortening rate of the Piedmont back mountain in the southern segment of the Longmenshan fault zone since the late Pleistocene is about 0.015mm/a.5) the regional tectonic environment of the Lushan earthquake includes the Dachuan-bimolith fault. The structural system composed of bottom plate thrust fault, Lushan main seismic fault and Lushan recoil fault. The main seismic faults are Lushan main seismic fault and Lushan recoil fault at the leading edge of Dachuan-Shuangshi fault. The maximum horizontal displacement of the vertical fault of the Lushan earthquake observed by GPS represents the horizontal shortening of the front shape of Longmen Mountain in each earthquake, then the recurrence interval of the Lushan earthquake is about 2000 脳 2600a. The earthquake of Lushan earthquake is characterized by small magnitude and high frequency. 6) although the source distance between the Lushan earthquake and the Wenchuan earthquake is only 85km and the interval is only five years, the seismic fault of the Wenchuan earthquake is the central fault and the Qianshan fault. The seismic fault of Lushan earthquake is related to the front fold of the southern segment of Longmenshan section. The two earthquakes are independent seismic events, because they are not on the same fault, so they do not have the relationship of filling each other. Therefore, there is still the risk of large earthquakes in the southern section of Longmenshan fault zone in the future, and the seismic structure in this area may be the Yanchi-Wulong fault, which is dominated by thrust. The mode of stress release in the southern section may also be the release of some relatively small secondary faults in front of Longmen Mountain, such as the seismic fault of the Lushan earthquake.
【學(xué)位授予單位】：中國地震局地震預(yù)測研究所
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P315.2
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