【作者】 刘玉法；

【导师】 黄润秋； 裴向军；

【作者基本信息】 成都理工大学 ， 地质工程， 2018， 博士

【摘要】 越来越多的研究表明,单条断层的强震活动与其所处的断裂系统存在明显的大震响应关系,因此,单条活动断层的地震危险性研究不仅要考虑断层本身的活动特点,更应将其放置于断裂系统中从总体上把握。而活动块体边界断裂是大震的主要发震构造,在我国,块体边界断裂控制了全部的8级以上及约80%的7级以上强震,在1973年以前的150多年里,鲜水河-安宁河断裂系统共发生10次7级以上强震,现今随时都有发生强震的可能。南河断裂正是处于川滇块体东边界鲜水河-安宁河断裂系统的一条活动断裂,长期以来由于无强震记录而被忽略,尚未开展系统性研究,那么南河断裂的空间展布如何?晚第四纪活动强度如何?南河断裂与安宁河断裂的大震如何响应?由南河断裂参与的川滇块体东边界的区域地球动力学模型该如何构建?南河断裂未来的强震危险性如何?未来在强震作用下的最大位错、地质灾害又如何分布?这些问题的解决不仅可以为南河断裂的地震危险性评价提供定量资料,对川西地区的灾害防治提供指导,而且有助于理解川滇块体东边界断裂系的破裂行为、滑动行为及大震响应模式。鉴于目前地震短临预报存在具体的科学难题,建立活动断裂的地震危险性到强震引起的灾害预测关联显得尤为必要。本论文在卫星遥感影像解译的基础上,通过详细的野外地质、地貌调查,确定了南河断裂的空间展布与活动性;通过对断错微地貌的精细测量与被错断地貌年龄测试,确定了南河断裂的晚第四纪滑动速率。通过对断裂的探槽研究,确定了南河断裂的晚全新世古地震序列与最大发震能力,并在此基础上讨论了南河断裂与安宁河断裂的大震响应模式,构建了川滇块体东边界的区域地球动力学模型。并在总结以往震例最大位错和砂土液化分布规律的基础上,提出了未来在强震作用下,南河断裂的最大位错分布范围与砂土液化的风险性分布范围。论文主要取得了以下认识:1)查明了南河断裂的空间展布。南河断裂位于川滇菱形块体东边界,断裂北起于安宁河谷与安宁河断裂相交,总体走向N45°E,穿越冕宁盆地,过芫根地、河里乡、西昌卫星发射中心、东方村,向南西延伸,在尔马嘎村一带线性消失,总体长度约70km。断裂结构在北段分为南北两支,北支隐伏通过冕宁县城,南支分布于冕宁盆地南麓。两条分支断层北端与安宁河断裂相交,南端在芫根地一带交汇。继续向南西延伸,过河里乡、卫星发射中心,在东方村一带形成左旋右阶结构,表现为地貌上的线性挤压脊,而探槽揭露断裂在南段形成左旋左阶结构,表明南河断裂为以走滑性质为主,同时存在张剪破裂与压剪破裂样式。2)查明了南河断裂的活动性、滑动速率及古地震序列。南河断裂为一条全新世活动的断裂,断裂以左旋走滑为主,兼具少量逆冲性质,本论文共揭露了三次地震事件,分别距今为468a—118a、891a—468a和5690a-6400 a。古地震事件反映了断裂发生过全段破通性事件,断裂活动可能表现为丛集特征。断错地貌表现为断层陡坎、断层槽谷、断层垭口、堰塞塘、断错水系与洪积扇体、断尾沟等活动地貌特征。断面擦痕揭露水平与垂直分量约为4:1,断裂晚全新世以来的水平滑动速率约为2.6±0.2mm/a,垂直约为0.6±0.1mm/a。3)提出了南河断裂与安宁河断裂的大震响应模式为级联破裂和大震触发。古地震表明南河断裂与安宁河断裂产生两次级联破裂事件,分别为Event(5690a-6400aBP)和(118a-468aBP),最新一次级联破裂的历史地震可能为1786年康定7?级地震;南河断裂上的事件Event(468a-891aBP)可能是对安宁河断裂紫马垮—野鸡洞段地震事件Event(1030a-1050aBP)的响应,二者最短的时间间隔为39a。同时说明南河断裂即可以与安宁河断裂发生级联破裂,也可以独立成为发震构造。历史记录中的1480年越西地震的发震构造可能为普雄河断裂。4)提出最大同震位错一般位于地表破裂的中后段,地表最大位错的主控因素为断面的构造样式,局部的岩性差异为次要控制因素。倒转逆断层、顺层断面及岩性差异是形成最大同震位错的有利地质条件。5)分析了南河断裂的强震危险性。通过南河断裂所处的构造位置、断层规模及最新一次地震事件的地表位错值,综合确定认为南河断裂的最大发震能力为7.5级。估算的南河断裂的同震最大水平位错为3.1±0.43m,分布于纸厂河沟—东方村一带的可能性最大。6)构建了南河断裂参与的川滇块体东边界区域地球动力学模型。南河断裂分解了来自安宁河断裂约2.6mm/a的水平滑动速率,较合理的解释了安宁河断裂与则木河断裂的滑动亏损问题,本结论支持GPS反演结果,支持川滇块体东边界的非连续变形模式。7)提出了砂土液化风险性评估的构造地质学方法,能较快速的判定震后砂土液化的分布范围,对防灾、救灾有一定的指导作用。利用该方法得到南河断裂设定7.5级地震的液化的高风险区主要分布于冕宁县城一带、惠安乡、大桥水库、河里乡以及林里乡-泸沽镇一带,这些地区可能会发生砾石土液化,尤其是在冕宁县城一带的南河河谷;中等液化风险区主要分布于彝海乡、礼州-西昌一带;液化低风险区主要位于Ⅵ度区,如拖乌乡、黄联关镇一带。更多还原

【Abstract】 More and more studies have shown that the strong earthquake activity of the single fault is closely related to the large earthquake response in the fault system.Therefore,the study of the seismic risk of single active fault should not only consider the characteristics of the fault itself,but also hold it in the fault system as a whole.However,the boundary faults of active block are the main sites where many major earthquakes occur frequently,the boundary faults have generated all major earthquake events with magnitude of 8 and higher and earthquakes with magnitude more than 7 of 80% in China,the Xianshuihe-Anninghe fault system had generated 10 major earthquakes with magnitude exceed 7 in the past 150 years prior to 1973,presumably,large seismic events would occur at any time.The Nanhe fault located at eastern boundary of Scihuan-Yunnan block is an active fault belonged to the Xianshuihe-Anninghe fault system with a low slip rate,it has been neglected for a long time due to lack of strong earthquake records,and it has not been systematically studied as well.Therefore,what about the spatial distribution feature of the Nanhe fault? How about the activity intensity of the fault in the late quaternary? How to response the major earthquake where generated between Anninghe fault and Nanhe fault? How to build regional dynamic model that the Nanhe fault has engaged in? How should we consider the future strong earthquake risk of Nanhe fault? What is the maximum dislocation in the future under strong earthquake and how to distribute it? And how is the geological hazard distributed? The study of above questions will contribute greatly to the assessment of seismic risk of the Nanhe fault,and provide guidance for disaster prevention and mitigation in the region,in particular,it will throw light on the understanding of rupture behavior,slip behavior and large earthquake response pattern among the Xianshuihe-Anninghe+Daliangshan-Zemuhe fault system.In view of the fact that there are specific scientific problems in earthquake short-term and temporary prediction,it is particularly necessary to establish the correlation between the earthquake risk of the active fault and the prediction of the disaster caused by the strong earthquake.Based on interpretation of high-resolution satellite images,combined with field geological and geomorphological investigation,we determined the spatial geometry of the Nanne fault and its activity.We also determined the slip rate in late quaternary using precise topographic measurements on faulted landform and dating of displaced landform surface.Through the study of the trenches,the late Holocene paleoearthquake sequence and maximum seismogenic ability of the Nanhe fault are determined,and on this basis,the large earthquake response model of the Nanhe fault and Anning River fault is discussed,and the regional geodynamic model of the east boundary of the Sichuan-Yunnan block is constructed.On the basis of the previous maximum dislocation and the distribution law of sand liquefaction,the distribution of maximum offset on the Nanhe fault and the risk distribution of sand liquefaction in the future under strong earthquake are put forward.The main achievements of this paper are as follows:1)The spatial distribution of the Nanhe fault has been ascertained.The Nanhe fault is located in the eastern border of the Sichuan Yunnan rhombus block,started near the Aninghe valley on northeastern segment intersecting with the Anninghe fault,crossed Mianning basin,Yuangendi,Heli town,Xichang satellite launch center,Dongfang village,and terminated southwest of Ermaga village with a length of about 70 km,striking N45°E.In north section,the fault consists of two branches: the northern strand and the southern strand.The northern branch crossed the Mianning basin as a buried fault and the southern cut mountain lied to south to Mianning basin extending southwestward,intersecting with the northern branch near Yuangendi.At the location of Dongfangcun village,the fault become right-stepping with expression of linear pressure ridge,however,the left-stepping construction was discovered in southern trench,indicating that the fault is dominated by left-lateral strike slip motion with minor reverse faulting,and including ringent shear and pressed shear in part.2)The activity,slip rate and paleoearthquake sequence of the Nanhe fault have been identified.The Nanhe fault is active in Holocene.The fault is dominated by left-lateral strike slip,with a small amount of thrusting.The three earthquake events were revealed on the fault,which were 468a-118 aBP,891a-468 aBP and 5690a-6400 a BP respectively.The paleoearthquake events reflect that an event had ruptured the whole fault,and the fault activity may be characterized by clustering.The faulting geomorphology is characterized by fault scarp,fault trough valley,fault pass,weir pool,fault water system and alluvial fan body,and tail ditch.The horizontal and vertical components of striation are about 4:1,and the horizontal slip rate since late Holocene is about 2.6 + 0.2mm/a,and the vertical is about 0.6 + 0.1mm/a.3)The pattern of large earthquake response between the Nanhe fault and the Nnninghe fault is characterrized by cascading rupture and strong earthquake triggering.The paleoseismic event indicated that two cascading breaking events(Event 5690a-6400 a BP and even 118a-468 a BP between the Anninghe fault and Nanhe fault.The latest seismic event on the Nanhe fault could be the Kangding 1786 7? earthquake.The event 468a-891 a BP on the Nanhe fault could be a response to event 1030a-1050 a BP on the Anninghe fault with a shortest interval of 39 a,indicating that at the same time,the Nanhe fault can be cascaded with Anning River fault,and it can also become a seismogenic structure independently.The seismogenic structure of the Yuexi earthquake in 1480 is probably the Puxionghe fault.4)It is suggested that the largest coseismic displacement is generally located in the middle and rear segments of the surface rupture.The main controlling factors of the maximum dislocation of the surface are the structural style of the section,and the difference of the local lithology is the secondary control factor.Over-turned reverse plane,bedding plane and lithology difference are favorable geological conditions for forming the largest coseismic offset.5)The strong earthquake risk of the Nanhe fault is analyzed.According to the tectonic location,fault scale and the surface dislocation value of the latest earthquake event,the maximum seismic capacity of the Nanhe fault is 7.5.The largest horizontal dislocation of the Nanhe fault is estimated to be 3.1±0.43 m,and it is most likely to be distributed along the fault in the Zhichanghegou-Dongfang village.6)A regional geodynamic model for the east boundary of Sichuan-Yunnan block is constructed.The Nanhe fault partitioned the horizontal slip from the Anninghe fault being about 2.6mm/a,which explains the problem of the slip loss of the Anninghe fault and the Zemuhe fault.This conclusion supports the GPS inversion result and the discontinuous deformation model of the east boundary of the Sichuan-Yunnan block.7)A structural geologically method of the risk assessment for seismic liquefaction is put forward,which can quickly determine the distribution range of the liquefaction of sand soil after the earthquake,and it has a certain guiding role for the disaster prevention and relief.By using the method,the high risk area of liquefaction of Nanhe fault given 7.5 magnitude earthquake is mainly distributed in the area of Mianning County,Huian Town,Heli Town and Linli-Lugu Town,which may produce gravel soil liquefaction,especially in Mianning county-the Nanhe valley.The middle risk area of liquefaction is mainly distributed in the area of Yihai town and Lizhou-Xichang.The low risk area of liquefaction is mainly located in the area of VI,such as Tuowu town and Huanglianguan town.更多还原