【作者】 任治坤；

【导师】 田勤俭；

【作者基本信息】 中国地震局地震预测研究所 ， 构造地质学， 2007， 硕士

【摘要】 古地震研究,是指利用地质、考古等方法查明史前地质时期和有地震记载以前的、浅源强震产生的地表和沉积物变形的地质标志。由于大规模的古地震分布在活动构造断裂带上,因此,古地震研究是活动构造研究的重要组成部分。而且通过古地震研究可以增补地震目录、为地震烈度区划提供可靠的科学依据、对地震小区划也有很大意义、为地震研究和预报提供了较可靠的地震重复周期资料(黄培华,1982)。孔子曰:“温故而知新”。地震研究也一样,如果将古地震研究好了,则对将来地震预测是大有裨益的。川滇菱形块体位于青藏高原东南侧,处于印度板块向中国大陆NE向挤压作用的前沿地带,受甘孜-玉树断裂带、鲜水河断裂带、安宁河断裂带、则木河断裂带、小江断裂带、红河断裂带和金沙江断裂带等NW和近SN向活动断裂所围限的最新构造活动单元(李坪等,1975;阚荣举,1977;徐锡伟等,2003;吕江宁等,2003),鲜水河-小江断裂带作为该活动单元东北边界,是一条重要的活动断裂带和强地震带。其中,则木河断裂是鲜水河-小江断裂带内走向NW的一条左旋走滑断裂,从李金堡向南东经西昌、普格、松新、宁南延入巧家盆地,连接近南北向的安宁河断裂带与小江断裂带,成为控制川滇菱形块体的东北侧边界,是中国大陆强震集中、频度较高的地区之一。本论文以则木河断裂带为研究对象,以活动断裂的定量地貌研究为基础,结合遥感解译和古地震组合探槽,深入定量解析断裂带的运动学特征与大震复发间隔。1、遥感解译断裂结果与地质体位错利用数字高程模型(DEM),合成则木河断裂带三维地貌图,通过对地貌面、盆地形态和地形剖面的研究,结合地表构造分析,位错量从1.9m到1800m不等,确定其中1.9m的位错量为1850年地震形成,其他稍大点的几十米的位错为几次地震断错的积累,上百米及以上位错为断裂长期活动累计位移,对应于断裂带内主干河流、阶地的位错。2、后差分GPS定量地貌测量地貌过程与断裂变形过程的关系是活动断裂定量地貌研究的基础。地震微地貌测量最重要的就是反映微地貌与断裂之间关系,因此需要精确测量其相对距离;地震地貌起伏大,需要选用不受地形影响的测量手段。而差分GPS能够精确测量移动站与基站之间相对距离(David L.Higgitt et al,1999),在基站位置足够准确的情况下可以得到精确的测量结果。后差分GPS测量时移动站与基准站之间不需要实时通讯,实施测量时不受地形影响,比实时差分GPS更适合地震微地貌测量。曾经有人利用后差分GPS进行过地籍测量与滩涂测量(张显峰,2000;王春瑞,2002),本节尝试利用高精度后差分GPS来定量化的研究该活动断裂地震微地貌特征。根据1850年西昌地震位移统计数据可知,1850年地震所造成的位移最大为10m,且集中分布在四呷布史-五道箐一带,因此本次后差分GPS测量区域选择在了大箐梁子-五道箐一带,大箐梁子-五道箐之间测量得到大比例尺断裂地貌图。获得大箐村西鼓包数据表,四呷布史村阶地、水系位错分布图以及断裂三维结构图。大箐梁子上一系列鼓包沿断裂分布,本次测量得到7个鼓包数据表;在大箐村南山坡上宽60余米的地堑内发育50cm高断层陡坎;四呷布史村东发育小规模长梁、断塞塘及三级局部阶地,其中T3阶地年龄为17.00±2.56 ka.BP,T2阶地年龄为7.70±0.69 ka.BP;以上均可说明此处经历过至少2次古地震事件。3、古地震研究大箐村西最大的鼓包被左旋错开成两个鼓包,其间形成宽仅一米的构造楔。此处除了这个最新形成的构造楔之外,南侧冲沟肘状拐弯处发育一规模较大的断塞塘。该处断塞塘的形成是由于断裂早期活动形成鼓包,鼓包阻挡水流,造成冲沟肘状拐弯,在拐弯处水流由于受阻,在原冲沟北岸形成细粒断塞沉积。随着断裂的不断活动,断塞塘的沉积区域也随着冲沟北岸不断向南运动。据此判断此处断塞塘属于断塞型。此处开挖组合探槽可以揭露不同时期断塞塘沉积所形成的含碳层。本次研究在此处开挖组合探槽,TC1东西向横跨最新形成的构造楔,TC2和TC3分别在TC1南侧距其2m和4m处。此次组合探槽开挖共揭露地层17层,采取14C样品11个,光释光样品1个。根据构造现象分析,共揭露古地震事件3次,古地震事件E3,形成TC1内③-⑥沉积序列,根据测年结果分析认为古地震事件E3发生时间为5470±70a.BP.之前;古地震事件E2形成崩积楔②,根据测年结果分析认为古地震事件E2发生时间为3160±60 a.BP.之后;古地震事件E1形成TC1与TC2内崩积楔⑿,根据测年结果分析认为古地震E1发生时间<300 a.BP.,推测为1850年西昌地震事件。由此计算M7.5地震原地复发间隔为由此计算三次古地震事件间隔分别为2300年左右、3000年左右。由此可得则木河断裂带强震原地复发周期为2300～3000年左右。更多还原

【Abstract】 Paleo-earthquake research based on the records of strong earthquake on the fault to discover problems such as: the evolvement of the fault, recurrence of strong earthquake using geology survey. As a proverb of Confucius states“Study the past if you would divine the future”,paleo-earthquake research is one of the most important methods on active structures and provides clues on earthquake prediction.Sichuan-Yunnan block lies south-east to Tibet Plateau, is under the compression between India block and Eruasia block and restricted by Ganzi-Yushu Fault zone, Xianshuihe Fault zone, Anninghe Fault zone, Zemuhe Fault zone, Xiaojiang Fault zone, Honghe Fault zone and Jinshajiang Fault zone. (Li Ping et.al.,1975;Kan Rongju et.al.,1977;Xu Xiwei et.al. 2003;LǚJiangning et.al.,2003).Zemuhe Fault is sinistral strike slip fault developed between Anninghe Fault zone and Xiaojiang Fault zone and now is the north-east boundary of Sichuan-Yunnan Block.We carry out our work along Zemuhe fault zone, and try to get further on the fault kinematics and the recurrence of this fault based on the precise geomorphology and combining with RS interpretation and trench array.1、Offset of geological block according to the RS interpretationWe can try to find the relationship between geomorphology and fault through research on Earthquake-Geomorphology. We need new methods to survey related earthquake geomorphology. We can get the relative distance between the base station and moving station by Difference GPS(DGPS) (David L.Higgitt et al,1999), we needn’t worry about relief reflection on our survey like total station.Zhang Xianfeng(Zhang Xianfeng,2000) and Wang Chunrui(Wang Chunrui,2002) have made some DGPS survey on field survey and beach survey. In this dissertation we try to do some survey on earthquake geomorphology to get some data on active faults research.Using DEM to get the 3D map, analysis the topography and form of the basin, and finally we get the interpretation map of Wudaoqing, Sishiluomo,and Songxin. We get the offset data from 1.9m to 1800m along Zemuhe fault, among them the data of several meters such as 1.9m is due to one earthquake, the data of several ten meters is due to several earthquakes, and the offset of several hundreds even up to thousands meters is corresponding to the terraces of the main river of this region for long time activity of this fault.2、Quantitative measurement by virtue DGPSRelationship of topography and fault evolvement is the foundation of quantitative geomorphology. In this thesis we measured several typical places along the fault by using virtue GPS. Finally we get big scale geomorphology map between DaqingLiangzi and Wudaoqing, data of mole track at Daqing village, terrace data and offset map of gullies at Sixiabushi village,and build the 3D model of the fault. We find that offset of 1.9m was due to earthquake of 1850, tens of meters offset were due to several times of earthquakes, and the offset of hundreds of meters were corresponding to main rivers and terrace in this region.3、Paleo-earthquakeAt Daqing village the biggest mole track was offset to two mole tracks, between them a little sag pond about 1m wide was formed. And there is another big sag pond developed south of it at the turn point of the gully. This big sag pond was formed due to the mole track, the mole track block the gully and make the gully turn at this point, and the sag pond deposition start at the northern bank of the gully. Along with the movement of the fault, sediment area of the sag pond move southern.We can get several layers material contains carbon of the sag ponds of different epoch. This time we make the trench array of three trenches. TC1 cover the little sag pond from east to west,TC2 and TC3 are parallel to TC1 and south of it about 2m and 4m. We discover 17 different layers in the three trenches and get 11 14C samples and 1 OSL(Optical stimulated luminescence, OSL) sample. Finally we get three events by analysis the geology evidence from the trench, according to the age data the three events are E1: Xichang earthquake of 1850,with the evidence of wedge⑿; E2: late than 3160±60a ago, the wedge②being the evidence; E3: early than 5470±70a,with the evidence of sequence from③-⑥. The interval are about 3000a and 2300a,so we get the recurrence interval of M7.5 at the same place are about 2300～3000a.更多还原