【作者】 皇甫岗；

【导师】 陈颙；

【作者基本信息】 中国科学技术大学 ， 固体地球物理， 2009， 博士

【摘要】 云南(21-29°N,97-106°E)处于印度板块与欧亚板块中国大陆碰撞带东缘,地震活动频度高、震级大、分布广,属于板缘、板内地震混合型地区。基于急剧的地震能量的积累与释放,明显的活动块体分级与协调运动,相对固定的动力边界及来源,地震预测预报的特别需求,云南地震活动性成为一个令人关注的重要问题。本文以地震活动规律性以及孕震环境为研究重点。研究者把介质、结构、动力作为揭示地震活动特别是区域强震活动的主要方面,大量前人相关研究成果及已取得共识的地震活动性特征、参数等作为刻画区域地震活动性的背景,通过地震活动图像、区域地震活动关联度、地壳介质品质、地质构造演化、活动块体及主要断层几何学、运动学、动力学等分析方法,对云南地震活动水平、地震活动时空分布、地震类型分区、地震复发间隔、地震呼应关系等等方面进行了较为系统的研究,取得了7个方面的认识。云南主要动力源来源于印度板块对欧亚板块中国大陆的强烈挤压,具体表现为不同序次力源的联合作用。云南主要动力来源为印度板块与欧亚板块中国大陆的碰撞,但东、西部动力同源不同级。西部为印度板块直接作用,表现为侧向强烈的挤压;东部是多级转换的结果:印度板块在北东方向上正面碰撞青藏地区,青藏高原缩短、抬升过程中,伴随着羌塘地块向东挤出,在具强结晶基底的四川盆地中部受阻,川滇菱形块体受驱向南南东楔入。在云南,由西向东的动力与由北向南的动力通过相应的块体传递,在相汇区域联合作用,甚至会出现此强彼弱的动力格局,这是研究和认识云南地震活动规律及特征的重要基础。云南地震记录漏载十分严重。b值研究反映20世纪仍然存在较严重的5级以上地震漏载现象,漏载次数可能超过140次。滇西南地区在早期由于社会发育程度低、文字记载能力弱、民居过于简陋等原因,成为地震漏载的重要地区。在云南开展地震活动性研究,应当采用仪器观测地震目录,并考虑各档次地震目录完全性。20世纪30年代初云南(滇西南地区选取50年代以来)5级以上地震事件以及1965年以来3级以上地震事件,能够较客观地反映云南地震活动性状。另外,应重新审视“历史有感地震”的研究成果,其可能成为被漏载大震的重要线索。云南孕震能力很强。印度板块每年向云南输入的能量约相当于一次6.7级地震的应变能释放。在云南的某些典型地区,研究发现7级地震约为50年、6级地震约为15年、5级地震约为10年的地震复发间隔,且由西向东有逐渐增长的趋势,有代表性地反映了云南地震能量快速积累与释放的水平。需要注意,地震活动不总是以确定的震级等时间间隔地爆发,孕震环境可能因经历的地震活动在改变,不同的地震触发因素也可能产生影响。云南主体地区强震活动时空成丛特征显著。Ms6.7级以上大震活动可以划定为4个强震活跃期,分别为1913-1925年、1941-1955年、1970-1979年、1988-1996年;活跃期持续时间为8-14年,其间相对平静时间为9-16年。活跃期大震容量约为3-4次;地震活动的主体地区有东西部交替的特征,20世纪第Ⅰ、Ⅲ活跃期在东部,第Ⅱ、Ⅳ活跃期在西部,而且首发地震位于同一断裂系。云南东、西部孕震过程具有相对独立,西部相对于东部地区地震能量的积累速率快,平静期偏短,因此在一定的时间段内,可能出现一次东、西部同时爆发大震的时段。与此同时,本文还通过深化云南东部(川滇菱形块体)强震活动模型研究,建立块体滑动速率变化与成丛大震孕育、发生和调整过程的关系,同时发现一个地震活跃期大震连发后,出现块体滑动速率远大于平均速率,则活跃期业已结束;地震平静持续时间较长且块体滑动速率较低,属于首发强震的危险信号;一个大震发生后,块体滑动速率未快速增大,说明强震活跃水并未降低,仍要注意大震发生的可能。云南地震具有明显的地震类型分区特征。通过地震序列和强震震源机制的研究发现,云南总体上地震断层以走向滑动为主,地震序列以主-余型为主。但在此背景下,考虑非走滑地震断层和非主-余型地震序列所占的比例,可以将云南划分为滇东和滇西南2个走滑-主余型区、滇西北倾滑-震群型区和滇西准走滑-双震型区。滇东区走滑特征明显,块体相对完整,震前变形不显,主震释放能量较为彻底;滇西北倾滑分量可能是北东向丽江—小金河断裂带附近川滇菱形块体向南“爬坡”派生的上冲力所致;滇西南在侧向强烈挤压下,先存北东向断裂带继承性活动与北北西向新生断裂正在形成,共轭地震发育。由于不同类型地震的前兆组合样式及演进过程不尽相同,地震类型分区可以为本地区多点孕震过程监控提供理论指导。丽江-小金河断裂带和红河断裂带分别为划分川滇菱形块体地区和云南地区的重要边界断裂带。丽江-小金河断裂带反映地壳的上隆,块体“爬坡”派生的张力可能通过大震表现出来;红河断裂带历史上所具有的边界作用在逐渐减弱,但该带仍为云南地震活动区的一级分界,整体起到弱边界作用。近代川滇菱形块体向南运动过程中,附加顺时针旋动,动力及变形可能通过红河断裂带某些段落及层位影响到滇西南地区。云南地震活动与相关地区存在呼应关系,由远至近,分别为与滇缅弧-安达曼海构造带的关系、与珠峰以东地区的关系以及与川滇菱形块体北部的关系。云南地震活跃期的启动与滇缅弧-安达曼海构造带关系密切。对于上一世纪云南4个地震活跃期,有3次首发大震前安达曼-缅甸弧形带都发生了巨震。云南东部与四川西部的地震同为川滇菱形块体活动的结果,通过历史地震活动研究,通常是云南先于四川活动,这可能是南南东运移的川滇菱形块体通过前端地震才能为后缘提供让位空间之故。另一个值得注意现象是,川西北地区大震后云南弱呼应特征明显。这一认识有效地指导了2008年5月12日汶川8.0级地震后对云南地震形势的判断。在本文中,研究者运用了地震活动性以及孕震环境的研究成果,对云南中长期地震预测以及1975年孟连西7.3级地震、2000年姚安6.5级地震、2007年宁洱6.4级地震的预测基础和依据进行探讨和概括。本文还针对云南地震活动性研究,提出进一步研究的重点。如:1)加强地震孕育-发生-调整过程的主控因素研究;2)开展强震活动主体地区东西交替成因分析;3)强化区域地震危险性的宏观判断;4)建立云南东部首发大震模式;5)启动慢地震观测与研究。研究者认为,慢地震可能成为影响地震活动性特别是建立地震活动规律的一个重要因素,没有慢地震的地震目录是不完全的地震目录,也就不能真正建立强震活动规律。更多还原

【Abstract】 Yunnan(21-29°N,97-106°E) is located at the eastern edge of the collision zone between Indian plate and Chinese continent in Eurasian plate,with high frequency of seismic activity,large earthquake magnitudes,and a broad distribution area, belonging to a region with mixed types of interplate and intraplate earthquakes. Based on rapid accumulation and release of seismic energy,obvious classification of active blocks and coordination movements,the relatively fixed dynamic boundaries and source,and special need for earthquake forecast and prediction,seismicity has become a major concern.This dissertation focuses on seismic regularity and seismogenic environment. The researcher takes medium,structure,and dynamic source as the major aspects,as well as the seismic characteristics and parameters,which have been generally accepted based on the relevant research results by the previous investigators,to describe the background of regional seismicity.Through analytical methods, including the imaging of seismic activities,correlation of regional seismic activities, quality of crustal medium,evolution of geological tectonics,active blocks,as well as the major fault geometry,kinematics,dynamics,and so on,the researcher systematically studied the seismic activity level in Yunnan,spatio-temporary distribution of seismic activities,earthquake type classification,earthquake repetition interval,earthquake correlation,and so forth.Based on these studies,the researcher has obtained important under- standings in 7 aspects.The major dynamic source for Yunnan originates from the intensive extrusion and compression by Indian plate against Chinese continent in Eurasian plate,displaying a joint action by sources with different order of strengths.The major dynamic source for Yunnan comes from the collision between Indian plate and Chinese continent in Eurasian plate;yet,the strengths are different for eastern and western Yunnan,though the source is the same.The dynamic source for western Yunnan is from the direct action of Indian plate,showing intensive lateral extrusion and com- pression;the dynamic source for eastern Yunnan is the results from several transforms:Indian plate collides with the Qinghai-Tibet region in the northeast direction,leading the shortening and uprising of the Qinghai-Tibet plateau, accompanied with the Qiangtang block squeezed out eastward,which is blocked in the middle of Sichuan basin with strong crystalline basement,and then the Sichuan-Yunnan rhombic block(SYRB) is wedged in the south-south-east direction. In Yunnan,the dynamic source from west to east as well as that from north to south transmits though the related blocks,acts in the joint area,and even displays a pattern that one is weak and the other is strong,which is the important basis for studying and understanding the regularity and characteristics of earthquake activities in Yunnan.There is a serious omission in records for historic seismic events in Yunnan.It is about 300 events omitted in every century on average.This situation is the most obvious in western Yunnan,where the major reasons for the omission are as the following:the high earthquake frequency,strong intensity,weak ability for written records,crude residence of common people,and frequent transitions of the political and economic centers.We should carefully reexamine the research results based on the "historic felt-earthquakes",which may provide import clues for the omitted large earthquakes.The researcher suggested study the seismicity in Yunnan using catalogs determined by instruments,and check the completeness of the catalogs.Seismic events with magnitude equal to or greater than 5.0 since the early 20th century(using seismic events since the 1950s for southwestern Yunnan area) and seismic events with magnitude equal to or greater than 3.0 since 1965 may objectively reflect the states of seismicity in Yunnan.There exits strong seismogenic capacity in Yunnan.On average,the annual energy input from Indian plate to Yunnan is approximately equal to the strain energy release by an earthquake with magnitude 6.7.Based on analysis of the repetition intervals of earthquakes in different ranges in typical areas,it is estimated that Yunnan is able to generate an event with magnitude 7 in about 50 years,an event with mag- nitude 6 in about 15 years,an event with magnitude 5 in about 10 years, and the capacity shows a trend to increase from west to east.Yet,it should be noted that earthquakes do not always occur with the predetermined magnitudes and in the equal intervals,and they may also be affected by the different trigger factors,for the seismogenic environment may be changed with the occurrences of earthquakes.There are obvious characteristics of spatio-temporary clustering for strong seismic activities in Yunnan.Activities of strong earthquakes with magnitude greater than 6.7 may be divided into 4 active periods.They are 1913-1925,1941-1955, 1970-1979,and 1988-1996 respectively;the duration for an active period is 8-14 years,with the relative quiescence for 9-16 years.The number for large earthquakes during an active period is about 3-4;the major areas for seismic activities show a pattern of alternative changes in east and west.In the 20th century,the first and third active periods were located in eastern Yunnan,the second and fourth active periods were located in western Yunnan,and the leading earthquakes were all located on the same faulting systems.The seismogenic processes are relatively independent in eastern and western Yunnan,though the rate for seismic energy accumulation is faster in west than in east,and the quiescent period is shorter in west than in east. Therefore,there may be a time period when large earthquakes occur in eastern and western Yunnan in the same time period.In this dissertation,we established a relation between the change of block moving speed,the clustering of large earthquake preparation,occurrence,and adjustment process,by deepening studies of the model for strong earthquake activities in eastern Yunnan(SYRB).Meanwhile, we found that after the continuous occurrences of large earthquakes during an active period of strong seismic activities,there would occur the block slip rate much greater than the average one,then the active period ended;it was a risk signal when the duration of the seismic quiescence lasted for a relatively longer time and the block slip rate became smaller,which was a risk signal for the starting of a strong earthquake;if the block slip rate did not increase rapidly after a large earthquake,it indicated that the seismic level did not lower down,and we have to note the possibility of large earthquake occurrences.There are obvious characteristics for classification of earthquake types in Yunnan.Results from studies of seismic sequence and focal mechanism of strong earthquakes show that the major seismic faults in Yunnan as a whole are strike-slip types,and the major seismic sequences are main-aftershock types.Under these conditions,considering the proportion by all the other non-strike-slip faults,and non-main-aftershock sequences,the researcher divided Yunnan into 2 strike-slip-main- aftershock areas in eastern and southwestern Yunnan,1 oblique-slip-swarm area in northwestern Yunnan,and 1 quasi-strike-slip-double-mainshock area in western Yunnan.In eastern Yunnan,the strike-slip characteristics is obvious,the blocks are relatively complete,the deformation is not distinguishable before earthquakes,and the energy release by a mainshock is relatively complete;in northwestern Yunnan,the oblique slip component in northwestern Yunnan may be resulted from the uprising force of the SYRB climbing to south at a place near the Lijiang-Xiaojinhe fault with striking in northeast;in southwestern Yunnan,the coseismic activities developed well because of the inherited movements of the preexisted faults with striking in northeast,and the forming of the newly-developed faults with strike in north-north-west,under the strong lateral extrusion and compression.For the reason that the patterns of combined precursors and evolution processes are different for different earthquake types,classification of earthquake types may provide theoretical guidance for monitoring seismogenic processes at multiple sites in Yunnan.The Lijiang-Xiaojinhe fault zone and the Red River fault zone are the import fault boundaries dividing the SYRB area and Yunnan area.The Lijiang-Xiaojinhe fault zone demonstrated the crustal uprising,and the extension force derived from the block "climbing" may be manifested by large earthquakes;the historic role of the Red River fault zone as a boundary is gradually weakening,though the fault is still the level-Ⅰboundary for seismic activities in Yunnan,playing a role of a weak boundary as a whole.During the process of SYRB moving southward in modern time,accom- panied by an additional clockwise rotation,the dynamic and deformation may affect the southwestern Yunnan area through some sections or layers of the Red River fault zone.There are three levels of correlations for seismic activities in Yunnan and the relevant areas.From far to near,there are the correlations with the Yunnan-Burma Arc-Andaman sea tectonic belt,with the eastern area of the Everest,and with the north of the SYRB respectively.The initiation of seismic active periods in Yunnan is closely related with the Yunnan-Burma Arc-Andaman sea tectonic belt.Before the leading large earthquakes in Yunnan in three of the four seismic active periods,great earthquakes occurred in the Burma Arc-Andaman sea tectonic belt.Earthquakes in eastern Yunnan and western Sichuan are mainly resulted from activities of the SYRB. Results based on studies of historic earthquakes show that seismicity in Yunnan is usually occurred earlier than that in Sichuan,which may be resulted from the cause that earthquakes occurred in the back edge of SYRB may need space from earthquakes in the front edge of SYRB.Another noteworthy phenomenon is the weak correlation between the large earthquakes in northwestern Sichuan and the strong seismic activities in Yunnan,which effectively guided the judgment for seismic trend in Yunnan after the 12th May 2008 Wenchuan earthquake.In this dissertation,based on the research results from seismicity as well as the seismogenic environment,the researcher conducted the discussion and summary for the medium-long-term earthquake forecast in Yunnan,and the foundations and bases for forecasts of the 1995 Menglian M7.3 earthquake,the 2000 Yao’an M6.5 earthquake and the 2007 Ning’er M6.4 earthquake.This dissertation also proposed 5 important suggestions for further studies on seismicity in Yunnan:1) strengthening studies on the major controlling factors for earthquake preparation,occurrence and adjustment;2) conducting analyses of causes for alternative changes of the major areas for strong seismic activities in east and west;3) strengthening the macroscopic judgment for regional seismic risk;4) establishing the initiation model for large earthquakes in eastern Yunnan;and 5) starting the observations and researches for slow earthquakes.The researcher even believes that the slow earthquake may become an important factor that may affect the seismicity and in particular the establishment of seismic regularity;an earthquake catalog can not be considered as a complete one without the slow earthquakes, neither can the strong seismic regularity be established.更多还原