【作者】 张建国；

【导师】 傅容珊； 马宗晋；

【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】 本文基于对越南红河断裂带几何结构、地质地貌特征和断裂活动性定量数据的野外调查,以及深部地球物理场、跨断层形变测量、仪测与历史地震记录等相关资料的收集与综合分析,结合对我国云南境内红河断裂带相关研究工作的系统消化和整合,实现了对该断裂新生代以来右旋走滑活动时空特征的总体把握。完成的主要工作及获得的认识包括:1.首次获得了红河断裂带越南部分长达370km范围的大量地质、地球物理、大地测量、地形地貌、历史及现代地震活动等诸多方面的资料和证据。其中特别是通过两次约50天的越南红河断裂实地野外考察,所获得的关于红河断裂越南部分断裂空间展布与几何结构、第四纪地质与地貌特征、断裂最新活动时代与右旋走滑累积位错量等方面的定量数据,填补了过去对红河断裂研究诸多方面的空白。此外,通过参加由联合国教科文组织发起的亚洲及西太平洋自然灾害与地球动力学、IGCP430大陆动力学等相关国际学术会议,获得了越南红河断裂数字地震观测、跨断层形变测量和GPS观测等相关资料,为开展跨国界的整体研究奠定了基础;2.云南境内红河断裂带在断裂几何结构与历史演化过程、断裂活动的地质地貌表现与活动方式、断裂最新活动时代与累积位错量、地震活动的频度与强度等诸多方面都表现了异常突出的时空不均匀性。特别是断裂带第四纪以来的总体活动水平,包括活动时代、活动强度等都表现了非常明显的自北而南逐渐减弱的趋势。通过本文的研究证明:红河断裂带越南部分的活动性继续保持了这样的总体趋势,即其强烈活动时代更老、右旋走滑累积位错量更小、地震活动水平更低。这不仅对越南北部未来国土规划与利用具有重要的现实意义,而且对于重新认识青藏高原侧向挤出的影响范围和作用方式,从而进一步探讨与青藏高原发育演化相关的动力学机制问题更具有十分重要的科学意义;3.对红河断裂带强震和中小地震震源机制解、中小地震综合断层面解以及强震破裂宏观特征的分析均表明,沿红河断裂带既存在SSE-SN向近水平的主压应力场背景,同时又明显存在不同方向和较高仰角的局部主压应力场。其中,具有明显倾向滑动的震源机制主要出现在红河断裂北段;中段主压应力优势方位出现向SE-SEE的偏转。此外,无论是主应力方位,还是主应力作用方式,自北向南总体上都表现出由复杂到单一的变化趋势。震源机制分析刻画的红河断裂现今构造应力场状态与GPS观测结果基本吻合,也与地质资料所揭示的断裂晚第四纪以来的运动状态基本一致。4.为提高包括断裂与地震的空间关系、震源参数与断裂深部介质环境特征以及整条断裂带地震活动性等相关研究的可靠性,采用小震双差精确定位技术,对红河断裂带1233次仪测地震的24168条记录进行了重新定位处理。得到了震中分布相对离散、震源深度优势分布相对集中的结果。从一个方面佐证了本文关于红河断裂作为川滇活动块体西南边界作用弱化和壳内具备跨红河断裂动力传递条件的判断;5.利用云南区域台网和部分越南数字化地震资料,采用经典Brune模型对1142次(M≥2)数字记录地震的震源参数进行了测定和分析。结果显示,红河断裂两侧块体之间、断裂东侧各次级块体之间由震源参数反映的介质性质均存在较为明显的差异。其中特别是断裂东侧各块体之间深部介质性质的差异是决定其时空不均匀活动的重要条件之一。此外,在资料选取时段内地震位错量与GPS观测滑移量之间的协调性也在一定程度上支持这两种分别代表深、浅运动和变形之间的相关性;6.利用在越南收集到的历史和现代地震记录,结合国内相关资料,对中越红河断裂的地震活动性按照历史地震活动和现代地震活动分别进行了分析与研究。结果表明,尽管越南红河断裂历史与现代地震记录资料存在着一定的不完整性,但综合分析认为整条断裂地震活动性的总体特征是北区段最强、中区段次之、南区段最弱;在上述研究和认识基础上,鉴于以往关于红河断裂带第四纪活动性研究多集中于上世纪80年代至90年代中期,而之后包括区域数字地震观测与地壳及上地幔结构反演、GPS大地形变观测两大方面取得的许多重要资料和成果尚未被系统地引入红河断裂活动性研究的实际。重点开展了三个方面的工作:一是在全面掌握前人有关红河断裂右旋走滑活动相关时空参数和成果基础上,系统收集、整理、归纳和分析了上述两方面近年来取得的最新资料数据和研究成果;二是从大地构造分区与活动块体划分的角度出发,采用远震接收函数计算方法,对红河断裂两侧若干活动块体的地壳平均波速、泊松比等开展了分区块的反演计算。试图以此更清晰地刻画红河断裂的深部介质结构与动力学环境;三是将最新GPS大地形变观测与分析成果与深部介质结构与动力学环境研究成果相结合,以探寻它们之间的深浅耦合关系为目的,重点探讨了与红河断裂活动显著不均匀特征相关的若干动力学机制问题。通过上述工作在以下几方面取得了一些新的认识:1.通过对红河断裂新生代早期左旋与后期右旋走滑不同驱动机制的分析,提出作为红河断裂右旋走滑主动盘的以东地区是由若干地质发育演化历史各异、地壳及上地幔结构和介质性质各不相同,甚至某些方面存在显著差异的次级块体或单元构成。这是红河断裂活动性存在显著时空不均匀性最重要的原因之一;2.从青藏高原东南缘川滇广大地区地壳增厚主要体现为具有韧性流变特性的下地壳增厚的实际出发,结合川滇块体内部以北东向小金河断裂为界南北两侧地壳结构的显著差异,提出了红河断裂带弥渡以北地区的裂陷伸展变形可能与跨小金河断裂的下地壳“爬坡”、蠕散和沿红河-小金河深断裂地幔热流的上涌和透入效应有关;3.基于红河断裂东侧若干构造单元或块体变形沿断裂走向垂直差异运动与水平走滑运动交替、沿垂向深浅脆韧转换等耦合关系的综合分析,指出主要依据浅表几何结构和地质地貌调查对断裂进行活动性分段,尤其是较细的分段可能是存在问题的。提出应更加注重分段的深部依据以及与横向过渡、深浅耦合相关的,具有流变学意义的“段间转换”、“段间过渡”变形机制;4.通过将空间对地GPS大地形变观测与地壳及上地幔地震层析成像研究结果进行对比,结合中越红河断裂的右旋走滑自北而南活动时代趋老、累积位错量变小、活动性变弱的实际,以及在浅表与红河断裂近平行展布的楚雄-建水、无量山等断裂在上地壳发生归并的深部反演结果。综合分析证明云南境内红河断裂在下地壳甚至上、中地壳存在两侧低速层的部分连接和贯通。加上其中滇中块体和华南块体的阻挡作用,使川滇块体具备深部跨红河断裂动力传递和顺时针旋转的条件。在对GPS观测所揭示的川滇地块顺时针旋转和跨红河断裂连续变形动力学机制做出较合理解释的同时,提出了红河断裂带作为所谓川滇活动块体西南边界作用已经弱化的推论。更多还原

【Abstract】 Based on the geological and geomorphological characteristics, the quantitative data of fault activity from field investigation, and the geometric structure of the Red River fault zone in Vietnam, as well as the collection and comprehensive analyses of deep geophysical fields, cross-fault deformation measurements, earthquakes determined by instruments and historical records, and other related data, combined with the systematic integration and analyses of related research work of the Red River fault zone in Yunnan of China, we realize the overall grasp of the tempo-spatial characteristics of right-lateral strike-slip fault activity for the Red River fault since Cenozoic. The completed major tasks and understandings include:1. For the first time, we obtained a large number of data and evidence for the Red River fault zone up to 370 km range in Vietnam, including geological, geophysical, geodetic, topographic, historical, modern seismic activity, and many other aspects. In particular, the spatial distribution, geometric structure, the characteristics of Quaternary geology and geomorphology, and the quantitative data for the latest active times and the cumulative right-lateral strike-slip dislocations of the Red River fault zone in Vietnam, etc., obtained through two times of field investigation in a total of about 50 days for the fault, filled in a number of gaps in the past studies on the Red River fault zone. In addition, we also obtained digital seismic observation, cross-fault deformation measurement, GPS observation, and other relevant data of the Red River fault in Vietnam from international meetings in Asia Pacific Natural Disasters and Geodynamics initiated by UNASCO, and IGCP430 Geodynamics, which provided bases to carry out cross-border and comprehensive studies on the fault.2. The Red River fault zone in Yunnan demonstrated unusually prominent tempo-spatial heterogeneity in the fault geometric structure, historical evolution processes, the geological and geomorphological performance and active style of the fault activities, times of the latest activities, the cumulative amount of dislocation, the seismic frequency and intensity, and many other aspects. In particular, the overall level of activities, including the active times and active intensity, and etc, demonstrates a very clear trend of gradually weakening from north to south since Quaternary. It is proved through our work that the activity of the Red River fault zone in Vietnam continues to maintain this general trend, namely, the times for strong activities are older, the cumulative right-lateral strike-slip dislocations in the amount are smaller, and the level of seismic activity are lower. This is not only practically significant for planning and utilization of land in northern Vietnam, but also scientifically significant for us to reconsider the impact of the Qinghai-Tibet plateau lateral extrusion to Yunnan, so as to further explore the future earthquake risk in Sichuan-Yunnan region. 3. The analysis on seismic focal mechanism and macro-characters of strong earthquake demonstrate that, there is a major horizontal compressive stress field setting in SSE-SN direction along Red River Fault, but meanwhile, the other major compressive stress fields in different direction and with higher vertical angle exist locally. The focal mechanisms with prominent dip-slip component mainly appeared in northern segment of the fault, and the dominant direction of major compressive stress field deflects to SE-SSE in middle segment. Moreover, the tendency that the complicate turns into the simple both of the direction of major compressive stress field and the manner of action is very clear from northern to southern segment. The state of modern tectonic stress field along Red River Fault accords the result of GPS observation, and also in agreement with the movement state described by geological data.4. In order to improve the reliability of the related researches, including the spatial relation of faults and earthquakes, seismic focal parameters and the environmental characteristics of the deep fault medium, we relocated 1,233 earthquakes along the Red River fault zone with 24,168 digital seismic records using Double-Difference Hypocenter Location technique, and obtained results showing the discrete distribution of epicenters and a concentrated trend of focal depth distribution, provided evidence from one aspect for our inference that the role of the Red River fault as the southwest boundary of the Sichuan-Yunnan active block is weakening, and the Red River fault has the conditions for shallow-deep decoupling and detachment.5. Digital seismic data from Yunnan Regional Seismic Network and a part from Vietnam were used to determine and analyze the focal parameters of 1142 earthquakes (M>=2.0) based on Brune model. Results show that there are relatively obvious differences between blocks on both sides of the Red River fault, and between various sub-blocks on eastern side of the fault. In particular, the difference between deep media of the blocks on eastern side of the fault is one of the import conditions for their uneven tempo-spatial activities. In addition, in the time period represented by the selected data, the coordination between the seismic dislocation and slip observed by GPS also support to a certain extent the two correlations between shallow-deep movements and deformation.6. By making use of the historical and modern earthquake records obtained in Vietnam, and integrating with the relative data in Yunnan, we have studied and analyzed the seismicity of Red River Fault during history and recent period respectively. The results demonstrate that the general character of the seismicity along Red River Fault is gradually weakened from northern to southern through comprehensive analysis, though there are some non-integrity of the data in Vietnam.Based on the above-mentioned studies and understandings, in view that the previous studies on the Quaternary activities of the Red River fault were more concentrated in the last century, the 80s to mid-90s, and from then on to present, many important data and results have not yet been systematically introduced into the seismic researches for the Red River fault, in particular the research on the dynamic mechanism for the uneven activities of the Red River fault, we focused on the three aspects of work:First, based on the understanding of the related tempo-spatial parameters for right-lateral strike-slip activities of the Red River fault and research results by the previous investigators, we systematically collect, collate, summarize and analyze the latest data and research results for the above-mentioned two aspects obtained in recent years.Second, from a point of view of classification for tectonics and active blocks, using seismic wave tomography inversion technique, transfer function, we calculated the Earth’s crust average velocity, Poisson’s ratio, and etc. for the active blocks on both sides of the Red River fault, an attempt to more clearly describe the deep medium structure and dynamic environment of the Red River fault.Third, combining the latest results based on geodetic deformation GPS observation and analysis, deep medium structure, and research results from dynamic environment, as the purpose, we explored the shallow-deep coupling relations, and systematically studied in-depth the dynamic mechanism for the significant heterogeneity of the Red River fault in Quaternary.New understandings are obtained based on the researches mentioned-above:1. Through analyses of the different driving mechanism for the early left-lateral strike-slip and late right-lateral strike-slip of the Red River fault in Cenozoic, we proposed that the area on the eastern active wall of the Red River fault, during right-lateral strike-slip period, was composed of several sub-blocks or units with different evolution history of geological development, different structure and medium characteristics of the crust and upper-mantle, and even significant differences in some aspects, which is one of the most important reasons for the significant tempo-spatial heterogeneity of the activities of the Red River fault.2. With a point of view that the crustal thickening in the large Sichuan-Yunnan area, southeast edge of the Qinghai-Tibet Plateau, is mainly the thickening of the lower crust with the rheological and ductile properties, combined with the significant difference between the crustal structures on both sides of the Xiaojinhe fault with strike in northeast direction and located inside the Sichuan-Yunnan block, we proposed that the rift extensional deformation in the area to northern of Mizu may be related with the "climbing" and creep of the lower crust crossing the Xiaojinhe fault, and effects of the going up and penetration of mantle heat flow along the Red River-Xiaojinhe deep faults.3. Based on the comprehensive analyses of the alternative exchanges for the vertical differential movements and horizontal strike-slip movements, and the vertical brittle-ductile coupling conversion in shallow and deep depth of some structure units or blocks, we pointed out that there may be some problems in segmentation of a fault activities based on the dislocation and age data from investigation of the shallow geometric structure and geological geomorphology, in particular, for the small segmentations. We put forward that we should pay much attention to the deep evidence, and the deformation mechanism of the transverse transition, shallow-deep coupling relation, and "conversion between segments" and "inter-segment transition" with a rheological sense.4. By comparing the research results obtained from geodetic GPS observation of space-to-ground and seismic tomography for crust and upper mantle, combining the findings that the characteristics for the whole Red River fault zone in China and Vietnam, from north to south, the active times of dextral strike-slip become older and older, the cumulative quantity of dislocation smaller and smaller, and the seismicity weaker and weaker, as well as the deep inversion results that the incorporation occurred in the upper crust for the Chuxiong-Jianshui fault and Wuliangshan fault which are almost parallel to the Red River fault zone on the shallow surface, it is comprehensively analyzed that there are partial connection and link up for the low-velocity layers on both sides of the Red River fault in the lower crust, even in the upper and middle crust, so as to provide conditions for clockwise rotation for the Sichuan-Yunnan block, when which is blocked by the central Yunnan block and south China block. We reasonably explained the clockwise rotation of the Sichuan-Yunnan block and the dynamic mechanism for the continuous deformation on both sides of the Red River fault revealed by the GPS observation; meanwhile, we put forward the inference that the role of the Red River zone as the southwest boundary of the so-called Sichuan-Yunnan block is weakening.更多还原