【作者】 肖根如；

【导师】 甘卫军；

【作者基本信息】 中国地震局地质研究所 ， 固体地球物理学， 2011， 博士

【摘要】 纵观全球中强地震的空间分布,除一系列的洋脊、裂谷、海沟、转换断层和大陆内部的古板块边缘等大型构造活动带被清晰地勾画和显示外,在亚洲大陆东部地区相对密集的地震还清楚地勾画了一个面状的三角形区域。自1898年以来,该区域记录到的6级及以上地震占到全球地震的4.4%。在如此小的范围内发生如此多的强地震,前人将这一特殊区域称之为“中亚大三角地震构造域”。中亚大三角地震构造域位于亚洲的中东部地区,地处经度E60°-120°,纬度N10°-60°的矩形范围内,总体形态大致呈正三角形,其西南边界为平行于喜马拉雅山脉的区域,是大三角形的底边；东边界大致沿东经105°线,即从中国境内的南北地震带沿华南地块、鄂尔多斯地块西边缘向北延伸至贝加尔湖；西北边界则从帕米尔高原开始,穿越天山、阿尔泰山至贝加尔湖地区。自1900年以来,中亚大三角地震构造域内共发生过121次7级以上大地震。其中8级以上大地震有22次,这些大地震主要发生在青藏高原、天山造山带以及贝加尔断裂带上。最近十多年来发生的破坏性地震有：1997年11月8日玛尼Ms7.9地震、2001年11月14日昆仑山Ms8.1级地震、2008年3月21日于田Ms7.3级地震、2008年5月12日汶川Ms8.0地震、2010年4月14日玉树Ms7.1地震等。中亚大三角地震构造域是一个由密集的中强地震所自然呈现出的特殊区域,其内部跌宕起伏的高原、山脉、山间盆地和地堑,以及错综复杂的活动断裂直接反映了该区域强烈的地壳运动和构造形变。中亚大三角地震构造域主要包含青藏高原和西域二大构造区域。其中,青藏高原构造区域内部发育有一系列规模宏大、活动性强的弧形断裂带,主要的大型断裂带有：喜马拉雅主中央断裂带、西昆仑断裂带、喀喇昆仑—嘉黎断裂带、鲜水河断裂带、东昆仑断裂带、阿尔金断裂带和红河断裂带；西域构造区内部发育有天山断裂带、戈壁阿尔泰断裂带、蒙古-阿尔泰断裂带、Bolnay断裂带等。本论文以高精度、高密度、大范围的GPS观测资料为主,并结合活动断裂资料和最近百余年的中强地震资料,对中亚大三角地震构造域的现今地壳形变特征以及地壳形变与地震活动性的关系进行探讨。具体研究方法与成果包括：1.在吸纳国内外关于高精度GPS数据处理方法和策略的基础上,完善了一套基于GIPSY和QOCA的高精度、高效率的自动化GPS数据处理系统。在USGS(United States Geological Survey, USGS)的自动化GPS处理软件包GP的基础上,吸收和采纳目前国际上GPS数据处理的最新模型与方法,利用TEQC、GIPSY、Ambizap以及QOCA等软件,完善出一套实用化的GPS前期数据处理与后期数据分析系统,实现了从GPS数据准备、GPS数据处理、联合平差及结果可视化展示等一系列步骤的自动化,实现了高效的GPS数据处理。2.融合国内外多渠道GPS资料,获得中亚大三角地震构造域的综合GPS速度场。主要通过二种方式获得中亚大三角地震构造域的GPS速度场：①野外流动加密观测；②将不同机构、不同区域、不同时期、不同参考框架下的GPS速度场资料,以不同数据的公共点为“桥梁”,通过球面欧拉旋转变换,融合、归化至相同的参考框架。通过一致性检核和粗差剔除等环节,最后得到1647个GPS站点的速率。首次给出中亚大三角地震构造域及其周缘的GPS速度场。3.基于高精度、高密度的GPS速度场结果,并结合中亚大三角地震构造域的活动构造概要,总结出中亚大三角地震构造域GPS速度场的主要特征和区域内部的差异运动特点：①相对于稳定的欧亚板块,中亚大三角地震构造域的北东向水平地壳运动速度的大小,从南部喜马拉雅地区的～40mmm/a向北依次梯度变小至北部贝加尔地区～3mm/a。反映出中亚大三角在印度板块北东向俯冲、推挤作用下的缩短、隆升。②在整个中亚大三角地震构造域,青藏高原表现出了最强烈的水平向地壳差异运动。由于塔里木块体、阿拉善块体和鄂尔多斯块体的“准刚性”阻挡,以及高原北部区域对南部区域的自然阻挡作用,青藏高原在发生北东向强烈挤压缩短的同时,产生了明显的东向挤出式“逃逸”。③在青藏高原的东南部,由于“阿萨姆犄角”的北东向强烈插入,再加之华南“准刚性”块体在东部的阻挡,使该区域的高塑性地壳物质围绕喜马拉雅东构造结产生强烈的顺时针流滑式挤出逃逸。④塔里木地块在整个中亚大三角地震构造域的的现今地壳变形中扮演着重要的角色：由于塔里木地块的调节和转化作用,使中亚大三角地震构造域中部的水平地壳运动,呈现出从NNE到NE方向的扇状发散特征。在塔里木盆地内部,速度大小比较均匀,反映出较小的内部形变。⑤天山地区是中亚大三角地震构造域仅次于青藏高原的强烈挤压变形区。在跨越天山前后,GPS速度场从15-20mm/a迅速变小到1-5mm/a。⑥在蒙古中西部及贝加尔湖地区,站点的运动速度普遍在2-5mm/a之间,且运动方向无明显规律性,反映出该区域相对比较微弱的地壳形变背景。⑦在帕米尔高原地区,由于缺少足够的GPS观测站点,我们尚无法直观判定其内部的地壳运动差异性,但根据其周缘的GPS速度场状况,可推测其可能存在塔里木刚性块体阻挡下强烈的逆时针旋转。4.基于优选的空间内插算法,给出中亚大三角地震构造域连续分布的GPS应变率场。采用二维“高张力样条”(t=0.95)内插算法,对非均匀的GPS速度场进行了0.5°×0.5°的均匀预测加密,然后根据每个1°×1°网格边界及内部的9个内插速度矢量,计算出相应1°×1°网格内的均匀应变率。由此得出中亚大三角地震构造域各个区域定量、直观的地壳形变状况。①整个喜马拉雅弧形地块,在沿印度板块与欧亚板块会聚的方向上承受着强烈的挤压缩短,典型的压缩应变率为(30-60)nanostrain/a,局部量值高达(80-90) nanostrain/a。其中,喜马拉雅地块西部挤压应变比东部更强烈。同时,在大致垂直于板块会聚的方向上,喜马拉雅地块还承受着轻微的横向拉张。②拉萨地块沿印度板块与欧亚板块会聚的方向上,挤压缩短的典型应变率明显地减小为(20-30)nanostrain/a。但是,在该地块的中部,横向拉伸应变率变得非常明显,典型量值为(20-30)nanostrain/a,局部高达(40-60)nanostrain/a。这种明显拉张应变与该地区广泛发育的南北向正断层是相一致的。③羌塘地块的中西部典型的应变是近南北向的挤压和东西向的拉伸,量值在(15-25)nanostrain/a。而在青藏高原的东部,应变场表现出明显的近南北向拉伸,典型量值为(20-30)nanostrain/a。④祁连地块东边的四川盆地及其以北区域,并无显著的应变,典型的量值在10nanostrain/a以下。整个祁连地块和柴达木地块的应变状况比较均匀,主要表现为NE-SW向挤压和NW-SE向拉伸,挤压应变的典型量值为(15-25)nanostrain/a,拉张应变的典型量值为(10-15)nanostrain/a。⑤青藏高原东南角的川滇地区,应变强烈且方向变化较复杂,不过,大致东西向的扩散拉张和南北向的挤出式压缩特征非常清晰。⑥天山地区主要为天山南北向挤压缩短变形为主,挤压缩短呈现非均匀分布特征。挤压的最大量值为30nanostrain/a;⑦贝加尔地区整体上处于NW-SE向的拉张状态,拉张的最大量值为40nanostrain/a,在东部地区存在少量NNW向和NNE向的压缩状态,压缩的最大量值为10nanostrain/a,面膨胀应变的结果表明贝加尔地区整体上呈膨胀状态。5.中亚大三角地震构造域地壳形变块体的划分和平均应变状况的研究。中亚大三角地震构造域内主要有青藏高原-喜玛拉雅挤压区、天山挤压造山带、贝加尔拉张区以及川滇剪切区。本文在前人关于活动地块划分的基础上,以地壳形变特征为依据,划分出5类地壳形变块体,包括准刚性块体、纯拉张变形块体、纯挤压变形块体、拉张为主变形块体、挤压为主变形块体等。在中亚大三角地震构造域所划分出的具体形变块体包括：东塔里木块体、西塔里木块体、阿拉善块体、萨彦块体、阿穆尔块体、准噶尔块体、天山块体、祁连块体、巴颜喀拉块体、羌塘块体、拉萨块体、滇南块体、川滇块体。其中鄂尔多斯块体、塔里木块体、阿拉善块体为刚性块体。6.综合采用半无限弹性空间的断裂位错模型、准刚性块体欧拉旋转模型和弹性块体应变与旋转模型,对中亚大三角地震构造域的现今地壳形变GPS速度场进行了拟合、解释。综合与简化中亚大三角地震构造域内主要活动断裂带,建立每一条断裂在半无限空间的三维几何模型,并赋予必要的运动方式先验信息。以中亚大三角地震构造域的1233个GPS速度矢量为约束,通过在合理的范围内约束和调整各断层段运动速率的先验值,用半无限弹性空间的深断裂位错模型最佳拟合了GPS速度场,并反演获得了所有断裂段的运动速率。同时对于无法利用该模型解释的GPS速度场残差,进一步采用准刚性块体旋转模型以及弹性块体应变与旋转模型进行了拟合、解释。亦即,尝试采用非连续形变模型和连续形变模型相结合的方法,初步解释了亚大三角地震构造域的地壳运动与形变特征。7.分析、研究了中亚大三角地震构造域地震活动性与地壳形变关系,包括地震空间分布与地震矩累积率场、面膨胀率场和最大剪切应变场的高值对应关系,并首次对比了地震矩累积率与地震能量释放量之间的空间对应关系。结果表明：在中亚大三角地震构造域内,虽然应变率场、面膨胀率以及剪切应变率场与研究区域内的地震存在一定的空间相关性,但关系复杂。而采用地震能量释放量与地震矩累积率的的空间对比发现,尽管两者有着一定的相关性,但并不明显,最可能的原因是我们的地震能量释放计算,仅采用了100年的地震资料,与板内地震的平均复发周期相比,这样短时间段内统计、计算的地震能量释放分布,完全不能代表一个地震周期内的能量释放分布。更多还原

【Abstract】 Although most major earthquakes occur on plate boundaries, including ocean mid-ridges, trenches, and transform faults, some of continental interiors are also seismically active, such as central Asia. A map of epicenter distribution in this region delineates a huge triangular area with relatively densely populated quakes (M≥6.0) which account for 4.4% of all events since 1898. It is called the "Great Triangular Seismic Region". It covers 60°-120E and 0°-60°N. Viewed as a plane, it as three boundaries. The southwestern boundary of the triangle lies parallel to the Himalayas. The eastern boundary lies roughly along 105°E, and tectonically along the eastern edges of South China and the Ordos block, and extending northward to Lake Baikal. The third side is the northwestern boundary, which roughly begins at the Pamirs and continues northeastward through the Tian Shan Mountains, the Altai, and onwards to Baikal.Since 1900,121 quakes greater than M7.0 have occurred in this region, including twenties of greater than M8.0. Almost all these earthquakes happened in the Tibetan Plateau, Tien Shan orogen and Baikal rift zone. In recent years, the devastating events in this region include the Mani Ms7.9 in Qinghai on November 8,1997, Kunlun Ms8.1 in Qinghai on November 14,2001, Yutian Ms7.3 in Xingjiang on March 21,2008, Wenchuan Ms8.0 in Sichuan on May 12,2008 and Yushu Ms7.1 in Qinghai on April 14,2010.This great triangular seismotectonic region is a particular natural domain formed by densely distributed major and large earthquakes, laced with plateaus, mountains, basins, and grabens, and complicated active faults, indicative of intensive crustal movement and tectonic deformation. In tectonics it mainly comprises the Tibetan plateau block and Xiyu (West domain) block. A series of large-scale and active arcuate fault systems characterize the Tibetan plateau, such as the West Kunlun fault, Karakorum-Jiali fault, Xianshuihe fault, East Kunlun fault, Altyn Tagh fault and the Red River fault. In the Xiyu block exist the Tienshan fault, Gobi-Altay fault, Altay fault and Bolnay fault and so forth.This thesis focuses on data processing and analysis of high-precision and large-scale GPS measurements. Combined with data of active faults and major earthquakes over 100 years, this work attempts to reveal present-day crustal deformation of the great triangular seismic region in central Asia and its relationship with seismicity. Detailed approaches and research results are described as follows.1. Establishment of a set of high-efficiency and high-precision GPS data automatic processing system. Based on the GP programs developed by USGS, this work has absorbed and adopted the latest models and methods of GNSS data processing. By utilizing and modifying the software TEQC, GIPSY, Ambizap and QOCA, a complete set of perfect pre-processing and post-processing GPS data analysis system was formed. It realizes a series of automatic procedures, including GPS data preparation, GPS data processing, joint adjustment and visual displaying of results. All these have facilitated GPS data processing with high efficiency.2. Integrating GPS data from many channels abroad and determination of the GPS velocity field for the great triangular seismic region in central Asia. This GPS field was determined with two methods:①field campaign GPS observations,②The GPS data of different times and under various frameworks from varied institutions and regions are reduced to a same reference frame using the common points among the data, and rotation transform on the Euler sphere. By consistency tests and eliminating the data of sites that were too dense in distribution, of bad quality or obviously inconsistent with surrounding sites. Finally, the rates at 1647 GPS sites are obtained. It is the first time to show a GPS velocity field in the great triangular seismic region in central Asia and its surroundings.3. Based on the resultant high-accuracy and high-density GPS velocity field, combined with the outlined active tectonics in the great triangular seismic region in central Asia, this thesis summarizes the following main characters of the GPS velocity field and differential motions in the study area:①With respect to the stable Eurasian plate, the northeastward horizontal crustal velocities become smaller successively from-40mm/a at the south Himalaya to-3mm/a at north of Baikal, which reflect the uplift and shorten in the great triangular seismic region in central Asia plunged northeastward by the Indian plate.②In the whole great triangular seismic region in central Asia, the most remarkable differential horizontal crustal motions appear in the Tibetan plateau. Due to hampering of the rigid Tarim and Alashan blocks and the quasi-rigid Ordos block as well as the natural impedance of the northern plateau to the southern regions, notable eastward extrusion-like escape of the Tibetan plateau occurs as it experienced northeast directed compression and shortening.③In the southeastern Tibetan plateau, because of the northeastward intensive insertion of the Asam corner plus the hampering of the quasi-rigid South China block, the highly plastic crustal material of this region rotates clockwise about the East Himalayan syntaxis and slides toward southeast.④The Tarim block plays an important role in the present-day crustal deformation of the whole great triangular seismic region in central Asia. Due to its accommodation and transform, the horizontal motions in this region exhibit a divergence feature in NNE to NE directions. Within the Tarim basin, velocities are relatively uniform implying little deformation of its interior.⑤The Tian Shan area also experiences strong compressive deformation only inferior to the Tibetan plateau. Across the Tian Shan, GPS velocities become rapidly from 15-20mm/a to 1-5mm/a.⑥In the central and western Mongolia and the Baikal region, GPS velocities are generally 20-5mm/a, without obvious regularity. It means that these regions have relatively weak deformation of the crust.⑦As the Pamir region lacks sufficient GPS sites, its differential crustal motions cannot be determined directly. Considering the GPS velocity fields surrounding this region, it is speculated that it may strongly rotate under the hampering of the rigid Tarim block.4. The continuous GPS strain field in the great triangular seismic region in central Asia derived from preferred spatial interpolation. Adopting the 2D high tension spline (τ=0.95) interpolation algorithm, this work made interpolation uniformly to the irregular GPS velocity field with a 0.5°×0.5°grid. Then the regular grid strain rate with 1°×1°grid was calculated by 9 velocity vectors of the boundaries and interiors of each grid, yielding situations of crustal deformation of each area in the great triangular seismic region of central Asia quantitatively and intuitively.①The whole Himalayan arc-shaped terrain is subject to intensive compression and shortening along the convergence direction of the India plate and Eurasia plate with typical compression and shortening strain rate of 30-60×10-9/a, locally reaching 80-90×10-9/a. Such deformation in the western Himalaya is more intensive than that of the eastern Himalaya. Meanwhile, it also experiences slight lateral extension in the direction roughly normal to the plate convergence.②In the Lhasa terrain, the strain rate of compression and shortening in the plate convergence direction declines to20-30×10-9/a. While in the middle its lateral extension is very notable with representative values 20-30×10-9/a, and locally as high as 40-60×10-9/a, which is consistent with widespread NS trending normal faults in this region.③The typical strain rate of mid-west of the Qiangtang block is approximate NS compression and EW extension. The value is about 15-25nanostrain/a.While in the eastern Tibetan plateau, the strain field exhibits obvious nearly NS extension with a rate 20-30 nanostrain/a.④No obvious strain is seen in the Sichuan basin and its north, with the value below 10 nanostrain/a. The Kunlun block and Qaidam block have a uniform strain rate, mainly in a NE-SW compression and NW-SE extension. The strain rate values are 15-25nanostrain/a for compression and 10-15nanostrain/a for extension, respectively.⑤The strain in the Chuandian region southeast of the Tibetan plateau is strong and complex with variable directions. Nevertheless, it is a clear pattern that the approximately EW extension and NS compression characterize this region.⑥In the Tien Shan region, NS compressive deformation is dominant. But the compressive shortening is not uniform, where the maximum strain rate value is about 30nanostrain/a⑦In the Baikal region. NW-SE extensional strain exists in the whole zone. The largest strain rate is 40nanostrain/a. In the eastern Baikal exists some NNW and NNE compression, with the maximum value 10nanostrain/a. Analysis of plane dilatation strain of Baikal shows that it is a whole expansion.5. Division of deformed crustal blocks and average strain analysis for the great triangular seismic region in central Asia. This region comprises the Tibet-Himalaya compression area, Tien Shan compressive orogen, Baikal extensional area and Chuandian shear area. Based on previous studies, according to characteristics of crustal deformation, this work subdivides the whole region into five types of deformed blocks, i.e. quasi-rigid block, purely extensional block, purely compressive block, extension-dominant block, and compression-dominant block. Consequently, the great triangular seismic region in central Asia comprises the following blocks:East Tarim, West Tarim, Ordos, Alasan, South China, Sayan, Amur, Zhungeer, Tien Shan, Qilian, Bayan Hara, Qiangtang, Lhasa, South Yunnan and Chuandian. Among them, the Ordos block, Tarim block, and Alasan block are rigid massifs.6. Fitting and interpretation of the present-day GPS velocity field in the great triangular seismic region in central Asia based on joint usage of the fault dislocation model in half-space, Euler rotation model of the quasi-rigid block and strain-rotation model of the elastic block. This work simplifies and synthesizes the major active faults in the great triangular seismic region in central Asia, builds up the 3D fault segment geometries of each fault in half infinite elastic space, and gives an necessary prior information of fault movements. Constrained with 1233 GPS velocity vectors in the great triangular seismic region, it adjusts the prior slip rate of each fault segment within reasonable ranges, then makes the best fit of GPS velocity vectors with a model of half infinite elastic space containing deep fault dislocations as well as inversion of slip rates of all the fault segments. At the same time, it adopts the rigid block rotation model and elastic block strain and rotation model to describe the rest residuals which can not be well explained.7. Relationship between seismic activity and crustal deformation in the great triangular seismic region. This work analyzes the relationships among spatial-temporal distributions of earthquakes, the field of accumulative seismic moments, field of plane expansion rates and field of maximum shear strains. And it compares the spatial corresponding relationship between the accumulation rates of seismic moments and release of seismic energy. The result shows that although there exists some spatial correlation among the strain rate field, planes expansion rate field, shear strain rate field and earthquakes in the study region, it is of a complicated relationship. On the other hand, the correlation between the seismic energy release and accumulation rate of seismic moments is not obvious. The most possible reason for this result is that only quake data of 100 years are used for calculation of seismic energy release. Compared with the average recurrence intervals of intraplate earthquakes, such a time span is too short to describe the distribution of seismic energy release in a complete seismic cycle.更多还原