【作者】 牛之俊；

【导师】 王乘；

【作者基本信息】 华中科技大学 ， 系统分析与集成， 2006， 博士

【摘要】 中国大陆受周缘板块的挤压、各块体间的相互作用影响,致使其内部聚积了特别强大的构造作用力,历史上成为板内构造最活跃、板内地震最强烈的地区,构造变形覆盖了印欧碰撞带以北两到三千公里的范围。正确理解大陆构造变形运动过程及其动力机制,是探求地震成因和进行中、长期或短临地震预报的首要前提。因此,必须首先获取分辨精细、精度一致的岩石圈构造变动速度场,而岩石圈构造变动速度场的获取必须以质量均匀、分布广泛、密度适当的地壳变形和应变的实测资料作基础。迄今为止,对此运动、动力过程的认识基本来自第四纪以来主要活动断层大量观测调查及百余年来地震矩张量反演。中国大陆的晚新生代构造变形分布十分广泛,获取第四纪活动断裂和活动褶皱的定量数据需要漫长的时间和大量的投入,短时间内很难完成。地质学、地震学对地壳整体运动研究仍是一种间接推算,受资料来源及分析方法上制约,其准确性与可靠性在短期内难有根本提高,对现今地壳运动形态的精细观测更难有作为。与地质、地震资料相比,GPS观测结果具有量化清晰、精度高,时间尺度一致,动力学意义明确等优点,逐步成为岩石圈大尺度构造运动与动力学研究的重要基础资料。自上世纪八十年代开始,中国大陆现今地壳运动的GPS监测资料日益丰富,一张全面反映中国大陆地壳运动的速度图像已经形成,使利用GPS测定的站点速率,研究构造变形的模式速度场成为可能。本文继续了前期工作,主要用“中国地壳运动观测网络”实测速率值(1200个测站),通过数值模拟技术构建了南至青藏高原南侧的印欧板块碰撞边界和南中国海,北至贝加尔湖,西至咸海以东的中亚地区,东以日本海以西为界的中国大陆构造变形的整体速度场。为此本文针对构造变形是以连续还是以分块的方式进行了对比研究。首先在地块细分的多样性和块体边界的不确定性条件下,中国大陆的构造变形运动虽然块体或断裂带之间的非连续性是绝对的,可当假定中国大陆运动在重力驱动下类似流体缓慢流动,认为可将变形描述为连续粘性介质运动。基于此,本文利用球面上双三次样条函数数值模拟方法,将离散的值在空间域上连续化,来求解中国大陆的构造变形场,应变场。然后本文根据块体、非连续变形假定反演中国大陆GPS速度场,结合中国大陆活动构造背景,建立地块运动模型。以整个变形区域内的主要走滑断层、正断层和逆断层为边界细致划分块体来同时模拟弹性岩石圈块体的旋转和边界断层闭锁产生的应变。给出了33个块体的细致模型和29个块体的简化模型;得到了各主要断层的活动速率、地块运动速率、欧拉矢量以及应变率。两种模拟GPS观测结果显示:(1)印度板块与欧亚板块的碰撞、挤压是构成中国大陆内部岩石层水平形变的主要驱动力;对中国大陆及周边地区构造活动的连续变形分析还表明GPS推算的数年尺度应变场的平均最大、最小水平主压应变率方向与长期地质资料、百年尺度地震资料展示的应力状态基本吻合;(2)绕东喜马拉雅构造结,模型速度场和主应力方向有近似180o的顺时针旋转,说明中国东南部的应力场主要受到了周边特定板块边界的作用;(3)太平洋板块和菲律宾板块作用力虽然比印度板块的作用力小,但仍然是影响中国大陆东部的重要因素;(4)以玛尼-玉树-甘孜-理塘断裂带为中心构成了一条现今地壳物质东流带,并且青藏高原物质向东的挤出或流动没有超出其东边界,而是在东边界一带转化成绕东喜马拉雅构造结的顺时针旋转;(5)青藏高原内部以连续地壳变形或均匀地壳缩短为现今构造变形的主要特征,印度和欧亚板块之间相对运动量的90%被青藏高原的现今地壳缩短速率所吸收和调节,且西藏中部东西存在东西向的拉张,其拉张速率为16mm/yr左右;(6)阿尔金断裂带的左旋走滑速率是5.8±1.5 mm/yr ,祁连山和阿拉善之间的左旋走滑速率是6.5±2.0mm/yr,横穿喜马拉雅和青藏的南北向压缩速率为19.0+/-2.0 mm/yr,穿过西天山的南北向压缩速率为14.0±1.1 mm/yr,穿过中天山的南北向压缩速率为7.9±1.2mm/yr;(7)塔里木块体围绕欧拉极(37.39°N, 96.4°E,-0.533°/Ma)相对西伯利亚作顺时针旋转,华南块体则围绕欧拉极(63.38°N,159.87°W)作轻微的顺逆时针方向旋转,鄂尔多斯块体围绕欧拉极(49.06°N,118.51°E,0.213°/Ma)相对西伯利亚作逆时针方向旋转。从统计结果和GPS残差图来看两种模型在中国大陆范围内都得到了较好的模拟效果。但连续模型似乎得到更好拟合效果,但这并不表明分块模型不能适用于大陆构造研究。实际上,本文得到的块体滑动速率、活动断裂滑动速率说明无论青藏高原,还是整个中国大陆,现今活动构造变形仍可以视为有限制的较低速率岩石圈和块体运动,不过进一步比较有待今后更多的GPS数据和地质、地震资料。更多还原

【Abstract】 China continent is characterized by considerable intraplate deformation that is witnessed by widespread earthquakes, arisen from the continental collision between Eurasia and Indian plates and interactions among sub-plates. A quantitative description, with suitable resolution and precision, of tectonic kinematics is a prerequisite for qualitative understanding of physical properties of continental lithosphere and its dynamic aspects which control the continent deformation, which are of critical to reveal earthquake mechanism and forecast earthquake. In the last decade, kinematic demonstration of continent deformation at a large scale of 2-3 thousands of kilometers in Asia was mainly rooted in the observations of Quaternary active faulting and a summation of one-century long seismic moment tensors. Because of the limited amount geologic works in critical areas such as Tibet and rather shorter catalog of historic earthquakes available for inversion, the derived velocity field depicting the ongoing crustal movement was poorly constrained.And any attempt to improve its precision and resolution in relative short period is hampered by many limiting factors that remains nowadays. To the contrary, Global Positioning System (GPS) measurement, with its outstanding merits such as high precision, low expense, dense distribution and flexible survey mode revolutionizes monitoring of the crustal movement at all scales ranging from global plate motion for several thousands of kilometers to local fault slip within several kilometers. From 1990s, the GPS data have been accumulating progressively in China. As yet, a unified measurement of crustal deformation velocity field for the Chinese mainland has been available, based on the sophisticated analysis of these data. With that, tectonic deformation velocity field and its gradient field are inferred through fitting to the GPS-derived velocity data. This work advances the former studies by matching directly over 1000 GPS velocities with a continuous horizontal velocity field for the entire China using the method assumed that continental deformation is distributed continuously.The instantaneous active deformation in Asia was approximated numerically by various methods such as f crustal flow and rigid blocks. The tenet of these methods is attributed to assumptions describing the kinematic behavior of crust deformation as continuum flow or block-like motion. Although active faults which delineate generally boundaries of rigid blocks in Asia are distributed over the Tibet and its adjacent regions with moderate and major faulting, A school of thoughts suggested that the kinematics of crust deformation is analogous to response of a thin viscous sheet drived by gravitational potentional difference, therefore it can be treated as continuous viscous medium. Base on this, this study applies Bi-cubic Spline interpolation function on the earth sphere to best matching GPS site velocities in order to recovery a unified crustal deformation field.This paper summarizes the tectonic movement and dynamics background in China, and firstly simulates the contemporary horizontal velocity and strain rate fields (~1200 velocity vectors) in China, assuming that the crust can be treated as a continuum, the velocity field inferred from the GPS rates has an overall precision better than 2 mm/yr. Secondly, on the basis of block-like model on framework of active tectonics in China continent, two kinds of block-like kinematic model to fit the GPS velocity field are investigated . The GPS vectors are inverted simultaneously for the rotation and fault locking . the slip rates of the major faults are inferred. and motion velocity and Euler rotation poles are calculated for each block of which the internal strain rate are assessed too.Our modeling demonstrates that:(1) The collision between India and Eurasia plate is the main driving force which controls horizontal component of crustal deformation in most of China continent;(2) The velocity field and direction of principal stress axis have a clockwise rotation of about 180°around the Eastern Himalaya Syntaxis. The rotation shows that the stress field in southeast China is mainly influenced by the combined forces transferred from plate boundaries to east and southwest;(3) The Pacific and Philippine Sea plates are important factors modulating the stress field of the eastern China;(4) The extrusion rate toward N13.5°E direction increases from south to north, and reaches to the maximum along the Mani-Yushu-Ganzi-Litang, which suggests there exists an eastward crust flow, bounded to the north, by the Mani-Yushu-Ganzi-Litang zone. The eastward extrusion doesn’t extend beyond the east boundary of the Tibetan Plateau. The eastward extrusion is translated into a clockwise rotation around the Eastern Himalaya Syntaxis;(5) In the velocity field, a large fraction, ~90 %, of India’s convergence with Eurasia is absorbed by crust thickening, especially the north-south shortening across the Himalaya. The Tibetan plateau is subject to widespread E-W extension at a rate up to 16mm/yr;(6) localized deformation is concentrated on the Altyn Tagh faul associated with 5.8±1.5mm/yr of left-lateral strike-slip, and N-S compression of 6.5±2.0mm/yr is founded to occur within a zone between Qilian Shan and Alashan. The convergent rate is estimated to 19.0 +/-2.0mm/yr across Himalaya and south Tibet, 14.0±1.1 mm/yr in the western Tien Shan, and 7.9±1.2 mm/yr on central segment of Tien Shan;(7) India rotates relative to Eurasia about a pole at (27.9°N 19.6°E 0.395°/Ma), south of China moves at 8.0±1.5 mm/yr in the direction of N120°±7.4°E, corresponding to a pole at 63.38°N,159.87°W,0.088°/Ma. Tarim Basin rotates clockwise relative to Eurasia about a pole (37.39°N,96.4°E,-0.533°/Ma), Erdos block rotates counterclockwisely relative to Eurasia about a pole at 49.06°N,118.51°E with a rate of 0.213°/Ma.The studies indicate that the GPS velocity field can matched equally well with plate-like model and continuous deformation model at a uncertainty of 1-2 mm/yr attained by existing measurements, though overall misfit of the GPS inversion is in slightly favor of the continuous deformation model. In fact the consistency between GPS velocity and the block model also preclude the conclusion that the continuous deformation model is superior to the block model in kinematic description of continental deformation. To the contrary, this studies argue for a widely accepted opinion that the continent tectonic deformation may be described best by block-like motion and interaction among them along the edges but the present-day motion rates of blocks are in generally not so fast as we thought before.更多还原