最小二乘配置下的天山地区应变场特征分布

利用已有的GPS观测数据,借助球面最小二乘配置方法对天山地区的GPS速度场进行研究,得到了研究区域应变场的空间分布特征．其最大主压应变表明,大地震多发生在主压应变快速交替变化的地带,主压应变最大值主要分布于西南天山与帕米尔弧及塔里木西北交汇的地区,强地震(M7.0—8.0)基本发生在该区域．面膨胀值表明天山地区应变呈挤压收缩的特征．     

Coupling characteristics of stress and strain at different layers of different sub-regions in Yunnan and its adjacent areas

In this paper,we collect 6 361 waveform data to calculate the shear wave splitting parameters from a regionalseismic network of 22 digital stations in Yunnan and its adjacent area from July 1999 to June 2005.By using thecross-correlation method,64 splitting events of 16 stations are processed.We also collect the splitting results ofeight earthquake sequences to present the characteristics of shear wave splitting in Yunnan and its adjacent areas.The orientations of maximum principal compressive stress of three sub-regions in this area are derived from theCMT focal mechanism solutions of 43 moderate-strong earthquakes provided by Harvard University by the P axisazimuth-averaging method.The principal strain rate at each observatory is deduced from the observations ofCrustal Movement Observation Network of China during the period from 1999 to 2004.In addition,the data of Pnaniso-tropy and SKS splitting of Yunnan and its adjacent areas are also collected.We have discovered from thisstudy that the continental lithosphere,as a main seismogenic environment for strong earthquake,can be dividedinto blocks laterally;the mechanical behavior of lithosphere varies with depth and can be divided into differentlayers in the vertical orientation;the information of crustal deformation obtained from GPS might be affected bythe type of blocks,since there are different types of active blocks in Yunnan and its adjacent areas;the shear wavesplitting in this region might be affected mainly by the upper crust or even the surface tectonics.     

Numerical analysis of contemporary hori-zontal tectonic deformation fields in China from GPS data

Introduction To correctly understand the tectonic deformation of continental lithosphere, its dynamical mechanics and seismic activity, we should firstly acquire the velocity field and strain field of lithospheric tectonic motion with fine resolution and consistent accuracy (Molnar and Lyon-Caen, 1989; Molnar, 1990). And the quality, distribution and density of observed data are the basis for studying crustal tectonic deformation. In the past, crustal deformation is usually determined indi-r…     

Research on present crustal deformation in the southern Tianshan (Jiashi) region by GPS geodesy

IntroductionSinceaMs=6.9earthquakeoccurredinArtux,Xinjiang,ChinaonMarchl9,l996,7earth-quakeswithmagnitudeofMs>6werefollowedsuccessivelynearbyJiashi,southemnanshan.Thephenomenonthatagroupofstrongearthquakes(Jiashiearthquakeswann)concentratedwithinashorterperiodoflyearormoreisanunprecedentedeventsincetheinstrUmentalrecordofseis-micityinthecontinent,drawingconsiderableattentionofseismologists.TheJiashiearthquakeswarmhaPpenedonthenortheastemflankofthewestCmsyntaxofHimalayancollisionbeltwheret…     

鄂尔多斯块体南缘现今水平应变特征分析

根据陕西省2001和2003年两期的GPS测站的观测资料,给出了鄂尔多斯块体南缘现今地壳水平应变场。结果表明,最大剪应变和面应变的高值区主要集中在该区中部和东部,尤其是在中部的咸阳、泾阳附近,东部的合阳、大荔、渭南一带以及西北部的陇县附近,主要受面收缩影响,分别形成了几个较为显著的应挛高值区。等值线较密集并且应变梯度也较大,这些区域具备一定的孕震条件,有可能是未来发震地点。     

黑龙江及邻近地区北西向断裂与滨州断裂地震活动特征分析

依据地震空间缺震、频度增强、b值和GL值扫描等结果,分析了黑龙江省及附近地区第5活跃期以来北西向断裂和滨州断裂地震活动特征,确定了未来地震的危险区。     

重庆及邻近地区水平向基岩地震动加速度峰值与反应谱衰减关系

结合重庆及邻近地区地震烈度衰减关系,选择有丰富强震记录和地震烈度资料的美国西部作为参考地区,采用转换方法,得到重庆及邻近地区基岩水平地震动加速度峰值与反应谱衰减关系。     

Upper mantle convection beneath northwest China and its adjacent region driven by density anomaly

Introduction The northwest of China includes Tarim, Junggar and Qaidam basins, and Kunlun, Tianshan, Altun and Qilian mountains, as well as the north part of the Tibetan Plateau. For a long time, the study of lithosphere structures and dynamics in this area has been a popular topic in geoscience, and has yielded many results. For example, TANG (1994) and LI et al (1998) suppose that the tectonic structure of Tarim Basin is various with geological periods, which changes many times betwee…     

新疆地区现今地壳形变特征与地震活动分析

新疆地区GPS区域站1999—2007年、 2009—2011年观测资料分析结果表明, 该地区水平运动速率分区性明显; 2011年6月以来该地区中强地震增强. 该文在分析区域站水平运动速率特征的基础上, 对2011年1月—2012年3月20个GPS连续观测站基线变化时间序列进行了分析. 结果表明, 各观测站坐标变化量在2011年4月后整体上变大, 新疆地区地壳运动增强, 但具体到不同的山区和盆地, 基线变化趋势各异． 其中, 塔里木盆地和准噶尔盆地内部变形相对较小, 主要变化发生在天山中南部, 出现明显的南北向挤压缩短．     

基于GPS的云南地区活动地块现今运动及应变特征分析

利用GAMIT/GLOBK软件,对云南境内以及川滇交界区域2009年、2011年、2013年3期陆态网络区域网联测数据进行处理,得到欧亚框架下的测站运动速度场。将云南地区划分为4个活动地块及7个次级构造单元,以GPS速度场为约束,建立块体的整体旋转与均匀应变模型(REHSM),采用最小二乘法,得到华南、滇东、滇中、川滇菱块南段、印支、保山及腾冲地块的运动速度。对活动块体运动进行分析,认为云南地块运动方向由SSE向逐渐至SSW向变化,具有顺时针旋转特征,运动幅度由西向东、由北向南逐渐减弱,菱形块体外各块体运动速度大幅衰减。从应变率参数结果看,华南地块、滇东块体主要受SE向压应力场控制,到滇中地块转为SE—SSE向,滇西北地区应力场方向为SSE向,滇西南印支地块为NNW向,滇西南腾冲—保山地块主要受NE—NNE向应力场控制。     

2001～2004年陕西关中地区地壳运动及应变分析

根据2001-2004年陕西省地震局GPS测站的观测资料，做出了陕西关中地区地壳运动速率和地壳水平应变场，结果表明：①相对于稳定的欧亚板块，陕西关中东西部在不同期次地壳运动差异明显；②该区最大剪应变与面应变高值区主要分布在关中地区中部的铜川-三原-西安-咸阳一带、华县以及宝鸡一眉县附近，应变梯度较大，并且主要受面收缩影响，地震危险性相对较高。     

北京及邻近地区中等以上地震地下流体异常识别与特征研究

系统分析了北京及其邻区多年积累的震例资料, 提出该区的地下流体异常分为趋势上升型中期异常、 转折型中短期异常、 突发型短期异常和短临异常等类型。 运用“同一化”思路、 从属函数、 剩余曲线及原始曲线均方差等异常判定方法, 提取了中等以上地震, 特别是5级以上地震的中、 短、 临异常实例。 通过对流体异常特征的统计分析, 给出了北京及邻近地区的中期、 中短期、 短期和短临异常的时间分布特征, 并对地震前各阶段异常的超前时间进行了总结, 该时间可作为发震时间的预测指标。 在实际应用中可为该区的震情判定提供依据。     

利用地震和爆破资料反演宁夏及邻区浅层三维速度结构

将有限差分正演及LSQR反演方法应用到宁夏及邻区,利用该区2003-2009年7年间的地震和爆破记录,经过重新细致分析,得到了具有4个以上台站清楚记录到初至波Pg和Pn到时的地震426次、爆破52次,剔除到时离散较大的数据后共有2 788条记录.获得了不同深度的速度平面分布图像以及不同位置的深度速度剖面图像.得出深度0...     

京津唐及邻区地壳结构的中新生代构造运动响应

以华北地块作为实施“国际地壳与上地幔模型计划（IGCP-474）”示范区,我们综合京津唐及邻区的8条宽角反射地震剖面地壳速度结构, 计算了该区域不同构造域上、中及下地壳平均速度和厚度.利用格里金插值技术构建上、中、下地壳平均速度、厚度和底界深度在空间上变化图像.这些图像指示出,京津唐及邻区发育沿近东西和北东两个方向展布的隆起与拗陷,发育受北东向断裂控制的断隆和断坳.这些地质构造的形成与该区域发生在中生代以来的构造运动密切相关,推断京津唐及邻区在中新生代至少发生三期较强烈的构造运动.结合区域构造研究成果得出,近东西向展布的隆起和拗陷形成于三叠纪,北东向展布的隆起和拗陷形成于侏罗纪,受北东向断裂控制的断隆和断坳则形成于白垩纪以来.由于中地壳为壳内低速层,与上、下地壳的变形规律截然不同,以塑性变形为主,造成中地壳在隆起部位厚度大、速度低,拗陷部位厚度小、速度高,其厚度较大的部位地壳强度整体降低,在后期构造运动中易发生断裂变形,进而控制京津唐及邻区现今地震活动.     

汶川地震前后川滇及其邻区GPS水平运动演化特征

利用川滇及其邻区2004-2007年、2007-2009年GPS水平运动观测资料,对汶川地震前、震时与震后地壳运动及主要活动断裂带构造变形演化特征、汶川地震可能的同震与震后影响进行了分析.结果表明:2007-2009年汶川震区呈现出显著的右旋逆冲同震变形;大震在一定程度上对甘川交界及其北侧的西秦岭构造区、安宁河—则木河断裂的构造运动有所促进;对鲜水河断裂构造运动总体反映调整影响但对其南段可能有促进作用.     

区域网GPS观测得到的2008年汶川M_S 8.0地震前的地壳水平运动

2008年5月12日汶川（31.0°N,103.4°E）MS8.0大地震发生在中国地壳运动观测网络区域网GPS观测站相当密集的地区．1000个站的GPS 非连续观测区域网分别在1999,2001,2004年和2007年作了4次观测．震前区域网GPS观测站得到的水平位移表明,汶川大地震主要力源是印度板块向北对中国大陆的挤压,但同时也受到东部与南部板块的挤压．与其它地区相比,震前震中附近水平位移最显著的特点是,汶川地震发生在南北地震带上位移分叉部位,即震中北部明显向东北位移,震中南部明显向东南位移,而震中附近的水平位移则明显小于其北面和南面的水平位移．简要讨论了应变计算结果的精度．为获取地震前的异常信息,分别采用趋势曲面拟合和统计方法研究了汶川地震前（1999—2007年）区域网的应变积累,寻找震中的大致区域．除了2001年昆仑山口西大地震震中及其周围地区外,1999—2007年震前区域网的应变积累的趋势曲面拟合表明,汶川地震发生在中国大陆第一剪应变积累大、范围最广的区域的东侧,且在此区域内积累较大的面压缩区的东北边缘．应变分量的统计分析表明,震前其分布在此区域及其附近同样有明显的异常,剪应变和面膨胀积累均增强．      

The deformation pattern and fault rate in the Tianshan Mountains inferred from GPS observations

Based on GPS measurements conducted from 1992 to 2006, we present the current crustal movement velocity field for approximately 400 sites in the Tianshan Mountains and their adjacent areas, and estimate slip rates on the major faults using a 2-D elastic dislocation model. Our studies show slip rates within the range of 1―4 mm/a on the NW-SE trending strike-slip faults (such as Talas-Fergana fault) in the Tianshan Mountains. We also found the slip rates on the approximately WE-SN trending gently-dipping detachment fault vary from 10―13 mm/a for the southwest Tianshan Mountains to 2―5 mm/a for the eastern Tianshan Mountains, and to 6―12 mm/a for the Kyrgrz Tianshan. The GPS velocity field reveals that the total convergence is not uniformly distributed across the Tianshan Mountains, with 80%―90% of the N-S shortening absorbed along the southern and northern edges, and relatively little deformation accommodated within the interior. This first-order feature of strain pattern is explained best by underthrusting of adjacent blocks beneath the Tianshan Mountains along a basal detachment fault. We found the occurrence of historical M7―8 earthquakes somewhere in the locked ramp that connects the creeping and locking segments of the detachment, thereby resulting in elastic strain concentration and accumulation around it. The elastic strain confined in the upper crustal layer above the detachment ultimately releases through infrequent great earthquakes in the Tianshan Mountains, resulting in considerable folding and faulting at their margins. The Tianshan Mountains propagated outward and rose progressively as a wedge-shaped block.     

Horizontal crustal movement before the great Wenchuan earthquake obtained from GPS observations in the regional network

The great Wenchuan earthquake of M8.0 on May 12, 2008, occurred in an area with dense GPS observation stations in the regional network of the Crustal Movement Observation Network of China (CMONOC). Non-continuous observations were carried out at the 1 000 GPS stations of the regional network in 1999, 2001, 2004 and 2007. The horizontal displacements at GPS stations in the regional network before the Wenchuan earthquake show that the main driving tectonic force of the earthquake was the northward pushing of the Indian plate, added at the same time by the pushing of plates on the east and south. In comparison to the displacements in other regions, the horizontal displacements near and around the seismic area is characterized by diverging eastward displacements, that is, the stations to the north of the epicenter moved in the ENE direction while those to the south of epicenter moved in ESE direction with smaller displacements at stations near the epicenter. The accuracy of the estimated strain results is briefly discussed. In order to obtain the anomalous information before the earthquake, the methods of both best fits by trend surface and statistics have been used in the study for finding the future epicentral area from the strain accumulations in the regional network observed from 1999 to 2007 before the Wenchuan earthquake. Besides the epicentral area of the western Kunlun mountain pass earthquake of M8.1 in 2001, the results of best fits by trend surfaces of the strain accumulations from 1999 to 2007 in the regional network show that the Wenchuan earthquake occurred at the eastern fringe of a large area with relatively large accumulations of the first shear strains and also at the northeastern fringe of a smaller area with significant accumulated areal compressions. The statistics of the accumulations of the strain components demonstrates that they also showed anomalous distribution patterns in this area and its neighborhood with increasing accumulations of both shear strains and areal compressions.     

空间大地测量GPS揭示的汾渭盆地及其邻域现今地壳应变场变化特征

利用汾渭盆地及其邻域2001-2007年与2009-2011年高精度GPS监测资料,基于区域构造特点,采用块体运动应变模型结合数理统计假设检验法,建立了区域合理的地壳运动应变模型,基于此定量研究了区域现今地壳应变场及其变化特征,特别是2008年汶川强震对汾渭盆地区域变形特征的作用影响,同时从盆地整体上分析了盆地内多发的地裂缝灾害与区域整体构造变形特征之间的内在关系.研究结果表明:经统计检验判断,选择合理的区域地壳运动应变模型,对获取真实反映区域实际构造变形特性的应变参数具有重要的作用;2008年汶川强震对青藏东边缘地块及渭河盆地西侧局部地区应变场造成一定的影响,但是震后上述区域并没有出现显著的应变积累而是呈现出应变量值较震前减小的特征,分析其原因可能是因为此区域并不是强震造成的库仑应力显著增加区,在震后2009-2011年时间段内处于构造应力场的松弛调整期;汶川强震没有显著改变研究域现今整体的构造变形背景特征,区域地壳构造活动特征仍具有较好的继承性;基于研究域构造块体具有各向同性连续弹性变形的前提,初步推断整个汾渭盆地内多发的地裂缝灾害可能是区域NW-SE向拉张应力场作用下的地表破裂响应.