Current horizontal strain field in Chinese mainland derived from GPS data

Introduction In the years when the reliable data could not be obtained and in the analysis of strain property and magnitude in history, the intensity, property and activity pattern of strain field were mainly inferred on the bases of geometric characters of surface traces and behaviors (especially the faults) as well as the characteristics of petrology (XIE, et al, 1993; Molnar, Tapponnier, 1975, 1977; Tapponnier, Molnar, 1977; FU, et al, 2000). However, they are the averaged results accumu…     

Characteristics of present-day active strain field of Chinese mainland

On the basis of the GPS data obtained from repeated measurements carried out in 2004 and 2007,the horizontal principal strain of the Chinese mainland is calculated,which shows that the direction of principal compressive strain axis of each subplate is basically consistent with the P-axis of focal mechanism solution and the principal compressive stress axis acquired by geological method.It indicates that the crustal tectonic stress field is relatively stable in regions in a long time.The principal compressive stress axes of Qinghai-Tibet and Xinjiang subplates in the western part of Chinese mainland direct to NS and NNE-SSW,which are controlled by the force from the col-lision of the Eurasia Plate and India Plate.The principal compressive strain axes of Heilongjiang and North China subplates in the eastern part direct to ENE-WSW,which shows that they are subject to the force from the collision and underthrust of the Eurasia Plate to the North America and Pacific plates.At the same time,they are also af-fected by the lateral force from Qinghai-Tibet and Xinjiang subplates.The principal compressive strain axis of South China plate is WNW-ESE,which reflects that it is affected by the force from the collision of Philippine Sea Plate and Eurasia Plate and it is also subject to the lateral force from Qinghai-Tibet subplate.It is apparent from the comparison between the principal compressive strain axes in the periods of 2004～2007 and 2001～2004 that the acting directions of principal compressive stress of subplates in both periods are basically consistent.However,there is certain difference between their directional concentrations of principal compressive stress axes.The sur-face strain rates of different tectonic units in both periods indicate that the events predominating by compressive variation decrease,while the events predominating by tensile change increase.     

菲律宾海板块的整体旋转线性应变模型与板内形变-应变场

用菲律宾海板块上7个站ITRF2000的速度建立了菲律宾海板块的整体旋转线性应变模型. 结果认为菲律宾海板块的现今运动是顺时针方向旋转，与NNR_NUVEL_1A估计的旋转方向一致，但与NNR_NUVE_1A估计的旋转极位置和旋转角速度有较大差别. 本文模型与Sella等建立的刚体运动模型相比能更精确地描述菲律宾海板块的现今构造运动与板内形变. 菲律宾海板块内部存在强烈的形变-应变场. 在板块上存在一致的向东形变，形变速率在中央构造线附近小，东、西边界附近大，南、北两端小，中部大，在Mariana弧上向东的形变速率达到484 mm/a. 板块上南北方向的形变，东、西部存在明显差别，东部的南北向形变速率很小，西部在Manila海沟附近南北向形变速率较大，北端向北的形变速率为113 mm/a，南端向南的形变速率为293 mm/a. 板块的中央构造线把板块的主应变场分为东、西两个区. 东区存在非常强烈的张应变，压应变则很弱. 主张应变为近东西方向，从中央构造线向东主张与主压应变率逐渐增加，板块东南边界附近（148°E，15°N）主张应变率最大为858×10-8/a. 在西区，存在很强的主压应变而主张应变则较弱，主压应变为NW-SE方向，主压与主张应变率呈现从中央构造向西逐渐增加的特征，在板块西北边界（122°E，23°N）附近，主压应变率最大为571×10-8/a. 菲律宾海板块主应变场的空间变化与板块内部及周围的构造背景密切相关，是构造应力场的反映.     

弹性板块运动模型研究进展

传统板块构造理论认为板块是一个刚体，实际上板块是可变形的.板块内部几年到几十年时间尺度的变形主要是弹性变形,因此应当用弹性模型描述板块运动.推导了板块的弹性运动方程，由空间大地测量新的观测成果建立了菲律宾海、太平洋和澳大利亚板块的弹性运动模型.发现三个板块内部都存在明显的水平形变.板内应变场的空间变化有明显的规律：板块边界附近的应变率最大，从边界向内部逐渐减小；在板块扩散边界附近，主张应变率大于主压应变率，主张应变轴基本上与边界的扩张方向一致；在俯冲边界附近，主压应变率大于主张应变率，主压应变轴基本上与板块的俯冲方向一致；在走滑兼有俯冲性质的边界附近，最大剪应变的方向与边界断裂的走向基本一致.由GPS观测得到的主压应变轴与由震源机制解得到的主压应力轴方向具有很好的一致性.板内的应力－应变场基本上遵循广义胡克定律.     

Horizontal movement and strain characteristics in Tianshan and its adjacent region with GPS deformation data

Introduction The Tianshan Mountain is the youngest cordillera in the present-day continental Asia, and its tectonic evolution is closely related to the collision and subduction between Indian Plate and Eurasian Plate in the Himalayas orogen since Cenozoic…     

对中国大陆地壳水平变形的初步探索

根据全国ＧＰＳ网１９９４和１９９６年两期观测资料的处理结果,讨论了中国大陆地区现阶段应变场和应力场。青藏亚板块的西部和东部张应变起主导作用,中部压应变占优势,主压应变方向为北北东向;青藏亚板块东南部东南段云南地区的主压应变方向为北西向,压应变和张应变量级相当。新疆亚板块的主压应役北北东向至北东向为主,应变量存在差别。华北亚板块的主压应变方向是北东至近东西向为主导,局部地段存在差别,大部分地区压应变     

中国大陆应变应力场研究

根据1999～2009年网络工程GPS观测资料计算得到的应变率参数,研究了中国大陆地壳的应变应力场及其地壳现今的水平活动特征。结果表明,中国大陆地壳西部青藏亚板块的压应力主方向围绕藏南和阿萨姆构造结向北、东、南依次辐射撒开。新疆亚板块自西向东由近SN向变为NE向。中国大陆东部地壳的压应力主方向自北向南由NEE变为近EW向,再变为SEE向。中国大陆主压应力作用强度西部显著大于东部。中国大陆地壳西部强于东部,南部强于北部,现今西部地壳以挤压、走滑为主,东部地壳既有挤压、走滑,也有拉张。     

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．      

GPS初步结果揭示的中国大陆水平应变场与构造变形

根据中国大陆不同来源的多个GPS区域监测网1991～1999年间的观测资料和“中国地壳运动观测网络”基本网1998～2000年的观测资料，联合处理得到中国大陆地壳水平运动速度场结果，通过最小二乘配置法建立中国大陆水平运动速度场模型，获得了基于连续介质假设的中国大陆水平应变场（或称为视应变场）初步结果. 分析了水平运动、应变场空间分布特征及其与强震的关系，并简要分析了2001年11月14日昆仑山口西8.1级大地震的区域构造变形背景. 结果表明：中国大陆中西部构造变形强烈，应变速率值高，又以青藏块体及其边缘和新疆西部最为显著. 除川滇、新疆西部外，大部分地区的近东西向断裂存在左旋剪切变形，近南北向的断裂存在右旋剪切变形. 而东部地区构造变形相对较弱. 强震通常发生在剪切应变率的高值区及其边缘，尤其是与构造变形背景相一致的剪应变率高值区. 昆仑山口西8.1级地震发生在最显著的东西向左旋剪切应变率高值区，从该区域的应变状态分析，具备近东西向断裂产生巨型走滑破裂错动的构造变形背景.     

中国大陆及其周边地区应力场特征

本文收集了1976—2018年发生在中国大陆及其周边地区(15°~55°N, 65°~125°E)的4303个地震震源机制解, 分析了该区震源机制解和P、 T轴空间分布特征, 并使用这些震源机制解, 反演得到了中国大陆及周边地区二维构造应力场分布。 应力场反演结果表明, 云南大部、 青藏高原大部以及华北华南大部以走滑型应力性质为主, 印度洋板块与欧亚板块的强烈碰撞控制着中国西部地区, 大量的逆断型地震集中分布在青藏高原周缘和西域活动地块的天山地区。 青藏高原内部也存在正断型地震, 且应力场方向在26°N发生了很大的变化。 位于青藏高原东构造线以南的滇缅活动块体, 最大主压应力σ₁方向在大致100°E发生突变, 由以西的NNE方向偏转到NNW方向。 中国东部的东北块体到华北块体再到华南块体, 最大主压应力方向有一个从NE向逐渐转变成EW向再变化到NW向的旋转趋势。 应力场总体结果表明, 中国东部应力场主要受到太平洋板块和菲律宾板块对欧亚大陆俯冲的作用, 中国西部主要受印度板块向北碰撞欧亚大陆的影响, 块体内部相互作用、 块体与断裂带相互作用也对应力场变化产生影响。     

昆明地区现代构造应力场分析

利用1965～2002年强震震源机制资料,对昆明及附近地区现代构造应力场空间分布、地震震源破裂特征进行了分析,认为昆明地区区域现代构造应力场以水平作用为主,主压应力优势方位为SSE-SE,主张应力优势方位为NE—NEE。     

Movement and strain conditions of active blocks in the Chinese mainland

The definition of active block is given from the angles of crustal deformation and strain. The movement and strain parameters of active blocks are estimated according to the unified velocity field composed of the velocities at 1598 GPS stations obtained from GPS measurements carried out in the past years in the Chinese mainland and the surrounding areas. The movement and strain conditions of the blocks are analyzed. The active blocks in the Chinese mainland have a consistent E-trending movement component, but its N and S components are not consistent. The blocks in the western part have a consistent N-trending movement and the blocks in the eastern part have a consistent S-trending movement. In the area to the east of 90°E, that is the area from Himalayas block towards NE, the movement direction of the blocks rotates clockwisely and the movement rates of the blocks are different. Generally, the movement rate is large in the west and south and small in the east and north with a difference of 3 to 4 times between the rates in the west and east. The distributions of principal compressive strain directions of the blocks are also different. The principal strain of the blocks located to the west of 90oE is basically in the SN direction, the principal compressive strain of the blocks in the northeastern part of Qingzang plateau is roughly in the NE direction and the direction of principal compressive strain of the blocks in the southeastern part of Qingzang plateau rounds clockwisely the east end of Himalayas structure. In addition, the principal strain and shear strain rates of the blocks are also different. The Himalayas and Tianshan blocks have the largest principal compressive strain and the maximum shear strain rate. Then, Lhasa, Qiangtang, Southwest Yunnan (SW Yunnan), Qilian and Sichuan-Yunan (Chuan-Dian) blocks followed. The strain rate of the blocks in the eastern part is smaller. The estimation based on the stain condition indicates that Himalayas block is still the area with the most intensive tectonic activity and it shortens in the NS direction at the rate of 15.2±1.5 mm/a. Tianshan block ranks the second and it shortens in the NS direction at the rate of 10.1±0.9 mm/a. At present, the two blocks are still uprising. It can be seen from superficial strain that the Chinese mainland is predominated by superficial expansion. Almost the total area in the eastern part of the Chinese mainland is expanded, while in the western part, the superficial compression and expansion are alternatively distributed from the south to the north. In the Chinese mainland, most EW-trending or proximate EW-trending faults have the left-lateral or left-lateral strike-slip relative movements along both sides, and most NS-trending faults have the right-lateral or right-lateral strike-slip relative movements along both sides. According to the data from GPS measurements the left-lateral strike-slip rate is 4.8±1.3 mm/a in the central part of Altun fault and 9.8±2.2 mm/a on Xianshuihe fault. The movement of the fault along the block boundary has provided the condition for block movement, so the movements of the block and its boundary are consistent, but the movement levels of the blocks are different. The statistic results indicate that the relative movement between most blocks is quite significant, which proves that active blocks exist. Himalayas, Tianshan, Qiangtang and SW Yunnan blocks have the most intensive movement; China-Mongolia, China-Korea (China-Korea), Alxa and South China blocks are rather stable. The mutual action of India, Pacific and Philippine Sea plates versus Eurasia plate is the principal driving force to the block movement in the Chinese mainland. Under the NNE-trending intensive press from India plate, the crustal matter of Qingzang plateau moves to the NNE and NE directions, then is hindered by the blocks located in the northern, northeastern and eastern parts. The crustal matter moves towards the Indian Ocean by the southeastern part of the plateau.     

阿尔金地区构造应力场研究

用软材料和激光全息光弹模拟实验方法,分析了阿尔金地区现代构造应力场的特征和在区域应力场作用下阿尔金断层的活动规律以及大震前后震区应力场的调整情况,结果表明:阿尔金地区现今构造应力场主压应力轴近南北向,南边印度板块向北推进的过程中,使得青藏高原西北边界的阿尔金断裂各段的活动性质和滑移速度不同。东西两段左旋位移较明显;中段呈明显压性;应力集中区分布在一些特殊构造部位。模拟大震应力释放反映,大震后震中区附近剪应力值迅速下降,周围一些地区的剪应力值升高,形成未来地震危险区。     

欧亚地震带现代构造应力场及其分区特征

利用美国哈佛大学矩心矩张量目录中的2818个地震的震源机制解资料,分析了欧亚地震带及其5个分区现代构造应力场的基本特征,给出了5个分区的震源机制主压应力方向分布图。结果表明:①欧亚地震带以逆断型和走滑型断层活动为主;②地中海地震区以走滑断层活动为主,主压应力方向为SSW向;③伊朗—阿富汗—巴基斯坦地震区以逆断型断层活动为主,主压应力优势方向为NNE—NS向;④喜马拉雅地震以逆断型为主,主压应力优势方向为NS和NE向;⑤川—滇—缅地震区以走滑断层活动为主,主应力场方向为NNE向;⑥印度尼西亚地震区以逆断型断层活动为主,主压应力优势方向为NE—SSW向。各分区的主压应力方向明显受其所在区域板块运动的影响,由此推测板块运动可能是产生欧亚地震带构造应力的主要力源。     

Refined models of gravitational potential energy compared with stress and strain rate patterns in Iberia

This study examines the role of gravitational potential energy (GPE) in generating second-order (spatial scale ∼10² km) variations in the Iberia stress and strain-rate patterns. We present a new map of present-day strain rate field derived from the secular velocity field computed using all available continuously operating Global Navigation Satellite Systems (GNSS) stations in Iberia. The estimated strain rate field is generally consistent with the tectonic framework of the Iberian region, even though sporadic sharp local variations downgrade its correlation with the regional stress patterns. Many of the sharp spatial variations in the strain rate map are consistent with local changes of deformation style determined by prevailing faults. To obtain a more accurate estimate of GPE we use new data on the structure of the crust and apply a thin sheet approach using a 3-D definition of deviatoric stress. The GPE is derived from two isostatically compensated models (GPEd and GPEe compensated by density and elevation adjustment, respectively) and from the truncated geoid (GPEg). The GPE stresses are then summed with the first-order stress field due to the Eurasia–Nubia (EU–NU) convergence and the results compared with both the stress and strain rate data. In agreement with previous studies, we find that the GPE does not significantly change the NW–SE average direction of the most compressive stress (SHmax) imposed by the EU–NU collision, its main effect being to cause spatially changing stress regimes. From the analysis of the different GPE models we find: (1) in the Pyrenees, the tectonic forces have a secondary role when compared to the GPE. In this region, the model that best correlates with observations is the one emphasizing the role of surface elevation as a source of GPE (GPEe); (2) in the Iberian Chain and the Betics, the GPE imposes NE–SW extension consistent with a strike-slip regime and is equally (GPEe) or more (GPEg) important than the tectonic forces. In these regions, both deep heterogeneities associated with mantle convection and elevation are important sources of GPE; (3) in western Iberia, the GPE differences work against dominant tectonic forces by reducing the SHmax magnitude. The GPEg model is the one that best predicts the average strike-slip regime in Galicia; and finally (4) in the Gulf of Cadiz the gravitational potential stresses have a minor role and the style of deformation is clearly controlled by the tectonic forces.     

基于GPS应变与震源机制解应力反演喜马拉雅构造带现今地壳形变特征

喜马拉雅构造带及其临近区域是印度板块与欧亚大陆板块挤压碰撞的前缘地带.本文利用GPS实测速度场与震源机制解数据分别计算了研究区域现今地壳岩石圈表面的GPS应变场及岩石圈内部的主应力分布,研究了印度板块持续挤压作用下板块边界带地壳岩石圈现今地壳形变的空间分布特征.结果显示,南北向的剧烈挤压变形与东西向的拉伸变形是现今青藏高原南缘地壳岩石圈的主要变形特征.其中南北向的地壳挤压变形主要集中在主前缘冲断带与雅鲁藏布江缝合带之间.东西方向上,南北走向的亚东—谷露断裂是区域地壳东西向伸展变形的重要分界断裂.75°E是研究区域地壳形变的另一条显著不连续边界,其西侧地壳主压应变强度低、方向弥散且最大主压应力方向一致性较差,而东侧地壳主压应变方向与主压应力方向以及地壳水平运动速度场方向均具有较好的一致性.布格重力异常的小波多尺度辨析结果显示该分界带与循喜马拉雅西构造结楔入欧亚大陆的印度板块密切相关.     

渭河盆地及邻区现今地壳形变及构造特征研究

基于2009—2014年渭河盆地及邻区GPS资料,利用Shen提出的连续形变场与应变场计算方法,获得渭河盆地及邻区的水平形变场及应变率场,结合构造地质、地震目录等资料对渭河盆地及邻区的现今地壳形变及构造特征进行研究,并得到如下结论:(1)鄂尔多斯地块南缘西段和东段GPS形变场变化差异明显,六盘山—陇县—宝鸡断裂带形变场以挤压变形为主,渭河盆地中部西安—咸阳地区的形变场呈现EW向挤压、SN向拉张特征;(2)主应变率、剪应变率、面应变率变化明显的区域位于鄂尔多斯地块西南缘的六盘山—陇县—宝鸡断裂带、渭河盆地中部的长安—临潼断裂与渭南塬前断裂以及韩城断裂与双泉—临猗断裂附近;(3)未来需要警惕六盘山—陇县—宝鸡断裂带、长安—临潼断裂与渭南塬前断裂以及韩城断裂与双泉—临猗断裂附近的地震危险性。     

利用GPS数据分析四川“Y”型构造区地壳运动状态

四川地区地质构造复杂,地壳活动剧烈,为了深入揭示该区“Y”型构造区地壳1999年以来近20年的动态演化规律,基于1999—2017年7期GPS数据,解算各周期网格速度场、应变率场,研究地壳应变场演化过程。结果表明：①2008年以前的3期GPS速度场相对稳定,汶川地震后,速度场变化最大的龙门山断裂带由4.0—5.0 mm/a增至8.0—10.0 mm/a;②汶川震后,“Y”型构造区最大剪应变高值区出现在汶川以东,由2.0×10^-8/a增到22.0×10^-8/a;龙门山断裂带以SE或SEE向主压应变为主,变化速率约5.0×10^-8/a—12.0×10^-8/a,鲜水河断裂由震前NS向主拉应变转为震后EW向主压应变,安宁河断裂东侧由震前SE向主压应变6.0×10^-8/a减至震后的2.0×10^-8/a;面膨胀结果显示,由震前低密度梯度带瞬间变为平行于龙门山断裂带走向的高密度变化区,且存在以金川至都江堰、北川至青川为条带的2个正负交替过渡区;③汶川地震发生压应力释放后,该区SEE向压性特征又逐渐增强,且持续至2017年,释放了龙门山断裂带地壳内部SEE向压应力多年累积能量,但汶川地震对鲜水河断裂与安宁河断裂的整体运动状态则无明显触发作用。     

基于GPS技术的2016年呼图壁M_S6.2地震形变特征研究

利用2013~2017年3期GPS观测资料,通过结合区域构造背景分析呼图壁MS6.2地震震中及附近区域水平运动速率、主应变率、面膨胀率及最大剪应变率动态变化特征。结果表明,呼图壁地震前发震构造南部区域地壳速率高于北部区域运动速率,造成发震构造两盘运动速率不同,地壳能量积蓄。呼图壁地震释放了区域积蓄的应变能量,由于区域构造因素,影响范围较小。震前震中附近区域处于压缩环境,易于聚集应变能量;震时震中区出现面膨胀等值线密集高梯度带,是地壳应变能量交换和释放剧烈区域。震中区最大剪应变变化不大,反映呼图壁地震逆冲性质,最大剪应变高值区对地震危险性有预示作用。     

青藏高原及邻区现今地应变率场的计算及其结果的地球动力学意义

许多研究人员利用GPS测量的速度资料计算了地应变率场，但其结果差异较大. 本文将地质统计学中的Kriging方法引入到GPS观测的速度场研究中, 通过Kriging插值得到青藏高原及邻区均匀网格节点上的速度值，然后运用有限单元中形函数(Lagrange插值函数)的求导方法，计算每个网格单元积分点处的地应变率分量，从而获得青藏高原及邻区的地应变率场的分布. 计算结果显示，青藏高原主体处在南北向受挤压、东西向被拉张的应变状态之中，但高原东部地区则正好相反，即南北向拉张、东西向出现挤压. 青藏高原及邻区主应变率的方位与震源机制解中P轴、T轴的方向基本一致；最大主压应变率的高值区分布在喜马拉雅主边界冲断带及附近地区，高原内部出现主张应变率大于压应变率的现象，且高原内部处在拉张应变状态. 面膨胀率结果也表明，喜马拉雅山及附近地区为面收缩区，而高原内部其他地区主要为膨胀区；最大剪应变率分布清晰地显示出青藏高原周边的主要断裂带轮廓. 文中的应变率计算结果预示青藏高原及周边地区现今的地应变与较长期的地质活动之间有一定的继承关系.