Monitoring the horizontal movement along the Shanxi fault zone by GPS measurement

IntroductionShanxi is a significant seismic activity area in North China (WANG, 1995), named as Shanxi fault zone. One can see how important it is by the name. Up to now, a large number of achievements have been obtained from the studies mainly by the geological method. In order to improve the seismic research and carry out earthquake monitoring and prediction in this area, a GPS horizontal deformation monitoring network is established along the fault from the north to the south by the Se…     

山西地区应力场变化与地震的关系

收集了1970～2006年37年的小震初动符号建立了震源机制解数据库,研究了山西断陷带小震综合机制解时空演化特征.结果表明:山西断陷带小震综合机制解以走滑正断层为主,断陷带两端以拉张作用为主,中部地区以剪切作用为主,忻定盆地、太原盆地的区域应力场与华北区域应力场差异较大.利用沿山西断裂带布设的GPS监测网1996～2007年12期复测资料,分析了山西断裂带水平运动与地震活动的关系.结果表明:山西断裂带现主要受NWW-SEE向压应力场、NNE-SSW向张应力场的控制.1998～1999年有一次较为明显的应力扰动,空间上表现为北强南弱,接着发生了1999年11月1日大同-阳高5.6级地震.     

Activity Tendency and Dynamic Characteristics of Shanxi Fault Zone

INTRODUCTIONTheShanxifaultzoneisoneofthemajorseismiczonesinNorthChinaandmanymoderateandsmallearthquakeshaveoccurredthere (WangXiuwen ,1995 ) .TheM6 1Datongearthquakewhichoccurredatthenorthernendofthefaultin 1989isoneofthem (YangGuohuaetal.,1994 ) .Inordertomakeearthquakepredictionsandtostudytherelationshipbetweentheseismicityandfaultactivityofthefault,theSeismologicalBureauofShanxiProvinceestablishedaGPSmonitoringnetworkalongthefaultfromthesouthtothenorthin 1995 .Now ,thereisalarge…     

山西地震带形变应变场及中强地震危险性分析

利用沿山西断裂带布设的 GPS监测网的四期复测资料 (1 996～ 1 999年 ) ,分析了山西断裂带近期水平运动状态及与位于监测区北端 1 999年 1 1月 1日大同 -阳高 5.6级地震的关系 ,在震源区、忻州地区和介休东北地区出现了 3处相对较高的应变区 (1× 1 0 - 6)。山西断裂带主要受来自于 NWW- SEE向压应力场、NNE- SSW向张应力场的控制 ,不存在走滑运动。从长趋势看 ,今后应注意的是上述 3个运动单元的接合部位     

华北地区近期地壳水平运动与应力应变场特征

利用华北GPS监测网 1 992年、1 995年、1 996年的观测资料 ,应用最小二乘配置给出了华北地区相对水平位移场、应变场的分布图像 .经初步研究表明 :华北地区 1 992-1 995年间的水平位移和应变场表现为整体性不均匀的压性运动 ,1 995- 1 996年测区东部仍以水平压性运动为主 ,但测区西部则主要表现为张性运动 .水平运动 （方向、大小 ）发生显著变化和应变高值区的地带主要位于块体边界带和主要断裂带附近 .燕山断块南边界的北东向断裂存在着较显著的左旋运动 .区内最大剪应变、面膨胀的高值区在天津、北京、唐山一带 .结合非连续变形数值分析方法 （DDA）初步分析认为 ,1 992- 1 995年GPS观测结果显示的华北地区存在东、西部构造应力作用的明显差别 ,华北东部以东西向压应力作用为主 ,而西部的南北向构造应力作用又明显大于东部 .     

用形变资料分析腾冲火山区岩浆的活动特征

联合1998~2004年的五期水准测量资料以及2002~2004年的GPS观测成果,分析了腾冲火山区岩浆的活动特征。垂直形变资料显示,火山区南部发生较明显下降,这可能是由岩浆和水的流失及放气等原因引起;水平形变资料显示,以固东—腾冲断裂(F2)的西支为界,断层两盘分别向东、西两个方向运动,断层活动表现出明显的拉张特征;综合分析表明,岩浆可能沿断层从南部向北部运移,并在断层内重新聚集形成岩墙;垂直形变的多个极值区以及水平位移的不规则性表明,火山区岩浆体不很规则或有多个岩浆囊体存在;从形变量大小分析,岩浆的活动量远小于中等程度火山喷发的质量,表明火山近期喷发的危险性较小。     

2001年8.1级昆仑山大震破裂过程及对2008年汶川8.0级大震孕育发生影响的研究

本文用三维流变非连续变形(块体边界)与有限元(块体内)相结合(DDA+FEM)的方法,在青藏高原及其东侧四川盆地,鄂尔多斯块体地区三维构造块体相互制约的大环境中,考虑了龙门山断裂带东西两侧地势、地壳厚度和分层的明显变化,及断裂带东侧四川盆地及鄂尔多斯块体坚硬地壳阻挡的影响,通过用GPS资料做位移速率边界约束和震源机制约...     

Preliminary Study on the Horizontal Crustal Deformation in Chinese Continent

In the paper, the current strain field and stress field in Chinese continent have been discussedbased on the processed data from two GPS campaigns of national GPS network carried out inthe years of 1994 and 1996. With a principal compressional strain direction of NNE, thewestern and castern parts of Qinghai-Xizang subplate are dominated by extensional straiu andthe central Part by compressional strain. Along the southwestern segment of southeastern partof Qinghai-Xizang subplate, i. e. Yunnan area, the princiPal compressional strain direction isNW and the compressional strain is equivalent to the extensional strain in magnitude. Theprincipal compressional strain of Xinjiang subplate is mainly NNE and NE with a difference inthe strain magnitude. The principal compressional strain in North China subplate is quite effective in NE and nearly EW directions with differences along some segments. However, thecompressional strain is corresponding to the extensional strain in magnitude in most areas. Theprincipal     

郯庐断裂带鲁苏皖段构造应力场及分段特征研究

利用Snoke方法求解和收集得到的77次中小地震的震源机制解资料, 采用Gephart应力张量反演方法, 获得了郯庐断裂带鲁苏皖段构造应力场, 最大主压应力方位角为80°, 最小主压应力方位角为172°, 最大、 中等和最小主压应力倾角分别为15°、 65°和19°, 反映了研究区处于近EW向水平作用和近NS向的水平拉张作用环境下。 根据地震活动、 地质构造及震源机制解差异, 我们将郯庐断裂带鲁苏皖段分5个区段开展研究, 结果显示: 5个分区应力场存在局部差异, 最大主压应力方位角处于63°～88°之间, 从北往南总体方向成顺时针偏转的趋势。 跨郯庐断裂带两侧的应力场研究结果显示, 从西到东最大主压应力方向有一个逆时针偏转的趋势, 西侧最大主压应力方向更接近EW向, 东侧更接近NE向, 郯庐断裂带内处于两侧的过渡地段。     

STUDY ON RELATIONSHIP BETWEEN THE ACTIVITY OF MIYALUO FAULT AND WENCHUAN EARTHQUAKE SEQUENCE

Under the background of thrusting stress regime, a large number of strike-slip earthquakes occurred on the Miyaluo Fault during the Wenchuan earthquake sequence process, which is in the southern part of the Longmenshan Fault. In order to find the cause of their occurrence, stress tensors in subregions near the Miyaluo Fault are estimated. The result shows that in both north and south side of the Miyaluo Fault, the direction of principal compressive stress is nearly perpendicular to the Longmenshan Fault, and its dip is nearly horizontal, and the direction of tensile stress is nearly vertical. While in the Miyaluo fault zone, the direction of principal compressive stress is SWW-NEE, and its dip is nearly horizontal, the direction of principal tensile stress is NNW-SSE, also its dip is nearly horizontal. It is consistent with sinistral shear stress state in the Miyaluo fault zone. It was referred that the behavior of Miyaluo Fault during the Wenchuan earthquake sequence process was caused by tearing effect generated from unbalanced forces of two sides of the fault. To understand the rupture mode of the aftershocks in subregions as described above, the total seismic moment tensors are estimated by adding the corresponding component separately of the seismic moment tensor of aftershocks in each region. The result shows the similar trend of total seismic moment tensor components in the north and south side of the Miyaluo Fault(indicating the consistency of rupture mode in the north and south side of the Miyaluo Fault), and most seismic moment tensor components in the south side is higher than that in the north side, especially the compression component perpendicular to Longmenshan Fault and expansion component in the vertical direction. It indicates that thrusting component in the southeast direction in the south side is greater than that in the north side, and the thrusting difference causes the sinistral tearing effect of the Miyaluo Fault. We also find that the sinistral tearing component of the Miyaluo Fault is the same order of magnitude with the thrusting difference of its two sides, which indicates that the tearing effect of Miyaluo Fault can be completely explained by thrusting difference of its two sides. According to the analysis, we put forward the dynamic model of the Miyaluo Fault, which can explain the above phenomenon.     

鲜水河断裂带北段GPS测量及其运动特征

鲜水河GPS监测网由18个沿鲜水河断裂带分布的点组成．1991年对该网进行了首次观测,1996和2000年进行了两期整网复测．本利用该网199l和2000年的二期GPS观测资料结合川西地区20世纪70年代以来的常规大地测量资料,计算给出了这一强震活动带现今运动图像：由测区的北西虾拉沱测点到南东的乾宁测点水平位移速率逐渐增大,而断层两盘的相对运动不明显．表明利用短边GPS测量可有效监视活动断裂带两侧一定区域的地壳运动．对比有形变测量资料以来川西地区6级以上地震分布的特点,认为可根据鲜水河断裂带断层两盘的相对运动和跨越断层的地壳整体运动的强弱这两种运动图像来研究区域强震的活动特征．     

2016年青海门源MS6.4地震震前应变积累及同震变形特征

2016年1月21日青海省门源县发生了M_S6.4地震, 发震断裂为冷龙岭北侧断裂, 震中位置与1986年门源6.4级地震相同。 本文收集了本次地震震中及其周边区域1999—2015年GPS观测资料, 解算了GPS速度场、 跨断裂连续观测站基线时间序列和应变率场。 结果显示, 祁连山断裂带为一条宽度约60 km的连续变形带。 在断裂带南侧地壳运动以顺时针旋转为主, 运动量值没有显著差异; 跨过断裂带到达其北部之后, 地壳运动量值明显减小, 显示出该断裂带的强烈活动特征。 冷龙岭断裂左旋走滑速率为6.17±0.41 mm/a, 挤压速率为1.83±0.38 mm/a, 断层闭锁深度为22.1±3.1 km。 利用GPS连续观测站数据解算的地震同震位移显示, 震中西南侧26.8 km处的青海门源(QHME)测站记录到了明显同震位移, 其水平运动方向为北东向, 与逆冲为主的震源机制解一致。     

Study on Dynamic Characteristics of Crustal Deformation in the Yunnan Area Using GPS

Based on the GPS velocity field data of 1999-2007 and 2011-2013,we used the least squares configuration method and GPS velocity profile results to synthetically analyze the dynamic evolution characteristics of crustal deformation in the Yunnan area before and after the Wenchuan earthquake. The dynamic evolution of GPS velocity field shows that the direction is gradually changed from the south in the southern part of the Sichuan-Yunnan block to the south-west in the southern Yunnan block and there is a clear relative motion characteristic near the block boundary fault zone. Compared with the GPS velocity of 1999-2007, the results of 2011-2013 also reflect segmental deformation characteristics of the block boundary fault zone. Southeast movement shows a significant increase, which may be related to crustal deformation adjustment after the Wenchuan earthquake. The dynamic evolution of strain parameters shows a pattern of "extension in the middle and compression at both ends" in the whole area and the distribution of deformation (shear, extension or compression) is closely related to the background motion and deformation characteristics of the main fault zone. Compared with the results of the period of 1999-2007, the extensional deformation zone of 2011-2013 is expanded eastward and southward. The compressional deformation of the eastern boundary (the Xiaojiang fault zone) of the Sichuan-Yunnan block is no longer significant, which is mainly concentrated in the northern section of the Xiaojiang fault zone and may be related to the post-seismic deformation adjustment of the Wenchuan earthquake. The GPS velocity profile results show that the left-lateral slip velocity of the Xiaojiang fault zone reduced gradually from north to south (10mm/a-5mm/a), and the width of the northern section is wider. The right-lateral slip rate of the Honghe fault zone is about 4mm/a, and the deformation width is wider. The dynamic results show that the Wenchuan earthquake has little effect on the deformation modes of these two fault zones.     

青藏高原东南缘地震各向异性及其深部构造意义

青藏东南缘是青藏高原物质东流的通道,为了更全面了解复杂的岩石圈结构和强烈的变形特征,本文介绍了青藏东南缘岩石圈各向异性的形态,综合其他研究者得到的该区域壳幔各向异性结果,增加了部分新的资料,更新了青藏东南缘岩石圈方位各向异性图像,探讨了区域深部构造意义.
基于近场小震、远震和背景噪声资料计算结果,青藏东南缘地震各向异性展现出独特的区域空间分布和垂向层次性分布形态,展现了3个主要特征.（1）青藏东南缘上地壳各向异性与地表变形测量结果相符,快剪切波偏振方向（即快波方向）呈现与地表运动特征一致的发散性,与主压应力方向一致,但受到地质构造的影响.（2）青藏东南缘下地壳方位各向异性展现了更好的方向一致性,但方位各向异性程度相对较弱,在红河断裂带西北端部和小江断裂带下方有两个下地壳低速区,其方位各向异性程度与上地壳相当.（3）青藏东南缘岩石圈方位各向异性,呈现南、北分区特征,南北分界线大致在26°20'N,快波方向在北部近似为NS方向,在南部近似为EW方向.
本文推测：（1）在26°20'N北侧的上地幔有较厚的高速体,高速体南侧边缘呈现出近EW走向的直立墙形构造,其南侧软弱的上地幔物质在EW方向上流动,导致了岩石圈方位各向异性特征在空间发生突然的变化,快波方向由北部的NS变为南部的EW方向;（2）小江断裂带是现今的华南地块的地壳西边界,但岩石圈尺度的方位各向异性展现出的趋势性表明,华南地块的上地幔物质越过了小江断裂带到达其西侧,揭示了华南地块与青藏地块接触碰撞造成的岩石圈物质变形和上地幔软流圈物质运移的深部图像.地震各向异性能揭示区域深部构造与介质变形的信息,不同观测资料的综合分析有助于获得更清晰的各向异性三维图像.     

滇中汤郎-易门断裂构造活动的地貌特征

汤郎-易门断裂位于青藏高原东南缘,走向近南北,按地貌特征及区域构造背景可将其划分为北段（营盘村-插甸断裂）、中段（插甸-碧城断裂）及南段（碧城-易门断裂）。针对汤郎-易门断裂构造地貌差异,利用30 m分辨率的DEM数据,基于GIS技术提取与断裂活动相关的水系,并计算其陡峭指数,结合野外考察及遥感影像讨论断裂在不同分段的活动习性与地貌特征。研究发现,区域内降水及基岩抗风化能力对亚流域陡峭指数的影响较小,认为陡峭指数能够较好地反映汤郎-易门断裂的垂直构造运动。陡峭指数显示,断裂走向呈两端高、中间低的特点,其分段性与前人划分结果具有较好一致性,所表征的基岩垂直活动性差异可作为断裂带活动分段的依据。断裂带东西侧陡峭指数在不同分段上表现出差异性,北段断裂东西侧陡峭指数显示出东、西向差异性抬升不显著,其与地貌上断裂北段表现的左旋走滑运动一致,以水平运动为主;断裂中段及南段陡峭指数在东西侧表现出东高西低的特点,显示东侧较西侧基岩抬升更快,可能以垂直差异运动为主。     

西昌地区现今地壳运动及主要断裂活动研究

利用2009—2017年GPS水平速度场和1990—2018年跨断层短水准资料, 分析西昌地区现今三维地壳活动及主要断裂的活动性。 结果表明: 在西昌地区, GPS水平运动场及应变场的大小和方向发生变化。 E向运动速率由北部的平均约8 mm/a减小到南部的平均约4 mm/a; S向运动以安宁河—则木河断裂为界, 西侧点位的运动速率明显大于东侧的点位。 相对华南地块的水平形变场也显示西昌地区水平运动的差异性。 主应变场在西昌地区以SW—NE向拉张和NW—SE向挤压为主。 大凉山次级块体东侧的张应变和压应变均大于西侧; 最大剪应变率在此次级块体以条带形式展布, 条带上的最大剪应变率大于东、 西两侧; GPS水平运动速率和变形宽度相比1999—2007年资料得到的结果大, 表明安宁河—则木河断裂带处于剪切应变积累阶段, 闭锁程度有所提高。 跨断层水准资料显示, 该断裂存在新的活动迹象, 应力持续积累。 综合分析两种资料结果, 推测区域地震危险性将进一步增强。     

华北地区现今水平运动场的动态特征

在整体无旋转基准的基础上, 采用了以提取中、 低频应变信息为主的连续应变模型, 处理并分析了《中国地壳运动观测网络》在华北地区400余个GPS测站的复测资料(1999—2001—2004年)和2006年130余个测站的复测资料, 获得了1999—2004年、 2004—2006年的相对运动速率以及2004—2006年偏离1999—2004年运动的位移结果。 结果表明: ① 华北地区非均匀应变比较明显, 不同时段的结果在空间上的表现形式也不一样; ② 前后两个时段的运动特征具有一定的不一致性; ③ 2006年存在着较明显的偏离位移, 并显示了右旋形变的迹象, 面应变表现为北、 中收缩, 南部膨胀的特征; ④ 近两年东西向的压性作用较前明显, 北京以南地区是运动的转化地区及面应变象限的准中心地区。 这可能表明, 在昆仑山口西8.1级地震之后, 华北地区又进入了常态能量的积累阶段。     

THE THREE DIMENSIONAL DENSITY STRUCTURE OF CRUST AND UPPER MANTLE IN THE CENTRAL-SOUTHERN PART OF LONGMENSHAN

In recent years, strong earthquakes of M_S8.0 Wenchuan and M_S7.0 Lushan occurred in the central-southern part of Longmenshan fault zone. The distance between the two earthquakes is less than 80 kilometers. So if we can obtain the inner structure of the crust and upper mantle, it will benefit us to understand the mechanism of the two earthquakes. Based on the high resolution dataset of Bouguer gravity anomaly data and the initial model constrained by three-dimensional tomography results of P-wave velocity in Sichuan-Yunnan region, with the help of the preconditioned conjugate gradient(PCG)inversion method, we established the three dimensional density structure model of the crust and upper mantle of the central-southern segment of Longmenshan, the spatial interval of which is 10 kilometers along the horizontal direction and 5 kilometers along the depth which is limited to 0~65km, respectively. This model also provides a new geophysical model for studying the crustal structure of western Sichuan plateau and Sichuan Basin. The results show obvious differences in the crustal density structure on both sides(Songpan-Ganzê block and Sichuan Basin)of Longmenshan fault zone which is a boundary fault and controls the inner crustal structure. In Sichuan Basin, the sedimentary layer is represented as low density structure which is about 10km thick. In contrast, the upper crust of Songpan-Ganzê block shows a thinner sedimentary layer and higher density structure where bedrock is exposed. Furthermore, there is a wide scale low density layer in the middle crust of the Songpan-Ganzê block. Based on this, we inferred that the medium intensity of the Songpan-Ganzê block is significantly lower than that of Sichuan Basin. As a result, the eastward movement of material of the Qinghai-Tibet plateau, blocked by the Sichuan Basin, is inevitably impacted, resulting in compressional deformation and uplift, forming the Longmenshan thrust-nappe tectonic belt at the same time. The result also presents that the crustal structure has a distinct segmental feature along the Longmenshan fault zone, which is characterized by obviously discontinuous changes in crustal density. Moreover, a lot of high- and low-density structures appear around the epicenters of Wenchuan and Lushan earthquakes. Combining with the projection of the precise locating earthquake results, it is found that Longmenshan fault zone in the upper crust shows obvious segmentation, both Wenchuan and Lushan earthquake occurred in the high density side of the density gradient zone. Wenchuan earthquake and its aftershocks are mainly distributed in the west of central Longmenshan fault zone. In the south of Maoxian-Beichuan, its aftershocks occurred in high density area and the majority of them are thrust earthquake. In the north of Maoxian-Beichuan, its aftershocks occurred in the low density area and the majority of them are strike-slip earthquake. The Lushan earthquake and its aftershocks are concentrated near the gradient zone of crustal density and tend to the side of the high density zone. The aftershocks of Lushan earthquake ended at the edge of low-density zone which is in EW direction in the north Baoxing. The leading edge of Sichuan Basin, which has high density in the lower crust, expands toward the Qinghai-Tibet Plateau with the increase of depth, and is close to the west of the Longmenshan fault zone at the top of upper mantle. Our results show that there are a lot of low density bodies in the middle and lower crust of Songpan-Ganzê Block. With the increase of the depth, the low density bodies are moving to the south and its direction changed. This phenomenon shows that the depth and surface structure of Songpan-Ganzê Block are not consistent, suggesting that the crust and upper mantle are decoupled. Although a certain scale of low-density bodies are distributed in the middle and lower crust of Songpan-Ganzê, their connectivity is poor. There are some low-density anomalies in the floor plan. It is hard to give clear evidence to prove whether the lower crust flow exists.     

基于PS-InSAR的蓟运河断裂震间形变监测研究

采用2014年10月22日至2019年4月11日之间的26景Sentinel-1升轨数据,基于PS-InSAR技术对蓟运河断裂这一隐伏断裂进行形变监测试验。结果表明：(1)研究区受地面沉降干扰强烈地区在南部宁河一带,向北地面沉降逐步减弱,在蓟运河断裂北段以北一带基本无地面沉降现象。(2)研究区北部的视向线形变速率在蓟运河断裂北段一带在0 mm·a^-1左右,向北随远离断裂形变速率增大,表明研究区北部受近东西向燕山隆起控制,有向南掀斜运动的趋势。(3)蓟运河断裂北段活动方式为黏滑,其两盘的视线向相对形变速率差约为1.83 mm·a^-1,蓟运河断裂南段两盘形变速率差小于2.96 mm·a,与2005—2012年的水准测量结果相近,表明蓟运河断裂2005年以来活动速率较为稳定。(4)在受到地面沉降影响下,隐伏断裂的InSAR形变场包含更多的非构造信息,无法获取断裂的具体形变速率。但断裂活动会导致断裂两盘含水层厚度不同,地下水超采造成的地面沉降幅度也不同,相应的其InSAR形变场在断裂两盘出现突变,对隐伏断裂的位置判定有一定意义。     

鄂尔多斯地块周围的现代地壳应力场

根据近十年来区域台网的P波初动方向观测资料,得到了鄂尔多斯地块周围13个分区的综合地震节面解;结合已有的结果进行分析,地块周围确实存在有别于华北地区地壳应力场基本情况的小区域应力场:地块西南边缘的六盘山褶皱带处于北东东向的水平挤压应力状态;地块边缘的断陷盆地处于北西向的水平拉张应力状态,尤其是渭河盆地到临汾盆地的主压应力轴已近于直立;地块西北角和东北角处于北西向的水平拉张与北东向的水平挤压共同作用的应力状态;在地块的西面与北面,从北到南和由西往东,主压应力轴的走向由北北东向逐渐转变为近东西向。 此外,还对本文结果在板内动力学中的意义进行了简要的讨论。