Quality analysis of crustal tilt and strain observations in China's earthquakes in 2014

This work analyzes the quality of crustal tilt and strain observations during 2014, which were acquired from 269 sets of ground tiltmeters and 212 sets of strainmeters. In terms of data quality, the water tube tiltmeters presented the highest rate of excellent quality,approximately 91%, and the pendulum tiltmeters and ground strainmeters yielded rates of81% and 78%, respectively. This means that a total of 380 sets of instruments produced high-quality observational data suitable for scientific investigations and analyses.

Horizontal crustal deformation in Chinese Mainland analyzed by CMONOC GPS data from 2009-2013

In this study, we analyze the regional GPS data of Crustal Movement Observation Network of China （CMONOC） observed from 2009-2013 using the BERNESE GPS software, and then the preliminary results of horizontal velocity field and strain rate field are presented, which could reflect the overall deformation features in the Chinese mainland from 2009-2013. Besides, the velocity error and the probable factors that could influence the estimate of long-term deformation are also discussed.

Characteristics of regional crustal deformation before 2016 Menyuan Ms6.4 earthquake

On January 21, 2016, a strong earthquake with a magnitude of Ms6.4 happened at Menyuan, Qinghai Province of China. In almost the same place, there was another strong earthquake happened in 1986, with similar magnitude and focal mechanism. In this paper, we analyze the characteristics of regional crustal deformation before the 2016 Menyuan Ms6.4 earth- quake by using the data from 10 continuous Global Positioning System （GPS） stations and 74 campaign-mode GPS stations within 200 km of this event： （a） Based on the velocity field from over ten years GPS observations, a regional strain rate field is calculated. The results indicate that the crustal strain rate and seismic moment accumulation rate of the Qilian- Haiyuan active fault, which is the seismogenic tectonics of the event, are significantly higher than the surrounding regions. In a 20 km~ 20 km area around the seismogenic region, the maximum and minimum principal strain rates are 21.5 nanostrain/a （NW-SE extension） and -46.6 nanostrain/a （NE-SW compression）, respectively, and the seismic moment accumulation rates is 17.4 Nm/a. The direction of principal compression is consistent with the focal mechanism of this event. （b） Based on the position time series of the continuous GPS stations for a time-span of about 6 years before the event, we calculate the strain time series. The results show that the dilatation of the seismogenic region is continuously reduced with a ＂non-linear＂ trend since 2010, which means the seismogenic region has been in a state of compression. However, about 2-3 months before the event, both the dilatation and maximum shear strain show significant inverse trends. These abnormal changes of crustal deformation may reflect the non-linear adjustment of the stress-strain accumulation of the seismogenic region, when the accumulation is approaching the critical value of rupture.

Crustal Deformation Revealed by GPS in Kumaun Himalaya,India

The foremost Global Positioning System(GPS) derived measurements in the Kumaun Himalaya indicate that most of the crustal motion of the Indian plate is accommodating towards the base as well as on the hanging wall of Main Central Thrust(MCT).Deformation pattern within the Kumaun Himalaya varies from south to north and indicates maximum deformation rate near MCT.Our study,based on the campaign mode GPS survey during 2003- 2006,reveals that the area between north of North Almora Thrust(NAT) and at the base of Great Himalaya registers maximum strain rate,which is lowered towards the Trans Himadri Fault(THF).The GAMIT-GLOBK processed campaign data of the area show that currently,the Himalayan Frontal Fault(HFF) and Main Boundary Thrust(MBT) are locked with the Indian plate,and a 6.7 ± 2.5 mm/yr of horizontal shortening is taking place between the Lesser Himalaya and Peninsular India.

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.

Contemporary crustal tectonic movement in the southern Sichuan-Yunnan block based on dense GPS observation data

We analyzed 360 permanent and campaign GPS data from 1999 to 2017 in the southern Sichuan-Yunan block, and obtained crustal horizontal deformation in this region.Then, we derived the strain rate using a multi-scale spherical wavelet method.Results reveal a complex pattern of tectonic movement in the southern Sichuan-Yunnan block.Compared to the stable Eurasian plate, the maximum rate of the horizontal deformation in the southern Sichuan-Yunnan block is approximately 22 mm/a.The Xiaojiang fault shows a significantly lower deformation—a left-lateral strike-slip movement of 9.5 mm/a.The Honghe fault clearly shows a complex segmental deformation from the north to south.The northern Honghe fault shows 4.3 mm/a right strike-slip with 6.7 mm/a extension; the southern Honghe fault shows 1.9 mm/a right strike-slip with 1.9 mm/a extension; the junction zone in the Honghe and Lijiang–Xiaojinhe faults shows an obvious clockwise-rotation deformation.The strain calculation results reveal that the maximum shear-strain rate in this region reaches 70 nstrain/a, concentrated around the Xiaojiang fault and at the junction of the Honghe and Lijiang–Xiaojinhe faults.We note that most of the earthquakes with magnitudes of 4 and above that occurred in this region were within the high shear strain-rate zones and the strain rate gradient boundary zone, which indicates that the magnitude of strain accumulation is closely related to the seismic activities.Comparison of the fast shear-wave polarization direction of the upper-crust with the upper-mantle anisotropy and the direction of the surface principal compressive strain rate obtained from the inversion of the GPS data reveals that the direction of the surface principal compressive strain is basically consistent with the fast shear-wave polarization direction of the upper crust anisotropy, but different from the polarization direction of the upper mantle.Our results support the hypothesis that the principal elements of the deformation mechanism in the southern Sichuan-Yunnan block are decoupling between the upper and lower crust and ductile flow in the lower crust.

GPS数据揭示的喜马拉雅东构造结地区现今应变特征及其动力学机制

喜马拉雅东构造结位于印度与欧亚板块碰撞的前缘,是地壳缩短和构造旋转变形十分强烈的部位。本文收集东构造结及其周边区域大范围、长时段的最新GPS速度场资料,采用“二维张力样条”方法计算获得区域构造应变场,研究其现今地壳运动与构造变形特征。结果显示,高应变率区集中在喜马拉雅主逆冲断裂、实皆-阿帕龙断裂、鲜水河-小江断裂、东构造结的环形地区和印度东北部及缅甸西部的巴坎-若开山脉地区,而在跨嘉黎断裂和红河断裂区域并无显著的应变。区域最大剪切应变率主要沿着实皆-阿帕龙断裂、鲜水河-小江断裂等构造带分布,区域最大面压缩率发生在阿萨姆东北部一带(N28°~29°、E95.5°~96.5°),最高量值为151.8×10^(-9)a^(-1);反映喜马拉雅东构造结的最强变形核心部位已经由南迦巴瓦峰地区向其东南方向发生了转移,移至位于阿萨姆东北部地区的喜马拉雅主边界逆冲断裂与阿帕龙断裂的交汇处。综合分析认为,喜马拉雅东构造结地区在印度板块强烈的楔入挤压作用下,大陆变形以地壳增厚为主,深部以黏塑性为特征的下地壳和上地幔物质的流动驱动着上覆脆性上地壳地块。

乌什M_(S)7.1地震前地倾斜、地应变加卸载响应比异常分析

基于岩石应力的本构关系,以2024年1月23日乌什M_(S)7.1地震前震中及周边500 km范围内地倾斜、地应变数据作为“响应量”,利用库伦应力触发模型的加卸载响应比方法进行计算,结果显示,乌什洞体应变等3个测项均出现震前LURR异常,这表明震源区介质存在明显的应力积累过程,同时也说明从倾斜、应变的潮汐频段中能够提取出地震预测的有效信息。

Active tectonic deformation around the Tarim Basin inferred from dense GPS measurements

The surrounding area of the Tarim Basin is featured by active tectonic deformation and intense seismic activity.The study of the crustal deformation characteristics of this area will help revealing the role of the Tarim Basin in the crustal evolution.In order to accurately obtain the deformation characteristics of this area,we firstly obtained the highly detailed and accurate three-dimensional(3D)crustal deformation velocities of the Tarim Basin and its surrounding areas through high-precision processing of existing Global Positioning System(GPS)data.Thereafter,the slip rate and strain rate fields of the main faults in the region were calculated based on the updated velocity results.The strain rate of the Altyn Tagh fault is dominated by shear strain and the strike slip rate is 8-10 mm/yr.The strain rate between the Tien Shan and Tarim Basin is dominated by extrusion strain,and the extrusion rate is 4-6 mm/yr.In addition to the large shear strain,there is also a certain tensile strain in the Tibetan Plateau.Geodetic results show that the main driving force for the deformation of the Tien Shan is the northward thrust of the Tarim Basin.The relative movement mode between the Tarim Basin and Tibetan Plateau mainly comprises the strike slip movement along the strike direction of the Altyn Tagh fault,with a small extrusion deformation.Therefore,the Tarim Basin has little influence on the northesouth shortening deformation of the Tibetan Plateau.

Analysis of the Motion and Deformation Characteristics along the Zhangjiakou-Bohai Fault

We have collected GPS data in the period of 1999-2007 from the Crustal Motion Observation Network of China along the Zhangjiakou-Bohai fault and its adjacent regions to study the characteristics of present-day crustal horizontal motion velocities in the research zone.Strain rate components are computed in the spheric coordinate system by the least square collocation method.According to the spatial distribution of the principal strain rate,dilation rate and maximum shear strain rate derived from GPS measurements,this paper analyses the deformation of the subordinary faults of the Zhangjiakou-Bohai fault.The principal compression strain rates are apparently greater than the principal extension strain rates.The larger shear strain rate is mainly in and around the Xianghe,Wenan and Tangshan areas in Hebei Province.According to the profiles across different segments of the Zhangjiakou-Bohai fault,the three segments glong the Zhangjiakou-Bohai fault show an obviously left-lateal strike-slip and compression characteristics.By analysis of the motion characteristics of the blocks,e.g.the Yanshan block,North China Plain block,Ordos block,and Ludong-Huanghai block in and around the North China region,this paper speculates that the dynamics of the motion styles of Zhangjiakou-Bohai fault may directly come from the relative movement between the Yanshan block and the North China plain block,and the ultimate dynamics may be the results of the collison between Indian plate and Eurasian plate,and the persistent northeastward extrusion of the Indian plate.

Developments of borehole strain observa- tion outside China

Borehole strain observation is playing an increasingly important role in the study on the crustal movements. It has been used by many countries such as China, USA, Japan, Peru, Australia, South Africa, Iceland and Italy, in re- search fields of plate tectonics, earthquake, volcanic eruption, dam safety, oil field subsidence, mining collapse and so on. Borehole strainmeter has been improved rapidly and tends to get more and more components included in one probe. Based on observations by this kind of instruments, studies on seismic strain step, slow earthquake, earthquake precursor and volcanic eruption forecasting have made remarkable achievements. In the coming years, borehole strain observation is going to become one major geodetic means, together with GPS and InSAR.

GNSS deformation characteristics of North China in the past two decades

Based on the Global Navigation Satellite System(GNSS)velocity in North China from 1999 to 2018,the deformation parameters,such as the strain rate,the velocity profiles,and the fault slip rates,are analyzed.The principal conclusions are as follows:1)the GNSS results during 1999-2007 can effectively reflect the deformation characteristics of North China,and the strain rate shows SEE tensile feature in the Shanxi seismic zone with a maximum value of 0.7×10^(-8)/yr.Meanwhile,the deformation is characterized by left-lateral features in the Yinshan seismic zone and Zhangjiakou-Bohai seismic zone with a maximum shear strain rate of 0.7×10^(-8)/yr.2)In the period of 1999-2007,the GNSS velocity profiles show that the deformation is mainly distributed in a range of 100-km width crossing the Yinshan seismic zone and the middle section of the Zhangjiakou-Bohai seismic zone,and 50-km width crossing the Zhangjiakou-Bohai seismic zone near the Bohai Bay.3)The deformation response to the 2011 Japan MW9.0 earthquake shows a significant difference between the middle and east sections of the Zhangjiakou-Bohai seismic zone,and the deformation loading rate decreased from 3.3 mm/yr in 1999-2007 to 2.6 mm/yr and 0.9 mm/yr in the 2013-2018 period for above two sections respectively.Furthermore,the fault slip rates inverted from GNSS measurements show a similar dynamic adjustment process,reflecting the weak impact of the Japan MW9.0 earthquake on the deformation around the central section of the Zhangjiakou-Bohai seismic zone.4)From the results of GNSS strain rate,velocity profile and fault slip rate,we suggest that the potential of the strong earthquake should be high in the Yinshan seismic zone and the middle section of the Zhangjiakou-Bohai fault zone.

Regional Tectonic Deformation Background and Medium- and Short-Term Precursors to the Minle-Shandan Earthquakes1

Using GPS observations of horizontal movement from 2001 to 2003 and the cross-fault mobile short-levelling data of 1988～2003, and with the aid of the improved negative dislocation model and the time-varying curve of strain intensity ratio of fault deformation, the regional tectonic deformation background and medium- and short-term precursors related to the preparation of the Minle-Shandan earthquakes of M S6.1 and M S5.8 on October 25, 2003 are investigated. The results reveal that, under the background of the wide-range deformation adjustment, short-term relaxation and recovery caused by the Kunlun Mountains earthquake of M S8.1, the hypocenters of the earthquakes are located on the north edge of the shear stress enhancement zone between the compressional locked segments of block boundary fault, a place which may represent an accelerated strain accumulation. An obvious anomaly of strain intensity ratio appeared in short-levelling measurements crossing over the fault at the Shihuiyaokou site, the closest to the epicenters, 3 months before the occurrence of the earthquakes. In addition, the variation in number of anomalies from 10-odd days to months before the earthquakes in the entire monitoring area and the anomaly concentration and local enhancement relative to near source in the 3 months before the earthquakes are regarded to be precursors to the two events.

Mapping three-dimensional co-seismic surface deformations associated with the 2015 MW7.2 Murghab earthquake based on InSAR and characteristics of crustal strain

Three-dimensional(3 D) co-seismic surface deformations are of great importance to interpret the characteristics of coseismic deformations and to understand the geometries and dynamics of seismogenic faults. In this paper, we propose a method for mapping 3 D co-seismic deformations based on InSAR observations and crustal strain characteristics. In addition, the search strategy of correlation points is optimized by adaptive correlation distance, which greatly improves the applicability of the proposed method in restoring deformations in decorrelation areas. Results of the simulation experiment reveal that the proposed method is superior to conventional methods in both the accuracy and completeness. The proposed method is then applied to map the 3 D co-seismic surface deformations associated with the 2015 MW7.2 Murghab earthquake using ascending and descending ALOS-2 PALSAR-2 images. The results show that the seismogenic fault is the Sarez-Karakul fault(SKF), which is dominated by NE-SW strike slips with an almost vertical dip angle. The north section and the south segment near the epicentre have obvious subsidence along with a southwestward motion in the northwest wall, and the southeast wall has northeast movement and surface uplift trend along the fault zone. The strain field of the earthquake is also obtained by the proposed method. It is found that the crustal block of the seismic area is obviously affected by dilatation and shear forces, which is in good agreement with the movement character of the sinistral slip.

2022年1月8日M_(S)6.9青海门源地震震前三维地壳变形与应变分配

2022年01月08日在祁连山断裂带中东段的青海门源县发生了M_(S)6.9强震,然而,迄今为止对于该地区的三维地壳变形特征和强震孕育背景鲜有研究.本文基于高精度的GPS和水准等大地测量资料,厘定了该区域主要活动断裂的滑动速率,并分析了此次地震之前的三维地壳变形特征和强震孕育背景.研究结果表明,(1)祁连山断裂带中东段地壳变形呈现出较强的左旋剪切和缩短变形,且地壳缩短主要以垂直隆升的形式实现;(2)托莱山断裂的走滑、缩短和垂直速率分别为2.5±0.3 mm·a^(-1)、1.3±0.4 mm·a^(-1)和1.2±0.6 mm·a^(-1),高于其北侧的民乐-大马营断裂的1.1±0.3 mm·a^(-1)、0.8±0.3 mm·a^(-1)和0.5±0.5 mm·a^(-1),冷龙岭断裂的走滑和缩短速率分别为3.1±0.7 mm·a^(-1)和3.0±0.6 mm·a^(-1),结合应变率场,表明该区域地壳变形满足连续-弥散变形模式;(3)此次门源地震震前剪应变和压性面应变明显积累,其中部分压性面应变被2016 M_(S)6.4地震所释放,而在托莱山和冷龙岭断裂以南地区垂直变形并不显著,震前应变持续增加.此外,GPS速度剖面揭示出托莱山断裂存在明显的震间闭锁,其闭锁深度为15.0±7.8 km,表明其具有发生强震的背景.

TY系列高精度体应变仪研制及映震能力分析与应用

文章综述了钻孔体应变仪的发展历程,针对体应变仪目前存在的稳定性和带宽不足、标定精度低等问题,创新与改进液压传感器、控制电路、标定方法等技术,研制出TY-2B型钻孔体积应变仪。改进的液压传感器提高了仪器精度,缩小了仪器体积;改善了控制电路,提高了仪器采样率、带宽及稳定性;创新的压电陶瓷标定技术提高了监测数据可靠性。测试结果表明改进型的TY-2B型体应变仪功耗低,小于3 W;长期稳定性好;灵敏度高,分辨率达到10-11ε;高频特性和低频特性好,采样率10~100 Hz,可采集完整地震应变波波形,固体潮波形清晰稳定;体积小重量轻,外径缩小至Φ89 mm,适用于Φ100 mm钻孔,长度1300 mm,重量45 kg,运输和安装方便。经室内检验、野外台站15年的测试,获取了良好的监测数据,体现了高灵敏的映震能力,龙门山北段体应变台站对2010年玉树地震及2023年土耳其地震的观测响应表明TY系列高精度体应变仪不仅是静态应变仪,还是宽频应变地震仪,具有动-静态标定能力,且相对于摆式地震仪有着极宽响应频带的独特优势,既可以观测地壳长期缓慢变形及其积累的特征,还可观测地壳破裂变形的瞬态细微特征。汶川地震以来青川—汉中地区体应变台站及2021年以来广州台站获取的监测曲线长期变化趋势与地震、构造地质等资料所反映的区域地质特征相符,表明TY-2B型体应变仪可在地球动力学研究、地质灾害预测预警等领域推广使用。

2022年门源6.9级地震的GPS形变特征

利用1999~2021年的GPS观测资料研究2022年门源6.9级地震震中附近区域的地壳形变特征。速度场在祁连山-海原地震带两侧呈现出明显的“南大北小”特性。发震断层速度剖面结果显示,断层两侧挤压速率为3.1 mm/a,走滑速率为3.9 mm/a,这与走滑为主的震源机制解一致。门源地震位于主应变率场和面膨胀率场高值区向低值区过渡的梯度带上,发生在最大剪应变率场和应变率第二张量不变量高值区边缘地区。同震库仑应力触发了大部分的余震,对冷龙岭断裂到海原断裂的地区有一定的应力加载作用。综合地壳形变特征和库仑应力等分析结果认为,冷龙岭断裂到海原断裂地区的地震危险性有所提高。

青藏高原东北缘地壳地震各向异性研究进展

青藏高原东北缘是青藏块体与华北块体的接触前缘部位,是研究青藏高原隆升扩张和深部动力学问题的重要区域。本文收集了青藏高原东北缘及其邻区由不同方法和不同资料获得的地壳地震各向异性结果,介绍了中上地壳和全地壳各向异性特征;结合区域地质构造、地表运动、构造应力和深部结构,分析了研究区域地壳各向异性的区域分布特征及其与地质构造的关系。结果表明,青藏高原东北缘地震各向异性存在明显的横向区域差异性,体现区域深部构造和地壳介质变形的复杂性;上地壳与全地壳的垂向差异性,反映出该区域可能存在各向异性分层现象。由于青藏高原隆升在其东北缘的伸展边界、物质运移及深部动力模式等尚处在探讨之中,结合多种数据并综合多种方法分析,有助于获得精细、准确的地震各向异性信息,为研究青藏高原隆升演化机制和深部动力模式提供有效的约束。

2021年青海玛多7.4级地震前应变演化特征分析

计算1999~2016年、2017~2020年青海玛多及其周边地区GNSS速度场,同时采用连续滑移回归方法获取该地区震前面膨胀率、主应变率及最大剪切应变率,分析其动态演变特征。结果表明:1)震前该地区构造运动并未出现明显调整;2)震前震中附近区域面膨胀率下降,说明震中附近区域应变能累积降低;3)震前震中附近区域最大剪切应变率和主应变率有所增强,说明震中附近出现应力调整现象,剪切作用增强。

2022年云南定点形变台网观测背景与变化态势分析

经过近半个世纪的发展,2022年云南定点形变台网向国家中心报送数据的观测站点已有17个,这些站点主要分布在云南6.0级以上地震频发区。本研究通过对2022年本省定点形变观测数据形态变化、观测精度计算、观测日志及工作日志梳理,对云南定点形变数据的观测背景。及其变化态势进行综述。