Discussion on Characteristics of Crustal Deformation along the Zhangjiakou-Bohai Sea Seismotectonic Zone

INTRODUCTIONThe Zhangjiakou-Penglai fault zone has drawnextensive attentionfromseismologists and geologistssince it was determinedinthe1980’s(Zheng Binghua,et al.,1981).Ma Xingyuan,et al.(1989)consideredit asthe north boundaryof North China sub-block.Int…     

Research of pattern dynamics parameters of crustal deformation field in seismogenic process

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山西及邻区中强地震前断层形变特征及预报指标研究

通过对山西地震带及邻区近年来发生的一系列中强地震前断层位移测量进行处理，综合研究了观测的映震能力，通过分析山西5年来5期GPS观测资料，对水平形变做出了解释，在此基础上，讨论了震前地震形变特征及应力场变化情况，获得了用形变预报中强地震的指标。     

On the physical model of earthquake precursor fields and the mechanism of precursors’ time-space distribution (III) — anomalies of seismicity and crustal deformation and their mechanisms when a strong earthquake is in preparation

By studying the seismicity pattern before 37 earthquakes withM?6.0 in North China and the pattern of crustal deformation in the Capital Area from 1954 to 1992, some abnormal characteristics of these patterns before strong earthquakes have been extracted. A comparison has been made between the anomalies of these two kinds of patterns. From the results we can know the following. (1) Before a strong earthquake, the seismicity will strengthen and the crustal deformation rate will increase. (2) Several years before a strong earthquake, there will be seismic gaps and deformation gaps around the epicenter of the quake. (3) The dynamic parameters of patterns all show a decrease in information dimension. This means that the crustal deformation has become more and more localized with time and it gives an important indication showing that a strong earthquake is in preparation. At the end of the paper, the physical mechanisms of the abnormal patterns of seismicity and crustal deformation have been explained in a unified way in terms of the earthquake-generating model of a inhomogeneous strongbody in inhomogeneous media.     

Research on temporal and spatial distribution, evolutionary character and mechanism of crustal deformation field before and after the Tangshan earthquake

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Construction of GPS MonitoringNetwork,Characteristics of RecentCrustal Movement,and Relationbetween Stress Field andEarthquake Activity in the NingxiaRegion

INT正ODU**!0厂Nln以la Is located In the nol’th segmentdthe North－southselsnuc Belt,Whlchls thejuncturedthe Qinghai－Xizang(Dbet)block,Alxa block and Odos block．In that region,the tectonic activity。svery strong;。y strong earthquakes occu。d In history,such as the 1739 ingluo M。8．0 earthqu拙eandl920 Halyuan M。8．5 eafthquake,etc．; Merately strongeaFthquakes are still veryactlve atpresent,onlyln the Wuzhong－un斟m area,there have been7 e血hquakes tvlth M。＞5．0 to occ…     

张家口-渤海地震构造带的地壳形变研究

华北北部地区的张家口-渤海断裂带是控制现代强震的一条地震构造带。新近纪以来,在区域NEE向主压应力的作用下,新发育了一系列的NE向构造活动带,与张家口-渤海断裂带组成1组共轭的剪切破裂系统,控制了近代强震的发生。文中主要探讨了这条断裂带的地壳形变特征。长趋势GPS地壳形变图像反映了这条活动断裂带相对完整的左旋走滑活动。分期的地壳形变图像揭示了在中强地震前,沿该断裂带出现一系列的NE向梯度异常带,分别指示了唐山-河间、三河-涞水以及延怀-山西地震构造活动带的活动,表明了沿张家口-渤海断裂带出现了中强地震的中期前兆。研究认为,强震前地壳形变揭示的是深部蕴震层的应变活动信息,而强震之后比较杂乱的图像特征体现了盖层的调整运动     

文安5.1级地震前后地壳形变特征研究

应用文安地震200km范围内的定点形变观测资料,在研究断层活动性质的基础上,进一步综合分析在文安地震前后地壳形变的时空演化特征及其与地震活动的关系,结果表明：（1）部分测项在震前均出现张性或者压性转折变化,或者阶跃变化;（2）地表潮汐平面应变状态在中强地震前后表现出不同的变化特征;（3）平面应变参数曲线2011年前后发生同步转折变化,且变化幅度很大,但首都圈及附近地区并没有中强以上地震发生,可能与引发2011年3月日本9.0级特大地震的板块构造应力场变化有关。     

地壳垂直形变速率梯度,断层形变速率变化与强震危险区研究

应用最新的全国垂直变形速率图和各地区不同年代的形变图。编绘相应的形变速率梯度图，计算了若干跨断层测量台、点资料的低通滤波残差及其一阶和二阶差分。结合在相应空间和时间域内所发 生的强震，讨论了地壳形变与强震的关系，得到了一些有意的结果。     

Kinematic features of the seismogenic fault of the Tangshan earthquake and the recurrence period of large earthquakes

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COMPREHENSIVE ANALYSIS OF RECENT GRAVITY AND CRUSTAL DEFORMATION IN NORTHWESTERN GUANGXI

Northwest Guangxi is located in the Youjiang fold belt and the Hunan-Guangxi fold belt of secondary structure unit of South China fold system. The South China fold was miogeosyncline in the early Paleozoic, the Caledonian fold returned and transformed into the standard platform, and the Indosinian movement ended the Marine sedimentary history, which laid the basic structural framework of this area. Since the neotectonic period, large areas have been uplifted intermittently in the region and Quaternary denudation and planation planes and some faulted basins have been developed. Affected by the strong uplift of Yunnan-Guizhou plateau, the topography of the region subsides from northwest to southeast, with strong terrain cutting and deep valley incision. Paleozoic carbonate rocks and Mesozoic clastic rocks are mainly exposed on the earth's surface, and its geomorphology is dominated by corrosion and erosion landforms. The dating results show that most of the structures in northwest Guangxi are middle Pleistocene active faults, and the movement mode is mainly stick-slip. According to the seismogeological research results of the eastern part of the Chinese mainland, the active faults of the middle Pleistocene have the structural conditions for generating earthquakes of about magnitude 6. In the northwest Guangxi, the crustal dynamic environment and geological structure are closely related to Sichuan and Yunnan regions. Under the situation that magnitude 6 earthquakes occurred successively in Sichuan and Yunnan region and magnitude 7 earthquakes are poised to happen, the risk of moderately strong earthquakes in the northwest Guangxi region cannot be ignored. Based on the analysis of deep structure and geophysical field characteristics, it is concluded that the Tian'e-Nandan-Huanjiang area in the northwestern Guangxi is not only the area with strong variation of the Moho surface isobath, but also the M_L3.0 seismic gap since September 2015, and the abnormal low b value area along the main fault. Regions with these deep structural features often have the conditions for moderately strong earthquakes. The paper systematically analyzes the spatial and temporal distribution features and mechanism of regional gravitational field and horizontal crust movement and further studies and discusses the changes of regional gravitational field, crustal horizontal deformation and interaction between geologic structure and seismic activity based on 2014-2018 mobile gravity measurements and 2015-2017 GPS observation data in the northwestern Guangxi. The results show that:1)On July 15, 2017, a M_S4.0 earthquake in Nandan happened near the center of four quadrants of changes of gravity difference, and the center of abnormal area is located at the intersection of the Mulun-Donglang-Luolou Fault, the Hechi-Nandan Fault and the Hechi-Yizhou Fault. The dynamic graph of differential scale gravitational field reflects the gravity changes at the epicenter before and after the Nandan earthquake, which is a process of system evolution of "local gravity anomaly to abnormal four-quadrant distribution features → to earthquake occurring at the turning point of gravity gradient zone and the zero line to backward recovery variation after earthquake". Meanwhile, according to the interpretation of focal mechanism of the Nandan earthquake, seismogram and analysis of seismic survey results, the paper thinks that the four-quadrant distribution of positive and negative gravity, which is consistent with the effect of strike-slip type seismogenic fault before Nandan earthquake, demonstrates the existence of dextral strike-slip faulting; 2)The pattern of spatial distribution of gravitational field change in northwestern Guangxi is closely related to active fault. The isoline of cumulative gravity generally distributes along Nandan-Hechi Fault and Hechi-Yizhou Fault. The gravity on both sides of the fault zone is different greatly, and gradient zone has influences on a broad area; the spatial distribution of deformation field is generally featured by horizontal nonuniformity. Tian'e-Nandan-Huanjiang area is located at the high gradient zone of gravity changes and the horizontal deformation surface compressional transition zone, as well as near the intersection of Hechi-Yizhou Fault, Hechi-Nandan Fault and Du'an-Mashan Fault; 3)The geometric shape of gravitational field in northwestern Guangxi corresponds to the spatial distribution of horizontal crustal movement, which proves the exchange and dynamic action of material and energy in the region that cause the change and structural deformation of fault materials and the corresponding gravity change on earth's surface. The recent analysis of abnormal crustal deformation in northwestern Guangxi shows that Tian'e-Nandan-Huanjiang is a gradient zone of abnormal gravity change and also a horizontal deformation surface compressional transition zone. It locates at the section of significant change of Moho isobaths, the seismicity gap formed by M_L3.0 earthquakes and the abnormal low b-value zone. According to comprehensive analysis, the region has the risk of moderately strong earthquake.     

2021年甘肃阿克塞5.5级地震前区域地壳变形异常特征分析

为研究2021年甘肃阿克塞5.5级地震前震中周边的地壳变形运动特征,根据CMONOC提供的GPS观测资料,通过GPS速度场、面应变率场和站间基线时间序列分析,探讨了震前的地壳变形特征。研究结果表明,震中处于发震断层西南侧远场速度大、近场速度小且断裂两侧速度场方向明显不同的位置,同时位于与发震构造类型一致的面应变率场的压缩高值区,即挤压应变累积区。跨发震断裂的基线长度在震前3年多时间出现的转折变化,表明震前发震断裂两侧左旋走滑速率明显减缓;而断裂两侧的挤压速率有所加快则反映出本次地震前震中区域存在一定程度的应变能积累。研究结果有助于认识该地震的孕震过程,并可为相似构造类型区域的强震预测提供参考依据。     

理解前兆异常变化机理和地震短临前兆

本文概要介绍了国内外近几年在地壳形变一地球自转日长变化十年尺度相关性、静寂地震、前驱波三方面的重要研究发现,并分析了这三项研究发现在地震前兆异常机理认识中的作用。初步分析表明：深部核幔耦合作用引起的地壳形变、地球物理场十年尺度波动,是数年至十年尺度地震场兆波动性变化的重要调制因素之一;源于断层脆韧转换带(过渡层)的静寂地震一慢地震缓慢破裂过程,是数天至数月尺度地震短期异常变化产生的重要原因;源于脆韧转换层上部或弹脆性层薄弱部分慢地震过程所辐射出来的低频前驱波(慢地震波),是目前已发现的可重复出现的短临前兆信号,具有数小时至7天左右的地震短临预报指标意义。     

南北地震带地壳结构多参数成像及强震触发机制研究

通过反演由大量的纵、横波地震数据组成的综合数据集,获得了南北地震带地壳的多参数三维精细结构,探讨和分析了南北地震带的高地震活动性和强震频发的原因.成像结果表明,尽管1976年松潘一平武地震(M7.2)与2008年汶川地震(M8.0)以及2013年芦山地震(M7.0)均发生在高速、低泊松比异常区域,并且在其震源的下方均有一低速、高泊松比异常区域.我们认为,上述三个地震的触发与流体侵入导致的地壳形变之间有密切的联系.1955年炉霍地震(M7.4)和1973年康定地震(M7.1)均发生在鲜水河断裂带上,其震源中心区域表现为低速、高泊松比异常,可以解释为下地壳中的流体沿断层面上涌.在震源区的周边区域兼有高速、高泊松比异常,低速、高泊松比异常以及高速、低泊松比异常,可能分别与含流体的岩石、沿断裂带发育的变质岩以及坚硬的克拉通块体对应.流体的侵入不仅能够改变断层面上的应力情况,还能降低岩石骨架的岩石力学强度,进而触发地震.1970年云南通海大地震(M7.1)发生在哀牢山一红河断裂带附近的曲江断裂上,其震源处于高速度、低泊松比异常与低速度、高泊松比异常之间的边界区域,被认为是流体挤压后的应变能积累,最终导致脆性破裂,以至于发生地震.根据本次研究获得的多参数结构图像,结合前人的研究成果,我们认为南北地震带地壳强烈形变与流体侵入是造成该区域地震活动性较高及强震频发的两个主要因素.     

1997年以来巴颜喀拉块体周缘强震之间的黏弹性触发研究

本文利用考虑黏弹性地壳结构和精确震源参数的震后形变模型,计算了玛尼、昆仑山口西、汶川地震所形成的同震和震后形变场的变化过程与特征,结果显示玛尼地震的震后形变场有利于昆仑山口西地震的能量积累,玛尼地震与昆仑山口西地震的震后形变场对汶川地震的作用不明显,而这三次地震总的震后形变场在玉树断裂带附近形成了一个明显带有左旋性质的...     

3-D Modelling of Plate Interfaces and Numerical Simulation of Long-term Crustal Deformation in and around Japan

— We developed a 3-D simulation model for long-term crustal deformation due to steady plate subduction in and around Japan by incorporating viscoelastic slip-response functions into a realistic 3-D plate interface model, constructed on the basis of the topography of ocean floors and hypocenter distributions of earthquakes. The lithosphere-asthenosphere system is modelled by an elastic surface layer overlying a Maxwellian viscoelastic half-space. Kinematic interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity (fault slip) across the interfaces. With this model, giving the steady slip rates at plate interfaces calculated from NUVEL-1A, we simulated long-term crustal deformation due to steady plate subduction in and around Japan. The simulated crustal deformation pattern is characterized by steep uplift at island arcs, sharp subsidence at ocean trenches and gentle uplift at outer rises. The numerical results show the strong dependence of the deformation pattern on the 3-D geometry of plate interfaces.     

青藏高原及周边2001年以来三次特大地震引起的形变场分布特征

基于地壳黏弹模型在GPS观测资料和地震位错数据为约束条件下,应用有限元数值模拟方法对2001年昆仑山8.1级、2008年汶川8.0级和2015年尼泊尔8.1级特大地震引起的地壳形变分布特征进行了模拟计算,获得了地震位移场和形变场.这3次大地震分别发生在青藏高原的北部、东部边界和南部边界,尽管震级大小基本相当,但发震区域和发震断层性质都各不相同,其各自产生的地壳形变场分布特征存在明显的差异,主要表现为形变场区域大小、幅值大小等的差异,以及在不同地壳深度也存在明显的差异,这些差异主要取决于地震断层性质和地下介质结构的不同.通过模拟计算,可以进一步了解大地震产生的应力加卸载区分布特征,对预测未来地震发生区域范围提供重要参考依据.     

区域垂直应变率动态图像与丽江(Ms7.0)、门源(Ms6.4)等强震关系的研究

利用从区域精密水准重复测量资料中分离提取区域性垂直应变率与跨断层形变观测相配合生成的动态图像方法,分析了发生于滇西和祁连山－河西地形变监测区及附近的丽江（Ｍｓ７．０）、门源（Ｍｓ６．４）等中强以上过程中的区域垂直应变率动态演化特征;在此基础上,对孕震过程区域垂直应变率动态信息的时空非均匀性与应变能积累状况的研究探讨,提出了一些根据区域垂直应变率动态信息判定中短期强震危险区的判据。     

characteristics of recent crustal movement in the north section of north-south seismic belt

Tectonic activity is intense and destructive earthquakes occur frequently in the northern section of the North-South Seismic Belt(NSSB). After the May 12, 2008 Wenchuan earthquake, the North-South Seismic Belt enters a new period of high seismicity. On July 22, 2013, the Minxian-Zhangxian earthquake occurred, which broke the 10-years seismic quiescence of magnitude 6 of the area, indicating an increasing trend of strong earthquakes in the region. Earthquake is the product of crustal movement. Understanding the dynamics of the process of crustal movement may provide basis for earthquake prediction. GPS measurement can provide high-precision, large-scale, quasi-real-time quantitative crustal movement data, that allows us to explore the evolution of crustal movement and its relationship with earthquake, thus providing the basis for determining the seismic situation. Since 2009, the density of mobile GPS measurement stations has significantly improved in the Chinese mainland, and moreover, the Wenchuan earthquake has brought about adjustment of the regional crustal deformation regime. So the introduction of the latest repeat GPS data is important for understanding the features of crustal movement in the northern section of the North-South Seismic Belt. In this paper, we obtained the GPS velocity field, fault profile and baseline time series and analyzed the dynamics of recent crustal movement in the northern section of the North-South Seismic Belt using the 1999a-2014a GPS data of mobile and continuous GPS measurement stations. The results show that: the Qilianshan Fault has a high strain accumulation background. There are locked portions on the Liupanshan Fault, especially in the region of Jingning, Pingling, Dingxi, Longxi. In 2004-2009a, the degree of locking of the Liupanshan Fault got higher. In 2009—2013a, crustal movement on the northern section of the North-South Seismic Belt weakened compared with 1999-2004, 2004-2009, and showed some features as follows: ① The velocity field weakened more markedly near the Qilian-Haiyuan-Liupanshan faults; ②The velocity decreased more significantly in the region north of Qilianshan-Haiyuan Fault than that of the south, resulting in enhanced thrust deformation on the Qilianshan Fault in 2009-2013a and the decreased sinistral shear deformation on the Qilianshan Fault and Haiyuan Fault; ③the velocity field decreased more remarkably at 50km west of Liupanshan Fault, compared to the east region, which led to the locked range on the Liupanshan Fault extending to the range of 100km near the fault zone during 2009-2013 from the previous locked range of 50km near the fault. The GPS baseline time series analysis also reveals a number of structural features in the region: Yinchuan Graben is continuing extending, and the extension in the west is stronger than that in the east. On the southern end of Yinchuan Graben, the deformation is very small.