中国大陆活动地块边界带强震趋势研究

已有研究表明, 中国大陆活动地块边界带是我国大陆强震的主体带和集中区, 因此有必要对各边界带开展强震危险性的跟踪分析。本文分别从加卸载响应比时序演化特征、 基于对数正态分布的概率方法和b值变化特征3个方面对各边界带未来强震趋势进行了分析; 并分别根据加卸载响应比时序演化特征、 综合累积概率与条件概率、 b值下降判断了各边界带未来发生强震的危险程度。最后, 根据3种方法的分析结果, 探讨了中国大陆未来5年发生强震的可能区域。     

中国大陆活动地块边界带与强震活动

本文在前人对中国大陆及周边活动地块研究和划分的基础上，系统研究了6个Ⅰ级活动地块区和22个Ⅱ级活动地块之间共26个活动边界带的构造变形与强震活动，包括强震分布与活动边界带的关系，边界带构造活动速率与地震活动水平及强震复发期等的关系. 给出了边界带强震活动水平与构造活动速率之间的线性关系和强震复发期长短与构造活动速率的反向变化关系. 从而进一步揭示了中国大陆活动地块构造及其块体运动特征，以及块体边界带的构造变形对强震的控制作用.     

Correlation between movement of tectonicblocks and earthquakes in groups

Introduction ZHANG and ZHONG (1977), ZHANG, et al (1978) and ZHANG (1984) pointed out that Chinese mainland is divided into two parts by the NS-trending tectonic belt, i.e., the eastern area and the western area, and each area is divided into tectonic blocks by faults. In the eastern area, the faults are trending NNE and NNW, mainly NNE, and the long axis strike of blocks is nearly trending NS. In the western area, faults are trending NEE and NWW, mainly NWW, long axis strike …     

A STUDY REVIEW ON CHARACTERISTICS OF SEISMIC ACTIVITY OF ACTIVE-TECTONIC BLOCK BOUNDARIES IN MAINLAND CHINA

More than 80 percent of strong earthquakes(M≥7.0)occur in active-tectonic block boundaries in mainland China, and 95 percent of strong earthquake disasters also occur in these boundaries. In recent years, all strong earthquakes(M≥7.0)happened in active-tectonic block boundaries. For instance, 8 strong earthquakes(M≥7.0)occurred on the eastern, western, southern and northern boundaries of the Bayan Har block since 1997. In order to carry out the earthquake prediction research better, especially for the long-term earthquake prediction, the active-tectonic block boundaries have gradually become the key research objects of seismo-geology, geophysics, geodesy and other disciplines. This paper reviews the research results related to seismic activities in mainland China, as well as the main existing recognitions and problems as follows: 1)Most studies on seismic activities in active-tectonic block boundaries still remain at the statistical analysis level at present. However, the analysis of their working foundations or actual working conditions can help investigate deeply the seismic activities in the active-tectonic block boundaries; 2)Seismic strain release rates are determined by tectonic movement rates in active-tectonic block boundaries. Analysis of relations between seismic strain release rates and tectonic movement rates in mainland China shows that the tectonic movement rates in active-tectonic block boundaries of the eastern region are relatively slow, and the seismic strain release rates are with the smaller values too; the tectonic movement rates in active-tectonic block boundaries of the western region reveal higher values, and their seismic strain rates are larger than that of the eastern region. Earthquake recurrence periods of all 26 active-tectonic block boundaries are presented, and the reciprocals of recurrence periods represent high and low frequency of seismic activities. The research results point out that the tectonic movement rates and the reciprocals of recurrence periods for most faults in active-tectonic block boundaries exhibit linear relations. But due to the complexities of fault systems in active tectonic block boundaries, several faults obviously deviate from the linear relationship, and the relations between average earthquake recurrence periods and tectonic movement rates show larger uncertainties. The major reason is attributed to the differences existing in the results of the current earthquake recurrence studies. Furthermore, faults in active-tectonic boundaries exhibit complexities in many aspects, including different movement rates among various segments of the same fault and a certain active-tectonic block boundary contains some parallel faults with the same earthquake magnitude level. Consequently, complexities of these fault systems need to be further explored; 3)seismic activity processes in active-tectonic block boundaries present obvious regional characteristics. Active-tectonic block boundaries of the eastern mainland China except the western edge of Ordos block possess clustering features which indicate that due to the relatively low rate of crustal deformation in these areas, a long-time span is needed for fault stress-strain accumulation to show earthquake cluster activities. In addition, active-tectonic block boundaries in specific areas with low fault stress-strain accumulation rates also show seismic clustering properties, such as the clustering characteristics of strong seismic activities in Longmenshan fault zone, where a series of strong earthquakes have occurred successively, including the 2008 M8.0 Wenchuan, the 2013 M7.0 Lushan and the 2017 M7.0 Jiuzhaigou earthquakes. The north central regions of Qinghai-Tibet Plateau, regarded as the second-grade active-tectonic block boundaries, are the concentration areas of large-scale strike-slip faults in mainland China, and most of seismicity sequences show quasi-period features. Besides, most regions around the first-grade active-tectonic block boundary of Qinghai-Tibet Plateau display Poisson seismic processes. On one hand, it is still necessary to investigate the physical mechanisms and dynamics of regional structures, on the other hand, most of the active-tectonic block boundaries can be considered as fault systems. However, seismic activities involved in fault systems have the characteristic of in situ recurrence of strong earthquakes in main fault segments, the possibilities of cascading rupturing for adjacent fault segments, and space-time evolution characteristics of strong earthquakes in fault systems. 4)The dynamic environment of strong earthquakes in mainland China is characterized by “layering vertically and blocking horizontally”. With the progresses in the studies of geophysics, geochemistry, geodesy, seismology and geology, the physical models of different time/space scales have guiding significance for the interpretations of preparation and occurrence of continental strong earthquakes under the active-tectonic block frame. However, since the movement and deformation of the active-tectonic blocks contain not only the rigid motion and the horizontal differences of physical properties of crust-mantle medium are universal, there is still need for improving the understanding of the dynamic processes of continental strong earthquakes. So it is necessary to conduct in-depth studies on the physical mechanism of strong earthquake preparation process under the framework of active-tectonic block theory and establish various foundation models which are similar to seismic source physical models in California of the United States, and then provide technological scientific support for earthquake prevention and disaster mitigation. Through all kinds of studies of the physical mechanisms for space-time evolution of continental strong earthquakes, it can not only promote the transition of the study of seismic activities from statistics to physics, but also persistently push the development of active-tectonic block theory.     

Assessment of strong earthquake risk in the Chinese mainland from 2021 to 2030

The long-term earthquake prediction from 2021 to 2030 is carried out by researching the active tectonic block boundary zones in the Chinese mainland. Based on the strong earthquake recurrence model, the cumulative probability of each target fault in the next 10 years is given by the recurrence period and elapsed time of each fault, which are adopted from relevant studies such as seismological geology, geodesy, and historical earthquake records. Based on the long-term predictions of large earthquakes throughout the world, this paper proposes a comprehensive judgment scheme based on the fault segments with the seismic gap, motion strongly locked, sparse small-moderate earthquakes, and apparent Coulomb stress increase. This paper presents a comprehensive analysis of the relative risk for strong earthquakes that may occur in the coming 10 years on the major faults in the active tectonic block boundary zones in the Chinese mainland. The present loading rate of each fault is first constrained by geodetic observations; the cumulative displacement of each fault is then estimated by the elapsed time since the most recent strong earthquake.     

中国东部海域断裂构造格架与地震活动研究

渤海、黄海和东海等中国东部海域在地质构造上是大陆向海的自然延伸,海域内的构造方向与大陆一致,均为NNE-NE向,但属于不同的二级大地构造单元,渤海和北黄海属于华北地块,南黄海属于扬子地块,东海属于华南地块.由于各地块与现今活动板块边界位置不同,构造与地震活动性差异较大,渤海和北黄海地区地震活动主要受印度板块与欧亚板块碰...     

中国大陆活动地块边界带地震活动过程及其趋势研究

通过计算前人研究所给出的中国大陆26条活动地块边界带上地震过程的变异系数, 分析了各边界带的地震活动类型, 结果表明中国大陆东部地区的边界带地震都表现为丛集过程, 西部地区大多是泊松过程或者准周期过程, 尤其是大陆板块俯冲作用强烈的边界带上地震活动主要呈现为泊松过程, 青臧高原北部和东部地区的边界带都表现为准周期过程, 并讨论了可能的物理机制。 并在以往研究的基础上, 基于对数正态分布函数, 计算了各边界带目前地震发生的累计概率以及未来五年内地震发生的条件概率, 探讨了各活动地块边界带的危险程度等。     

中国大陆活动地块边界带强震活动特征的研究

在中国大陆及周边活动地块与活动地块边界带研究和划分的基础上,研究了中国陆区6个Ⅰ级活动地块区和22个Ⅱ级活动地块之间的共计24个活动边界带上的强震活动特征。从各边界带上强震活动的频次和单位时间、单位长度的地震应变能释放出发,讨论了各活动地块边界带的强震总体活动水平;并从震级频度关系出发,计算了各带的理论最大震级与复发周期。通过与实际地震记录对比发现,由中国大陆各主要活动地块边界带的地震活动参数(a/b)所推算的强震活动强度与实际地震活动强度总体上具有较好的一致性,强震复发期与构造活动速率则呈明显的反向变化关系,这也表明本研究给出的各边界带的a,b值具有一定的参考意义。文中还利用历史强震资料以及各带强震活动的离逝时间,基于泊松分布,探讨了各活动边界带的现今地震活动水平及其危险程度     

PROGRESS IN APPLICATION OF GNSS TO DIVISION OF ACTIVE TECTONIC BLOCKS IN CONTINENTAL CHINA

Chinese scientists proposed that large earthquakes that occurred in mainland China are controlled by the movement and deformation of active tectonic blocks. This scientific hypothesis explains zoned phenomenon of seismicity in space. The active tectonic blocks are intense active terranes formed in late Cenozoic and late Quaternary, and the tectonic activity of block boundaries is the intensest. Global Navigation Satellite System(GNSS)has advantages of high spatio-temporal resolution, broad coverage, and high accuracy, and is utilized to monitor contemporary crustal deformation. High accuracy and resolution of GNSS velocity field within mainland China and vicinities provided by previous studies clearly demonstrate that different active tectonic blocks behave as different patterns of movement and deformation, and block interaction boundaries have intense tectonic deformation. The paper firstly introduces the GPS networks operated by the Crustal Movement Observation Network of China(CMONOC)since 1999, and GNSS data processing methods, including GAMIT, BERNESE and GIPSY/OASIS, and discusses the advantages of using South China block as a regional reference frame for GNSS velocity field, then proposes three strategies of block division, F-test, quasi-accurate detection(QUAD), and clustering analysis. Furthermore, we introduce rigid and non-rigid block motions. Rigid block motion can be denoted by translation and rotation, while non-rigid block motion can be described by rigid motion and internal strain deformation. Internal strain deformation can be divided into uniform and linear strains. We also review the usage of F-test to distinguish whether the block acts as rigid deformation or not. In addition, combining with recent GNSS velocity results, we elaborate the characteristics of present movement of rigid block, such as the South China, Tarim, Ordos, Alashan, and Northeast China, and that of non-rigid block, such as the Tibetan plateau, Tian Shan, and North China plain. Especially, the Tibetan plateau and Tian Shan seem to deform continuously with significant internal deformation. In order to enrich and perfect the active tectonic block hypothesis, we should carefully design dense GNSS networks in inner blocks and block boundaries, optimize utilizing other space geodesy technologies such as InSAR, and strengthen combining study of geodesy, seismogeology and geophysics. Through systematic summary, this paper is very useful to employing GNSS to investigate characteristics of block movement and dynamics of large earthquakes happening in block interaction boundaries.     

Implication of fault interaction to seismic hazard assessment in Sichuan-Yunnan provinces of southeastern China

Coulomb stress changes associated with the strong earthquakes that occurred since 1904 in Sichuan and Yunnan provinces of China are investigated. The study area comprises the most active seismic fault zones in the Chinese mainland and suffers from both strong and frequent events. The tectonic regime of this rhombic-shaped area is affected by the eastern extrusion of the Tibetan highland due to the collision of Eurasian Plate against the Indian lithospheric block along the Himalayan convergent zone. This movement is accommodated on major strike-slip intraplate fault zones that strike in an E-W direction. The gradual 90° clockwise rotation of the faults in the study area contributes to the complexity of the stress field. The seismic hazard assessment in this region is attempted by calculating the change of the Coulomb Failure Function (?CFF) arising from both the coseismic slip of strong events (MS≥6.5) and the stress built-up by continuous tectonic loading on major regional faults. At every step of the stress evolutionary model an examination of possible triggering of each next strong event is made and the model finally puts in evidence the fault segments that apt to fail in an impending strong event, thus providing fu-ture seismic hazard evaluation.     

Segmentations of active normal dip-slip faults around ordos block according to their surface ruptures in historical strong earthquakes

IntroductionThe downfaulted system around Ordos block is a typical area in China, in which active normal dip-slip or strike-slip faults with normal dip-slip faults developed, and is also an area in which historical strong earthquakes actively occurred. According to historical records, there were ten strong earthquakes with M(7 occurred during past 1 500 years, including 4 M=8 earthquakes. Study on these historical large earthquakes in the area will be helpful to recognize segmentation charac…     

中国大陆特大地震的地震调整作用初步研究

为合理估计汶川8.0级特大地震后中国大陆的地震形势,本文通过对中国大陆特大地震后地震活动的统计分析,初步获得了对中国大陆特大地震调整作用的一些认识:①特大地震发生后1年内,除余震区外,中国大陆其他地区的地震活动以应力调整为主线,发生7级以上地震的可能性较小;②调整作用主要发生在西部的青藏活动地块区;③青藏地块区特大地震对华北地块区的地震调整作用较小.     

应用地震学方法研究中国大陆活动地块应力应变场

在中国大陆活动地块假说及活动边界研究的基础上，将中国大陆按照地震活动特征进行分区. 利用大地震的震源机制资料和历史强震资料，结合小震综合节面解，研究了各地震区的应力应变状态，给出了各地震区的平均应力主轴方向和平均应变率. 应用地震应变能积累释放模型研究了各地震区的地震活动水平. 结果表明最大剪切应变率与地震活动水平存在线性关系. 将地震资料给出的中国大陆地壳应力应变场与GPS测量给出的结果进行了比较，初步说明了两种结果存在着统一性，从而显示出活动地块运动变形与强震活动的内在联系.     

中国大陆强震时空分布特征及2021年玛多7.4级地震后趋势分析

对中国大陆强震活动的时空分布特征进行分析, 有助于中国大陆强震趋势的判定。 由于地震目录完整性的限制, 目前对中国大陆强震时间间隔的分析多基于1900年以来地震目录。 因为记录时长相对较短, 难以排除当前强震时序特征基于偶然的可能性, 并且可能导致过拟合而影响预测效果。 针对上述问题, 本文根据2021—2030年中国大陆地震重点危险区确定工作中的相关资料, 对合成地震目录进行了分析, 结果表明区域地震活动强弱交替是一种普遍现象, 当假设中国大陆活动断层具有准周期复发特征时, 合成地震目录时序特征与当前目录最为接近。 基于上述认识, 使用适用范围更广的单参数指数分布拟合了中国大陆强震间隔, 并结合相邻强震构造关联随时间的变化对2021年5月22日玛多7.4级地震后中国大陆的强震趋势进行了分析。 结果表明, 继玛多7.4级地震之后, 未来两年中国大陆再次发生7级以上地震的概率较大, 下次强震发生在2022年年底之前的概率为61.81%。 下次强震发生在2021年的概率为30.58%, 最有可能的发震区域是巴颜喀拉地块; 下次强震发生在2022年的概率为44.97%, 重点关注南北地震带中南段。     

青藏高原东北缘、鄂尔多斯和华北唐山震区的地壳结构差异——深地震测深的结果

划分大陆活动地块的重要标志之一是它们在地壳结构间的差异。大陆不同地块具有不同的地壳结构特征。这些结构和构造上的不同反映了它们在地壳内部的变形特征和动力过程的差异。文中利用深地震宽角反射 /折射剖面的结果 ,讨论了青藏高原东北缘东昆仑巴颜喀拉地块、鄂尔多斯地块和华北地块唐山震区地壳结构的差异。它们分别是变形强烈的活动地块、内部变形小相对稳定的地块和现代发生过强震的活动地块。在地壳结构上它们之间的差别是明显的。这些差异表现在地壳的分层性质、上地壳和下地壳的结构、地壳结构的不均匀尺度、壳 /幔分界的性质、壳内低速层的分布、地壳界面、特别是莫霍面的构造形态等方面     

THE CONCEPT,REVIEW AND NEW INSIGHTS OF THE ACTIVE-TECTONIC BLOCK HYPOTHESIS

The hypothesis that strong earthquakes in China mainland are controlled by the movement and interaction of active-tectonic blocks was advanced by Chinese scientists, with the remarkable ability to encompass geological and geophysical observations. Application of the active-tectonic block concept can illustrate 6 active-tectonic block regions and 22 active-tectonic blocks in mainland China and its neighboring regions. Systems of active-tectonic block boundaries are characterized by a zone of decades or hundreds of strong earthquakes. One of the greatest strengths of the modern active-tectonic block hypothesis is its ability to explain the origin of virtually all the M8 and 80% M7 earthquakes on the main continent in eastern Asia. In other words, active-tectonic block boundary stands in strong causal interrelation with recurrence behaviors of strong earthquakes and thus, it is possible to predict an earthquake occurrence in principle. After nearly two decades of development and improvement, the active-tectonic block hypothesis has established its theoretical foundation for the active tectonics and earthquake prediction, and is promoting the transition from probabilistic prediction to physical prediction of strong earthquakes. The active-tectonic block concept was tested by application to a well-documented, high-frequent earthquake area, and was found to be an effective way of describing and interpreting the focal mechanism and seismogenic environment, but there are still many problems existing in the active-tectonic block hypothesis, which confronts with rigorous challenges. Future progress will continue to be heavily dependent on the high-precision synthetic seismogram, especially of critical poorly documented settings. It is well known that strong earthquakes occur anywhere in the interactions among the active-tectonic block boundaries where there is sufficient stored elastic strain energy driving fault propagation, and then releasing the stored energy. Therefore, future studies will focus on the mechanism and forecast of the strong earthquake activity in the active-tectonic block boundary zone, with fault activity within the active-tectonic block boundary zone, quantifying current crustal strain status, upper crust and deep lithosphere coupling relation, strong earthquake-generating process and its precursory variation mechanism in seismic geophysical model as the main research contents, which are the key issues regarding deepening the theory of active-tectonic block and developing continental tectonics and dynamics in the modern earth science.     

中国西部及邻区活动地块边界带现代构造应力场

利用哈佛全球矩心矩张量解数据和许忠淮认为1920mdash;1999年可靠的中国大陆震源机制解数据, 反演了中国西部及邻区活动地块边界带上现代构造应力场．通过对FMSI反演程序多次的输入和检验, 得到了边界带上的应力场．边界带上最大主压应力sigma;1轴绝大多数近水平. 在90deg;E以西的中国西部大陆及邻区, sigma;1轴水平方向基本上为近SN向;在青藏高原的东北部, sigma;1轴水平方向基本上为近NE向;在青藏高原的东南部, sigma;1轴水平方向绕喜马拉雅构造东端顺时针方向旋转．最小主压应力sigma;3轴倾角呈两极分布,西域地块区内活动地块边界带和青藏地块区内东北缘部分段sigma;3轴倾角较陡, 而青藏地块区内sigma;3轴倾角近水平, 所以西域地块区和青藏地块区内东北部相对于其它大部分青藏地块区, 有更多的逆冲地震．应力场在同一个边界带具有非均匀性. 北天山带、南天山带、西秦岭mdash;德令哈带、岷山mdash;龙门山带和安宁河mdash;小江带的非均匀性相对要小一些, 西昆仑带、海原mdash;祁连带、东昆仑带、玛尼mdash;玉树带、澜沧江带和滇西西边界带的非均匀性相对要大, 而喀喇昆仑mdash;嘉黎带和喜马拉雅带的非均匀性最显著．由于震源机制解数据的限制, 本文给出的是边界带上部分段的应力场．      

由跨断层形变测量反映的华北地块近期断裂活动特征

通过对华北地块不同构造部位、不同地震活动时段的跨断层测量资料研究表明，华北地块对于NE走向断裂作用为主的构造单元(包括地块和边界带)的强震活跃时段的断层运动速率明显小于强震不活跃时段；对于NW走向断裂作用为主的构造单元，其强震活跃时段的断层运动速率明显大于强震不活跃时段；对于NE、NW走向断裂共同作用的构造单元，断层运动速率变化特征类似于NW走向断裂作用为主的构造单元。结果还表明，华北地块现今强震活动主要受NW走向断裂的控制。     

华北成组强震孕育过程及预测研究

利用华北丰富的历史地震资料, 通过研究地震与块体活动的联系, 揭示了地震高潮期的形成过程。 认为地震高潮期成组强震的孕育与区域块体的运动方式相联系。 一个地震活动期可分为二个阶段, 在前期块体边界的运动是很不平衡的, 各组地震主要是由于各局部范围若干闭锁段破裂和破裂间相互作用的结果, 当沿块体边界的破裂发展到一定程度时, 这些边界所围的地块就会进入以整体运动为主的阶段, 这时块体边界的运动具有一定程度的同步性, 加之闭锁段破裂后不再重新闭锁, 从而导致块体边界闭锁段由弱到强渐进式的破裂过程, 直至一组强闭锁段完成破裂, 形成地震活动高潮。 这是成组强震形成的根本原因, 另外强震间的诱发作用也是强震成组发生的重要原因。 最后概述了如何利用以上模式预测地震高潮期的时间、 强度和主体活动场所。     

汶川8.0级地震后中国大陆强震活动状态研究

本文从不同空间、 时间尺度对2008年四川汶川8.0级地震的影响意义进行了初步讨论, 并以此分析了其后我国大陆的强震活动状态。研究结果表明, 1800年以来中国大陆西部及邻区的大三角地区8级地震活动呈现为100年左右丛集性时间过程, 具有地震平静、 地震丛集、 地震丛集发生前的过渡和丛集发生后的调整等时间特征; 2001年11月14日昆仑山口西8.1级地震和2008年5月12日四川汶川8.0级地震的发生表明, 目前该地区可能处于8级地震丛集发生前的过渡时段。20世纪以来, 中国大陆7级强震的时间活动过程明显受大三角地区8级地震时间进程的影响, 在8级地震活动的1900—1955年时段内, 7级地震幕式活动划分不显著, 而在8级地震平静的1956—2000年时段内, 7级地震幕式活动划分清晰; 以2008年汶川8.0级地震为标志, 受大三角地区8级左右巨大地震活跃控制, 中国大陆可能将进入一组新的幕式活动不清晰的、 类似于1900—1955年的强震活跃时段。