中国大陆强震相近重复的50年周期及其对大陆西部强震趋势的预测

以中国大陆三十年代与八十年代强震对比证实，在各种相近重复周期中存在的五六十年的优势周期，１９８１－１９９４年发生的４６次强震，其中有３８次大五六十前（即１９３０－１９４３年期间）都曾相近重复发生过强震，其他８次强震主要分布在青海，新疆，西藏无重复发震记录，可能与三四十年代该区强震记录不全有关，按现有的资料上述两时段内５０年相近重复震率达８０％，本在讨论了震强相近重复的基本特征的差异性后认为，强震     

大陆地震活动和地震预报国际学术讨论会论文摘要

一 般问题中国大陆地区快速破裂场的主要特点及其形成的原因李永善、李金正(陕西省地震局)本文利用强震活动资料,探讨了快速弹性破裂面、破裂体、破裂区、破裂系和破裂场之间的关系.指出,破裂场是客观存在,可以用模糊数学方法来描述和分析.本文还从破裂场角度探讨了我国大陆地区的主要强震带的成因及其与板块边缘强震带的关系.认为,板内强震带以板块边缘破裂带向板内逐步扩展的结果,整个地壳和板内地壳快速弹性破裂的主要形态是网络式的破裂.破裂的次序是先大块后小块,先边缘后内部,先两端后中间.我国近百年来的强震活动和迁移图象与上述推论非常符合.最后提出了一个关于整个地壳和板内地壳的快速弹性破裂的初步假设(或模式).它可能对进一步研究板内强震有重要的理论和实用意义.     

地震新主体地区和失稳危险阶段的探寻

地震活动主体地区指在一定时期内,中国大陆及邻区强震活动相对集中发生的地区,时间尺度为几年,十几年或更长.一些作者的研究揭示了地震的成从性和成组性,不同历史时期地震主体活动地区不同.研究表明地震的成组性与大陆地壳的成块性的关联.     

华北地区地震震源机制分区特征

正反映地壳应力状态最常用的方法是对发生在地壳深部地震的震源机制研究。与数量少且分布集中的强震相比,中小地震数量众多,地理分布广泛,为探测区域地壳应力状态提供了可能。华北地区地震活动强度和构造变形强烈,是中国大陆强震活动最强烈的地区之一,加强对该地区应力状态的研究,具有重要意义。     

中国大陆与邻区强震分区活动性及其随时间演化

根据主要构造分布、震源机制解分布及地震活动状况，将中国大陆及邻区分成20个单元，6个区。利用中国地震局地球物理研究所提供的地震目录，计算近百年来各单元和各区的6级以上强震释放应变能，做出时间滑动后的应变能—时间曲线图，分析认为：(a)中国大陆及邻区百年来的强震活动是一个复杂的时空动态过程，每个区、带有其高、低潮，然而各地区没有统一的地震释放应变能高潮与低潮；(b)强震的活动与平静只是相对而言的，没有绝对的活动或平静；(c)微动态期划分较好的体现了强震活动特征，每个微动态期内至少有一个高潮期，且强震集中在一个主体地区内发生，各搬动态期的能量可以有起伏。通过进一步的讨论和分析，提出中国大陆地壳变形主要受三方面因素的控制：(1)印度板块、太平洋板块和菲律宾板块的活动及其变化控制中国强震活动图像的总体格局；(2)大陆地壳结构的非均匀性及其变化影响了主体地区的形态结构；(3)地壳形变的继承性影响强震活动主体地区形成与变迁的过程。     

强震活动主体地区形成机理的数值模拟研究

中国大陆内地震属于板内地震,有不同于板块边界地震的物理机制.中国大陆周围受到印度、太平洋和菲律宾海三大板块的联合作用,岩石圈结构复杂,具有横向和纵向不均匀性,这些因素必然影响大陆内的应力场分布,从而影响大陆内强震的活动,但其影响方式和物理过程,都需要进一步研究.本文从中国大陆动力学背景特征、应力在岩石圈中的传播特征、大陆岩石圈介质特征、前期强震活动对局部地壳的影响等方面进行较全面的计算和模拟,希望能较好地理解和探讨以上问题.     

地壳介质的流变性与孕震模型

在分析归纳中国大陆地区地震震源深度分布特征的基础上 ,着重分析了地壳介质的物理性质 ,特别是地壳介质的流变特征 ,进而探讨了震源深度分布的物理解释和孕震环境。文中应用中国陆区地热研究中的有关成果 ,推导了中国东、西部地区壳内脆韧性转换带的深度 ,给出东部地区壳内脆韧性转换带深度为 2 0～ 2 5km ,西部地区为 35～ 4 5km ,这一结果显示出壳内脆韧性转换带与我国东、西部震源深度的下界面基本一致 ,且中国大陆地震的深度大体上终止于壳内脆韧性转换带。从而表明 ,壳内脆韧性转换带有可能是控制大陆地震震源深度分布的主要原因。在这些研究的基础上 ,建立了大陆强震的震源模型 ,讨论了大陆地震的孕震过程和有关机理问题     

板内地震的成因及全球地震活动的分布特征—内波假说对地震活…

按内波假说的观点，讨论了典型板内地震即中国大陆地震的成因机制，认为造成地壳厚度分化的内波运动依靠地壳厚度差异中蕴藏的重力位能，推动地壳物质运动形成各种类型的板内地震。研究了全球地震活动的纬度分布特点以及地震活动与潮汐作用及大陆分布的联系，指出；外动力地质作用强烈的大陆因剥蚀，搬运和沉积以及负载重分布，使大陆地区始达不到重和均衡，成为地壳运动的活动区，因而陆壳“地震能量发射强度”曲线具有类似于潮汐剪     

用单元降刚法探索中国大陆强震远距离跳迁及主体活动区域转移

中国大陆强震有成组活动、远距离跳迁和不同时段形成主体活动地区的特征.本文利用强震发生位置处单元降刚法,对中国大陆地区强震的远距离跳迁和主体活动地区转移机理进行了数值模拟研究.得出的新认识是:(1)在地壳中存在初始应力场的环境中,已发生强震区部分丧失承载能力(模拟中作为显著降低单元组的弹性模量来处理),可以引起大范围兆帕量级的应力场调整,它是后续强震可远距离跳迁的主要因素;(2)一个活动期中,中国大陆强震主体活动地区及其迁移,受主要活动断层分布、初始应力场和边界载荷的配置方式的综合影响,但在十年左右的活动幕中,边界载荷的配置方式可能是控制主体活动地区及主体活动地区转移的重要因素.     

从地壳运行角度分析大陆强震机理的一种物理方法

为了从地壳运行角度利用重复大地测量数据分析大陆强震机理，提出了利用反映地壳内部密度变化或时变的物理量来分析强震发生的密度变化机理的一种物理方法：（1）介绍了地球内部密度时变的一般理论和单层密度时理论，提出了分步迭代算法；（2）简要分析了断层位错引起的单层密度变化效应；（3）分析了1996年丽江7级地震前震区南部地壳密度时变（变化）的特征,（4）初步探讨了强震孕育过程中可能的地壳内部密度时变（变化）前兆模式或发震机制。     

云南地区大震活动规律研究

云南地区处于印度板块与欧亚板块中国大陆碰撞带的东缘,地壳运动剧烈,活动块体特征明显,中强以上地震频发,是研究大震活动规律的理想场所。通过过去一个世纪的6.7级以上地震活动的时空分布以及地震动力分析认为,云南地区存在的4个具东西交替活动特征的地震活跃期,可能是东、西部各自地震活跃与平静过程叠加的结果,100a左右可能出现1次东、西部同时爆发大震的时段;云南地区地震活动与外围地区存在较好的呼应关系,安达曼-缅甸弧形带的巨震活动对云南地区地震活跃期的启动有一定的指示意义,而云南东部强震也与四川西部大震密切相关,四川大震活动往往滞后于云南地区;中强地震连发—平静—首发大震可能是云南以东部为活动主体的地震活跃期的启动模式。这些认识对云南地区大震预测、地震机理以及板缘动力学研究会有所帮助     

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.     

从地质构造探讨地震预测

在地震和地质构造关系上,作者对以下几个问题阐述了自己的看法:（1）地震发生的动力;（2）断层和地震的关系;（3）浅源地震和深源地震;（4）稳定区与活动区;（5）平静期与活动期;（6）垂直地形变与水平地形变.作者认为地壳的水平移动可能是发震的主要动力,因此认为在常发震区经常进行大地测量,观察各地的水平地形变,对中、长期地震预报可能起到有效的作用.     

中国大陆地壳应变能密度年变化率图像与强震活动关系的初步探讨

以现代构造应力场和地壳运动的观测结果为约束条件,利用有限元方法计算了中国大陆地壳应变能密度年变化率,三维有限元模型采用粘弹性本构关系,包含了中国大陆主要活动断裂带,在青藏高原考虑了因高海拔地势蓄集的附加重力势能和地壳山根浮力作用。     

大地震的重复时间和余震持续时间关系的理论研究

前人的工作曾给出大地震的强余震活动持续时间与大地震的重复时间之间存在正变化关系，即较长的余震持续时间对应较长的主震复发时间。应用地震孕育的流变模型，推导了大地震重复时间和大震后余震活动持续时间的数学表达式，并从理论上给出了大震重复时间和其余震持续时间之间的对数正比关系，从而为建立大地震的重复时间和余震持续时间的关系提供了一方面理论依据     

小江西支断裂的滑动速率与强震重复周期

本文通过对各种断错地质地貌现象及被错体年龄的分析,估算出小江西支断裂在第四纪、晚更新世及全新世以来的滑动速率分别为6.7毫米/年、7.0毫米/年及6.4毫水/年。在此基础上,结合历史地震及古地震活动讨论了强震的重复周期和断裂的活动特征,结果表明小江西支断裂的活动以重复错动发生强烈地震为主要特征,强震在断裂带上同一地段的平均重复周期为900年左右,沿整个断裂带的重复周期大于330年     

STUDY OF THE INFLUENCE OF STRONG EARTHQUAKE ON THE RECURRENCE BEHAVIOR OF MAJOR EARTHQUAKE ON ACTIVE FAULT-TAKING THE MIDDLE-NORTH SECTION OF XIANSHUIHE FAULT AS AN EXAMPLE

It is of great significance to determine the factors and causes that affect the recurrence of major earthquakes. This paper introduces the influence of strong earthquake on the recurrence of major earthquakes according to elastic rebound theory, and then proposes to calculate the impact time Δt respectively from the effect of strong earthquakes on the same and surrounding faults on the major earthquake recurrence by using seismic moment release rate method and Coulomb stress change. In this paper, we studied the change amount of major earthquake recurrence by taking four earthquakes with magnitude greater than 6.5 occurring at different fracture sections of the Xianshuhe fault zone as an example, they occurred on Daofu, Changcu, Zhuwo Fault, respectively. We used seismic moment rate method to calculate the impact time Δt of strong earthquake on the recurrence of major earthquakes on the Daofu-Qianning Fault. We further discussed the effect of the Coulomb stress change due to the interaction between faults on the recurrence of subsequent major earthquakes. The co-seismic and post-seismic Coulomb stress changes caused by strong earthquake on the surrounding faults on the Ganzi-Luhuo Fault are calculated. With the fault interaction considered, the importance of the interaction between faults in the middle-north section of the Xianshuihe fault zone to change the recurrence of large earthquakes is retested and evaluated. The results indicate that the two strong earthquakes occurring along Xianshuihe Fault in 1904(M=7.0) and 1981(M=6.9) resulted in a delay of 80 years and 45 years of major earthquake recurrence on the Daofu-Qianning Fault respectively, and the M7.3 earthquake in 1923 and the M6.8 earthquake in 1967 resulted in an advance of 35 years of major earthquake recurrence on the Ganzi-Luhuo Fault.     

SPECTRAL STRUCTURE OF VELOCITY INHOMOGENEITY OF CRUST MEDIUM BELOW THE SOUTHEASTERN MARGIN OF TIBETAN PLATEAU AND ITS ADJACENT REGIONS

In this paper we present results of spectral structure of crustal velocity inhomogeneity beneath the southeastern margin of Tibetan plateau and its adjacent region based on the S wave envelope broadening algorithm. The spectral structure of 8~16Hz band is selected to analyze the special character of crustal inhomogeneity and discuss the correlation between strong earthquakes and inhomogeneities. The result shows that strong and complex inhomogeneities of crustal medium are found in the southeastern margin of Tibetan plateau and its adjacent region. In the upper part of upper crust, the strong and small scale inhomogeneities are imaged in the Longmengshan fault zone and the north of the Anninghe fault zone, the weak and large scale inhomogeneites are imaged in the section from Huolu to Daofu of Xianshuihe fault zone and the south of the Anninghe fault zone. In the lower part of upper crust, strong inhomogeneites are found in the Longmengshan fault zone, Lianfeng fault zone, the north of the Anninghe fault zone and the sections from Huolu to Daofu of the Xianshuihe fault zone, weak inhomogeneites are found in the section from Daofu to Kangding of Xianshuihe fault zone. In the middle crust, strong inhomogeneities are observed in the section of the Baoxing to Dujiangyan, the Baoxing to Kangding, and Kangding to Shimian, and weak inhomogeneities are observed in the northwestern section from Huolu to Kangding, and the Lianfeng fault zone. Comparing the medium inhomogeneities with the location of the strong earthquakes, our results suggest existence of high correlation between them. Strong earthquakes are often located in the transitionary zone between the strong and the weak inhomogeneities. The spatial distribution of the strong and the weak medium inhomogeneities may be related to the broken medium from the strong movement of geological tectonic and the heat flow upwelling along active faults induced by frequent tectonic and volcanic activity.     

THE COMPREHENSIVE ANALYSIS AND RESEARCH OF RECENT GRAVITY AND CRUSTAL DEFORMATION IN NORTHEASTERN EDGE OF THE TIBETAN PLATEAU

In this study, we systematically analyzed the relationship between regional gravity changes, 3D crustal deformation, regional tectonic environment and strong earthquakes based on the relative gravity measurements(2011-2014), GPS data and the background vertical deformation from the leveling measurements conducted from 1970 to 2011. Subsequently, we further characterized the temporal-spatial patterns and discussed the mechanism of regional gravity changes and the crustal deformation. The results can be summarized as follows:1)The regional gravity changes, the GPS-derived horizontal deformation and the vertical deformational obtained from leveling data showed a close spatial relationship:The gravity increased along with the direction of horizontal movement, and the gravity decreased with the crustal uplift and vice versa, which reflects the inherited characteristics of neotectonic activities. 2)The crustal deformation was closely related to the active faults. The contour lines of gravity changes and vertical deformation were generally along with the Qilian-Haiyuan Fault(the strike is NWW), and the crustal horizontal deformation showed left-lateral strike slip motion near the Qilian-Haiyuan Fault. 3)The strong earthquakes usually occur in the active faults where intensive gravity change and vertical and/or horizontal deformation occurred. The extrusion deformation, surface compression rate and gravity changes were obvious near the epicenter of 2016 Menyuan earthquake. The 2013 Minxian-Zhangxian M_S6.6 earthquake occurred in the direction-turning area of intense gravity gradient zone and the transitional area of surface compression and vertical deformation. The first author of this paper has made a medium-term forecast before the Minxian and Menyuan earthquakes, especially the location of the earthquake. Based on the above understandings, we emphasized that:there are still possibilities of strong or huge earthquakes within medium-long term in the areas of crustal deformation anomalies in the study region.     

南北地震带北段深部构造特征

本文利用重力资料,采用单层地壳模式反演南北地震带北段的地壳厚度.根据艾利均衡假设,进行均衡补偿归算.编制莫氏界面图和11均衡异常图.根据地壳构造特征,划分六个地壳构造区.对天水-文县间立交构造格架进行初步的探讨.结合历史地震资料,讨论了地壳构造、均衡异常与地震的关系.