MIGRATION OF LARGE EARTHQUAKES IN TIBETAN BLOCK AREA AND DISSCUSSION ON MAJOR ACTIVE REGION IN THE FUTURE

On the basis of summarizing the circulation characteristics and mechanism of earthquakes with magnitude 7 or above in continental China, the spatial-temporal migration characteristics, mechanism and future development trend of earthquakes with magnitude above 7 in Tibetan block area are analyzed comprehensively. The results show that there are temporal clustering and spatial zoning of regional strong earthquakes and large earthquakes in continental China, and they show the characteristics of migration and circulation in time and space. In the past 100a, there are four major earthquake cluster areas that have migrated from west to east and from south to north, i.e. 1)Himalayan seismic belt and Tianshan-Baikal seismic belt; 2)Mid-north to north-south seismic belt in Tibetan block area; 3)North-south seismic belt-periphery of Assam cape; and 4)North China and Sichuan-Yunnan area. The cluster time of each area is about 20a, and a complete cycle time is about 80a. The temporal and spatial images of the migration and circulation of strong earthquakes are consistent with the motion velocity field images obtained through GPS observations in continental China. The mechanism is related to the latest tectonic activity in continental China, which is mainly affected by the continuous compression of the Indian plate to the north on the Eurasian plate, the rotation of the Tibetan plateau around the eastern Himalayan syntaxis, and the additional stress field caused by the change of the earth's rotation speed.
Since 1900AD, the Tibetan block area has experienced three periods of high tides of earthquake activity clusters(also known as earthquake series), among which the Haiyuan-Gulang earthquake series from 1920 to 1937 mainly occurred around the active block boundary structural belt on the periphery of the Tibetan block region, with the largest earthquake occurring on the large active fault zone in the northeastern boundary belt. The Chayu-Dangxiong earthquake series from 1947 to 1976 mainly occurred around the large-scale boundary active faults of Qiangtang block, Bayankala block and eastern Himalayan syntaxis within the Tibetan block area. In the 1995-present Kunlun-Wenchuan earthquake series, 8 earthquakes with M_S7.0 or above have occurred on the boundary fault zones of the Bayankala block. Therefore, the Bayankala block has become the main area of large earthquake activity on the Tibetan plateau in the past 20a. The clustering characteristic of this kind of seismic activity shows that in a certain period of time, strong earthquake activity can occur on the boundary fault zone of the same block or closely related blocks driven by a unified dynamic mechanism, reflecting the overall movement characteristics of the block. The migration images of the main active areas of the three earthquake series reflect the current tectonic deformation process of the Tibetan block region, where the tectonic activity is gradually converging inward from the boundary tectonic belt around the block, and the compression uplift and extrusion to the south and east occurs in the plateau. This mechanism of gradual migration and repeated activities from the periphery to the middle can be explained by coupled block movement and continuous deformation model, which conforms to the dynamic model of the active tectonic block hypothesis.
A comprehensive analysis shows that the Kunlun-Wenchuan earthquake series, which has lasted for more than 20a, is likely to come to an end. In the next 20a, the main active area of the major earthquakes with magnitude 7 on the continental China may migrate to the peripheral boundary zone of the Tibetan block. The focus is on the eastern boundary structural zone, i.e. the generalized north-south seismic belt. At the same time, attention should be paid to the earthquake-prone favorable regions such as the seismic empty sections of the major active faults in the northern Qaidam block boundary zone and other regions. For the northern region of the Tibetan block, the areas where the earthquakes of magnitude 7 or above are most likely to occur in the future will be the boundary structural zones of Qaidam active tectonic block, including Qilian-Haiyuan fault zone, the northern margin fault zone of western Qinling, the eastern Kunlun fault zone and the Altyn Tagh fault zone, etc., as well as the empty zones or empty fault segments with long elapse time of paleo-earthquake or no large historical earthquake rupture in their structural transformation zones. In future work, in-depth research on the seismogenic tectonic environment in the above areas should be strengthened, including fracture geometry, physical properties of media, fracture activity behavior, earthquake recurrence rule, strain accumulation degree, etc., and then targeted strengthening tracking monitoring and earthquake disaster prevention should be carried out.     

景泰5.9级地震的断层形变异常及中短期预报

初步研究了2000年6月6日甘肃景泰5.9级地震蕴育过程中近源区及外围地区断层形变异常的时空分布特征:震前断层形变异常分布范围广、异常形态复杂，断层形变（应变）类信息指标图象异常区明显．不同地域断层形变异常形态及幅度存在显著差异，与异常所处的构造部位密切相关:海原断裂带西段出现的，，相断层形变异常，显示了近源区断层运动由准线性走向非线性的过程，与断层形变（应变）类信息指标高值异常区相配合，反映蕴震区应变积累程度高；而构造汇聚部位的六盘山断裂带等远场区较大幅度的突跳尖点异常，并不反映所在地的应变积累，而可能是蕴震过程区域构造应力场增强的一个标志．在此基础上，结合对景泰5.9级地震中短期预报经验教训的初步总结，研究和探讨了断层形变异常在震情判定中的应用．      

2009年云南姚安6.0级地震震源机制与发震构造的分析研究

利用P波、SV波、SH波初动及其振幅比联合反演震源机制解的方法,计算了2009年7月9日发生在云南姚安6.0级地震余震序列的震源机制解,同时结合地震序列的空间分布,对姚安6.0级地震的发震断层性质和震区应力场特征进行综合分析。结果分析表明：（1）姚安6.0级地震发震断层为NWW—SEE向的直立右旋走滑断层,与美国哈佛大学的主震CMT解节面基本一致,也与余震优势方向分布一致,证明结果可靠;（2）震区主压应力场优势方向为NNW—SSE向,与其现今区域构造应力场主压应力NNW—SSE向一致,表明主震应力场主要受到现今区域构造应力场的控制,同时还有一些小的余震与主震应力场不同,表明震区应力场的多样性和复杂性;（3）结合本次地震序列的空间分布、震源机制解特征、震区断裂构造特征综合分析,综合判定姚安6.0级地震的发震构造属于马尾箐断裂。     

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.     

玉溪-临沧剖面宽角地震探测——红河断裂带及滇南地壳结构研究

云南位于南北地震带南段,地震活动具有频度高、强度大的特点,中小地震几乎遍及云南南部,是中国大陆内部地震活动最强的地区之一.滇南地区跨越多个重要的地质构造单元和多条地震带,其中红河断裂带是跨越该地区的一条大型的走滑断裂带,作为印支地块和华南地块两大地块的分界断裂,对人们认识板块相互运动及其深部动力学背景具有重要意义.中国地震局于2010年启动了"中国地震科学台阵探测--南北地震带南段"项目,在云南省中西部跨越红河断裂带布设一条近东西向的深地震宽角反射/折射探测剖面,本文利用该东西向深地震宽角反射/折射剖面来研究红河断裂带及滇南地区详细的地壳结构及其孕震背景.研究结果表明:沿测线地壳结构呈西薄东厚的特征,以红河断裂带为界,断裂带以西地壳较薄,约34 km,以东地壳加厚至44 km左右;红河断裂带两侧速度结构具有明显的差异,断裂带西侧速度较低,东侧速度明显偏高.由震相特征及获取的地壳结构可以看出,红河断裂带两侧由浅至深速度结构的异常特征说明该古缝合带两侧块体地壳结构岩性的巨大差异性.     

昆仑山口西8.1级地震前青藏块体边界断层异常活动

系统分析了青藏块体边界断层的形变资料，研究了断层活动的动态过程及空间分布。结果表明，昆仑山口西8．1级地震前孕震影响范围达到青藏块体的周边地区；发震断层所在的构造带震前断层活动最为剧烈；加强对构造块体断层整体活动的宏观动态比较和分析，有助于判定未来强震发生的危险地段；震后应力将转移并集中到西秦岭构造带及其邻近地区。     

大地电磁资料精细处理和二维反演解释技术研究(七)——云南盈江——龙陵地震区深部电性结构及孕震环境

本文对一条布设在滇西盈江—龙陵地区的大地电磁剖面(苏典—中山剖面)数据进行了精细处理和二维反演解释,得到了测区较高置信度的二维电性结构.该电性模型纵向上表现为高阻-低阻-高阻的"三明治"式岩石圈电性结构,上地壳为平均厚度约为10km的高阻地层,在约6～16km地壳深度范围发育有电阻率为几欧姆米的显著高导层,下地壳底部和上地幔顶部表现为电性较为均匀的相对高阻层.横向上自西向东划分出以大盈江断裂带、龙陵—瑞丽断裂带为限的3个主要构造区域.壳内分布的高导层沿剖面表现出一定的横向不均匀性,其在龙陵—瑞丽断裂带下方消失,在该处形成了腾冲地块和保山地块的电性构造边界.电性结构表明,大盈江断裂附近高导层顶界面浅,两侧高阻体厚度小,因此难以形成较大规模的相互作用,致其附近浅震源、小震级的地震活跃;龙陵—瑞丽断裂两侧的高阻体较厚,易积累较大的应力,具有大震的深部孕震环境,故其附近发生过多次7级以上强震.     

珠江三角洲地区新构造运动

概述了珠江三角洲地区新构造运动的基本特征：晚第三纪以来的构造运动经历了由强逐渐减弱，晚更新世（约50－30Ka B.P)又重新增强的演变。重点估算了晚第四纪珠江三角洲断块垂直构造运动速率，定量分析了分割断块的断裂构造的活动性。认为斗门断块区和广州－番禺断块区这两个次级断块构造以及围限它们的广州－从化断裂，三水－罗浮断裂，西江断裂，白坭－沙湾断裂的活动性相对较强。从区域地震构造而言 ，珠江三角洲新构造运动远弱于日本－琉球－台湾岛弧，也弱于奥东潮汕和桂东南灵山等强震危险区。但由于其震源浅及松软土层较厚，加上本区经济发达，人口稠密，因此地震造成的破坏和损失仍不可低估，必须加强抗震减灾工作。     

2004年苏门答腊地震粘滞性松弛效应对华南地区地壳水平活动的影响

2004年苏门答腊地震后, 不同学者根据不同观测数据(地震波、 GPS), 得到了此次地震的断层滑动模型。 反演过程中使用半无限空间模型时, 无法利用远场观测数据进行约束, 势必影响远场形变的解释。 基于Hoechner等使用的断层几何模型和GPS同震位移数据, 本研究利用球体位错理论反演方法反演了2004年苏门答腊地震断层滑动模型, 得到的矩震级为9.24, 最大滑移量为30.4 m, 由于考虑了曲率的效应, 该模型在远场同震位移的计算结果与GPS数据吻合较好。 然后, 选取了2001—2004年和2004—2007年两期的GPS水平位移速度场, 研究2004年苏门答腊地震对华南地区地壳水平活动的影响, 从两期的GPS水平位移速度场差异可以看出地震后华南块体有向西南方向的运动趋势, 华南块体受到此次地震明显的震后影响。 最后, 基于反演得到的断层模型, 利用Tanaka等提出的粘弹性球体位错理论对华南块体两期GPS水平位移速度场差异进行模拟, 得到华南块体内部粘滞性系数为2×10¹⁹ Pa·s, 当考虑地幔粘滞性松弛效应后, 两期的速度场差异的均方根值由3.2 mm减少为1.9 mm。 可见在研究2004年前后中国大陆GPS水平位移速度场时, 若继续以华南块体为基准, 需考虑此次地震的地幔粘滞性松弛效应。     

Southeastern extension of the Red River fault zone (RRFZ) and its tectonic evolution significance in western South China Sea

The tectonic evolution features in the western South China Sea (SCS) are directly related to the Tethys tectonic province. The Red River fault zone (RRFZ) comprises a large part of the Tethys tectonic province and is the boundary between the Europe Block and the India-Asia Block[1]. It serves as the contact between the uplift of the Qinghai-Tibet Plateau and the SCSopening. The RRFZ, which is an important dividing line in the geology of the SE Asia, is about 1000 km long in the co…     

利用凹凸体判断柯坪块体地震危险性

将柯坪块体作为研究对象,利用最大似然法进行b值计算,并结合利用双差定位法对柯坪块体上发生的M_L≥1.6地震重定位后的结果,寻找沿柯坪块体主要断裂带的凹凸体。研究发现,柯坪块体上发生地震的震中主要沿断裂带分布,沿柯坪塔格逆断裂带存在凹凸体,该区域虽已发生大地震,但依然处于高应力水平,因此初步判定沿柯坪塔格逆断裂带仍存在发生地震的危险性。     

安徽地区历史及现代地震活动与断裂活动性关系研究

安徽地区处于华北板块与扬子板块沿着大别造山带的陆一陆碰撞变形带,构造背景复杂多样,断裂十分发育。郯庐断裂带长期控制着两侧的构造格局,大别山东缘的霍山地区多条断裂在晚第四纪有新活动。史料记载表明安徽地区历史地震以中强震为主,最高震级为M6 1/4级。根据区域地震地质、历史地震近年最新研究成果,对第四纪特别是晚第四纪以来的断裂活动习性做出归纳和分类,并分析历史地震、1970年后有仪器记载以来中等强度地震和小地震密集与断裂活动的相关性,为中长期地震预测提供依据。     

太行山麓淇县—新乡—焦作地区现今构造应力状态与地震活动关系

本文根据现今断裂活动特征、地下水活动、震源机制等资料初步研究了河南省淇县—新乡一焦作地区的现今构造应力状态。并结合有限元分析计算,初步探讨了应力状态与地震的关系。最后指出了该区有可能发生中强地震的构造部位     

Fault deformation anomaly and intermediate and short-term prediction of the Jingtai M_s=5.9 earthquake

IntroductionOn June 6, 2000, an earthquake of MS=5.9 occurred in Jingtai county, Gansu Province. The epicenter (37.1(N, 104.0(E) was located in Maomaoshan-Laohushan zone of the western segment of Liupanshan-Haiyuan fault along the northeastern margin of Qinghai-Xizang Plateau, where is the middle-eastern part of crustal deformation monitoring area of Gansu-Ningxia- Qinghai region. There are more than 50 spanning-fault mobile monitoring sites in the earthquake area and its vicinity (Fig…     

华北地区跨断层垂直形变分区特征及其对块体划分的意义

对 70年代以来的华北地区跨断层形变测量资料进行了分区研究。按构造单元将华北地区的跨断层测量台站或测点分为五组 :山西带、郯庐带、阴山 -燕山带西段、阴山 -燕山带东段和首都圈。对 80项实测资料的计算结果表明 ,华北地区断层垂直活动平均年速率为 0 335mm/a ,但各分区之间的断层活动速率值相差很大。山西断陷带的断层形变速率最高 ,是华北地区最重要的活动块体边界 ;其它构造带的断层形变速率都比较低     

山东及附近区域地震断层错动性质与地壳应力场特征

利用P、SH、SV波的初动及振幅比获得2001年4月至2012年8月山东及附近区域132次地震震源机制解,对该区域地震断层的错动性质及地壳应力场特征进行分析.结果表明,山东及附近区域地震断层错动的基本方向为北东向和北西向,错动方式以走向滑动为主,部分为斜向滑动.分区研究表明：聊考断裂带附近区域所受挤压作用相对较强,逆断型地震破裂较多;胶东半岛及北侧海域所受拉张作用略占优势,逆断型地震破裂较少;沂沭断裂带南部附近区域逆断型与正断型的地震破裂所占比例差别不大.     

五大连池火山构造地震空间分布及其构造含义

在对五大连池地震台１９８３年以来观测到的五大连池火山区的地震记录复核的基础上，测定了火山构造地震的空间分布状态。研究结果表明该地区地震活动均为壳内地震。受火山构造环境影响，地震活动存在着外围边缘强，震源深度分布深；内部弱，震源深度分布浅的差异。火山区内部地震深度分布优势在５ｋｍ—８ｋｍ，有３个地震分布密集区，震中分布呈明显的沿火山构造断层成带分布特性。在地震条带交汇处，震源深度起伏变化大，是火山构造活动强烈部位     

色尔腾山山前断裂东段与西段转折处构造演化特征

色尔腾山山前断裂位于鄂尔多斯块体西北角,控制着临河凹陷（河套盆地西部）的持续沉降。对色尔腾山山前断裂东段与西段转折处构造演化模式的研究,有助于提高对正断层演化规律和区域地震风险的认识。本文在研究区大比例尺活动断裂填图的基础上,通过对重点区域进行无人机微地貌的测量、探槽开挖、钻孔资料与第四纪测年等方法获取数据,并运用构造地质学、地貌学和沉积地层学等理论,综合探讨断层转折处的构造演化模式及地震危险性。通过研究认为,近东西走向的色尔腾山山前断裂西段与北西走向的东段间以三角状的转换斜坡相连。现今的转折点为应力的积累区,具有较高的地震风险。水平拉伸力的持续作用使断层不断向盆地一侧迁移,同时使断裂转折部位更加平滑。     

Current tectonic deformation and seismogenic characteristics along the northeast margin of Qinghai -Xizang block

Introduction The northeast margin of Qinghai-Xizang block has become the place with close attentions from geo-specialists at home and abroad for its significant tectonic movement and intensive seismicity. Quite a number of achievements have been obtained from the studies on geological structures and strong earthquake activities (DING, LU, 1989, 1991; GUO, et al, 1992, 2000; GUO, XIANG, 1993; HOU, et al, 1999; Tapponnier, et al, 1990; Gaudemer, et al, 1995). In the Development Program…