Aseismic negative dislocation model and deformation analysis of crustal horizontal movement during 1999——2001 in the northeast margin of Qinghai-Xizang block

Through numerical simulation for GPS data, aseism/c negative dislocation model for crustal horizontal movement during 1999-2001 in the northeast margin of Qinghai-Xizang block is presented, combined with the spatial distri-bution of apparent strain field in this area, the characteristics of motion and deformation of active blocks and their boundary faults, together with the place and intensity of strain accumulation are analyzed. It is shown that: a) 9 active blocks appeared totally clockwise motion from eastward by north to eastward by south. Obvious sinistral strike-slip and NE-NEE relative compressive motion between the blocks separated by Qilianshan-Haiyuan fault zone was discovered; b) 20 fault segments (most of them showed compression) locked the relative motion between blocks to varying degrees, among the total, the mid-east segment of Qilianshan fault (containing the place where it meets Riyueshan-Lajishan fault) and the place where it meets Haiyuan fault and Zhuanglanghe fault, more favored accumulation of strain. Moreover, the region where Riyueshan-Lajishan fault meets north boundary of Qaidam block may have strain accumulation to some degree, c) Obtained magnitude of block velocities and locking of their boundaries were less than relevant results for observation in the period of 1993-1999.     

Aseismic negative dislocation model and deformation analysis of crustal horizontal movement during 1999~2001 in the northeast margin of Qinghai-Xizang block

Introduction So small is the hypocenter area of strong earthquake, but its formation is controlled by time-space evolution of present-day crustal movement in wider-range area, and related to motion and deformation of active blocks and their boundary faults. Aseismic negative dislocation model presented by Matsuura, et al (1986) is that, the relative motion between blocks driven by present-day crustal movement may be partly locked at the block …     

青藏块体东北缘弹性块体边界负位错反演与强震地点预测

利用青藏块体东北缘1993——1999年、1999——2001年和2001——2003年3个时段的GPS水平运动速度场成果,通过研究建立的弹性块体边界负位错模型反演,给出该区构造块体及其边界断裂运动与变形差异、构造应变场时空分布、高应变能积累部位以及强度的定性分析和定量描述. 在充分考虑区域构造及块体应变的前提下,研究与该区6级左右及6级以上地震地点预测相关的背景性前兆的共性特征.      

川滇地区地壳水平运动的弹性块体边界负位错模型与强震地点预测

利用川滇地区1991～1999年和1999～2001年GPS水平运动速度场成果,通过研究建立的块体弹性变形及其边界负位错部分锁定的复合作用模型反演,获取地壳水平运动反映的块体变形差异、边界断裂的高应变能积累部位和锁定能量强度,以及区域构造应变场的时空演化图像。在充分考虑区域构造和块体变形的前提下,研究与该区6级以上强震孕育及地点判定有关的背景性前兆的共性特征。     

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…     

Present-day tectonic movement in the northeastern margin of the Qinghai-Xizang (Tibetan) plateau as revealed by earthquake activity

Characteristics of present-day tectonic movement in the northeastern margin of Qinghai-Xizang plateau (Tibetan) are studied based on earthquake data. Evidence of earthquake activity shows that junctures between blocks in this area consist of complicated deformation zones. Between the Gansu-Qinghai block and Alxa block there is a broad compressive deformation zone, which turns essentially to be a network-like deformation region to the southeast. The Liupanshan region, where the Gansu-Qinghai block contacts the Ordos block, is suffering from NE-SW compressive deformation. Junction zone between the Ordos and Alxa block is a shear zone with sections of variable trend. The northwestern and southeastern marginal region of the Ordos is under NNW-SSE extension. The above characteristics of present-day tectonic deformation of the northeastern Qinghai-Xizang plateau may be attributed to the northeastward squeezing of the plateau and the resistance of the Ordos block, as well as the southeastward extrusion of the plateau materials. Foundation item: State Natural Science Foundation of China (49732090) and the Development Program on National Key Basic Researches under the Project Mechanism and Prediction of Continental Strong Earthquakes (95-13-02-05). Contribution No. 00FE2003, Institute of Geophysics, China Seismological Bureau.     

Gravity evolution and earthquake activities of the northeastern edge of Qinghai-Xizang block

The relationship between temporal-spatial evolution of gravity and earthquake activity during 1992–2001 has been analyzed systematically by integrally adjusting the gravity observation data of the northeastern edge of Qinghai-Xizang (Qingzang) block. The result shows that the gravity observation data of the northeastern edge of Qingzang block obtained by using the uniform starting datum can completely reflect the precursory gravity information appearing during the seismogenic process. In the genesis stage of an earthquake, regional gravity anomaly appears in a large area, resulting in related local gravity anomaly. The dynamic image of gravity field can clearly reflect the orderly evolution and earthquake activity. Foundation item: Key Project of China Earthquake Administration during the tenth Five-year Plan (100501-05-05).     

Gravity evolution and earthquake activities of the northeastern edge of Qinghai-Xizang block

Introduction Earthquake is closely tied up with gravity on the basis of crustal deformation and crustaldensity change. With the accumulation of stress around the epicenter, the spatial position ofground point and density crustal medium will change with strain during the seismogenic processof an earthquake. All these factors will bring about the change of gravity field. Since the Xingtaiearthquake in China in 1966, mobile gravity measurements in a large scale and the studies ongravity var…     

Present-day tectonic movement in the northeastern margin of the Qinghai-Xizang (Tibetan) plateau as revealed by earthquake activity

IntroductionAccording to the division of Neo-tectonically active blocks northeastern Qinghai-Xizang (abbreviated as QX thereafter) plateau is a juncture region where 3 intra-continental subplates, the Qinghai-Xizang, Xinjiang and North China subplate, meet with each other (DING, 1991). The subplates generally consist of blocks. Specifically, around the Yinchuan-Haiyuan (quasi-trijuncture( (TIAN, DING, 1998), where the 3 subplates meet, to the south locates the Gansu-Qinghai (GQ) blo…     

芦山MS7.0地震前水平位移和同震水平位移研究

本文利用“中国地壳运动观测网络（二期）”多个GPS连续观测站观测数据处理结果,将2013年4月20日四川芦山MS7.0地震区域参考框架同震水平位移与全球参考框架同震水平位移进行比较,结果表明两组框架解一致,说明两种参考框架均可当作位错参考框架,也即全球参考框架同震水平位移也可视为区域参考框架同震水平位移．区域参考框架下GPS连续观测站地震前的水平位移和同震水平位移结果表明,震前数年,SCTQ站西侧的GPS站构造运动十分显著,而该站水平位移却很小,即出现反常的闭锁．但该站的同震水平位移使其弹性回跳至正常构造水平位移水平,因此SCTQ站震前的位移闭锁是水平位移空间分布中的异常,是芦山MS7.0地震的前兆．水平位移时空变化表明,该站震前和震时位移完全符合里德的弹性回跳理论．区域参考框架中位移时间系列和同震水平位移的综合研究有助于对芦山地震地壳运动前兆的认识和解释．尽管本文未能直接采用其它GPS连续观测站的资料,但结合本文和其它研究结果可以证实,震中附近其它站地震前后的变化与SCTQ站类似．基于芦山地震前水平位移和同震水平位移及其与前兆关系的研究,本文进一步讨论了GPS监测网的布设、 数据处理和分析等问题．      

基于活动地块边界带的测震学参数Mf值对丽江地震的预测应用

地震构造是强震发生的必要基础,强震的孕育和发生与构造密切相关。强震的孕育和发生不仅与震中周围构造有关,而且与孕震区所在的整个构造带有关。这就表明整个构造带的地震活动性与未来强震都有关联。因此,在做测震学参数异常预测地震时,必须考虑整个构造带的地震活动。过去人们常以震中周围地区的地震活动资料来做测震学参数的异常分析,可能会丢失部分信息。文中以金沙江—红河边界带和地震学参量Mf值的结合为例,对基于活动地块边界带的测震学参数强震预测进行了探索,其结果对丽江地震预测效果很好,这对边界带的地震危险性判定有某种参考价值。     

川滇菱形块体东边界断层闭锁程度与滑动亏损动态特征研究

利用1999—2007期和2009—2013期中国大陆GPS速度场数据,采用DEFNODE负位错反演程序估算了川滇菱形块体东边界——鲜水河—安宁河—则木河—小江断裂带在汶川地震前后的断层闭锁程度和滑动亏损空间分布动态变化特征,讨论了汶川地震对该断裂系统的影响范围和程度,并结合b值空间分布和地震破裂时-空结果分析了断裂系统的强震危险段.结果表明,汶川地震前鲜水河断裂最南端为完全闭锁(闭锁深度25 km),中南段地表以下10~15 km深度为强闭锁状态,中北段基本处于蠕滑状态;安宁河断裂最南端闭锁很弱,其余位置闭锁深度为10~15 km;则木河断裂除最南端闭锁较弱以外,其余位置基本为完全闭锁;小江断裂在巧家以南、东川以南、宜良附近、华宁以北等四处位置闭锁较弱,其余位置为强闭锁.10年尺度的GPS速度场反演所得断层闭锁程度所指示的强震危险段,主要为鲜水河断裂道孚—八美段、安宁河断裂中段、则木河断裂中北段、小江断裂北段东川附近、小江断裂南段华宁—建水段,该结果与地质尺度的断层地震空区和30年尺度的b值空间分布所指示的危险段落具有一致性.汶川地震后断裂带远、近场速度分布和块体运动状态发生变化,这种区域地壳运动调整使得负位错模型反演得到的断裂带闭锁情况发生一定变化.汶川地震前后川滇菱形块体东边界平行断层滑动亏损速率均为左旋走滑亏损,且在安宁河断裂北端、则木河断裂中北段滑动亏损速率最大;除鲜水河断裂中南段与最南端和小江断裂东川附近以外,其余断裂震后滑动亏损速率均有所增加.垂直断层滑动亏损速率既有拉张亏损也有挤压亏损,且鲜水河断裂最南端由震前挤压转变为震后拉张,其余断裂除了安宁河断裂和小江断裂中段与最北端存在挤压滑动亏损速率外均为拉张速率.     

青藏块体东北缘GPS与水准资料的三维负位错联合反演

利用1999—2004年青藏块体东北缘分布密度不同的GPS与区域水准观测资料,实现三维负位错模型联合反演,综合研究该区活动块体边界断裂的应变积累状况及其分段差异性。分析结果表明:祁连山构造带东段及与庄浪河断裂、海原断裂交汇区域目前可能具有相对高应变能积累背景;而庄浪河断裂南段的兰州、临夏一带反映一定程度的应变积累特性。     

青藏高原东北缘岩石圈有效弹性厚度与地震分布关系

岩石圈有效弹性厚度（T_e）表征岩石圈综合力学强度,对理解区域深部构造孕震环境具有重要意义.青藏高原东北缘地质构造复杂,强烈地震活动频发.为进一步了解该区域深部岩石圈力学性质特征及其与地震活动的关系,本文利用基于Fan小波的谱方法,使用WGM2012重力异常数据、ETOPO1地形数据和CRUST1.0模型,通过导纳和相关联合反演计算了青藏高原东北缘的岩石圈有效弹性厚度（T_e）与荷载比（F）.结果显示研究区T_e整体呈明显的东高西低分布,青藏块体T_e变化剧烈,西部高值（>40 km）和东部低值（< 20 km）共存;鄂尔多斯地块T_e较高（>30 km）,变化相对平缓;荷载比F存在局部西南高,巴颜喀拉和羌塘地块荷载比F较高（>0.5）,说明以地下荷载为主,其他地块荷载比F较低（< 0.2）,以地表荷载为主.鄂尔多斯地块结构稳定,岩石圈强度较大,T_e值较高;内部构造活动性微弱,深部物质密度横向变化较小,岩石圈所受荷载以地表为主,荷载比F较低.柴达木地块东部与巴颜喀拉地块东部可能发生有下地壳流,岩石圈较为软弱,T_e值较低;巴颜喀拉地块内部与鲜水河断裂的荷载比F较高,岩石圈所受荷载以地下为主,可能是地壳物质向东流动导致岩石圈深部物质密度横向变化较大引起的.通过对比分析研究区T_e和T_e梯度、F和F梯度与地震之间的对应关系,发现地震一般发生在区域相对低T_e值、T_e梯度值和荷载比F梯度值较大的区域,震级较小的地震多发生在荷载比F较小的地区,6级以上强震则较多发生在荷载比F约为0.1和0.8的区域.因此,岩石圈有效弹性厚度T_e值较低、T_e梯度和荷载比F梯度较大的地区,更易出现地震.

     

巴颜喀拉块体北和东边界大地震序列的关联性与2008年汶川地震

2008年汶川地震发生在巴颜喀拉块体的东边界.为了探讨区域动力学背景与该地震发生的关系,本文基于活动构造、震源机制解、GPS站速度、地震破裂展布以及历史大地震活动等资料分析巴颜喀拉块体北、东两个边界断裂系统的运动、变形以及大地震序列发生的关联性.结果表明:由于受到华南地块的阻挡,巴颜喀拉块体朝东-南东方向的 "逃逸"运动—表现为该块体北边界的左旋走滑断层作用—在该块体的东边界转换成为逆冲或缩短兼走滑断层作用,亦即该块体的运动对其东边界断裂系统具有显著的"加载"作用.这种加载作用也反映在该块体北和东两个边界大地震序列发生的关联性上.19世纪中-晚期至2001年期间,一个由8次事件组成的大地震序列使巴颜喀拉块体北边界总长度的2/3破裂,该序列同时具有加速应变释放以及事件的间隔逐渐缩短的特征,反映最晚自1902年以来该块体发生了加速运动.作为对这一加速运动的响应,巴颜喀拉块体东边界大约自1933年以来发生一个由3次事件组成的大地震序列,也显示出加速释放以及事件的间隔逐渐缩短的特征;2008年汶川地震正是该响应序列中的最新事件.东边界的响应型大地震序列的发生至少滞后于北边界的数十年,可能与该块体的非刚性运动有关.另外,这两个大地震序列的事件序次-时间关系有助于分析该块体北与东边界的中-长期地震危险性.     

Relation between electricity structure of the crust and deformation of crustal blocks on the northeastern margin of Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau was formed by coales-cence of microcontinents of different geologic histo-ries, i.e. it consists of a series of blocks, such as Hi-malayas, Lhasa, Qiangtang, Kunlun, Qaidam and Qi- lian blocks from south to north. The blocks moved firstly in the NNE direction, then in the NE direction and at last in the ENE or E-W direction from south to north by a combined action of Indian Plate moving northward and obstruction of Tarim and other blocksnorth of the plateau. T…     

芦山地震前龙门山断裂带闭锁程度 与变形动态特征研究

利用1999-2007和2009-2011年中国大陆GPS水平速度场数据, 采用DEFNODE(反演计算弹性岩石圈块体旋转、 应变和块体边界断层闭锁或同震滑动的Fortran程序)负位错反演程序估算了芦山地震前龙门山断裂带的三维闭锁程度, 并结合剖面结果分析了断层深浅部变形特征. GPS反演结果表明, 1999-2007年, 龙门山断裂中北段(闭锁比例为0.99)处于强闭锁(本文将闭锁比例大于0.97的称为强闭锁)状态; 龙门山断裂南段地表以下深度16 km内为强闭锁, 深度16-21 km处闭锁比例降低为0.62, 深度21-24 km处整条断裂逐渐转变为蠕滑状态. 2009-2011年, 即汶川地震后, 龙门山断裂中北段处于震后蠕滑状态; 龙门山断裂南段深度16-21 km处闭锁比例降低为0.45, 其它位置闭锁程度保持不变. GPS剖面结果显示, 2009-2011年, 即汶川地震后, 龙门山断裂中北段为逆冲兼右旋走滑运动; 而南段断层不能自由滑动、 变形宽度较大. 综合分析认为, 汶川地震时, 龙门山断裂南段并没有发生破裂, 一直处于较强的闭锁状态, 汶川地震的发生又加速了芦山地震的孕育进程; 由于龙门山断裂带南段的闭锁深度较中北段浅, 因此芦山地震较汶川地震强度低、 震级小、 破裂范围窄.     

昆仑山口西8.1级地震前后地壳垂直运动的负位错模型

利用昆仑山口西8．1级地震震区外围格尔木一五道梁300km长水准测线在1979,1991和2002年3期垂直形变资料,借助研究改进的负位错模型获取发震构造及其相关断裂的运动、变形特征及应力应变积累部位和强度,对与此次大震有关的区域构造形变背景及可能的震后影响进行了研究。结果表明：1991～2002年相对1979～1991年垂直差异运动及应变积累加速增强的特征与昆仑山口西8．1级地震孕育有关;且这样的一个地壳垂直运动加速过程可能还未因地震发生而结束,发震构造相关的断裂构造部位仍有发生较强地震的可能。     

西南地区次级构造块体与分区强震预报

依据西南地区现今构造、活动断裂和历史地震活动特点以及西南地区断裂带间相互作用等，将西南地区划分为次级构造区或次级块体——即将西南地区划分为5个构造次级块体，川青甘块体、川西块体、滇中块体、滇西南块体、川东南块体；针对西南次级构造区或次级块体的现今强震活动特征和历史中强地震特点，将中强地震归属划分为5个地震预测跟踪区，探讨基于西南次级构造区或次级块体的分区强震预报。     

Active tectonic blocks and strong earthquakes in the continent of China

The primary pattern of the late Cenozoic to the present tectonic deformation of China is characterized by relative movements and interactions of tectonic blocks. Active tectonic blocks are geological units that have been separated from each other by active tectonic zones. Boundaries between blocks are the highest gradient of differential movement. Most of tectonic activity occurs on boundaries of the blocks. Earthquakes are results of abrupt releases of accumulated strain energy that reaches the threshold of strength of the earth's crust. Boundaries of tectonic blocks are the locations of most discontinuous deformation and highest gradient of stress accumulation, thus are the most likely places for strain energy accumulation and releases, and in turn, devastating earthquakes. Almost all earthquakes of magnitude greater than 8 and 80%-90% of earthquakes of magnitude over 7 occur along boundaries of active tectonic blocks. This fact indicates that differential movements and interactions of active tectonic blocks are the primary mechanism for the occurrences of devastating earthquakes.