立交构造与渭河盆地地震活动

分析了鄂尔多斯地块南部和渭河盆地构造的空间分布特征，认为鄂尔多斯地块南部存在3条NW向隆起带，渭河盆地内部存在3个近EW向斜列的次级沉降中心，这些隆起带与次级沉降中心及其间的横向隆起共同组成了立交构造，分析了渭河盆地内部及其周边地区历史地震和现代地震的空间分布，发现立交构造对盆地内地震活动有着较强的控制作用。     

鄂尔多斯活动地块及边界带1∶50万地震构造图编制

地震构造图是综合反映特定地区地震构造环境和地震活动水平的基础性图件,鄂尔多斯活动地块及边界带1∶50万地震构造图是国家重点研发计划“鄂尔多斯活动地块边界带动力学模型与强震危险性研究”项目的一个专题成果。该图以鄂尔多斯活动地块及边界带为编图范围,参照地震行业有关地震构造图编制标准和数据库标准,在系统收集和整理区域地理信息、地质、活动构造、地震、地球物理等资料的基础上,开展高分辨卫星影像解译,吸收项目最新研究成果,建设了编图所需的基础数据库;通过资料矢量化、地层界线修改、断层修改、图面修饰、图件复核等环节,编制成鄂尔多斯活动地块及边界带1∶50万地震构造图。该图反映了由银川盆地—贺兰山、弧形构造束、渭河盆地、山西地堑系、河套盆地等活动构造单元组成的鄂尔多斯活动地块边界带,以及相邻地块有关地震构造的最新资料,完善了鄂尔多斯地块及边界带活动构造几何学和运动学图像,建成了区域地震构造基础数据库。     

青藏高原东北缘-鄂尔多斯地壳上地幔地震层析成像研究

根据横跨青藏高原东北缘—鄂尔多斯地区的流动宽频带地震台阵和区域地震台网的走时数据,利用地震层析成像方法研究了该地区400km深度范围内地壳上地幔的P波速度结构. 结果表明：青藏高原东北缘—鄂尔多斯地区地壳上地幔结构呈明显的横向不均匀性. 这种不均匀性体现在不同块体之间,同时也存在于块体内部;青藏高原东北缘上地幔P波平均速度低,而鄂尔多斯地块的P波平均速度高,这与两个地块的地质构造活动特征相吻合. 在青藏高原东北缘与鄂尔多斯地块之间的上地幔存在宽约200km的过渡带,该过渡带在地表的界限在兰州—海原之间,在上地幔表现为向东45°左右的倾斜条带,基本结构特征表现为高速与低速物质的混杂;青藏高原内部的柴达木地块平均速度偏低,而祁连地块的上地幔的平均速度偏高,两者相差约8髎;在泽库、兰州和海原地区的上地幔顶部有明显的低速体侵入特征.     

祁连山—六盘山地震带中上地壳各向异性研究

正祁连山—六盘山地震带位于青藏高原东北部的大型边界变形带,地处青藏块体、阿拉善地块和鄂尔多斯地块的交汇处,是中国大陆内部强烈地震发生的主要地区之一。该地区在新构造运动上属于比较活跃的区域,有着较强的地震活动性,主要受到NE向的现代构造应力场的作用,使之产生强烈的地壳变形和断裂活动。祁连山—六盘山地震带总体形态为北西向     

汶川Ms8.0地震前渭河盆地的断层活动特征分析

本文对汶川地震前渭河盆地跨断层水准资料进行了回顾性分析,结果表明:(1)震前鄂尔多斯块体西南缘—南缘—东南缘与渭河盆地交界处的断裂带活动及渭河盆地内部近北东向的断裂带活动出现了远场形变异常;(2)北西向岐山—马召断裂带上的南大同场地处断裂带活动也出现了远场形变异常,可能与其位于汶川地震的烈度Ⅵ度影响区有关;(3)渭河盆地内近东西走向的断裂带活动基本上没有出现异常变化;(4)震前异常持续时间约在4个月～2年之间。     

渭河盆地及邻区重力异常小波多尺度分解与解释

基于EGM2008重力场模型计算获得了渭河盆地及邻区布格重力异常。采用小波多尺度分解方法对布格重力异常进行了4阶小波逼近和小波细节分解,同时基于平均径向对数功率谱方法定量化地计算出1~4阶小波细节和小波逼近所对应的场源平均埋深。结合区域地质和地震资料,对获得的重力场结果进行分析,得到如下结论:①鄂尔多斯地块、渭河盆地、秦岭造山带3个一级构造单元的布格重力异常之间存在明显差异;构造区内部重力异常也存在横向的显著差异。布格重力异常的走向、规模、分布特征与二级构造区及主要的断裂具有一定的对应关系。②渭河盆地及邻区布格重力异常1~4阶细节对应4~23 km不同深度的场源信息,鄂尔多斯地块南缘东、西部的地壳结构存在明显的差异;渭河盆地凹陷、凸起构造区边界清晰,断裂边界与重力异常边界具有较好的一致性;秦岭造山带重力异常连贯性不好,东、西部重力异常变化特征表现出明显的差异。③渭河盆地及邻区布格重力异常分布与莫霍面埋深具有非常明显的镜像关系。渭河盆地及邻区地震主要分布在六盘山—陇县—宝鸡断裂带、渭河断裂与渭南塬前断裂交汇处、韩城断裂与双泉—临猗断裂交汇处。渭河盆地及邻区重力异常主要由中上地壳剩余密度体所影响,这可能是该区地震以浅源地震为主的主要原因。     

川滇地块云南地区不同发育阶段边界断裂破裂特征研究

正青藏高原是我国现代构造活动和地震活动最强烈的地区,自有地震记录以来,在高原内记录到多达18次8级以上巨大地震和100余次7~7.9级地震,它们均发生在喜马拉雅板块边界构造带和板内地块区及其次级地块的边界活动构造带上。已有历史地震资料统计显示,青藏高原内活动地块边界构造带上大地震具有明显的空间丛集特征,有仪器记录以来的每次地震活动丛集期都形成以8级地震为核心的7级以上地震活动系列。这可能暗含着活动地块     

地震活动反映的青藏高原东北地区现代构造运动特征

用地震活动资料研究了青藏高原东北地区的现代构造运动特征．地震活动证据表明,青藏高原东北地区活动块体之间是以复杂的变形带接触的．甘-青地块与阿拉善地块之间有一个宽阔的挤压变形带,该挤压带东南端转变为以网络状水平剪切变形为主．甘-青地块与鄂尔多斯地块接触的六盘山地区处于NE-SW向的挤压变形之中．鄂尔多斯地块与阿拉善地块间有一个具有拐折结构的剪切变形带,鄂尔多斯地块的西北角和东南缘处于NNW-SSE方向的受拉伸状态．该区现代构造变形特征可能与青藏高原向东北的挤压作用、鄂尔多斯地块的阻挡作用以及高原物质向东南方向挤出运动有关．      

背景噪声和地震面波联合反演渭河盆地 及邻区壳幔S波速度结构

利用陕西及邻区测震台网和中国地震科学台阵探测项目共257个宽频带台站记录的连续波形与远震数据,采用基于射线追踪的面波频散直接反演方法获得了渭河盆地及邻区地壳上地幔顶部S波速度结构,成像结果显示:1)渭河盆地顶部形成于新生代的沉积层造成其浅部显著的低速异常,盆地中、上地壳为低速结构,低速带延深至约25km深处,莫霍面相对两侧突变上隆,上地幔高速体侵入下地壳,可能与中—新生代上地幔基性-超基性铁镁质物质底侵有关。2)南鄂尔多斯块体地壳浅层东薄西厚的低速结构可能与块体遭受的整体掀斜、差异性抬升和强烈而不均匀的剥蚀有关。壳内不存在明显的低速异常,说明壳内低速体并没有贯穿整个鄂尔多斯地块,鄂尔多斯南段仍保留着稳定克拉通属性,至今还未遭受明显改造。3)秦岭造山带东、西深部结构存在差异,具有分段特征。造山带下地壳底部的低速异常,可能与造山带受青藏高原东北缘隆升和向外扩展等构造活动的影响有关,分析认为秦岭造山带存在青藏高原物质E流的下地壳流通道的可能性不大。     

渭河盆地现今三维地壳运动及断裂活动性研究

正渭河盆地西起陕西宝鸡,东至潼关,总体上呈近东西向展布,向东渐转为北东东向。北缘为鄂尔多斯地块,南缘是秦岭造山带,西与鄂尔多斯地块西南边缘的弧形断裂束相连,东与山西断陷带相接。盆地南北边界受活动断裂控制,内部活动断裂发育。由于受秦岭、华山山前断裂带等相关阶状正断层的倾滑运动控制,整个断陷盆地带在时空上呈现出拗陷与隆起,凹陷与     

青海省河南MS5.1和玛沁MS5.0地震后库玛断裂带的地震活动趋势研究

根据地震活动特征、大武地震台尾波持续时间及长宁、湟源和西宁3个台水氡异常变化，讨论了1999年河南Ms5.1和玛沁Ms5.0地震发生后库玛断裂带的地震活动趋势，结果表明，河南-玛沁地区的中强地震活动与库玛断裂带上的强震活动有明显的对应关系；在库玛断裂带中东段存在一个由ML≥3.0地震围成的空区；上述2次地震发生后大武地震台尾波持续时间异常依然存在，长宁、湟源和西宁台水氡趋势异常仍然持续，据此认为库玛断裂带存在发生强震的背景。     

JOINT INVERSION OF AMBIENT NOISE AND SURFACE WAVE FOR S-WAVE VELOCITY OF THE CRUST AND UPPERMOST MANTLE BENEATH WEIHE BASIN AND ITS ADJACENT AREA

The Weihe Basin is the main component of the extrusion and escape shear zone between the ancient North China craton block in Ordos and the ancient Yangtze platform in Sichuan Basin, and carries the dynamic transmission from the main power source of the Qinghai-Tibet Block in the west to the North China and South China regions in the east. The basin itself plays multi roles in the east-west and north-south tectonic movement, and is an excellent site for studying the structural interlacing, dynamic transformation and transmission. At the same time, Weihe Basin is also a famous strong earthquake zone in China. Historically, there was a strong earthquake of magnitude 8 1/4 occurring in Huaxian County in 1556, causing huge casualties and property losses. In view of the special geological structures and the characteristics of modern seismicity activities in the Weihe fault-depression zone, it is necessary to carry out fine three-dimensional velocity structure detection in the deep part of Weihe Basin and its adjacent areas, so as to study the relationship between velocity structure and geological structural units and their evolution process, as well as the deep medium environment where earth￣quakes develop and occur. We investigate the S-wave velocity structure beneath Weihe Basin and its adjacent regions based on continuous background noise data and teleseismic data recorded by 257 broadband stations in Shaanxi Province and its adjacent regions and China Seismological Science Array Exploration Project, and by adopting seismic surface wave inter-station method and background noise cross-correlation method, a total of 10 049 fundamental-mode Rayleigh surface wave phase velocity dispersion curves in the periods of 5~70s are obtained. Firstly, using the average dispersion curve in this study area, we obtain the one-dimensional average S-wave velocity structure model of the study area, and then we apply the ray-tracing surface-wave-dispersion direct inversion method to obtain the S-wave velocity structure of the crust and uppermost mantle (3~80km) beneath Weihe Basin and its adjacent regions. The test results of a 1°×1° grid checker board show that the recovery is good, except for the areas east of 111° and south of 32° of the study area, where there is almost no resolution. The imaging results show that the velocity structure beneath each tectonic unit in the study area has a certain distribution rule, and there is a good correlation between surface geological structure and deep velocity structure. Based on the analysis of velocity slices at different depths and S-wave velocity structures of three profiles, and combined with existing geological structures, geophysics and other deep exploration research results, we obtain the following knowledge and conclusions:1)The thick sedimentary layer covering the top of Weihe Basin is the cause of low velocity anomaly in its shallow crust, the middle and upper crust of the basin are of low velocity structure, and the low-velocity zone extends about 25km, the Moho interface uplifts abruptly relative to both the Ordos Block and the Qinling orogenic belt on opposite sides, and high-speed materials from the upper mantle intrude into the lower crust, which may be related to the underplating of mafic-ultramafic materials from the upper mantle in Mesozoic-Cenozoic period; 2)The south Ordos Block is not a homogeneous whole, the low-velocity structure of the shallow crust in southern Ordos Block is thin in east and thick in west, which may be related to the overall tilting of the Ordos Basin since the Phanerozoic, as well as the differential uplift and strong and uneven denudation of the Ordos Block since the Late Cretaceous. The crustal structure of the south Ordos Block is relatively simple and homogeneous. There is no significant low-velocity structure in the curst of the block, which shows that the low-velocity structure in the crust does not penetrate the whole Ordos block. We speculate that the southern Ordos Block still maintains the stable craton property, and has not been reformed significantly so far; 3)The variation characteristics of deep structure of the Qinling orogenic belt reflect the deep crustal structure and tectonic deformation characteristics of the orogenic belt which are strongly reformed by land-land collision and suture between North China plate and Yangtze plate, intracontinental orogeny, uplift of Qinghai-Tibet Plateau and its northeastern expansion since the Late Hercynian-Indosinian period. The deep structure beneath the eastern and western Qinling orogenic belt is different and has the characteristics of segmentation. The low-velocity anomaly at the bottom of the lower crust of the orogenic belt may be affected by tectonic activities such as uplift and outward extension of the NE Tibetan plateau, and the analysis considers that there is little possibility of the existence of lower crustal circulation channel for the eastward flowing of Tibetan plateau materials in the Qinling orogenic belt. However, since the maximum depth from the inversion of this paper is 80km, which is located at the top of the upper mantle, our results cannot prove that there exists a mantle flow channel for the eastward flow of Tibetan plateau material beneath the Qinling orogenic belt.     

Crustal structure of the northeastern Tibetan plateau,the Ordos block and the Sichuan basin from ambient noise tomography

We apply ambient noise tomography to significant seismic data resources in a region including the northeastern Tibetan plateau,the Ordos block and the Sichuan basin.The seismic data come from about 160 stations of the provincial broadband digital seismograph networks of China.Ambient noise cross-correlations are performed on the data recorded between 2007 and 2009 and high quality inter-station Rayleigh phase velocity dispersion curves are obtained between periods of 6 s to 35 s.Resulting Rayleigh wave phase velocity maps possess a lateral resolution between 100 km and 200 km.The phase velocities at short periods (20 s) are lower in the Sichuan basin,the northwest segment of the Ordos block and the Weihe graben,and outline sedimentary deposits.At intermediate and long periods (25 s),strong high velocity anomalies are observed within the Ordos block and the Sichuan basin and low phase velocities are imaged in the northeastern Tibetan plateau,reflecting the variation of crustal thickness from the Tibetan plateau to the neighboring regions in the east.Crustal and uppermost mantle shear wave velocities vary strongly between the Tibetan plateau,the Sichuan basin and the Ordos block.The Ordos block and the Sichuan basin are dominated by high shear wave velocities in the crust and uppermost mantle.There is a triangle-shaped low velocity zone located in the northeastern Tibetan plateau,whose width narrows towards the eastern margin of the plateau.No low velocity zone is apparent beneath the Qinling orogen,suggesting that mass may not be able to flow eastward through the boundary between the Ordos block and the Sichuan basin in the crust and uppermost mantle.     

应用综合震源机制解法推断鄂尔多斯块体周缘现今地壳应力场的初步结果

利用2007年8月1日至2013年7月21日发生在鄂尔多斯块体周缘的8499个地震的49844个P波初动符号资料,应用综合震源机制解法获得了鄂尔多斯块体周缘0.25°×0.25°的精细地壳应力场,所得应力场结果基本上覆盖了整个鄂尔多斯周缘地区.研究结果表明鄂尔多斯周缘地壳应力场具有以下特征:(1)在环绕鄂尔多斯周缘的银川—吉兰泰断陷带、河套断陷带、岱海断陷带、山西断陷带和渭河断陷带内,综合震源机制解结果以正断层型为主,且综合震源机制解节面走向大体与控制断陷带边界的主要断裂走向相一致,与鄂尔多斯周缘断陷带现今的拉张状态相一致.(2)在鄂尔多斯西南缘,综合震源机制解类型主要为逆冲、逆冲走滑和走滑型,反映了鄂尔多斯块体在西南缘受到青藏高原北东向挤压作用.鄂尔多斯西南缘的应力场的主压应力方向在远处为东向,源自于青藏高原向东北挤压作用,靠近鄂尔多斯块体表现为北东—南西向.(3)P轴方位在局部地区变化较大,但总体呈现规律性变化.P轴方位在鄂尔多斯块体西缘,从南向北,主压应力轴方位更加偏北;在其北缘,由西向东,主压应力轴方位更加偏东.在其南缘和东缘,主压应力轴方位变化不大,大体上平行于控制各断陷带主要断裂走向.P轴倾角在西南缘为近水平,在其周缘各盆地内P轴倾角近直立.(4)T轴方位总体表现为北西—南东向;在鄂尔多斯周缘各断陷带内,T轴走向大体与控制断陷带主要断裂走向以及断陷盆地走向相垂直.(5)鄂尔多斯块体在其西南角受到来自青藏高原的北东向挤压和其东北角深部物质上涌形成的北西—南东向拉张力联合作用,上述作用使得鄂尔多斯块体周缘地区除西南区为挤压区外,其余区域均为剪切拉张区,与先前研究认为鄂尔多斯周缘地区处于引张应力场作用相符合,较好地解释了环鄂尔多斯周缘的断陷盆地构造,亦符合鄂尔多斯块体东西两侧的右旋剪切拉张带以及南北两侧的左旋剪切拉张带的认识.     

Mantle anisotropy across the southwestern boundary of the Ordos block,North China

Located at the northeastern margin of the Tibetan plateau,the Ordos block is a stable tectonic unit in North China.With its active boundary fault zones,the Ordos block played an important role in the eastward extrusion mechanism of the Tibetan plateau.Peking University deployed a linear array of 15 portable broadband seismometers across the western Weihe graben during September 2005 to August 2006 and later a 2-D seismic array(Southwest Ordos Array) of 14 portable broadband seismometers during 2007-2008 at its southwestern boundary.Analyses of shear wave splitting of SKS and SKKS phases at these stations show that the fast directions trend ～110° with an average delay time of 0.9 s in the southwestern margin of the Ordos block.The agreement between the lithosphere deformation indicated by GPS data and Quaternary fault slip-rate observations and the mantle flow represented by shear wave splitting implies that accordant deformation patterns from lithosphere to asthenosphere in relation to the eastward extrusion of the Tibetan plateau could extend at least to 200 km depth.Spatial distribution of splitting polarization directions indicates that the mantle flow driven by the Tibetan plateau is blocked by the Ordos block and locally restricted in a narrow channel along the Qinling-Dabie fault zones between the Ordos block and Sichuan basin.     

六盘山断裂带及其邻区地壳结构

新生代期间,中国大陆西部受印度一欧亚板块碰撞和青藏高原隆升影响,以地壳缩短、增厚、陆内造山和强烈地震活动等为主要特征.在青藏高原东北边缘,高原物质侧向移动被鄂尔多斯地块所阻,在六盘山地区发育了一系列左旋斜冲断裂.断裂带周缘构造变形强烈,地震活动频繁,是研究青藏高原横向扩展控制大陆内部弥散变形的理想场所.本文对穿越青藏高原东北缘一六盘山断裂带一鄂尔多斯地块的宽角反射与折射地震资料使用层析成像和射线反演算法进行成像,获得了研究区地壳速度结构模型,其结果反映出六盘山断裂带两侧地壳结构、构造特征差异显著:1)上地壳层析成像结果显示鄂尔多斯盆地一侧地壳上部速度较低,等值线呈近水平状,具有典型的沉积盆地特征,而青藏高原东北缘一侧上地壳速度相对较高,横向变化剧烈,呈褶皱状,二者的分界为海原一六盘山逆冲走滑断裂;2)全地壳射线反演结果显示鄂尔多斯地块地壳速度梯度大,下地壳底部速度高由铁镁质物质组成,具有典型稳定古老克拉通的特征,青藏高原东北缘地壳速度总体较低,主要由长英质及长英-铁镁质过渡物质组成,具有典型造山带的特征,而六盘山断裂带下方地壳速度结构复杂,层面呈拱形,部分层出现速度逆转,为两个构造单元的接触过渡带;3)青藏高原东北缘一侧地壳厚度~50 km,鄂尔多斯地块地壳厚度~42 km,六盘山断裂带下方莫霍面发生叠置,揭示出青藏高原东北缘、鄂尔多斯地壳在六盘山下汇聚,较薄且刚性的鄂尔多斯地壳挤入较厚且塑性的青藏高原东北缘地壳中的构造模式.     

Characteristics of horizontal crustal move-ment in Weihe basin and adjacent zones by GPS observation

Introduction GPS observation results provide high-accuracy and large-range crustal movement data with real time, which makes it possible to obtain the velocity field of current crustal movement in Chi-nese mainland within a short time and check the previous tectonic deformation model. Geoscien-tists at home and abroad have made a great number of researches on the crustal movement in Chi-nese mainland and have obtained many results in this field (JIANG, et al, 2001; WANG, et al, 2001; ZHA…     

THE COSEISMIC VERTICAL DISPLACEMENTS OF SURFACE RUPTURE ZONE OF THE 1556 HUAXIAN EARTHQUAKE

Coseismic displacement plays a role in earthquake surface rupture, which not only reflects the magnitude scale but also has effect on estimates of fault slip rate and earthquake recurrence intervals. A great historical earthquake occurred in Huaxian County on the 23^rd January 1556, however, there was lack of surface rupture records and precise coseismic vertical displacements. It's known that the 1556 Huaxian earthquake was caused by Huashan front fault and Weinan plateau front fault, which are large normal faults in the east part of the southern boundary faults in Weihe Basin controlling the development of the basin in Quaternary. Here, we made a study on three drilling sites in order to unveil the coseismic vertical displacements. It is for the first time to get the accurate coseismic vertical displacements, which is 6m at Lijiapo site of Huashan front fault, 7m at Caiguocun site, and 6m at Guadicun site of Weinan plateau front fault. These coseismic displacements measured based on same layers of drilling profiles both at footwall and hanging wall are different from the results measured by former geomorphological fault scarps. It's estimated that some scarps are related with the nature reformation and the human beings' activities, for example, fluviation or terracing field, instead of earthquake acticity, which leads to some misjudgment on earthquake displacements. Moreover, the vertical displacements from the measurement of geomorphological scarps alone do not always agree with the virtual ones. Hence, we assume that the inconsistency between the results from drilling profiles and geomorphological scarps in this case demonstrates that the fault scarp surface may have been demolished and rebuilt by erosion or human activities.     

渭河盆地中土层场地对地震动的放大作用

土层场地对地震动的影响较大,建(构)筑物的选址及其抗震设防必须考虑土层场地的放大作用,以避免或减轻其震害.汶川地震中,布设在渭河盆地中的数字强震动台网共有27个台站(包括2个基岩台站和25个土层台站)获得良好的主震加速度时程.利用这些加速度时程,选择汤峪台做为参考场地,基于考虑几何衰减的传统谱比法分析研究了25个土层场...     

基于GPS数据分析渭河盆地现今地壳形变特征

基于2001—2015年流动及连续GPS观测资料,借助多面函数拟合法建立渭河盆地水平速度场模型,并计算球面坐标下的应变特征参数。结合陕西地区地质构造背景,分析渭河盆地水平速度场及应变场分布特征。结果表明:(1)渭河盆地西部GPS速度场受青藏块体及鄂尔多斯块体共同作用明显,西部GPS速度场大于中东部,且GPS速度场有顺时针旋转的运动特征。(2)渭河盆地西部主应力场变化复杂,中部的西安地区主应变差异变化明显,与2009年11月5日高陵M_S4.4地震对应;渭河盆地西部出现最大剪应变及面应变高值区及差异变化高梯度带,在西安附近出现最大剪应变及面应变差异变化梯度带,高陵地震震中位于零值线附近。(3)2001—2010年的主应变、最大剪应变、面应变变化比2011—2015年显著,表明高陵地震发生后,应力场进行了释放调整,近期渭河盆地地震紧迫性相对较低。