Rupture model of the 2013 M_W 6.6 Lushan (China) earthquake constrained by a new GPS data set and its effects on potential seismic hazard          下载免费PDF全文

Rumeng Guo  Yong Zheng  Faqi Diao  Xiong Xiong  Jiao Xu 《地震科学（英文版）》2018,31(3):117-125

Vertical records are critically important when determining the rupture model of an earthquake, especially a thrust earthquake. Due to the relatively low fitness level of near-field vertical displacements, the precision of previous rupture models is relatively low, and the seismic hazard evaluated thereafter should be further updated. In this study, we applied three-component displacement records from GPS stations in and around the source region of the 2013 MW6.6 Lushan earthquake to re-investigate the rupture model.To improve the resolution of the rupture model, records from both continuous and campaign GPS stations were gathered, and secular deformations of the GPS movements were removed from the records of the campaign stations to ensure their reliability. The rupture model was derived by the steepest descent method(SDM), which is based on a layered velocity structure. The peak slip value was about 0.75 m, with a seismic moment release of 9.89 × 10~(18) N·m, which was equivalent to an M_W6.6 event. The inferred fault geometry coincided well with the aftershock distribution of the Lushan earthquake. Unlike previous rupture models, a secondary slip asperity existed at a shallow depth and even touched the ground surface. Based on the distribution of the co-seismic ruptures of the Lushan and Wenchuan earthquakes, post-seismic relaxation of the Wenchuan earthquake, and tectonic loading process, we proposed that the seismic hazard is quite high and still needs special attention in the seismic gap between the two earthquakes.  相似文献   

Mesozoic mafic magmatism in North China: Implications for thinning and destruction of cratonic lithosphere   总被引：3，自引：0，他引：3  

Yongfei Zheng  Zheng Xu  Zifu Zhao  Liqun Dai 《中国科学:地球科学(英文版)》2018,61(4):353-385

The North China Craton (NCC) has been thinned from >200 km to <100 km in its eastern part. The ancient subcontinental lithospheric mantle (SCLM) has been replaced by the juvenile SCLM in the Meoszoic. During this period, the NCC was destructed as indicated by extensive magmatism in the Early Cretaceous. While there is a consensus on the thinning and destruction of cratonic lithosphere in North China, it has been hotly debated about the mechanism of cartonic destruction. This study attempts to provide a resolution to current debates in the view of Mesozoic mafic magmatism in North China. We made a compilation of geochemical data available for Mesozoic mafic igneous rocks in the NCC. The results indicate that these mafic igneous rocks can be categorized into two series, manifesting a dramatic change in the nature of mantle sources at ~121 Ma. Mafic igneous rocks emplaced at this age start to show both oceanic island basalts (OIB)-like trace element distribution patterns and depleted to weakly enriched Sr-Nd isotope compositions. In contrast, mafic igneous rocks emplaced before and after this age exhibit both island arc basalts (IAB)-like trace element distribution patterns and enriched Sr-Nd isotope compositions. This difference indicates a geochemical mutation in the SCLM of North China at ~121 Ma. Although mafic magmatism also took place in the Late Triassic, it was related to exhumation of the deeply subducted South China continental crust because the subduction of Paleo-Pacific slab was not operated at that time. Paleo-Pacific slab started to subduct beneath the eastern margin of Eruasian continent since the Jurrasic. The subducting slab and its overlying SCLM wedge were coupled in the Jurassic, and slab dehydration resulted in hydration and weakening of the cratonic mantle. The mantle sources of ancient IAB-like mafic igneous rocks are a kind of ultramafic metasomatites that were generated by reaction of the cratonic mantle wedge peridotite not only with aqueous solutions derived from dehydration of the subducting Paleo-Pacific oceanic crust in the Jurassic but also with hydrous melts derived from partial melting of the subducting South China continental crust in the Triassic. On the other hand, the mantle sources of juvenile OIB-like mafic igneous rocks are also a kind of ultramafic metasomatites that were generated by reaction of the asthenospheric mantle underneath the North China lithosphere with hydrous felsic melts derived from partial melting of the subducting Paleo-Pacific oceanic crust. The subducting Paleo-Pacific slab became rollback at ~144 Ma. Afterwards the SCLM base was heated by laterally filled asthenospheric mantle, leading to thinning of the hydrated and weakened cratonic mantle. There was extensive bimodal magmatism at 130 to 120 Ma, marking intensive destruction of the cratonic lithosphere. Not only the ultramafic metasomatites in the lower part of the cratonic mantle wedge underwent partial melting to produce mafic igneous rocks showing negative ε_Nd(t) values, depletion in Nb and Ta but enrichment in Pb, but also the lower continent crust overlying the cratonic mantle wedge was heated for extensive felsic magmatism. At the same time, the rollback slab surface was heated by the laterally filled asthenospheric mantle, resulting in partial melting of the previously dehydrated rocks beyond rutile stability on the slab surface. This produce still hydrous felsic melts, which metasomatized the overlying asthenospheric mantle peridotite to generate the ultramafic metasomatites that show positive ε_Nd(t) values, no depletion or even enrichment in Nb and Ta but depletion in Pb. Partial melting of such metasomatites started at ~121 Ma, giving rise to the mafic igneous rocks with juvenile OIB-like geochemical signatures. In this context, the age of ~121 Ma may terminate replacement of the ancient SCLM by the juvenile SCLM in North China. Paleo-Pacific slab was not subducted to the mantle transition zone in the Mesozoic as revealed by modern seismic tomography, and it was subducted at a low angle since the Jurassic, like the subduction of Nazca Plate beneath American continent. This flat subduction would not only chemically metasomatize the cratonic mantle but also physically erode the cratonic mantle. Therefore, the interaction between Paleo-Pacific slab and the cratonic mantle is the first-order geodynamic mechanism for the thinning and destruction of cratonic lithosphere in North China.  相似文献   

Subduction and retreating of the western Pacific plate resulted in lithospheric mantle replacement and coupled basin-mountain respond in the North China Craton   总被引：4，自引：0，他引：4  

Jianping Zheng  Hongkun Dai 《中国科学:地球科学(英文版)》2018,61(4):406-424

The North China Craton (NCC) witnessed Mesozoic vigorous tectono-thermal activities and transition in the nature of deep lithosphere. These processes took place in three periods: (1) Late Paleozoic to Early Jurassic (～170 Ma); (2) Middle Jurassic to Early Cretaceous (160–140 Ma); (3) Early Cretaceous to Cenozoic (140 Ma to present). The last two stages saw the lithospheric mantle replacement and coupled basin-mountain response within the North China Craton due to subduction and retreating of the Paleo-Pacific plate, and is the emphasis in this paper. In the first period, the subduction and closure of the Paleo- Asian Ocean triggered the back-arc extension, syn-collisional compression and then post-collisional extension accompanied by ubiquitous magmatism along the northern margin of the NCC. Similar processes happened in the southern margin of the craton as the subduction of the Paleo-Tethys ocean and collision with the South China Block. These processes had caused the chemical modification and mechanical destruction of the cratonic margins. The margins could serve as conduits for the asthenosphere upwelling and had the priority for magmatism and deformation. The second period saw the closure of the Mongol-Okhotsk ocean and the shear deformation and magmatism induced by the drifting of the Paleo-Pacific slab. The former led to two pulse of N-S trending compression (Episodes A and B of the Yanshan Movement) and thus the pre-existing continental marginal basins were disintegrated into sporadically basin and range province by the Mesozoic magmatic plutons and NE-SW trending faults. With the anticlockwise rotation of the Paleo-Pacific moving direction, the subduction-related magmatism migrated into the inner part of the craton and the Tanlu fault became normal fault from a sinistral one. The NCC thus turned into a back-arc extension setting at the end of this period. In the third period, the refractory subcontinental lithospheric mantle (SCLM) was firstly remarkably eroded and thinned by the subduction-induced asthenospheric upwelling, especially those beneath the weak zones (i.e., cratonic margins and the lithospheric Tanlu fault zone). Then a slightly lithospheric thickening occurred when the upwelled asthenosphere got cool and transformed to be lithospheric mantle accreted (～125 Ma) beneath the thinned SCLM. Besides, the magmatism continuously moved southeastward and the extensional deformations preferentially developed in weak zones, which include the Early Cenozoic normal fault transformed from the Jurassic thrust in the Trans-North Orogenic Belt, the crustal detachment and the subsidence of Bohai basin caused by the continuous normal strike slip of the Tanlu fault, the Cenozoic graben basins originated from the fault depression in the Trans-North Orogenic Belt, the Bohai Basin and the Sulu Orogenic belt. With small block size, inner lithospheric weak zones and the surrounding subductions/collisions, the Mesozoic NCC was characterized by (1) lithospheric thinning and crustal detachment triggered by the subduction-induced asthenospheric upwelling. Local crustal contraction and orogenesis appeared in the Trans-North Orogenic Belt coupled with the crustal detachment; (2) then upwelled asthenosphere got cool to be newly-accreted lithospheric mantle and crustal grabens and basin subsidence happened, as a result of the subduction zone retreating. Therefore, the subduction and retreating of the western Pacific plate is the outside dynamics which resulted in mantle replacement and coupled basin-mountain respond within the North China Craton. We consider that the Mesozoic decratonization of the North China Craton, or the Yanshan Movement, is a comprehensive consequence of complex geological processes proceeding surrounding and within craton, involving both the deep lithospheric mantle and shallow continental crust.  相似文献   

Impact of anthropogenic drivers on subaqueous topographical change in the Datong to Xuliujing reach of the Yangtze River   总被引：3，自引：0，他引：3  

Shuwei Zheng  Heqin Cheng  Shengyu Shi  Wei Xu  Quanping Zhou  Yuehua Jiang  Fengnian Zhou  Minxiong Cao 《中国科学:地球科学(英文版)》2018,61(7):940-950

Changes of subaqueous topography in shallow offshore water pose safety risks for embankments,navigation,and ports.This study conducted measurements of subaqueous topography between Datong and Xuliujing in the Yangtze River using a Sea Bat 7125 multi-beam echo sounder,and the channel change from 1998 to 2013 was calculated using historical bathymetry data.The study revealed several important results:(1)the overall pattern of changes through the studied stretch of the river was erosion–deposition–erosion.Erosion with a volume 700×10~6m~3occurred in the upper reach,deposition of about 204×10~6m~3occurred in the middle reach,and erosion of about 602×10~6m~3occurred in the lower reach.(2)Dunes are the most common microtopographic feature,accounting for 64.3%of the Datong to Xuliujing reach,followed by erosional topography and flat river topography,accounting for 27.6%and 6.6%,respectively.(3)Human activities have a direct impact on the development of the microtopography.For instance,the mining of sand formed holes on the surface of dunes with lengths of 20–35 m and depths of 3–5 m.We concluded that the overall trend of erosion(net erosion volume of 468×10~6m~3)occurred in the study area mainly because of the decreased sediment discharge following the closure of the Three Gorges Dam.However,other human activities were also impact factors of topographic change.Use of embankments and channel management reduced channel width,restricted river meandering,and exacerbated the erosion phenomenon.  相似文献   

GMS－5水汽图象所揭示的青藏高原地区对流层上部水汽分布特征          下载免费PDF全文

许健民  郑新江  徐欢  方翔 《应用气象学报》1996,7(2)

该文利用１９９５年６月中旬至７月初ＧＭＳ－５水汽图象，对青藏高原地区对流层上部水汽分布进行了初步分析．发现高原地区对流层上部水汽的汇集主要通过以下４种方式进行：①水汽从高原东南方的雅鲁藏布江河谷等地进入高原，是主要路径；②从西南方越过喜马拉雅山进入高原；③从帕米尔及其以北地区漂过塔里木盆地后进入高原；④对流活动可以引起水汽在高原上空积聚．从多时相平均水汽图象上反映出高原上西北干、东南湿的水汽分布特征，并初步讨论了水汽图象所揭示的在高原生成的系统对我国东部天气的影响．  相似文献   

鄱阳湖洲滩湿地植物演替对土壤微生物量的影响     

温秀婷  郑博福  陈晨晨  龚磊强  詹慧英  余定坤  朱致睿  沈瑞昌 《湖泊科学》2024,36(3):881-889

湿地植物演替对土壤微生物量具有显著影响,但不同土壤理化环境下的植物演替对湿地土壤微生物量影响的具体差异还不清楚。以鄱阳湖土壤理化性质不同的4个碟形子湖(包括相对肥沃的东湖和白沙湖以及相对贫瘠的蚌湖和大湖池)为研究对象,运用空间代替时间的方法,在泥滩带、湿生植被带(苔草)和挺水植被带(南荻或芦苇)采集0～10 cm表层土壤,分析不同土壤理化性质条件下植物群落演替对土壤微生物量的影响。采用土壤微生物量碳(MBC)和微生物熵(qMB)指示土壤微生物量。蚌湖、大湖池、东湖和白沙湖洲滩湿地表层土壤MBC的平均值分别为1077.27、888.29、942.45和1162.46 mg/kg,土壤qMB的平均值分别为6.07%、6.17%、3.60%和3.79%。在泥滩—苔草—南荻植物演替洲滩,土壤MBC先增加后减少;但是在泥滩—苔草—芦苇植物演替洲滩,土壤MBC持续增加。植物演替没有显著改变土壤qMB。尽管植物的生长会增加所有洲滩湿地的土壤MBC,但增加的幅度在相对贫瘠的蚌湖和大湖池明显强于相对肥沃的东湖和白沙湖。蚌湖和大湖池的土壤qMB也显著高于东湖和白沙湖。在植被演替梯度上,洲滩湿地土壤MBC和...  相似文献   

多波束测深表层声速误差的动态影响及改正方法   总被引：1，自引：0，他引：1  

赵君毅  阳凡林  刘智敏  李真  赵相伟 《测绘科学》2010,35(6):23-25

表层声速不准确会对多波束测深波束的归位产生影响,对于平面换能器阵,使波束角产生偏差,从而影响波束最终位置,但Snell常数保持不变;对于曲面换能器阵,虽然波束未束控不产生波束角偏差,但Snell常数发生改变,会使波束在传播过程中出现折射误差,对深水环境测量不利。对于表层声速误差带来的水深误差,外部波束比内部波束受到的影响更严重。当表层声速无法实时准确获取时,根据内外部波束对水深的影响大小识别表层声速误差的存在,通过逐步调整表层声速值,计算波束指向角差值,再重新进行声线跟踪,计算改正后的波束位置,消除其带来的水深的影响,完成表层声速误差的改正。文中用实测数据进行了验证,对多波束测深数据质量的改善有一定的参考意义。  相似文献   

基于MODIS数据的2002～2006年中国陆地NPP分析   总被引：2，自引：0，他引：2  

王李娟  牛铮  旷达 《国土资源遥感》2010,(4)

对2002～2006年MODIS数据进行处理,统计得出5 a间全国年均陆地植被净初级生产力(NPP)为1.5 PgC;5 a全国NPP组成分析显示,NPP绝大部分集中在0～300 gC/m2区间,所占比例约为70%～85%;全国大部分地区年NPP呈现出减少的趋势,受城市扩张、新增工业用地等人类活动影响显著。  相似文献   

不同顶管组合方式的管幕冻结温度场模型试验   总被引：1，自引：1，他引：0  

段寅  荣传新  程桦  蔡海兵  解德柱  丁杨龙 《冰川冻土》2020,42(2):479-490

拱北隧道作为港珠澳大桥珠海连接线的关键性工程, 在国内外首次成功运用了管幕冻结技术。以此为背景, 为更加全面地掌握饱和软土地层中管幕冻结温度场的分布特点, 开展了不同顶管组合方式下的管幕冻结温度场模型试验研究。试验结果表明： 各测点温度曲线在积极冻结期前4 h急剧下降, 随后逐渐减缓, 降至砂土冰点后趋于平稳, 三种布管方式均满足冻结设计要求; 冻结管中低温盐水提供的冷量首先传递给顶管管壁, 再以“面”的形式均匀地传递给周围土体; 积极冻结21 h后, 采用四根空顶管组合的C区冻结壁竖向范围最大, 空管管壁正上方冻结壁平均厚度约为105 mm, 在满足管幕刚度设计要求的前提下, 可采此布管方式以达到快速形成冻结帷幕的目的。限位管开启后的4 h内, 实顶管中线垂直距离100 mm范围内测点温度曲线虽有明显回升但仍维持在冻土冰点以下, 超出此范围后温度变化影响逐渐减弱, 且顶管间冻结壁稳定存在, 表明限位管在满足管间有效封水的条件下, 能在一定范围内起到定向限制地层冻胀的作用。优化后的双圆形冻结管在满足冻结设计要求的同时, 更加便于安装且经济环保。  相似文献   

金华地区地下水同位素特征及更新能力研究     

雷明  张水军  珠正  库汉鹏  董贤哲  章泽军 《水文》2019,39(6):59-63

金华地区位于金衢盆地东段,对其地下水同位素特征及更新能力研究对于整个盆地地下水资源研究具有重要意义,通过分析研究区内稳定同位素氘(D)和氧(~(18)O)以及放射性同位素氚(~3H)和碳(~(14)C)的空间分布特征,建立了金华地区降水线方程为:δD=8.29δ~(18)O+15.9,讨论了地表水、潜水、红层地下水的环境同位素的组成特征,对潜水及红层地下水的更新能力进行了评价。结果表明,金华地区降水线方程斜率及截距均大于全球大气降水;潜水、红层地下水及地表水三者联系密切;潜水、红层地下水在接受降水的补给后经历了不同程度的蒸发作用;红层地下水D和~(18)O同位素明显向下游富集;潜水~3H值介于6.6～19.0TU,~(14)C年龄显示为现代水,因此其可更新能力较强,红层地下水放射性~(14)C年龄为3020～5360BP,可更新能力较弱,红层地下水3H值介于4.4～12.3TU,表明红层地下水中有现代水的混入,δ~(18)O随着地下水的年龄的增加而偏负。  相似文献