呼包盆地第四纪地层与环境演化^*     

李建彪  冉勇康  郭文生 《第四纪研究》2007,27(4):632-644

通过对呼包盆地钻孔岩芯进行系统的岩石学、年代学和孢粉带的分析,综合盆地已有的研究成果,并与邻区对比,划分了盆地第四纪地层单位,同时探讨了河套古湖泊在第四纪的演化特征。结果为:1)剖面存在两个假整合接触面(Q₁/Q₂和Q₂/Q₃),可划分为4个沉积旋回,7个孢粉带。2)剖面第四纪地层从下至上依次可划分下更新统(1070±150~844±126kaB.P.)、中更新统沟子板组(520±78~271±40kaB.P.)、上更新统萨拉乌苏组和城川组(108.7±7.8~14.80±1.03kaB.P.),以及全新统。3)河套盆地在第四纪存在4个古湖泊发育时期,即早更新世(80.0~107.0万年或更早),湖盆处于强氧化环境;中更新世早期(43.0~45.1万年),湖盆氧化强度降低;中更新世晚期(19.2~38.5万年),湖盆处于强烈的还原环境;晚更新世(2.4~11.3万年),湖盆处于还原环境。其间隔期为湖泊消亡或大规模萎缩时期,意味着盆地停止下降甚至处于上升隆起的剥蚀状态。  相似文献   

利用基阶面波反演地壳上地幔的Qβ结构   总被引：4，自引：1，他引：3  

胡家富  段永康 《地震研究》2000,23(3):318-323

根据中国数字化台网（ＣＤＳＮ）记录到的长周期Ｒａｙｌｅｉｇｈ面波资料,使用频变滤波技术从记录中提取基阶振型面波信号;根据与震源处于同一大圆弧上的两台记录的基附振型信号计算出台间格林函数,测定了经过中朝准地台地区周期１０－９８ｓ的基阶Ｒａｙｌｅｉｇｈ波衰减系数,在此基础上反演得到中朝准地台的地壳上地幔Ｑβ结构。所得结果表明：华北地区地壳的Ｑβ为２５０,而黄海地区地壳Ｑβ〉４５０,中朝准地台的地幔Ｑβ  相似文献   

爆破振动对岩锚梁的影响测试     

胡家富  段永康  胡毅力  华培忠 《地震地磁观测与研究》2000,21(2):19-24

讨论了爆破地震产生的地震波传播规律 ,以及地振动信号和仪器记录的电信号之间的关系。在此基础上 ,论述了振动影响测试的原理 ,记录仪器系统的标定以及从观测信号中消除仪器影响的方法。对云南某水电站主厂房施工中的爆破振动进行了测试 ,讨论了爆破地震测试中应注意的问题  相似文献   

Characteristics of Large Earthquake Recurrence and Determination of Average Recurrence Interval Value     

Ran Yongkang  Deng Qidong 《中国地震研究》2000,14(1):86-96

Paleoearthquakes in the Yanqing-Huailai basin and on the Haiyuan fault are studied in detail.The result indicates that the recurrence behavior of large earthquakes is of a wide variety.Characteristic earthquakes show the behavior characteristics of the activity of most faults,butthey are of different grades,the recurrence interval of large earthquakes is of staged nature,and the interaction between faults has effects on the recurrence sequence of large earthquakes.Thus,when the recurrence behavior of large earthquakes is staged in time or when thegradation of characteristic earthquakes has led to a sharp difference in recurrence intervalbetween paleoearthquakes of different intensities,for estimating the large earthquake risk bythe deterministic method and time-dependent probabilistic method,it is necessary to calculatethe recurrence interval value separately for each specific stage or grade in order that theaverage recurrence interval values of different stages can be determined.  相似文献   

Late Quaternary Large Earthquakes on the Western Branch of the Xiaojiang Fault and Their Tectonic Implications   总被引：1，自引：0，他引：1  

LI Xi  RAN Yongkang  CHEN Lichun  WU Fuyao  MA Xinquan  CAO Jun 《《地质学报》英文版》2015,89(5):1516-1530

The Xiaojiang fault is a major active left-lateral fault along the southeastern margin of the Tibetan Plateau.The largest historical earthquake in Yunnan Province, with a magnitude 8 and a mean coseismic left-lateral displacement of ~ 6.9 m, occurred on the western branch of the Xiaojiang fault.Studying this fault is important in understanding current deformation and kinematic characteristics of the Tibetan Plateau.Activities and stretches have been well undertaken on the Xiaojiang fault, while paleoseismic research work is always the weak link on this fault.To investigate the paleoseismic history and large earthquake activity of the Xiaojiang fault, we opened a large trench at the northern edge of Caohaizi sag pond on the western branch of the Xiaojiang fault.Six paleoseismic events have been identified, and named E1 through E6 from the oldest to the youngest.Charcoal and woods are abundant, 20 samples were dated to constrain the ages of the paleoseismic events at 40 000–36 300 BC, 35 400–24 800 BC, 9 500 BC–AD 500, AD 390–720, AD 1120–1620 and AD 1750–present.We associate the youngest event E6 with the 1833 M8 earthquake.Events E4, E5 and E6 show a continuous record of the western strand of the Xiaojiang fault in the late Holocene, with a average recurrence interval of 370–480 yr.Large earthquake recurrence in the late Holocene is far less than the recurrence of 2000–4000 yr posed in previous studies.Thus, the seismic hazard on the Xiaojiang fault should be reevaluated.Furthermore, the irregular recurrence of large earthquakes on the Xiaojiang fault and other faults in the Xianshuihe-Xiaojiang system, indicates the uneven southeastward extrusion of the Sichuan-Yunnan block along the southeastern margin of the Tibetan Plateau.  相似文献   

Assessment of Dynamic Downscaling of the Extreme Rainfall over East Asia Using a Regional Climate Model   总被引：1，自引：0，他引：1  

GAO Yanhong  Yongkang XUE  PENG Wen  Hyun-Suk KANG  Duane WALISER 《大气科学进展》2011,28(5):1077-1098

This study investigates the capability of the dynamic downscaling method (DDM) in an East Asian climate study for June 1998 using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research non-hydrostatic Mesoscale Model (MM5).Sensitivity experiments show that MM5 results at upper atmospheric levels cannot match reanalyses data,but the results show consistent improvement in simulating moisture transport at low levels.The downscaling ability for precipitation is regionally dependent.During the monsoon season over the Yangtze River basin and the pre-monsoon season over North China,the DDM cannot match observed precipitation.Over Northwest China and the Tibetan Plateau (TP),where there is high topography,the DDM shows better performance than reanalyses.Simulated monsoon evolution processes over East Asia,however,are much closer to observational data than reanalyses.The convection scheme has a substantial impact on extreme rainfall over the Yangtze River basin and the pre-monsoon over North China,but only a marginal contribution for Northwest China and the TP.Land surface parameterizations affect the locations and pattern of rainfall bands.The 10-day re-initialization in this study shows some improvement in simulated precipitation over some sub-regions but with no obvious improvement in circulation.The setting of the location of lateral boundaries (LLB) westward improves performance of the DDM.Including the entire TP in the western model domain improves the DDM performance in simulating precipitation in most sub-regions.In addition,a seasonal simulation demonstrates that the DDM can also obtain consistent results,as in the June case,even when another two months consist of no strong climate/weather events.  相似文献   

Dynamic downscaling of 22-year CFS winter seasonal hindcasts with the UCLA-ETA regional climate model over the United States     

Fernando De Sales  Yongkang Xue 《Climate Dynamics》2013,41(2):255-275

This study evaluates the UCLA-ETA regional model’s dynamic downscaling ability to improve the National Center for Environmental Prediction Climate Forecast System (NCEP CFS), winter season predictions over the contiguous United States (US). Spatial distributions and temporal variations of seasonal and monthly precipitation are the main focus. A multi-member ensemble means of 22 winters from 1982 through 2004 are included in the study. CFS over-predicts the precipitation in eastern and western US by as much as 45 and 90 % on average compared to observations, respectively. Dynamic downscaling improves the precipitation hindcasts across the domain, except in the southern States, by substantially reducing the excessive precipitation produced by the CFS. Average precipitation root-mean-square error for CFS and UCLA-ETA are 1.5 and 0.9 mm day^?1, respectively. In addition, downscaling improves the simulation of spatial distribution of snow water equivalent and land surface heat fluxes. Despite these large improvements, the UCLA-ETA’s ability to improve the inter-annual and intra-seasonal precipitation variability is not clear, probably because of the imposed CFS’ lateral boundary conditions. Preliminary analysis of the cause for the large precipitation differences between the models reveals that the CFS appears to underestimate the moisture flux convergence despite producing excessive precipitation amounts. Additionally, the comparison of modeled monthly surface sensible and latent heat fluxes with Global Land Data Assimilation System land data set shows that the CFS incorrectly partitioned most of surface energy into evaporation, unlike the UCLA-ETA. These findings suggest that the downscaling improvements are mostly due to a better representation of land-surface processes by the UCLA-ETA. Sensitivity tests also reveal that higher-resolution topography only played a secondary role in the dynamic downscaling improvement.  相似文献   

History of Paleoseismic Activity Along the Hohhot Segment of Daqingshan Piedmont Fault in the Late Quaternary   总被引：1，自引：0，他引：1  

Ran Yongkang  Zhang Peizhen  Hu Bo  Guo Wensheng 《中国地震研究》2001,15(2):190-204

INTRODUCTIONTheDaqingshanpledmont扭nit Is an irllt,oltant active normal tsult In the active fault－depressionzone——Hetao ault－depression zone In the northern part of Ordos Block,North China．It lies in ENEdirection long the southern pledmont of Daqingshan Mountain,dips to south,and extends for 200 kmor。。The fault was formed In the Eocene and strongly activated In the Cenozolc．Its verticaldlspl。ement exceeds 2400 m since the Quaternary(Rese。h Group on Ordos Block,State…  相似文献   

Paleoseismic study of the east Kalpintage fault in southwest Tianshan based on deformation of alluvial fans and 10Be dating     

An Li  Yongkang Ran  Liangxin Xu  Huaguo Liu 《Natural Hazards》2013,68(2):1075-1087

Multiple earthquakes produced by thrusting deformation have been recorded over the last century in the Tianshan area. Paleoseismic studies are very important in the exploration of the active quaternary tectonics and the risk assessment of great earthquakes in the Tianshan orogenic region. However, in this area, paleoseismic research is still lacking because of the lack of samples dated by ¹⁴C or optically stimulated luminescence (OSL) methods. We determined the ages of the alluvial fans by ¹⁰Be terrestrial cosmogenic nuclide (TCN) dating, measured the surface deformation of the fault scarp in a GPS survey, and evaluated the vertical displacements of the events in trenches in the east Kalpintage fault in the southwest Tianshan region. We estimated the displacement and recurrence intervals of the paleoseismic events and constrained the errors of the ¹⁰Be ages and slip rates using a Monte Carlo simulation method. Our study suggests that each paleoseismic event shows a similar displacement of ~1.5 m with a recurrence interval of ~5 kyr in the east Kalpintage fault. The calculated slip rate is 0.31(+0.21/?0.18) mm/yr. In such arid regions with large areas of coarse gravel that lack ¹⁴C or OSL samples, the integration of TCN dating, geomorphic deformation survey, and trenching methods is a reliable alternative for studying the active regional tectonics.  相似文献   

南天山低角度逆断层古地震破裂变形模式     

李安  杨晓平  冉勇康  黄伟亮  张玲  徐良鑫  刘华国  李胜强 《震灾防御技术》2016,11(2):173-185

近年来逆冲型破坏性地震频发,这对于逆冲型破裂的古地震研究方法提出了新的要求。由于逆断层角度的变化,在地震中可能表现出截然不同的破裂样式。通过对南天山大量古地震探槽开挖和古地震事件分析研究中发现,低角度逆断层的古地震具有一些常见的破裂类型。本文中挑选了位于南天山三个重要山前逆断裂褶皱带:西段柯坪推覆系、中段库车坳陷的秋里塔格褶皱带和东段焉耆盆地北缘和静逆断裂褶皱带的7个典型探槽剖面,对这类低角度逆断层的古地震进行变形模式、事件识别和位移量计算的总结归纳。低角度逆断层古地震破裂具有以下几种样式并具有各自识别古地震事件和计算位移量的方法:1一条断面对应一次事件的破裂形式,利用断面上断点位置识别古地震事件并判断事件的先后顺序。每个断面各自的位移量正好代表一次事件的位移量。2单条断面多次破裂的样式可以通过上下不同地层的位错量差异判断古地震事件,各个相邻地层之间的位错量差值代表古地震事件的位移量。3多条断面同时破裂的情况表现为多条断面被相同一套地层覆盖,事件位移量为多条断面的位错量之和。4挠曲变形和"推土机"作用是低角度逆断层古地震破裂常见的变形方式,这部分变形量不能忽略,可以通过线平衡和面平衡方法获得断层水平缩短量。  相似文献