Sedimentary records of environmental evolution in the Sanmen Lake Basin and the Yellow River running through the Sanmenxia Gorge eastward into the sea

A series of independent faulted basins developed in the present middle reaches of the Yellow River during late Cenozoic, among which the Sanmen Lake Basin is located in the east edge of the Loess Plateau, a transitional zone between the second and third macromorphological step of China. The thick strata of the Sanmen Group deposited in the large basin. The Sanmen Group is a perfect place for the study on paleoenvironmental change, tectono-climatic cycles as well as the formation and evolution of the Yellow River. In this paper, the paleoenvironmental changes, regional tectonic movement and the evolutionary process of the Sanmen Lake Basin during the past 5 Ma were reconstructed based on the analysis of paleomagnetic stratigraphy, pollen, TOC and carbonate content from the Huangdigou outcrop near the Sanmenxia Reservoir, Pinglu County, Shanxi Province. The sedimentary records from the outcrop indicate that the basin was first formated by fault activity at about 5.4 MaBP, and after the strong tectonic movement at 3.6 MaBP the lake enlarged and the rainfall of summer monsoon increased. There was no great climatic transition near 2.6 MaBP, corresponding to the bottom age of loess in the Loess Plateau. After Olduvai event (about 1.77 MaBP) the Picea and Abies were presented in the sediments, which indicates a colder climate. The tectonic movement at 1.2 MaBP caused the light angular discordance between the upper and lower Sanmen Group. The sedimentary records show a cold and wet climate during the prosperous periods of loess accumulation such as L15, L9, L6. The tectonic intensification periods of the Sanmen Basin correspond with the tectonic movements in the Qinghai-Xizang Plateau chronologically. The earliest age of the outflow from the Paleo-Sanmen Lake or the partly cutting off of the Sanmenxia Gorge was about 0.41- 0.35 MaBP. The age of cutting thoroughly the Sanmenxia Gorge by the Yellow River and the disappearance of the Paleo-Sanmen Lake was about 0.15 MaBP, which symbolized the formation of the present Yellow River and had an important influence on the environmental and morphological evolution in the middle and lower reaches of the Yellow River.     

中国—欧洲共同体地震科学合作项目“北京西北延庆—怀来盆地地震学研究”进展

为探索强烈地震的前兆，在欧洲共同体的支持下，中国和英国的地震学家共同在北京西北的延庆—怀来盆地建立了一个数字地震台网．延庆—怀来数字地震台网由５个野外台和一个中心台构成。研究工作的重点是探索强烈地震前地震横波分裂现象中的参数变化．１９９５年４月３０日台网建成并投入运作．１９９５年７月下旬．怀来地区发生ＭＬ＝４．０地震及其余震，延庆—怀来数字地震台网很好地记录了这一地震序列。初步的分析表明．这一地震序列表明了怀来县城以南６—８ｋｍ处，怀来盆地南缘下部的断层活动，它与怀来地区地表有明显出露的主要断裂没有明显的直接联系。     

1987年甘肃张掖地震和礼县地震的震源机制解

1987年在甘肃省境内发生了三次中强地震,这三次地震是1月8日迭部5.9级地震、9月12日张掖4.5级地震和10月25日礼县5.0级地震。我们根据甘肃省、青海省、陕西省地震台网以及全国部分基准台站记录到的P波初动资料得到这些地震的震源机制解。迭部地震的震源     

提高斜拉索索力估算精度的方法

振动法是测量实际索力的首选方法,但其测试精度会受到外界环境因素如温度、风和桥面对拉索作用等的影响。本文围绕如何将外界环境因素的影响降至最小,从测量时机的选取、数据处理方法的选择等方面,综合运用随机振动、风工程、非线性和误差分析理论,提出了提高拉索索力估算精度的实用改进方法,得出了一些有意义的结论。并通过哈尔滨松花江斜拉桥实例进行验证对比,结果表明,该方法具有较高的精度。     

库车5.6级、拜城5.3级地震形变前兆异常

分析研究了 1999年 3月 15日库车 5.6级、6月 17日拜城 5.3级地震前新疆克孜尔水库形变站观测到的前兆异常。库车 5.6级地震前 ,第一形变站基线具有突变性 ,异常幅度达 2 80μm,水准异常为渐进式 ,幅度稍小 ,但异常持续时间较长。在此次地震前其它测站的 14条垂直、水平形变测线都有程度不同的异常显示 ,最大异常量级为 1.2× 10 -5,中期异常达 1年以上 ,短期异常持续约 10 0天 ,临震异常在震前 7～ 15天出现。拜城 5.3级地震前各测线也观测到了较明显的前兆异常 ,最大异常量级为 8.3× 10 -6,短期异常持续近两个月。     

GPS坐标时间序列中非构造噪声的剔除方法研究进展

GPS台站坐标解算中包含多种地球物理参量造成的不确定性、系统误差和随机噪声.回顾了GPS台站坐标噪声分析的研究进展,包括功率谱分析、最大似然估计、区域叠加滤波、主成分变换以及质量负荷下的地壳弹性形变模拟等,并讨论了各种方法在分析噪声的类型和强度、共模误差(common-mode errors)的物理起源等方面的作用及局限性,展望了下一阶段的研究思路.     

Study on the processing method of nighttime CO2 eddy covariance flux data in ChinaFLUX

At present, using Eddy Covariance (EC) method to estimate the “true value” of carbon sequestration in terrestrial ecosystem arrests more attention. However, one issue is how to solve the uncertainty of observations (especially the nighttime CO₂ flux data) appearing in post-processing CO₂ flux data. The ratio of effective and reliable nighttime EC CO₂ flux data to all nighttime data is relatively low (commonly, less than 50%) for all the long-term and continuous observation stations in the world. Thus, the processing method of nighttime CO₂ flux data and its effect analysis on estimating CO₂ flux annual sums are very important. In this paper, the authors analyze and discuss the reasons for underestimating nighttime CO₂ flux using EC method, and introduce the general theory and method for processing nighttime CO₂ flux data. By analyzing the relationship between nighttime CO₂ flux and air fraction velocity u*, we present an alternate method, Average Values Test (AVT), to determine the thresholds of fraction velocity (u*_c) for screening the effective nighttime CO₂ flux data. Meanwhile, taking the data observed in Yucheng and Changbai Mountains stations for an example, we analyze and discuss the effects of different methods or parameters on nighttime CO₂ flux estimations. Finally, based on the data of part ChinaFLUX stations and related literatures, empirical models of nighttime respiration at different sites in ChinaFLUX are summarized.

     

When to conduct an isotopic survey for lake water balance evaluation in highly seasonal climates

One‐time or short‐term lake water isotopic surveys are often employed to evaluate regional lake water balance. However, it can be difficult to determine the optimal time‐window for sampling to obtain a representative long‐term perspective of lake water balance in settings influenced by seasonal variations in precipitation, evaporative loss, glacial/snow meltwater, and larger seasonal shifts in isotopic composition of precipitation. This is especially true for areas of the Tibetan Plateau that are influenced by the summer Indian monsoon. Although high‐frequency sampling is always preferred as the most rigorous approach to characterize the water budget of lakes or watersheds, this may be impractical in remote regions and over large spatial scales. To assess the potential sensitivity of isotope balance characterization to seasonal variability, we used a weekly lake water isotope data set acquired over a period of 3 years on the Tibetan Plateau to evaluate the potential inaccuracies that might have arisen from using isotopic data collected during narrower time‐windows. For this assessment, we use weekly isotopic data collected during the study and assume that these sampling events were stand‐alone one‐time surveys. We then demonstrate the sensitivity of the isotope balance method in this setting, particularly for the rainy season that significantly underestimated the evaporation/inflow. In contrast, isotopic composition of the lake water was found to be more representative of long‐term conditions when sampled in October on the Tibetan Plateau. To broaden our evaluation of seasonality effects over a range of climatic zones, published high‐frequency isotopic data were also compiled, and a similar assessment was carried out for selected regions of the world. The synthesized data and model outputs, which confirm pronounced variations in lake water isotopic composition and evaporation/inflow across a range of seasonal climates, were used to determine optimal sampling windows for these specific regions.     

秦王川盆地西缘断裂活动性综合研究及盆地成因分析

秦王川盆地西缘断裂发育于陇中盆地地震构造区内部,本文对其进行了综合研究。浅层人工地震探测表明,该断裂在最小埋深130m处有显示,联合钻探结果表明该深度处为新近纪湖相沉积地层,泥岩层顶面向盆地方向呈斜坡状,槽探未揭露出断层。综合研究表明该断裂发育在新近纪地层内部,并未上穿第四纪沉积物,属于前第四纪隐伏断层。秦王川盆地在古近纪—新近纪山间泛湖盆的基础上,由于区域构造应力不均匀挤压抬升,形成山间负向地形,成为第四纪多变环境下河流堆积的拗陷盆地。秦王川盆地西缘断裂不具有控制中强地震空间分布的作用和形成地表破裂的能力,对盆地的构造稳定性不构成影响,亦不影响兰州新区的规划发展。     

煤矿巷道围岩稳定性动态工程分类技术研究与应用

基于围岩质量计算，柱状图数字化与重组，围岩结构诊断，采动应力作用后围岩结构演化等研究成果，采用“工程要求，基本结构，演化结构、为一级指标，提出了巷道围岩稳定性动态工程分类技术，分类结构的表在技术及分类结果的应用方法。