华山新生代隆升-剥蚀历史的裂变径迹热年代学分析   总被引：10，自引：0，他引：10  

吴中海  吴珍汉  万景林  周春景 《地质科技情报》2003,22(3):27-32

综合分析前人的热年代学数据发现华山地区自晚白垩世以来至少经历了三次快速隆升阶段，在120—57Ma间华山经历了缓慢隆升过程，约57Ma以来华山开始相对渭河地堑的快速隆升。其中，57—42Ma间、32—22Ma间和约8Ma以来均为相对快速隆升阶段，视隆升速度约为0．18～0．23mm／a；而42—32Ma问和22～8Ma间则为相对缓慢隆升过程，视隆升速度约为0．01mm／a。约57Ma以来华山的隆升—剥蚀量约为8．5km，平均隆升速度约为0．15mm／a；约32Ma以来的总隆升幅度约为4．5～5．1km，平均视隆升速度约为0．14～0．16mm／a。晚中生代以来华山的隆升过程实际上反映的是东秦岭的隆升过程，与区域地貌结构和周缘断陷盆地的演化过程有密切的成因联系，它表明东秦岭地区的三级等高峰顶面是120—57Ma、42—32Ma和22～8Ma间山脉缓慢隆升—剥蚀的结果，同时反映57—55Ma是渭河盆地开始快速裂陷和秦岭北麓正断层开始强烈活动的时间。  相似文献   

The stability of a remediated bed in Hamilton Harbour,Lake Ontario,Canada     

Carl L. Amos  Ian G. Droppo  Eduardo A. Gomez  Tom P. Murphy 《Sedimentology》2003,50(1):149-168

ABSTRACT In situ measurements of lakebed sediment erodibility were made on three sites in Hamilton Harbour, Lake Ontario, using the benthic flume Sea Carousel. Three methods of estimating the surface erosion threshold (τ_c(0)) from a Carousel time series were evaluated: the first method fits measures of bed strength to eroded depth (the failure envelope) and evaluates threshold as the surface intercept; the second method regresses mean erosion rate (E_m) with bed shear stress and solves for the floc erosion rate (E_f) to derive the threshold for E_m = E_f = 1 × 10^?5 kg m^?2 s^?1; the third method extrapolates a regression of suspended sediment concentration (S) and fluid transmitted bed shear stress (τ₀) to ambient concentrations. The first field site was undisturbed (C) and acted as a control; the second (W) was disturbed through ploughing and water injection as part of lakebed treatment, whereas the third site (OIP) was disturbed and injected with an oxidant used for remediation of contaminated sediment. The main objectives of this study were: (1) to evaluate the three different methods of deriving erosion threshold; (2) to compare the physical behaviour of lacustrine sediments with their marine estuarine counterparts; and (3) to examine the effects of ploughing and chemical treatment of contaminated sediment on bed stability. Five deployments of Sea Carousel were carried out at the control site. Mean erosion thresholds for the three methods were: τ_c(0) = 0·5 (±0·06), 0·27 (±0·01) and 0·34 (±0·03) Pa respectively. Method 1 overpredicted bed strength as it was insensitive to effects in the surface 1–2 mm, and the fit of the failure envelope was also highly subjective. Method 2 exhibited a wide scatter in the data (low correlation coefficients), and definition of the baseline erosion rate (E_f) is largely arbitrary in the literature. Method 3 yielded stable (high correlation coefficients), reproducible and objective results and is thus recommended for evaluation of the erosion threshold. The results of this method correlated well with sediment bulk density and followed the same trend as marine counterparts from widely varying sites. Mass settling rates, expressed as a decay constant, k, of S(t), were strongly related to the maximum turbidity at the onset of settling (S_max) and were also in continuity with marine counterparts. Thus, it appears that differences in salinity had little effect on mass settling rates in the examples presented, and that biological activity dominated any effects normally attributable to changes in salinity. Bedload transport of eroded aggregates (2–4 mm in diameter) took place by rolling below a mean tangential flow velocity (U_y) of 0·32 ms^?1 and by saltation at higher velocities. Mass transport as bedload was a maximum at U_y = 0·4 ms^?1, although bedload never exceeded 1% of the suspended load. The proportion of material moving as bedload was greatest at the onset of erosion but decreased as flow competence increased. Given the low bulk density and strength of the lakebed sediment, the presence of a bedload component is notable. Bedload transport over eroding cohesive substrates should be greater in estuaries, where both sediment density and strength are usually higher. Significant differences between the ploughed and control sites were apparent in both the erosion rate and the friction coefficient (φ), and suggest that bed recovery after disruption is rapid (< 24 h). τ_c(0) increased linearly with time after ploughing and recovered to the control mean value within 3 days. The friction coefficient was reduced to zero by ploughing (diagnostic of fluidization), but increased linearly with time, regaining control values within 6 days. No long‐term reduction in bed strength due to remediation was apparent.  相似文献   

Digital model of corrected accumulated flow for peak discharge data acquisition and drainage system design     

F. J. Fern  ndez  R. Men  ndez-Duarte  R. Vald  s-Riera 《Engineering Geology》2003,69(3-4):345-358

The design of a drainage system for a roofing slate quarry was implemented by the enhancement of discharge peak estimation, and the uncertainty inevitably associated with the engineering model was reduced.

The development of a topographical, geological, and vegetation cover database developed from a Geographical Information System (GIS) allowed for the definition of the drainage network for a hydraulic system, along with the calculation of the runoff coefficient. This is applied to the digital model of accumulated flow (DMF) as a weight correction coefficient, using a matrix-based model at 5×5 m resolution. The new digital model of corrected accumulated flow (DMCF) is the result of combining the thematic maps with the map of slope <3%, which was previously created from the slope model. It is demonstrated that this new model allows to apply the “Rational Method” on cartographic units defined by the GIS.

The DMCF is compared with other traditional applications of the Rational Method based on the calculation of the discharge peak considering: (1) the drainage basin as a single watershed or (2) defining an average runoff coefficient in each sub-watershed. Both approaches have bigger discharge peaks than those obtained by the DMCF since the slope, lithology, and vegetation cover have average values, and the runoff coefficient is poorly defined, increasing the uncertainty in the discharge peak.  相似文献   

印度洋春、夏季海温对西藏高原夏季降水的影响   总被引：3，自引：1，他引：3       下载免费PDF全文

周顺武  丁锋  假拉 《气象科学》2003,23(2):168-175

利用NCEP提供的1950—1997年全球月平均海表面温度场资料，首先通过EOF分解得到不同季节印度洋海温场空间分布特征，并在此基础上使用合成分析、相关分析和SVD分解等多种方法讨论了印度洋前期和同期海温异常与西藏高原夏季降水变化的关系。寻找出影响高原夏季降水的关键海区，目的为高原夏季早涝预测提供参考依据。  相似文献   

泰山顶部近地层风的方差与谱分析   总被引：2，自引：0，他引：2       下载免费PDF全文

王秀梅  王海英冯磊  丁善文赵勇 《应用气象学报》2003,14(6):739-744

风在速度与方向上的不稳定性可引发结构振动并可导致损坏。山顶风较少受局地作用影响, 流场较稳定，作为典型风况对山顶风湍流脉动情形进行的观测和分析，对于研究建筑结构风载振动情形有着重要意义。在不同风况下对泰山气象站近地层风的风速和风向进行了同时、逐秒测记，所得样本经检验符合正态分布。计算表明，风向样本方差显著大于风速样本方差。绘制了各风速、风向样本自、互谱密度曲线图。谱图显示诸样本具有红噪声序列特征，不同样本自、互谱密度曲线具有相近形状，而以风速自谱曲线吻合程度最好，谱密度曲线在周期为4秒及2秒处有峰值。此后的研究应结合记录仪器的改进增加采样频率，对周期为2秒以下谱曲线作进一步分析。  相似文献   

淮河洪峰与致洪暴雨   总被引：1，自引：0，他引：1       下载免费PDF全文

李国杰  张业雯  徐东明  马红  周晓林 《大气科学》1997,21(1):111-117

本文从气象与水文角度， 首先研究淮河关键地段（王家坝）水位变化规律和洪峰出现的特征， 并从数理统计理论上对超定量出现次数和洪峰数值进行了随机变量的独立性检验， 然后求出淮河洪峰遵从的概率分布， 并定性和定量地给出超定量大小与超定量历时关系。最后， 结合多年气象资料分析， 指出洪峰出现与淮河致洪暴雨有密切关系。  相似文献   

西太平洋副高活动与平流层QBO关系的研究   总被引：10，自引：1，他引：10       下载免费PDF全文

李崇银  龙振夏 《大气科学》1997,21(6):670-678

资料分析表明，西太平洋副高活动有准两年振荡特征，副高的相对强度和副高脊线的纬度位置都清楚地表现出这种振荡。而且分析还表明，平流层低层纬向风的垂直切变同西太平洋副高活动有关，东（西）风切变对应着脊线位置偏北的较强（弱）副高形势。平流层低层东（西）垂直切变在赤道对流层上部所引起的异常上升（下沉）运动，导致Hadley环流的异常加强（减弱）可能是平流层QBO影响西太平洋副高准两年振荡的重要机制。用IAP-GCM所作的数值模拟试验得到了同观测资料分析相一致的结果。  相似文献   

青藏高原冬季积雪异常对东,南亚夏季风影响的初步数值模拟研究   总被引：10，自引：2，他引：10  

范广洲  罗四维 《高原气象》1997,16(2):140-142

利用一个耦合了简化的简单生物圈模式的大气环流谱模式（ＳＳｉＢ－ＧＣＭ），初步探讨了青藏高原冬季积雪异常对东、南亚夏季季风环流和降水的影响及其机理。结果表明，高原地区积雪增加将使随后地夏季东、南来季风明显减弱，主要表现为东、南亚季风区降水减少，索马里急流、印度季风的印度西南气流弱弱。另外，还提出欧亚大陆雪盖与整个高原雪盖和高原东部雪盖对东、南亚夏季风影响的敏感问题。与欧亚大陆雪盖相比，高原雪盖是影响  相似文献   

集合预报及其在中期天气预报中的应用   总被引：3，自引：1，他引：3       下载免费PDF全文

李小泉  刘金达  汪迎辉 《气象》1997,23(8):3-9

作者概述了集合预报的基本概念，集合预报中期天气预报中的意义与作用，现有的主要集合预报产品以及集合预报在美国美国国家气象中心和欧洲中期天气预报的业务运行。简要介绍了我国国家气象中心在动力延伸预报和集合预报方面的试验研究情况。  相似文献   

河南省短期区域性暴雨动力诊断及综合预报方案          下载免费PDF全文

李平  孙景兰  张金彬  孔海江  李保生  闫少伟 《气象》1997,23(8):25-28

介介绍了（１）用Ｔ６３数值预报产品对河南省省６－８月区域性暴雨进行物理量诊断分析。（２）用人工智能研制的河南省６－８月分片大－暴雨短短期自动化预报系统与用Ｔ６３数值预报产品资料采用逐步回归分析法和预测误差平方和最不上准则两种选取回归自变量的方法，建立处分片预报方程的综合判别预报。（３）在１９９５，１９９６年７－８月业务预报中试验结果。  相似文献