2007年宁洱6.4级地震监测与研究

利用宁洱地震现场流动台网监测资料进行精确定位,结合云南区域测震台网地震波资料,给出了宁洱地震主、余震的震源参数,分析讨论了宁洱地震的震源过程。研究显示,宁洱6.4级地震发震构造为NW向断裂,主破裂走向约N50°W,倾向WS,倾角约80°,断层性质为走滑型。断层破裂长度约为30km,宽度约5km,破裂面深2～12km,断层走向与宏观等震线长轴方向基本一致。震源参数研究表明,宁洱震区地震矩范围为1012～1018N·m,震源破裂半径为300～3500m,应力降为0.0044～14MPa。高应力降地震事件主要发生在4～10km深度范围内,表明该深度区是宁洱地震的主要活动区域。地震应力降随时间逐渐衰减,表明宁洱地震序列类型为主震—余震型。     

基于GIS的攀枝花城市地质环境质量分区评价

攀枝花是一座典型的矿业城市,随着经济发展,矿山地质环境问题严重.在(GIS)地理信息系统技术的支持下,结合多种地质环境因素对该地区进行了地质环境质量现状分析评价,采用层次分析法建立了评价模型,结果表明区内大部分地区地质环境较好.地质环境差的地方主要分布在各大采矿区,地质灾害较严重.文中除了论述评价要素的识别,重点讨论了评价模型的确立和基于GIS的分析方法,最后对评价结果作了分析.     

Influences of coupled wind–water processes on suspended sediment grain size: an example from tributaries of the Yellow River / Influences de processus couplés éoliens-hydriques sur la granulométrie des matières en suspension: exemple d'affluents du Fleuve Jaune

Abstract

Some unique coupled wind–water erosion processes exist in the desert-loess transitional zone in the middle Yellow River basin. Based on data from 40 stations on 29 rivers, a study was made on the influence of such processes on suspended sediment grain-size characteristics of the tributaries of the Yellow River. Results show that the percentage of >0.05-mm grain size decreases with the increased annual mean precipitation, but increases with the increase in the annual mean number of sand-dust storm days. The percentage of <0.01-mm grain size increases with the increase in the annual mean precipitation, but decreases with the increase in the annual number of sand-dust storm days. Based on annual mean data from 40 stations, multiple regression equations were established between the percentages of >0.05-mm grain size (r _>0.05) and <0.01-mm grain size (r _<0.01), annual mean precipitation (P _m) and annual mean number of sand-dust storm days (D _ss). On this basis, the relative contributions of the variations in D _ss and P _m to the variation in r _>0.05 and r _<0.01 were estimated. The results indicate that the variation in sand-dust storm frequency exerts greater influences on the variation in grain-size characteristics of suspended load than does the variation in annual mean precipitation. With the increase in the coupled wind–water processes index, expressed by P _m/D _ss, the percentage of >0.05-mm grain size in suspended sediment decreases and the percentage of <0.01-mm grain size increases. With the variation in P _m/D _ss, different combinations of r _>0.05 with r _<0.01 appear, which have some influence on the formation of hyperconcentrated flows. There exist some optimal ratios of coarse to fine fractions in suspended sediment that make sediment concentrations of hyperconcentrated flows the highest. The optimal r _>0.05/r _<0.01 value is related to some range of the index P _m/D _ss. When the P _m/D _ss index falls in this range, the optimum combination of relative coarse with fine sediments in the suspended load appears, and thus results in the peak values of sediment concentration.     

On the modelling of sand bedforms using the semivariogram

This study shows the usefulness of the semivariogram for modelling sand ripples created by water flows of varied flow intensity. A combination of two mathematical functions is fitted to each sample semivariogram, that is an exponential (or stochastic) component and a periodic component. The parameters of each of these components have direct physical meaning. A non-dimensional ratio combining the two parameters of the exponential model is interpreted as a regularity index (which increases with the degree of regularity of bedform arrangement). This regularity index is inversely related to the Froude number of the flow. The non-dimensional wavelength, estimated from the dominant periodic function, is also inversely and closely related to the Froude number. The wave height, accurately estimated from properties of the two fitted components, is a direct function of flow velocity and is also proportional to the standard deviation of bed elevations. The bedform shape introduces a considerable discrepancy between the generally assumed normal frequency distribution and the empirical distributions of bed height. The series of bed elevations are generally characterized by a mixture of normal distributions having the same variance but different means. The calculation of a covariance assuming a constant and single mean (as in spectral analysis) can therefore be misleading and the problem may be avoided by using the semivariogram.     

A comprehensive approach to drought and desertification in Northern Nigeria

Drought has been a recurring feature of the arid and semi-arid areas of Nigeria. This paper reviews the extent, severity, and consequences of drought and desertification in Nigeria with particular emphasis on the northern part of the country. The haphazard manner in which these environmental hazards have been tackled is examined and a systematic approach for the formulation of a national policy is proposed. It is recommended that a detailed formulation and implementation of the proposed policy plan is imperative to mitigate the often devastating impacts of drought and desertification in the very prone areas of Nigeria. Until such is done, some areas of Nigeria will always be vulnerable to the whims of an inevitable climatic hazard of drought and associated land degradation in the form of desertification.     

Growth Dynamics of the Middle Devonian Jukoupu Bioherm,Xinshao, Hunan

The growth process, palaeoecological features and the function of organisms in reef-building of the Jukoupu bioherm in Hunan are discussed in detail. The bioherm is divided into 10 microfacies. Organisms are very abundant in the reef. Thirty-two genera Belonging to 7 phyla have been recognized. They make up 5 communities composed mainly of stromatopoids, Corals and algae, each of which has its own salient ecological features. An analysis of all communities shows that the organic functions are very complex. The same organisms may possess diverse functions simultaneously as the reef growth enters the late stage. The growth process of the reef may involve five stages' (l)biostrome stage, (2) stabilization stage, (3) frame-type reef-building stage, (4) binding and covering-type reef-building stage, and (5) baffle- type reef -building stage.     

北京市北山泥石流分布规律及形成过程

北京北山泥石流的分布受构造控制，呈北东方向展布。其分布在时间上和空间上均有一定的规律可寻。一条泥石流沟谷的形成从开始到结束，概括分为形成、位移和堆积。区内泥石流的形成主要有三种形式：以水力侵蚀为主，以坡面侵蚀为主和以沟源崩、滑塌形式触发沟床物质活动而形成的泥石流。     

内蒙古乌拉山金矿带中大桦背花岗岩与金矿床成因联系探讨

乌拉山金矿带大体背花岗岩成因属陆壳（改造）重熔型。花岗岩在成矿作用中的贡献，不仅能直接提供矿源，而且更重要的是间接提供矿源，花岗岩与金矿床在成因上、空间上、时间上有着密切联系，是形成（花岗岩）与被形成（矿床）的关系。指明乌拉山金矿具有三位一体成矿地质条件，即大古代变质岩系是金等成矿元素的提供者──—成矿基础，中生代构造──—岩浆活动是金等成矿元素的地质营力──—关键成矿作用，随之而进行的是金沿着构造裂隙（与之配套的断裂构造）集中、沉淀的成矿作用。     

江苏北部开敞淤泥质海岸的侵蚀过程及防护

开敞淤泥质海岸是淤泥质海岸的主要类型，其自然演变过程，主要受沿海河流泥沙供应条件的制约，一旦泥沙供应消失，海岸往往进入不可逆转的侵蚀过程。江苏北部淤泥质海岸的侵蚀过程，起自１８５５年黄河入海口北归利津入海以后，主要是在近岸破波对岸滩物质的冲刷和潮流的输移扩散作用下进行的。通过对淤泥质海岸动力和沉积物性质的认识和概化，对海岸侵蚀过程作出定量模拟，并对该地区海岸防护工程作出评价和讨论。