The effect of random velocity functions on the travel times and amplitudes of seismic waves   总被引：2，自引：0，他引：2  

S. B. Ojo  R. F. Mereu 《Geophysical Journal International》1986,84(3):607-618

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Modelling of nitrate leaching from arable land into unsaturated soil and chalk 2. Model confirmation and application to agricultural and sewage sludge management     

R. J. Andrews  J. W. Lloyd  D. N. Lerner 《Journal of Hydrology》1997,200(1-4):198-221

A layered deterministic N-leaching model, IMPACT, has been calibrated using data from two study sites on the unconfined Chalk aquilfer of East Anglia, UK. The model predicts nitrogen species movement resulting from the application of sewage sludges and fertilizers to arable land for different vegetation-soil-hydrogeological conditions. One site received sludge in the form of digested sewage cake (DSC) for the first time during the study period, whilst the other site had over 15 years history of liquid undigested sludge (LUS) applications at 3 year intervals. Site data included: 3-monthly concentration profiles at 0.3 m intervals to depths of up to 6 m for N-species and chloride; unsaturated potential measurements; water level and saturated groundwater solute concentrations, fertilizer and sludge input; daily recharge, and soil/chalk type and moisture content. The observed average movement rate for nitrate peaks in the Lower Chalk, measured at one site, was 0.2 m year⁻². Leachate peaks were not observed annually but approximately every third year, being associated with large sludge applications and ploughing of grass crops. Significant correlation between observed and modelled nitrate profiles in soil and chalk were obtained which demonstrated applications. The relationship between crop demand, application times of fertilizers and sludge, nitrate availability and recharge was shown strongly to control the shape of nitrate profiles in the soil and chalk and the quantity of nitrate leached tochalk. The change in hydrogeological conditions at the soil-chalk contact and associated potential for denitrification was also shown to exert a significant control on the shape of the nitrate profile. Following calibration, different arable crop and sludge application regimes were examined for a 6 year period and ranked according to their nitrate leaching risk. Of the modelled cereal farming scenarios, the crop/sludge regime giving the least nitrate leaching was a late autumn surface spread application of DSC followed by winter cereals, while highest nitrate leaching was generated by an autumn injection of LUS followed by spring cereals. Field and modelled results may be used in the development of sludge disposal policies to arable land particularly with regard to sludge types, application times, and following crop types and fertilizer requirements. Overall, observed and model data demonstrate the importance of examining nitrate leaching as a continuum from the soil through the chalk to the water table.  相似文献   

大安台形变与山西运城地震     

沈平新  翟志强 《山西地震》1997,(3):51-53

分析了１９８６年１１月山西运城地区小震群活动前大安地震台ＪＢ型水平摆倾斜仪出现的异常情况。认为异常的表现形式为大速率的倾斜变化、倾向变化及固体潮汐的严重畸变等，叙述了根据这些异常变化预报该次地震后运城地区的地震活动的情况。  相似文献   

爆炸防雹中的云微物理机制的探讨   总被引：6，自引：0，他引：6  

段英  许焕斌 《气象学报》2001,59(3):334-340

在综合实验和观测结果的基础上 ,提出了能形成大雹的雹胚 ,在它运行增长中常会有一个下伸到 0℃层以下融化 ,又再进入主上升气流区上升到 0℃层以上再次冻结的过程。发生这一过程的位置是雹云的悬挂回波所在的冰雹胚胎帘区的底部 ,如果在这个位置利用爆炸引起由雹胚融化而形成的液滴破碎 ,会改变大雹的运行轨迹 ,从而抑制大雹的形成。同时还利用数值模式模拟研究了该机制 ,结果表明该机制是合理的。  相似文献   

21世纪初新疆棉花生产趋势调研报告     

季元中  杨舵等 《沙漠与绿洲气象(新疆气象)》2001,24(1):20-23,27

分析了“九五”期间新疆棉花生产的状况，指出了存在的主要问题；调查了国内外棉花市场和棉花生产对气象服务的需求；并提出了相应对策。  相似文献   

Crustal structure and local seismicity in Colombia     

Anibal Ojeda  Jens Havskov 《Journal of Seismology》2001,5(4):575-593

Using P-wave travel time data from local seismicity, the crustal structure ofthe central and southern part of Colombia was determined. A very stableand narrow range of possible velocity models for the region was obtainedusing travel time inversion. This range of models was tested with earthquakelocations to select the best velocity model. The 1D velocity modelproposed has five layers over a halfspace, with interfaces at depths of 4,25, 32, 40 and 100 km and P-wave velocities of 4.8, 6.6, 7.0, 8.0, 8.1and 8.2 km/sec, respectively. According to this model the Moho lies at32 km depth on average. For P-waves, the station corrections range from–0.62 to 0.44 sec and for S-wave they range from –1.17 to 0.62 sec.These low variations in station residuals indicate small lateral velocitychanges and therefore the velocity model found should be well suited forearthquake locations and future starting model for 3D tomography studies.Using this new velocity model, the local earthquakes were relocated. Theshallow seismicity, < 30 km, clearly shows the borders betweentectonic plates and also the main fault systems in the region. The deepseismicity, > 80 km, shows two subduction zones in the country: theCauca subduction zone with a strike of N120^°E, dip of 35^°and thickness of 35 km, and the Bucaramanga subduction zone which has,for the northern part, a strike of N103^°E, dip of 27^° andthickness undetermined and, for the southern part, a strike ofN115^°E, dip of 40^° and thickness of 20 km. Based ondifferences of thickness of brittle crust in the subducted slab and spatialdistribution of the seismicity, the Cauca and Bucaramanga subduction zonesseem to represent independent processes. The Cauca subduction seems tobe connected to the process of the Nazca plate being subducted under theNorth Andes Block. In the Bucaramanga subduction zone, the transitionbetween southern and northern parts and changes in geometry of the slabseem to be gradual and there is no evidence of a tear in the slab, howeverthe local seismicity does not allow us to determine which plate or plates arebeing subducted. The Bucaramanga nest appears to be included into thesubducted slab.  相似文献   

21世纪初大连市水资源供需保障与解决途径研究   总被引：3，自引：1，他引：3  

王茂军  张学霞  盖美  宋薇  赵雅静 《地域研究与开发》2001,20(1):65-69

在简要论述大连市资源基本特点和利用现状的基础上，分析了区域供水系统，城市供水系统和农村用水系统的供需平衡状况，研究表明前二者供不应求，后者供大于求，并提出了解决供需矛盾的主要途径，包括：超前研究地表水源地，扩大海水利用范围，提高中水利用量等开源措施，结构调整，技术挖潜等节流措施以及差异提价和尝试工业用水配额交易等市场措施。  相似文献   

中国华北和西北地区水量短缺对农业的压力及对策   总被引：2，自引：7，他引：2  

李新 《干旱区地理》2002,25(4):290-295

华北平原的耕地占全国的 31.19% ,人口占全国的 2 6 .0 1,但水资源只占全国的 6 .14 % ,水资源的供需矛盾很大。而西北地区的水资源分布不均 ,内陆河流域的引水率过高造成了河水断流、湖泊干涸和土地沙漠化。至 2 0 5 0年 ,全国工业和城镇用水将消耗 5 0 %的供水 ,农业用水将比现在减少 ,但黄河流域和西北农业需水量将比2 0 0 0年增加 73× 10 8m3 ,保障农业用水的难度将比现在更大。要避免中国干旱区农业用水的短缺 ,需采取从中国南部的长江流域调水到华北、提高水资源的利用效率、应用节水灌溉技术、调整种植结构和在城市循环用水、净化工业和生活废水等措施  相似文献   

Seismic evidence for thick and underplated late Archaean crust of eastern Dharwar craton     

S. S. Rai  P. V. S. S. Rajagopala Sarma  K. S. Prakasam  V. K. Rao 《Journal of Earth System Science》1996,105(4):431-439

The deep crustal structure of eastern Dharwar craton has been investigated through τ-p extremal inversion of P-wave travel times from a network of seismographs recording quarry blasts. Travel times have been observed in the distance range 30–250 km in a laterally homogeneous lithospheric segment Main features of the inferred velocity-depth relationship include: (a) 29 km thick combined upper and middle crust velocity varying from 6 km/s to 7 km/s, with no observable velocity discontinuity in this depth range; (b) a lower crust (∼ 29–41 km) with velocity increasing from 7.0 to 7.3 km/s; (c) an average upper mantle velocity of 8.1 km/s; and (d) presence of a 12 km thick high velocity crustal layer (7.4 – 7.8 km/s) in the depth range 41–53 km, with a distinct velocity gradient marking a velocity increase of 0.4 km/s. The anomalous 53 km thick crust is viewed as a consequence of magmatic underplating at the base of the crust in the process of cratonization of the eastern Dharwar craton during late Archaean. The underplated material reflects here with the velocity of 7–3 to 7–8 km/s below the depth of 40 km. Our proposition of magmatic underplating is also supported by the presence of large scale I-granitoid, a product of partial melting of the upper mantle material.  相似文献   

The water quality of the Ria de Aveiro lagoon, Portugal: from the observations to the implementation of a numerical model   总被引：1，自引：0，他引：1  

Lopes JF  Dias JM  Cardoso AC  Silva CI 《Marine environmental research》2005,60(5):594-628

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