Results of magnetotelluric and gravimetric measurements in western Nicaragua, Central America   总被引：1，自引：0，他引：1  

Sten-Åke Elming  Thorkild Rasmussen 《Geophysical Journal International》1997,128(3):647-658

Magnetotelluric and gravity data have been collected within a ca. 170 km long traverse running from the Pacific coast of Nicaragua in the west to the Nicaraguan Highland in the east. This part of Nicaragua is characterized by sedimentary rocks of the Pacific Coastal Plain, separated from the Tertiary volcanic rocks of the Highland by the NW-SE-trending Nicaraguan Depression. 2-D interpretation of the magnetotelluric (MT) data, collected at 13 stations, indicates four regions of high electrical conductivity in addition to the conductive coastal region. Two of these are associated with conducting sediments and pyroclastics in the upper part of the crust. Two other conductive structures have been defined at depth around 20 km and the one best defined is located below the depression. From the distribution of seismic events, volcanic activity in the depression and the similarity in geophysical characteristics with areas such as the Rio Grande Rift, this conductor is interpreted as a melt layer or a complex of magma chambers. Models of the upper lithosphere, constrained by the MT model, vertical electrical sounding (VES) data, seismic data and densities, have been tested using gravity data. A model that passes this test shows a gradual thickening of the crust eastwards from the Pacific coast. An anomaly centred over the depression is interpreted to have its origin in a thinning of the crust. In this model the melt layer is situated on top of the bulge of the lower lithosphere. A change in the composition of the crust, from the Pacific Coastal Plain to the Highland, is indicated from the change in character of the MT response and from the density distribution in the gravity model. This may support the hypothesis that the Pacific region is an accreted terrane. MT and gravity data indicate a depth to a resistive and high-density basement in the depression of ca. 2 km. On the basis of this, the vertical setting in the depression is estimated to be of the order of 2.5 km.  相似文献   

宁夏平原绿洲生态经济系统的问题与调控对策   总被引：2，自引：0，他引：2  

张兴平 《干旱区地理》1995,18(1):14-20

宁夏平原是我国绿洲主要分布地区之一。由于受传统开发模式的限制，其生态经济系统已产生了一系列的问题，如水资源供需矛盾日益突出，环境污染严重，人口压力过大和产业结构不合理等。要解决这些问题，就必须对绿洲生态经济系统进行调控。为此，本文提出了绿洲生态经济系统调控的具体措施。  相似文献   

河北平原地下水动力环境演化影响因素的关联度分析   总被引：7，自引：0，他引：7  

郭永海  张作辰 《工程地质学报》1995,3(3):62-66

本文以河北平原典型地区-石家庄、衡水、沧州地区为例,采用灰色关联度分析方法,分析了地下水动力环境演化的影响因素。结果表明,对于第一含水组地下水,水动力环境演化主要受气象因素控制,对于第三含水组及漏斗区地下水,人为开采是最直接的影响因素。  相似文献   

An alternative plate tectonic model for the Palaeozoic–Early Mesozoic Palaeotethyan evolution of Southeast Asia (Northern Thailand–Burma)     

O.M. Ferrari  C. Hochard  G.M. Stampfli   《Tectonophysics》2008,451(1-4):346-365

An alternative model for the geodynamic evolution of Southeast Asia is proposed and inserted in a modern plate tectonic model. The reconstruction methodology is based on dynamic plate boundaries, constrained by data such as spreading rates and subduction velocities; in this way it differs from classical continental drift models proposed so far. The different interpretations about the location of the Palaeotethys suture in Thailand are revised, the Tertiary Mae Yuam fault is seen as the emplacement of the suture. East of the suture we identify an Indochina derived terrane for which we keep the name Shan–Thai, formerly used to identify the Cimmerian block present in Southeast Asia, now called Sibumasu. This nomenclatural choice was made on the basis of the geographic location of the terrane (Eastern Shan States in Burma and Central Thailand) and in order not to introduce new confusing terminology. The closure of the Eastern Palaeotethys is related to a southward subduction of the ocean, that triggered the Eastern Neotethys to open as a back-arc, due to the presence of Late Carboniferous–Early Permian arc magmatism in Mergui (Burma) and in the Lhasa block (South Tibet), and to the absence of arc magmatism of the same age East of the suture. In order to explain the presence of Carboniferous–Early Permian and Permo-Triassic volcanic arcs in Cambodia, Upper Triassic magmatism in Eastern Vietnam and Lower Permian–Middle Permian arc volcanites in Western Sumatra, we introduce the Orang Laut terranes concept. These terranes were detached from Indochina and South China during back-arc opening of the Poko–Song Ma system, due to the westward subduction of the Palaeopacific. This also explains the location of the Cathaysian West Sumatra block to the West of the Cimmerian Sibumasu block.  相似文献   

Evaluation of trace-metal enrichments from the 26 December 2004 tsunami sediments along the Southeast coast of India     

S. Srinivasalu  N. Thangadurai  M. P. Jonathan  J. S. Armstrong-Altrin  T. Ayyamperumal  V. Ram-Mohan 《Environmental Geology》2008,53(8):1711-1721

The tsunami sediments deposited after the December 2004 tsunami were sampled immediately in the coastal environment of Tamil Nadu State on the southeast coast of India. Fifty-four sediment samples were collected and 14 representative samples were selected to identify the level of metal contamination in tsunami sediments. The results indicate that the sediments are mainly of fine to medium-grained sand and contain significantly high contents of dissolved salts in sediments (Na⁺, K⁺, Ca⁺², Mg⁺², Cl⁻) in water-soluble fraction due to seawater deposition and evaporation. Correlation of acid leachable trace metals (Cr, Cu, Ni, Co, Pb, Zn) indicate that Fe-Mn oxyhydroxides might play an important role in controlling their association between them. Enrichment of trace metals is observed in all the locations with reference to the background samples. High values of trace metals in the southern part of the study area are due to the large-scale industries along the coast, and they are probably anthropogenic in nature and of marine origin, which could cause serious environmental problems.  相似文献   

滇东南岩溶石山区布井取水实践   总被引：1，自引：0，他引：1  

YU Fu-you  段乔文 《云南地质》2008,27(1):108-113

滇东南岩溶石山地区干旱缺水严重制约了当地居民生存环境的改善。根据该区岩溶发育的主要控制因素及岩溶地下水的运移、富集规律,总结在碳酸盐岩呈大片状和带状两种不同分布条件下,以机井开发岩溶地下水的布井思路。  相似文献   

Spatio-temporal differences and factors influencing intensive cropland use in the Huang-Huai-Hai Plain   总被引：2，自引：1，他引：1  

Shuqin Shi  Yu Han  Wentao Yu  Yuqing Cao  Weimin Cai  Peng Yang  Wenbin Wu  Qiangyi Yu 《地理学报(英文版)》2018,28(11):1626-1640

This study developed a comprehensive system to evaluate the intensity of cropland use and evolution of cropland use in the Huang-Huai-Hai Plain. Delphi-entropy methods were adopted to determine the weight of the index, and the GeoDetector model was established to explore the influencing factors. The results are summarized as follows: (1) The intensity of inputs, degree of utilization, and production increased continuously, but the intensity of continuous conditions experienced an overall decline followed by a rebound towards the end of the study period. The number of counties with high and moderately high intensity increased by 56.8% and 14.6%, respectively, from 1996 to 2011. The number of counties with moderately low and low intensity declined by 35.9 % and 11.9 %, respectively. Areas with significant increases in intensity were mainly distributed in northeast Hebei Province, northwest Shandong Province, and north Jiangsu Province. The intensity is high in northern Jiangsu and Anhui; the output effect remained above moderate intensity mainly near Beijing, Tianjin, Tangshan, and counties in the suburbs of Shijiazhuang. (2) Natural disasters, elevation, slope, and road networks were the main factors influencing the intensity of cropland use in this region, with influence values of 0.158, 0.143, 0.129, and 0.054, respectively. Areas with moderately high and high levels of intensity were distributed in low-lying areas. Uneven distribution of precipitation, seasonal drought, and flood disasters can directly affect the stability index of croplands and reduce the intensity of cropland use. Developed road networks are associated with moderately high intensity. Our results suggest recommendations such as promoting agricultural intensification and large-scale management, promoting the construction of road networks, improving early warning systems for drought and flood disasters, and promoting moderate and intensive use of arable land, and focusing on restoration and sustainable use of cropland.  相似文献   

华北平原地下水灌溉对区域气候影响的数值模拟     

武利阳  左洪超  冯锦明 《气象学报》2018,76(4):635-648

在耦合模式WRF/Noah-MP中加入考虑地下水过程的动态灌溉方案,设计两组试验（分别为考虑和不考虑地下水灌溉）,连续模拟10 a（2001—2010年）,来研究华北平原地下水灌溉的区域气候效应。结果表明,地下水灌溉导致华北平原地下水位下降,在少雨的季节灌溉量大,水位下降较快。在灌溉期（3—9月）,灌溉引起的土壤湿度升高影响了地表能量的分配（潜热增加,感热减少）,导致2 m气温显著降低0.6—1.0℃,同时也降低了灌溉区夏季模拟偏高的气温。灌溉对灌溉区边界层大气有升高湿度和冷却降温的作用,对春季的影响局限在边界层内,而夏季的影响持续到5000 m以上。夏季灌溉对降水的影响远强于春季,灌溉的升高湿度和冷却效应分别对夏季降水产生正反馈和负反馈,共同影响灌溉区的降水变化。灌溉通过对水汽输送的影响,引起非灌溉区降水的变化,而长江中下游流域夏季降水的增多可能与高空西风急流轴位置南移有关。   相似文献   

热带西北太平洋与东南印度洋对流活动年际变化联系的年代际改变          下载免费PDF全文

张奔奔  管兆勇  张萌萌 《大气科学学报》2018,41(6):753-761

采用美国NOAA卫星观测OLR (outing longwave radiation)资料以及NCEP/NCAR、CM AP月平均资料,利用合成分析等方法,研究了热带西北太平洋(125°～140°E,10°～20°N)与热带东南印度洋(90°～105°E,5°～15°S)对流活动异常的联系。结果表明:热带西北太平洋与东南印度洋对流活动异常的联系有显著的年代际变化; 20世纪80—90年代存在显著的正相关,20世纪90年代至21世纪初有显著的负相关,其后转变为正相关。合成分析表明,热带西北太平洋与东南印度洋对流活动正相关时,两地区均存在反气旋性环流,低层辐散、高层辐合,对流活动弱,不利于降水产生,有降水负异常;当热带西北太平洋与东南印度洋对流活动负相关时,两地区环流异常存在明显差别,热带东南印度洋有正的海温异常,高层辐散、低层辐合,有上升运动,对流活动强,有降水正异常,而热带西北太平洋则相反。热带西北太平洋和热带东南印度洋之间的斜向垂直环流圈将这两个地区联系起来,并决定了这两个地区对流活动负相关关系的形成。  相似文献   

滇东南喀斯特峰丛地区灰岩土壤的基本性质和综合评价   总被引：2，自引：0，他引：2  

郝性中 《云南地理环境研究》1993,5(1):65-75

本文以云南省西畴西部为例,阐述了滇东南喀斯特峰丛地区灰岩土壤的形成、分类和分布规律。从土壤的颜色、结构、机械组成、化学组成、游离碳酸钙、pH值、有机质含量、碳氮比、氮磷钾含量、盐基代换量和盐基饱和度、微量元素含量等方面,对灰岩土壤的基本理化性质进行了分析和评价,提出了合理利用途径。  相似文献