Three-dimensional structure of the crust and upper mantle beneath the south China area from long period surface waves     

《地震学报(英文版)》1993,6(3):619-629

In the present study the long period surface wave records of 238 wave-paths from 79 earthquakes within China and its adjacent regions received by 30 seismic network stations are measured by using the improved match-filtering frequency-time analysis technique and the grid dispersion inversion method to obtain the rayleigh pure-path dispersion values for 147 slant grids of 4° × 4° in this area, then a three-dimensional shear wave velocity model of the crust and upper mantle beneath south China area to a depth of 170 km is inversed. It is found that there are obvious differences among the main structural units, and there are also certain differences among the subordinate elements even in the individual unit. The crustal thickness of this area is ranging from 30 to 43 km, and is getting thicker gradually from the east to the west. The average shear velocity of crust is ranging form 3.48 to 3.68 km/s with the lowest in the northeast part and highest in the west part. No obvious crustal low velocity layer of large scale is detected. There exist upper mantle low velocity zones in the most of south China area with the starting depth ranging from 75 to 106 km. The lowest shear velocity within the low velocity zones is about 4.28–4.38 km/s. Despite of the existing of upper mantle low velocity zones beneath the most of south China area, the interfaces between the important layers are quite clear, the variation of the bedding surfaces is very gentle, and the lateral changes measured in a larger scale of the underground structure are rather small. It may indicate that the crustal and upper mantle structure of the main part of south China area belongs to the relatively stable structure of the continental blocks except for the fringe areas such as the fold-faulted region in the west part and the fault system along the southeastern coast which may belong to the tectonically active area. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 159–167, 1993. This subject is supported by the National Science Foundation of China.  相似文献   

Evaluating the effect of land development on sediment transport using a probability density function     

T. V. Hromadka II  R. J. Whitely 《Stochastic Environmental Research and Risk Assessment (SERRA)》1993,7(2):102-108

An important problem in sedimentation analysis is the development of a channel section that preserves, as best as possible, the current sedimentation regime even though the flood frequency tendencies have been altered due to land development within the catchment. In order to accomplish this task, a methodology is needed that estimates sediment transport capacity for various channel configurations. Such a procedure is described which allows the computation of the total sediment transport capacity for each of several T-year return frequency runoff hydrographs. This information is used to obtain an approximate probability distribution for the total sediment transport capacity, and the mean and standard deviation of this distribution are computed.Comparing the results for the catchment in its present state with a future developed state, using a selection of new channel parameters, indicates how to improve the channel to control changes in sedimentation due to development. The analysis procedure provides a basis for estimating a new channel configuration such that the new flow conditions retain, as best as possible, the existing condition sedimentation effects, and hence retain the natural sediment supply and transport trends even though runoff flow rates have changed due to land development within the catchment.The results of Wilson Creek are typical of the several sites examined, see Table 3 below. The T=2, T=5, T=25, and T=100 year values for total sediment transport capacity, in kilotons, are 6.9, 39.4, 61.3, and 96.7 with a mean of 17.1 and standard deviation of 19.3. After development with no change in the channel the respective values increase to: 17.9, 84.6, 128.1, and 258.0 with a mean of 39.1 and standard deviation of 44.3. A new channel can be constructed which will reduce these sediment transport capacity values, after development, to 5.2, 41.0, 62.0, and 124.8 with a mean of 17.4 and standard deviation of 22.0.  相似文献   

冀东牛心山金矿区岩浆岩特征及其成因探讨     

曲以秀 《吉林大学学报(地球科学版)》1993,(3)

本区岩浆岩以花岗岩为主体,只在岩浆演化晚期有少量中性岩岩墙。岩浆演化及岩石化学、稀土元素、同位素等特征表明,岩浆是燕山运动早期构成下地壳的基性物质经部分重熔形成,熔融早期最低熔融组分形成花岗岩浆,进一步重熔,晚期形成少量中性岩浆。  相似文献   

太湖微囊藻的生长特征及其分离纯培养的初步研究   总被引：3，自引：0，他引：3  

陈宇炜  高锡云  陈伟民  秦伯强 《湖泊科学》1999,11(4):351-356

详细描述了鲂仔,稚,幼鱼不同发育阶段形态发生和发育特征;根据硬骨鱼类阶段发育理论,将其划分为４阶段１５时期针对其胚后发育特点,提出了鲂苗种生产应注意的问题．  相似文献   

21世纪世界的资源和环境   总被引：2，自引：0，他引：2  

张镜湖 《地球信息科学学报》1999,1(2):1-6

20世纪世界人口从15亿增长到60亿.而经济成长更为快速,自1950年至今已增长4倍.目前世界人口每年增加8000余万人,至2050年将达到90亿,世界经济是否能持续发展以提升或维持现有的生活水准,值得研讨.资源的消长和环境的变迁是具有决定性的两大重要议题.  相似文献   

广州信息密集服务业的空间发展及其对城市地域结构的影响   总被引：27，自引：0，他引：27  

阎小培 《地理科学》1999,19(5):405-410

采用第三产业普查资料,深入分析了改革开放以来广州信息密集服务业的发展水平,空间发展特征和原因及其对城市地域结构的影响,揭示了信息密集服务业发展与城市地域运动的关系。  相似文献   

辽中南地区经济发展与资源环境关系   总被引：8，自引：4，他引：4  

佟连军  张明祥 《地理科学》1999,19(6):517-520

分析了辽中南地区资源环境对经济发展的作用和经济发展对资源环境的影响,阐明了区域经济发展与资源环境密不可分的关系,资源环境是经济发展的物质基础,经济发展为促进资源合理开发利用和环境保护创造条件。  相似文献   

Essential variables for air quality estimation     

Andrii Shelestov  Tatiana Borisova  Olena Turos  Gennadi Milinevsky  Igor Gomilko 《International Journal of Digital Earth》2020,13(2):278-298

  相似文献   

天津地区一次局地大暴雨过程MCS传播发展机制     

刘一玮  王颖 《沙漠与绿洲气象(新疆气象)》2020,14(5):61-68

利用常规观测资料、卫星云图、雷达、风廓线组网资料对2017年8月8日-9日天津地区局部大暴雨天气进行分析,得到以下结论：A、B两个中尺度雨团先后影响天津,A雨团持续了4个小时,雨强相对较大；B雨团持续了3个小时,雨强相对较小；对应有两个MCS,强降水发生在TBB低值中心偏向温度梯度最大的区域；降水回波的移动路径和强度特征存在差异,A雨团回波为自西北向东南方向移动的带状的高质心降水回波；B雨团回波自西南向东北方向移动,为低质心降水回波带状回波,高质心降水回波雨强高于低质心降水回波。新型探测资料有助于分析中尺度影响系统,判断对流系统的移动方向。用风廓线组网资料对比两个阶段降水的中尺度系统,A雨团为上冷下暖的高低空配置,B雨团降水出现在整层西南气流中,引导风的不同,导致回波的移动方向、天气剧烈程度的不同；变压梯度、温度梯度等环境因素对判断局地对流暴雨发生的环境条件有一定指示性。  相似文献   

既找矿又开矿搞活地勘单位：赴疆考察的认识和体会     

张攀华 《湖南地质》1993,12(2):70-74,79

“六五”和“七五”期间,新疆地矿局强化了地质找矿的科学管理,充分发挥了地质科技在找矿中的先导作用,争取到了一个好的外部环境,取得了地质找矿的重大突破。他们既找矿又开矿,以找矿促开发,走找矿与开矿结合的道路,实行探、采、工、贸一体化,创造了搞活地勘单位,振兴地方经济的成功经验。  相似文献