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961.
An application of line simplification considering spatial knowledge is described. A method for identifying potential conflict regions, in order to avoid the self-intersection of generalized, lines, is also discussed. Further-more, a new progressive line simplification algorithm is presented. From the view point of spatial cognition, a spatial hierarchical structure is proposed, and its application to construction of spatial knowledge related to a line is explained. 相似文献
962.
High-resolution satellite gravity data have been generated and utilized to infer subsurface geological structures in the area of devastating earthquake that struck the Bhuj region in Gujarat on 26 January 2001. Latitudinal gravity profiles have been generated in the Bhuj, Anjar and IBF regions across the epicentres (23.5° N, 69.8° E/Mw 7.0 in 2001; 23.2° N, 70° E/Mw 7.0 in 1956; 24.2° N, 69.2° E/Mw 7.8 in 1819). Substantial differences in gravity anomaly patterns as high as 37 mGal could be observed existing near the epicentre regions. These gravitational differences might have caused due to the plate tectonic processes and due to the changes in densities of different lithospheric zones/sedimentary layers. Temporal variations of the satellite-derived gravity and their probable relations with already occurred major earthquakes in this region have been studied. Hence we conclude that drastic changes in gravity anomalies can be considered as a precursor for occurrences of substantially large earthquakes. 相似文献
963.
Salt affected soils occupy significant areas in western and central India manifested by the arid and semiarid climate, sandy/clayey soil texture, absence of natural drainage, and inadequate infrastructure and irrigation development. These soils are productive following reclamation and appropriate management. The National Remote Sensing Agency, Hyderabad (India) published state-wise maps of salt affected soils in India on 1:250,000 scale using a legend that includes physiography, soil characteristics, and the aerial extent of the mapping units. In the analogue form, voluminous data contained in such maps were difficult to handle by users of varied backgrounds. An attempt was made to prepare a computerized database of salt affected soils for easy access, retrieval, and manipulation of spatial and attribute data useful for management of salt affected soils. The salt affected soils maps were prepared, for Rajasthan, Gujarat, Madhya Pradesh, and Maharashtra states, overlaying digitized layers of SAS polygons and the Survey of India basemap using the ILWIS (Integrated Land and Water Information System) software. GIS was used to prepare a composite (master) database of western and central India that showed the extent and distribution of salt affected soils. A relational database was prepared combining the digitized polygons with soil characteristics such as nature and degree of salinity (presence of higher concentration of neutral salts and neutral soil reaction), sodicity (presence of higher concentration of basic salts and alkaline reaction) and ground coverage. The regional and zonal databases of salt affected soils were prepared at a suitable scale overlaying agro-climatic regions agro-climatic zones. Spatial relation of salt affected soils with physiography, climate, geology, and agro-eco-sub-regions were evaluated employing map calculations in GIS. Saline soils were prevalent in Gujarat, and Rajasthan while sodic soils were dominant in Maharashtra and Madhya Pradesh. These were distributed primarily in the arid (B) plain of Rajasthan, alluvial (A) and coastal (D) plains of Gujarat, and peninsular plain (F) of Maharashtra and Madhya Pradesh. It occupied 2,596,942 ha (78%) in the western (Rajasthan and Gujarat) and 733,608 ha (22%) in the central (Madhya Pradesh and Maharashtra) regions. The SAS occupied 3.3 million ha in the western and central region constituting 50% of the total salt affected soils in India. The saline and sodic soils occupied 2,069,285 ha (62%) and 1,261,266 ha (38%), respectively. 相似文献
964.
利用EAR5再分析气象数据,分析了两次昆明准静止锋天气过程的高低空环流形势、锋面结构、锋面位置、以及相关要素场等基本特征及其异同。结果表明:中高纬度地区阻塞形势的存在是昆明准静止锋形成的背景环流。当冷暖气团均强且势均力敌时,更有利于锋面的维持;冷空气较强时,锋面会向西移动,越过云贵高原地形的阻挡;反之,锋面则会向东移动。当锋面维持在高原地形东侧时,冷空气被地形阻挡时,锋面的移动缓慢,此时锋区最为明显。当锋面维持在地形东侧时,风场的最大水平切变、温度的最大水平梯度和相当位温的密集区,描述的锋面位置几乎相同。两次过程寒潮爆发时冷空气均只能维持到700hPa附近,且水平风场也均为600hPa以下的低空切变,说明昆明准静止锋为浅薄系统。昆明准静止锋与一般冷锋锋后不同,两次个例昆明准静止锋锋后低空为湿区,而锋前水汽是否充足则要看南支槽所处的位置。 相似文献
965.
通过对广西云开地区区域成矿特点和区域构造演化阶段的讨论,选择区内主要矿床的控矿地质因素、成矿时代、物质来源等特征进行对比,并根据典型矿床成矿模式概括区域成矿模式。指出加里东期、华力西-印支期、燕山期为本区矿床的成矿期,这是对广西云开地区成矿环境的认识进一步深化,以期指导区域矿产评价和找矿部署工作。 相似文献
966.
967.
腾冲火山岩年龄问题评述 总被引:1,自引:0,他引:1
腾冲火山及火山岩是国内新近纪火山及其喷发物九大分布区之一,研究程度较广较深,喷发序列岩石定岩及年龄值资料丰富,综合评述并指出今后研究方向。 相似文献
968.
地形地貌参数指标是分析区域活动构造的有力工具。本文以渭河上游流域的活动构造研究为例,通过提取地貌的参数指标,如面积-高程积分(Hi)、流域盆地不对称度(AF)、山前曲折度(Smf)以及谷底宽度与谷肩高度的比值(Vf)、盆地形状指数(Bs)等,然后对地貌参数指标等级进行算术平均化(S/n),可得到区域的相对构造活动程度(Iat),分为:低、中等、高、较高四类等级。研究认为渭河上游流域的构造活动程度相对高(Iat=1.50),这种方法对探讨整个区域活动构造的差异性具有很好的效果和意义。 相似文献
969.
西南三江北段是青海省重要的斑岩型铜钼矿成矿带,纳日贡玛铜钼矿是近年来在三江北段发现的与侵入岩有关的斑岩型铜钼矿。利用锆石U-Pb方法测得纳日贡玛黑云花岗斑岩的形成年龄为41.53Ma±0.24Ma,属于喜马拉雅早期。纳日贡玛斑岩型铜钼矿的成矿时代主要在40.86~40.80Ma之间。在多期热液叠加、多期成矿作用中,纳日贡玛斑岩型铜钼矿的热液应是纳日贡玛黑云花岗斑岩(41.53Ma±0.24Ma)和纳日贡玛斜长花岗斑岩(41.00Ma±0.18Ma)共同提供的。由于该区有较多的中酸性岩体存在,因而确定这些侵入体的形成年龄,对于在该区寻找同时代的斑岩型铜钼矿有重要的理论意义和现实意义。 相似文献
970.
大三江地区是中国东部重要的油气资源接替区,早白垩世时期该地区曾为一个统一的盆地,之后盆地遭受破坏分解。如何确定当时的盆地边界进而恢复盆地原型,是该地区亟待解决的关键地质问题之一。前人对盆地边界的确定大都以理论推测为主,缺乏实际证据。本次工作在黑龙江林口地区发现一套穆棱组底部砾岩,对砾石进行成分及分选特征、沉积特征等的统计与分析,结合古水流恢复和地震解释资料,认为该套砾岩整体为冲积扇相,以河道砾岩沉积和漫流砾岩沉积为主,物源主要来自盆地西部的张广才岭。结合地震资料分析,认为研究区穆棱组时期的沉积模型为冲积扇相向滨浅湖亚相的直接过渡。本研究不仅为大三江盆地西部边界的确定提供了直接证据,同时也为该地区今后的油气勘探指明了方向。 相似文献