ANALYSIS OF SOIL EROSION CHARACTERISTICS AND SEDIMENT SOURCES FOR THE YANTZE THREE GORGES REGION

In this paper the researches made in 1981-1990 have identified that the annual soil loss in the Three Gorges region is 157 million t. and the annual incoming sediment load of the Three Gorges reservoir is 40 million t. Soil erosion increases with the destruction of vegetative cover and its subsequent evolution. The annual amounts of sediment erosion for forest land, shrub land, grassland and farmland make up respectively 6.19%, 10.76%, 23.05% and 60% of the total erosion of the Three Gorges region; the quantities of incoming sediment load to the Yangtze River from the above four types of land account for 5.95%, 12.42%, 35.46% and 46.1 % of the total amount of sediment transported to the reservoir. The farmland of offers the main source of sediment. Gravitational erosion produces more bed loads, which will present serious threat to the Three Gorges Project if entering the reservoir. Resettlement of people to the upper parts of the mountainous areas for agricultural production will increase the sediment yield of the Three Gorges region by 10-20 million t and increase the incoming sediment of the Yangtze River by 50-60 million t. Consequently, it is necessary to make a realistic assessment of the soil erosion in the Three Gorges region.     

蒲江—新津—成都—德阳断裂带——成都平原内一条代表性弱活动地震带的地震地质特征

活断层是地震的潜在策源地。然而不同的活断层上地震潜在能力有极大的差别。客观地评价活断层上地震潜在能力不仅是地震预报研究的需要,对国民经济建设的布局和抗震决策也极为重要。在这个意义上,对弱活动性断裂的研究与对强活动性断裂的研究具有同样的重要性。本文以弱活动的蒲江—新津—成都—德阳断裂带为例,讨论了该断裂的晚第四纪活动性,断裂带的地质结构以及断裂的切割深度等因素对该断裂带地震潜在能力的可能影响。     

几种测震学指标的短临前兆异常的初步探讨

本文在国家地震局组织的实用化攻关研究的基础上,按日常预报实践中积累的经验,分析研究了江苏及邻近地区几次地震前缺震曲线、波速比变化、b值时间扫描、累计无震单元数、尾波参数特征和地震活动性时间分维6个指标的短临异常信息,得到以下初步结论:(1)一些测震学指标在中强震发生之前三个月左右出现前兆变化;(2)短临前兆异常的幅度与震级大小的关系不明显;(3)在预测检验过程中,对于多数指标R约为0.5—0.6左右。     

Pore fluid pressure effects in anisotropic rocks: Mechanisms of induced seismicity and weak faults

Many observations and studies indicate that pore fluid pressure in the crustal rocks plays an important role in deformation, faulting, and earthquake processes. Conventional models of pore pressure effects often assume isotropic porous rocks and yield the nondeviatoric pressure effects which seem insufficient to explain diverse phenomena related to pore pressure variation, such as fluid-extraction induced seismicity and crustal weak faults. We derive the anisotropic effective stress law especially for transversely-isotropic and orthotropic rocks, and propose that the deviatoric effects of pore fluid pressure in anisotropic rocks not only affect rock effective strength but also cause variation of shear stresses. Such shear stress variations induced by either pore pressure buildup or pore pressure decline may lead to faulting instability and trigger earthquakes, and provide mechanisms for the failure of crustal weak faults with low level of shear stresses. We believe that the deviatoric effects of pore fluid pressure in anisotropic rocks are of wide application in studies of earthquake precursors and aftershocks, oil and gas reservoir characterization, enhanced oil recovery, and hydraulic fracturing.     

柴北缘冷湖构造带古近系沉积体系及演化特征

通过对柴达木盆地北缘西段重点探井的岩心观测、重矿物分析、测井数据及地震资料的分析，研究了冷湖构造带古近系沉积体系及演化特征和不同时期沉积微相及砂体的展布规律.结果认为，冷湖构造带古近系主要发育冲积扇-辫状河-辫状河三角洲-湖泊沉积体系，物源来自北东方向的小赛什腾山和赛什腾山附近.古近系路乐河组（E₁₊₂）沉积期，主要发育辫状河以及辫状河三角洲平原沉积，仅在靠近山前发育少量冲积扇沉积；至下干柴沟组（E₃）沉积时期，主要发育辫状河、辫状河三角洲平原、辫状河三角洲前缘及滨-浅湖沉积.古近纪时期冷湖构造带表现为一次较大规模的水进过程，纵向沉积继承性明显，很好地记录了这一沉积演化过程.这一沉积体系及演化过程有利于粗碎屑和细碎屑交互沉积，形成较好的储盖组合，为柴达木盆地冷湖构造带下一步的油气勘探提供了可靠的地质依据.     

安徽东至查册桥矿区金矿地质特征及找矿潜力分析

查册桥矿区位于江南过渡带，包括牛头高家金矿床、程檀金矿床、路源金矿点和东边金矿化点、杨梅尖金矿点.其中牛头高家金矿是安徽省首次发现的具一定规模的红土型金矿.研究区主体位于东至断裂与高坦断裂带交汇处及其两侧，三岗尖-杨美桥背斜核部及北翼.区内存在多个重要的赋矿层位，主要包括南华系休宁组、南沱组，震旦系蓝田组，寒武系黄柏岭组、杨柳岗组，奥陶系仑山组、东至组.高坦断裂带、兰程畈断裂带、奥陶系/志留系间的推覆-滑覆断层界面均是重要的控岩控矿构造，区内岩浆岩主要受其控制，物化探异常也主要沿其分布.通过对矿床地质特征总结，并结合前人研究成果，对找矿潜力进行分析，认为区内具有寻找低温热液型-叠改型、层控夕卡岩型、岩浆热液脉型金、铜、钨、钼、银、铅锌等矿化的潜力.     

突变理论在工程地质中的应用

本文说明了突变理论应用于工程地质中的一般方法。着重通过实例介绍尖点突变理论在工程地质中的应用现状,其中包括用突变理论评价层状结构斜坡、地下洞室的顶板冒落及活断层的稳定性,以及斜坡失稳的时间预报等问题。同时对其应用前景作了展望。     

雅鲁藏布中新生代深水沉积盆地形成和演化(Ⅰ)——喜马拉雅造山带沉积特征及演化

通过对喜马拉雅三叠纪到第三纪区域沉积特征分析,阐明了雅鲁藏布喜马拉雅特提斯造山带从裂谷—被动大陆边缘—前陆盆地的沉积盆地演化史。随着以雅鲁藏布带为代表的喜马拉雅特提斯打开,三叠纪到早侏罗世为特提斯早期裂开的大陆边缘裂谷盆地。早期裂谷中心部位不是现在大陆缝合线的雅鲁藏布一带,而在低分水岭带。晚侏罗世到早白垩世,雅鲁藏布江南测为典型被动大陆边缘,其沉积盆地沉降、海平面变化与沉积作用相吻合。晚白垩世到第三纪为前陆盆地演化阶段,从沉积作用可以识别出晚白垩世晚期为造山第一暮,第三纪初为第二幕。