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101.
深圳地区中生代火山地层分布区是我国东南沿海浙闽粤港火山活动带的一个重要组成部分,是我国沿海地区侏罗纪—白垩纪火山地层较有代表性地段,也是研究我国东南沿海侏罗纪—白垩纪火山活动的天然博物馆。近期通过野外观察,测制火山地层剖面,进行锆石同位素激光定年测试,对大鹏半岛国家地质公园中生代火山地层的时代提出新的认识,将原划分为上侏罗统高基坪群划分为早—中侏罗世塘厦组(181.8 Ma?)、中侏罗世吉岭湾组(165.8 Ma)、晚侏罗世梧桐山组(156.9~145.6 Ma)、晚侏罗世—早白垩世七娘山组(146.3~131.0 Ma)、早白垩世官草湖群等。 相似文献
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2008年5月12日汶川(31.0°N,103.4°E)8.0级大地震,造成了数十万人员伤亡,震惊世界.对这次8级特大地震,没有做出短临预报,深感愧疚!对这次8级特大地震监测预报工作进行科学总结和反思,震前有否觉察?作者信箱:符干,fugan6618@tom.com 相似文献
104.
Interaction of a river plume with coastal upwelling in the northeastern South China Sea 总被引:5,自引:0,他引:5
Observational and modeling studies were conducted to investigate the Pearl River plume and its interaction with the southwesterly driven upwelling circulation in the northern South China Sea during the summer. After exiting the Pearl River Estuary, the discharged freshwater generates a nearly stationary bulge of freshwater near the entrance of the estuary. Forced by the wind-driven coastal upwelling current, the freshwater in the outer part of the bulge flows downstream at the speed of the current and forms a widening and deepening buoyant plume over the shelf. The plume axis gradually shifts offshore of the current maximum as a result of currents induced by the contrasting density at the nose of plume and by the intensified Ekman drift in the plume. In this plume–current system, the fraction of the discharged freshwater volume accumulated in the bulge reaches a steady state and the volume of newly discharged freshwater is transported downstream by the upwelling current. Enhancement of stratification by the plume thins the surface frictional layer and enhances the cross-shelf circulation in the upper water column such that the surface Ekman current and compensating flow beneath the plume are amplified while the shoaling of the deeper dense water in the upwelling region changes minimally. The pressure gradient generated between the buoyant plume and ambient seawater accelerates the wind-driven current along the inshore edge of the plume but retards it along the offshore edge. Along the plume, downward momentum advection is strong near the highly nonlinear source region and a weaker upward momentum advection occurs in the far field over the shelf. Typically, the plume is shaped by the current over the shelf while the current itself is adjusting to a new dynamic balance invoked by the plume-induced changes of vertical viscosity and the horizontal pressure gradient. The spatial variation of this new balance leads to a coherent change in the cross-isobath transport in the upper water column during upwelling. 相似文献
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106.
Influence of 2008 Wenchuan earthquake on earthquake occurrence trend of active faults in Sichuan-Yunnan region
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The Wenchuan earthquake coseismic deformation field is inferred from the coseismic dislocation data based on a 3-D geometric model of the active faults in Sichuan-Yunnan region. Then the potential dislocation displacement is inverted from the deformation field in the 3-D geometric model. While the faults' slip velocities are inverted from GPS and leveling data, which can be used as the long-term slip vector. After the potential dislocation displacements are projected to long-term slip direction, we have got the influence of Wenchuan earthquake on active faults in Sichuan-Yunnan region. The results show that the northwestern segment of Longmenshan fault, the southern segments of Xianshuihe fault, Anninghe fault, Zemuhe fault, northern and southern segments of Daliangshan fault, Mabian fault got earthquake risks advanced of 305, 19, 12, 9.1 and 18, 51 years respectively in the eastern part of Sichuan and Yunnan. The Lijiang-Xiaojinhe fault, Nujiang fault, Longling-Lancang fault, Nantinghe fault and Zhongdian fault also got earthquake risks advanced in the western part of Sichuan-Yunnan region. Whereas the northwestern segment of Xianshuihe fault and Xiaojiang fault got earthquake risks reduced after the Wenchuan earthquake. 相似文献
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108.
I~IOXThe northern South China Sea is the frontal region for the water exchange between the sleuthChina Sea (SCS) and its neighboring seas. Its northeast part connects to the East China hothrough the Taiwan Strait and the east part ~ates with the Pacific Ocean by the LUZOn Strait.The a~heric interface over the northern SCS is the important paSSage for the South China Seamourn. Therefore, the uPPer vallationS Of the northern SCS are not Only affected by the dynndc and thermed~c d… 相似文献
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110.
北京山区泥石流预警阈值初步研究 总被引:1,自引:0,他引:1
泥石流预警阈值,是突发地质灾害防灾减灾的重要参考指标。本文结合北京山区泥石流灾害特点和已有降雨阈值研究成果,一方面在泥石流沟易发性、物源和危害人数进行分级的基础上,提出不同级别沟谷在不同前期降雨条件下,不同发灾概率的激发雨量,极大地方便了中短期预警实际工作;另一方面将泥石流流域降雨量、土壤含水率、次声、泥位4个参数,作为泥石流短临灾害预警关键物理参数,开展了泥石流专业监测设备预警阈值研究。最终,从技术层面上构建不同时间维度的泥石流监测预警阈值体系,为北京山区泥石流监测预警提供技术支持。 相似文献