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Xiumei Zhang Shen Zhang Weimin Ying Tianshan Ren Cuihua Xu Zhizhao Zhong Shurong Zhang 《GeoJournal》1996,40(1-2):201-208
In this paper210 Pb and 137Cs dating methods were used to determine sedimentation rates of lakes Dianchi, Erhai and Poyanghu, and to establish the time scale of the sediments. Also based on geochemical records in the sediment column, the historical variation in heavy metal content over the past one hundred years was determined. Some element concentration increased rapidly after the 1970s, such as Cu, Zn and Mn in the sediments of northern Lake Dianchi, Cd and Mn in southern Lake Erhai and in the west central parts of Lake Poyanghu, Our investigations indicate that the increase in element concentration is caused by human activities. In order to understand the extent of the effect caused by human activities, we have calculated the flux of Zn, Cd and Mn. Results show that the flux caused by human activities is seven times greater than the natural one and the ratio is about 2 times in Lake Erhai and Lake Poyanghu. 相似文献
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本文测定了天津地区1985—1990.9年间M_L=3.0以下小震的震源参数,共125次。结果表明:地震应力降△σ一般都不高,多数低于1.3Mpa;区域剪切应力和地震应力降均有明显的增高趋势。1989年末开始下降。由P波测定的介质Q值蓟县平均为350,宝坻、宁河、静海为250,天津西稍高。小震平均震源机制主压应力轴由北西9°,向西偏转26°。这些变化,不仅反应本地区应力调整过程,而且是华北区域应力变化过程的局部显示。 相似文献
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分析地震液化引起地基侧移作用下的受力特性,并在此基础上提出桩基由于场地地基侧移引起震害的防治措施。 相似文献
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Chuang Shi Lei Fan Min Li Zhizhao Liu Shengfeng Gu Shiming Zhong Weiwei Song 《Journal of Geodesy》2016,90(2):161-177
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本文根据断层的力学性质、活动习性、褶皱、断陷盆地、平原、海湾的形成机理,火山活动、水系分布格局,震源机制解、地壳形变场、GPS观测成果和EDM(光电测距)资料等,对比研究了台湾海峡及其两岸现今的地球动力学环境。结果表明:台湾海峡处在北西方向引张的应力环境;台湾地区受到来自太平洋菲律宾海板块向北西方向的挤压和因台湾海峡下降而产生的向南东方向的挤压;福建沿海则受到印度板块向北向东的挤压和太平洋菲律宾海板块向北西方向的挤压以及台湾海峡下降而产生的向北西方向的挤压。 相似文献
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Single layer ionosphere models are frequently used for ionospheric modeling and estimation using GPS measurements from a network of GPS reference stations. However, the accuracies of single layer models are inherently constrained by the assumption that the ionospheric electrons are concentrated in a thin shell located at an altitude of about 350 km above Earths surface. This assumption is only an approximation to the physical truth because the electrons are distributed in the entire ionosphere region approximately from 50 to 1,000 km. To provide instantaneous ionospheric corrections for the real-time GPS positioning applications, the ionospheric corrections need to be predicted in advance to eliminate the latency caused by the correction computation. This paper will investigate ionospheric total electron content (TEC) predictions using a multiple-layer tomographic method for ionospheric modeling over a local area GPS reference network. The data analysis focuses on the accuracy evaluation of short-term (5 min in this study) TEC predictions. The results have indicated that the obtainable TEC prediction accuracy is at a level of about 2.8 TECU in the zenith direction and 95% of the total electron content can be recovered using the proposed tomography-based ionosphere model. 相似文献
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采用建瓯风廓线雷达(CFL-06)观测资料,分析不同季节天气条件下风廓线雷达的测风精度,同时还选取了永安风廓线雷达(CFL-03)数据进行了对比分析。结果表明,四个季节在探测高度低于4 km时,获得的对称波束水平风分量差值的平均值很小,且小于0.5m·s~(-1),标准差值也比较一致,且小于10 m·s~(-1),探测精度均较好。当探测高度超过4 km后,春、冬两季对称波束水平风分量差值的平均值和标准差值开始增大,在7.1 km高度平均值和标准差值达到最大,分别为9 m·s~(-1)和28 m·s~(-1),夏、秋两季探测精度高于春、冬两季的。在探测高度低于4 km时,不同季节4种方法计算的垂直速度基本一致,以春季大气最为均匀,其次是冬季的,夏、秋两季的最差。在探测高度超过5 km后,春、冬两季4种方法计算的垂直速度偏差增加较快,最大分别为0.9 m·s~(-1)和1.0 m·s~(-1),夏季4种方法计算的垂直速度偏差较小。夏、冬季水平风向和风速测量精度优于春、秋两季的,秋季测量精度最低,水平风速标准差值在0.0~1.5 m·s~(-1)和水平风向标准差值在0~15°范围内所占比例分别只有51.6%和54.0%。总的来说,风向和风速测量精度普遍不高,需要进一步改进算法,减少计算误差,提高探测性能。 相似文献