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排序方式: 共有109条查询结果,搜索用时 265 毫秒
71.
北京地区地震动的三维有限差分模拟 总被引:16,自引:0,他引:16
根据北京地区地壳结构和1679年三河-平谷8级地震的研究结果,对北京地区进行了三维有限差分地震动模拟研究,并研究了北京地区的盆地效应。结果表明,盆地效应非常明显。在北京盆地内的大部分地区,盆地效应的放大系数达到1.3,在某些地区甚至达到2.0。将盆地的放大效应与北京市区地表土层的放大效应进行了对比,发现它们的放大率为同等水平,在部分地区盆地的放大效应更为明显。我国现行的抗震规范中只考虑了地表土层效应的影响,由于许多城市位于盆地内,并且已经修建或正在修建大量的具有较长自振周期的高层建筑。因此,本文的研究结果对城市规划与防震减灾具有重要的指导意义。 相似文献
72.
Hong GH Kim YI Lee SH Cooper LW Choe SM Tkalin AV Lee A Kim SH Chung CS Hirose K 《Marine pollution bulletin》2002,44(7):660-665
The concentrations of 239+240Pu and 137Cs in zooplankton and nekton in the Northwest Pacific and Southern Oceans were measured during the period 1993-1996. The object of the sampling was to assess the potential impacts of existing submerged anthropogenic-radioactive materials in the western North Pacific as well as the East China Sea. Samples from the Bransfield Strait of the Antarctic Ocean provided a control source impacted by only atmospheric bomb fallout. No particularly elevated levels of 239+240Pu were found in zooplankton samples from the Northwest Pacific, although significantly lower levels of 239+240Pu were found in three mixed zooplankton samples from the Bransfield Strait. The body burden of 239+240Pu in zooplankton appears to reflect concentrations in ambient seawater with some variation. Some additional measurements of 137Cs in fish are also reported here to complement existing databases and for future reference in the regional marine environmental radioactivity monitoring effort. 相似文献
73.
Bolton JL Stehr CM Boyd DT Burrows DG Tkalin AV Lishavskaya TS 《Marine environmental research》2004,57(1-2):19-36
As part of a multinational workshop on marine environmental quality, sediments were collected from seven sites in Vancouver Harbour and analyzed for polynuclear aromatic hydrocarbons (PAHs) and organochlorines (OCs), and for trace metals. English sole were collected from five sites, and muscle was analyzed for trace metals and liver for OCs. As expected, sediment PAH and OC concentrations and tissue OC concentrations were higher at sites east of the First Narrows, compared to the outer harbor and reference sites. Sediment PAH concentrations east of the First Narrows were similar to concentrations at moderately contaminated sites in Puget Sound, south of Vancouver Harbour. In contrast, concentrations of OCs in sediments and tissue were low to moderate, even at relatively contaminated sites within Vancouver Harbour. Although several trace metals in sediments were higher than in contaminated sediments from Puget Sound, trace metals measured in fish muscle were lower. 相似文献
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This article reports the first joint paleomagnetic and U-Pb geochronologic study of Precambrian diabase dikes in the Anabar Shield and adjacent Riphean cover of Siberia. It was undertaken to allow comparison with similar published studies in Laurentia and to test Proterozoic reconstructions of Siberia and Laurentia. An east-trending Kuonamka dike yielded a provisional U-Pb baddeleyite emplacement age of 1503+/-5 Ma and a virtual geomagnetic pole at 16 degrees S, 221 degrees E (dm=17&j0;, dp=10&j0;). A paleomagnetic pole at 6 degrees N, 234 degrees E (dm=28&j0;, dp=14&j0;) was obtained from five Kuonamka dikes. An east-southeast-trending Chieress dike yielded a U-Pb baddeleyite emplacement age of 1384+/-2 Ma and a virtual geomagnetic pole at 4 degrees N, 258 degrees E (dm=9&j0;, dp=5&j0;). Kuonamka and Chieress poles are interpreted to be primary but do not average out secular variation. Assuming that the Siberian Plate has remained intact since the Mesoproterozoic, except for mid-Paleozoic opening of the Viljuy Rift, then the above results indicate that the Siberian Plate was in low latitudes at ca. 1503 and 1384 Ma, broadly similar to low latitudes determined for Laurentia from well-dated paleopoles at 1460-1420, 1320-1290, and 1267 Ma. This would allow Laurentia and Siberia to have been attached in the Mesoproterozoic, as suggested in several recent studies based on geological criteria. However, because paleomagnetic results from the Anabar Shield region do not average out secular variation and the ages of poles from Siberia and Laurentia are not well matched, it is not yet possible to distinguish between these reconstructions or to rule out other configurations that also maintain the two cratons at low paleolatitudes. 相似文献
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地震中基岩走滑断层活动引起跨断层地下结构物破坏,上覆土层的非一致响应机制尚不明确,隐伏裂缝影响规律认识不足。基于可模拟走滑断层活动的层状剪切箱,针对黏土地层展开两个离心机振动台试验,对比上覆土体中隐伏裂缝的影响。试验结果表明,当地层中不存在隐伏裂缝时,基岩走滑断层错动对两盘地层的非一致振动的影响不显著。当地层中存在隐伏裂缝,错动盘一侧土体的振动加速度幅值随振动循环次数的增加逐渐减小,固定盘和错动盘两侧土体出现非一致振动响应,固定盘一侧土体产生的超静孔压大于错动盘一侧。隐伏裂缝对土体非一致振动响应的影响范围受限于其在地层中的分布范围,探明隐伏裂缝上断点的埋深具有重要工程意义。 相似文献
80.
地铁作为人口密集且遭受地震破坏后难以修复的重要生命线工程,如何确保其地震安全具有越来越重要的意义。本文将以北京具有典型意义的地铁线路北京地铁五号线作为研究目标,在对沿线地震、地质条件分析的基础上,通过分析研究在不同场地条件、不同风险水平和不同深度条件下的地震动参数和反应谱变化规律,确定了地铁工程的抗震设防概率风险水平为50 a超越概率63%、10%、2%,设计地震动参数取地表计算值。并通过北京地铁五号线工程地震小区划及分区反应谱特征研究,确定北京地铁五号线工程的抗震设防要求。 相似文献