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Many highway bridges were severely damaged or completely collapsed during the 2008 Wenchuan earthquake.A field investigation was carried out in the strongly affected areas and over 320 bridges were examined. Damage to some representative highway bridges is briefly described and a preliminary analysis of the probable causes of the damage is presented in this paper. The most common damage included shear-flexural failure of the pier columns, expansion joint failure, shear key failure, and girder sliding in the transversal or longitudinal directions due to weak connections between girder and bearings. Lessons learned from this earthquake are described and recommendations related to the design of curved and skewed bridges, design of bearings and devices to prevent girder collapse, and ductility of bridge piers are presented.Suggestions for future seismic design and retrofitting techniques for bridges in moderate to severe earthquake areas are also proposed. 相似文献
73.
系统分析了地下流体短期前兆异常变化与中强地震的关系,提出祁连山地震带地下流体资料存在两类短期前兆异常,即转折型和单一型短期前兆异常,结合震例对这两类短期前兆异常的特征进行了分析,认为预报人员应特别注意该区内的这两类群体异常的特点,并把它应用到该区的地震预报中。 相似文献
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根据野外考察、粒度分析及历史文献资料,研究了西安北郊草店村剖面在距今900~660 a形成的渭河漫滩沉积和洪水变化。结果表明,在距今900~660 a形成的草店村剖面洪水沉积分层明显,能够指示洪水事件和洪水深度。草店村剖面洪水沉积厚度为5.25 m,可划分为26个沉积层,指示了26次规模不同的洪水事件。洪水沉积厚度和粒度成分显示,草店村剖面的26个洪水事件发生时河漫滩上的洪水深度均大于2.2m;剖面下部第17~第26层沉积时漫滩上的洪水深度为4.0~7.0 m,河床水深为6.2~8.5 m;中部第8~第16层沉积时漫滩上的洪水深度为3.0~5.0 m,河床水深为6.6~9.0 m左右;上部第1~第7层沉积时漫滩上的洪水深度为2.2~3.0 m,河床水深为7.2~8.6 m。草店村剖面中部和下部的洪水沉积以中砂和细砂为主,剖面上部以粉砂和极细砂为主,指示的洪水规模比距今120 a来西安渭河洪水显著大。草店村剖面中的第12、16~26层代表的是特大洪水事件。西安北郊渭河在距今900~660 a发生的大洪水主要是由当年降水量的明显增加引起的。 相似文献
76.
The genetic variation and differentiation of the razor clam Sinonovacula constricts distributed along the coast of China were studied through amplified fragment length polymorphism(AFLP)analysis. Six primer combinations generated 193 fragments. The He values varied from 0. 322 to 0. 463 and the percentage of polymorphic loci ranged from 74. 1% to 98. 4%, which indicates a high level of genetic diversity. Cluster analysis by Nei's pairwise distance grouped all specimens by geographical origins. AMOVA consistently showed that genetic variation among populations was 8. 71%, and most of the variation came from the genetic variation within populations(91.29%). Genetic differentiation among the six populations was moderate; pairwise FST ranged from 0. 0282 to0. 1480, which indicated that S. Constricts populations along the coast of China are genetically connected. Among all the six populations, the Beihai population is the mostly differentiated from the others, suggesting that Hainan Island and Leizhou Peninsula act as barriers to gene flow. All populations abide isolation by distance model as indicated by Mantel test, except for ZS(Zhoushan)and YQ(Yueqing)populations. Information obtained in this study will provide guidelines for conservation and fishery management of this species in the future. 相似文献
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明晰集体土地产权,加快推进农村集体土地确权登记发证是当前国土资源管理中的一项重要任务。我国农村集体土地建设用地具有分布广、范围大、分散凌乱等特点,如果按照城镇地籍调查规程开展农村地籍调查,则面临着基础薄、任务重、投入高、时间紧等问题。为此,本文提出一套以高分辨率遥感影像为底图,快速绘制农村集体土地建设用地地块图形、并与实地丈量的边长、面积等属性数据关联、实现图属一体化管理的技术方法,并进行了精度评定试验。基于该技术开发了农村集体土地建设用地数据库建库工具和管理系统,实现了网络化农村集体土地建设用地管理,并在三个试点地区得到较好的应用。 相似文献
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ZHANG Xi GUO Kun ZHANG Yu LAI Zhiqing JIANG Shulong JIANG Wenpeng LI Jingbo 《《地质学报》英文版》2022,96(5):1587-1599
The Taiwan mountain belt, one of the youngest orogenies in the world, is caused by the collision of the Luzon arc with the Eurasian margin, which leads to post-collisional extension and magmatism in the Northern Taiwan Volcanic Zone (NTVZ). The magma chamber process in this region has not previously been elucidated in detail. In this paper, the textural and compositional features of plagioclase phenocrysts in basalt from the Tatun Volcanic Group (TTVG) were studied to restrict the dynamics of magma system. Results show that the magma melts in TTVG are mainly sourced from the underlying MORB-like mantle wedge but influenced by incorporation of subduction components, causing the elevated Sr/Y and Ba/Y ratios in magma melts. The subduction components are mainly transported in the form of sediment melt. The plagioclase phenocrysts in the TTVG volcanic rocks are generally coarsely core-sieved with a clear rim. The An contents in the rims of plagioclase are much lower than those of cores, and elevated FeO concentrations are detected in the plagioclase rims. We propose there exists a double-layer magma chamber in this region. The core of the plagioclase was crystalized in the deeper quiescent magma chamber (~21 km), which was subsequently partially dissolved during the ascent of magma melt under H2O-undersaturated condition, forming the typical coarsely sieved texture and synneusis. When this crystal-rich melt migrates into the shallower chamber, water saturation is reached and more sodic plagioclase formed as the rim of phenocryst. Due to the considerably higher fO2 in the shallow chamber than in the deeper one, and the distribution of Fe between plagioclase and melt positively correlates with fO2, the FeO content in the plagioclase rim elevates in conjunction with increasing fO2. 相似文献