Paleoenvironmental implications of magnetic measurements on sediment core from Kunming Basin,Southwest China

Mineral magnetic measurements have been made on a long sediment core from Dianchi Lake, Southwest China. They have been used for sediment stratigraphy, for bulk lithological classification and for detailed particle-size-based characterisation. These results are set alongside those derived from geochemical, granulometric and pollen analysis to reconstruct the environmental processes recorded in the radiocarbon dated sediment column. It is suggested that the variations of magnetic properties in this sediment core are mainly the result of changes in particle size constitution or organic content, implying shifts in the sedimentary environment. Three distinctive stratigraphic horizons, with several subdivisions, have been identified on the basis of the magnetic measurements. They are coincident with the pollen assemblage zones, indicating the different climatic periods in the Kunming Basin since late Pleistocene times. This paper proposes that a major shift in sedimentation, from lake to reedswamp, occurred in approximately 10 000–12 000 BP, in response to climatic change.     

近断层地震作用下RC框排架结构易损性研究

为研究近断层地震作用下框排架结构破坏的可能性,以某钢筋混凝土框排架结构为原型建立有限元非线性分析模型,选取16条近断层地震波及8条远场地震波,采用增量动力分析方法绘制易损性曲线。结果表明:对于远场地震,8度多遇地震及基本地震时,结构正常使用、基本使用、修复后使用、生命安全及防止倒塌五个极限状态均未超越,满足“小震不坏,中震可修”的抗震要求;8度罕遇地震时,仅超越正常使用极限状态的概率为2.08%,满足“大震不倒”的抗震要求。而近断层地震时,在8度多遇地震时结构前四个极限状态均被超越,基本地震时结构超过修复后使用的极限状态概率为16.62%,有2.40%的概率达到生命安全的极限状态,罕遇地震时接近倒塌的概率为15\^4%。研究结果可为近断层地区框排架结构地震风险评估提供参考。