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991.
The 2008 MS8 Wenchuan earthquake occurs on a high angle listric thrust fault. It is the first time that the near and far field strong ground motion was observed for such special type thrust earthquake. This paper jointly interprets the distribution of peak acceleration of ground motion data with seismogenic structure and slip propagating process to investigate how high angle listric thrust fault controls the pattern of strong ground motion. We found that the distribution of peak acceleration of strong ground motion during the Wenchuan earthquake has four distinctive features: 1)The peak acceleration of ground motion inside the Longmenshan fault zone is large, that is, nearly twice as strong as that outside the fault zone; 2)This earthquake produces significant vertical ground motion, prevailing against horizontal components in the near field; 3)The far field records show that the peak acceleration is generally higher and attenuates slower versus station-fault distance in the hanging wall. It is doubtful that the attenuation of horizontal components also has the hanging wall effect since no evidence yet proving that the unexpected high value at long distance need be omitted; 4)As to the attenuation in directions parallel to the source fault(Yingxiu-Beichuan Fault), the far field records also exhibit azimuthal heterogeneity that the peak acceleration of horizontal components decreases slower in the north-northeastern direction in which the co-seismic slip propagates than that in the backward way. However, the attenuation of vertical component displays very weak heterogeneity of this kind. Synthetically considered with shallow dislocation, high dip angle, and prevailing vertical deformation during co-seismic process of the Wenchuan earthquake, our near and far field ground motion records reflect the truth that the magnitude of ground motion is principally determined by slip type of earthquake and actual distance between the slipping source patches and stations. As a further interpretation, the uniqueness of high angle listric thrust results in that the ground motion effects of the Wenchuan earthquake are similar to that due to a common thrust earthquake in some components while differ in the others. 相似文献
992.
Seismic demand on light acceleration‐sensitive nonstructural components in European reinforced concrete buildings 下载免费PDF全文
In this paper, a parametric study is conducted in order to evaluate the seismic demand on light acceleration‐sensitive nonstructural components caused by frequent earthquakes. The study is motivated by the inconsistent approach of current building codes to the design of nonstructural components; the extensive nonstructural damage recorded after recent low‐intensity earthquakes also encouraged such a study. A set of reinforced concrete frame structures with different number of stories, that is, 1 to 10 stories, are selected and designed according to Eurocode 8. The structures are subjected to a set of frequent earthquakes, that is, 63% probability of exceedance in 50 years. Dynamic nonlinear analyses are performed on the reference structures in order to assess the accuracy of the equations to predict seismic forces acting on nonstructural components and systems in Eurocode. It is concluded that the Eurocode equations underestimate the acceleration demand on nonstructural components for a wide range of periods, especially in the vicinity of the higher mode periods of vibration of the reference structures; for periods sufficiently larger than the fundamental period of the structure, instead, the Eurocode formulation gives a good approximation of the floor spectra. Finally, a novel formulation is proposed for an easy implementation in future building codes based on the actual Eurocode provisions. The proposed formulation gives a good estimation of the floor spectral accelerations and is able to envelope the floor spectral peaks owing to the higher modes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
993.
2016年2月,武汉大学卫星导航定位技术研究中心(Wuhan University,WHU)正式成为新的国际GNSS服务组织(International GNSS Services,IGS)电离层联合分析中心(Ionosphere Associate Analysis Center,IAAC).本文首次系统地评估和分析了武汉大学IGS电离层分析中心自2016年日常化运行以来(2016年1月到2018年9月,太阳活动低年)的全球电离层产品的精度,并与其他六家IAACs(CODE、JPL、ESA、UPC、EMR和CAS)进行了比较分析.结果表明:WHU的全球电离层产品能够长期稳定且有效地监测全球电离层总电子含量(Total Electron Content,TEC)的时空变化;和IGS综合全球电离层产品比较,WHU的模型均方根误差和CODE、JPL相差不大,均值约为1.4 TECU,产品一致性优于其他IAACs;和GPS实测电离层TEC比较,WHU的模型内符合精度和CODE基本相当,均值约为1.4 TECU,且与电离层活动水平和地理纬度存在显著的相关性;和Jason-2测高卫星VTEC比较,WHU的全球电离层产品的系统性偏差均值约为-0.7 TECU,在不同纬度约为-3.0到1.0 TECU,且与地理纬度存在近似抛物线函数的关系;WHU的模型外符合精度和CODE、JPL以及CAS基本一致,均值约为2.9 TECU,且在中高纬度地区优于低纬度地区,北半球优于南半球.
相似文献994.
The seismological model was developed initially from the fundamental relationship between earthquake ground motion properties and the seismic moment generated at the source of the earthquake. Following two decades of continuous seismological research in the United States, seismological models which realistically account for both the source and path effects on the seismic shear waves have been developed and their accuracy rigorously verified (particularly in the long and medium period ranges). An important finding from the seismological research by Atkinson and Boore and their co‐investigators is the similarity of the average frequency characteristics of seismic waves generated at the source between the seemingly very different seismic environments of Eastern and Western North America (ENA and WNA, respectively). A generic definition of the average source properties of earthquakes has therefore been postulated, referred to herein as the generic source model. Further, the generic ‘hard rock’ crustal model which is characteristic of ENA and the generic ‘rock’ crustal model characteristic of WNA have been developed to combine with the generic source model, hence enabling simulations to be made of the important path‐related modifications to ground motions arising from different types of crustal rock materials. It has been found that the anelastic contribution to whole path attenuation is consistent between the ENA and WNA models, for earthquake ground motions (response spectral velocities and displacements) in the near and medium fields, indicating that differences in the ENA and WNA motions arise principally from the other forms of path‐related modifications, namely the mid‐crust amplification and the combined effect of the upper‐crust amplification and attenuation, both of which are significant only for the generic WNA ‘rock’ earthquake ground motions. This paper aims to demonstrate the effective utilization of the latest seismological model, comprising the generic source and crustal models, to develop a response spectral attenuation model for direct engineering applications. The developed attenuation model also comprises a source factor and several crustal (wave‐path modification) component factors, and thus has also been termed herein the component attenuation model (CAM). Generic attenuation relationships in CAM, which embrace both ENA and WNA conditions, have been developed using stochastic simulations. The crustal classification of a region outside North America can be based upon regional seismological and geological information. CAM is particularly useful for areas where local strong motion data are lacking for satisfactory empirical modelling. In the companion paper entitled ‘response spectrum modelling for rock sites in low and moderate seismicity regions combining velocity, displacement and acceleration predictions’, the CAM procedure has been incorporated into a response spectrum model which can be used to effectively define the seismic hazard of bedrock sites in low and moderate seismicity regions. This paper and the companion paper constitute the basis of a long‐term objective of the authors, to develop and effectively utilize the seismological model for engineering applications worldwide. 相似文献
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本文尝试利用COSMIC低轨卫星对GPS信号的顶部TEC观测资料研究等离子体层电子含量(简称PEC)的变化规律.首先介绍从低轨卫星对GPS的顶部TEC观测资料提取等离子体层垂直电子含量的方法,然后利用该方法提取2008年全年的PEC数据,进而研究了2008年这一太阳活动低年PEC随地磁纬度(MLAT)、磁地方时(MLT)以及不同季节的变化规律.此外,还利用提取的120°E和300°E经度链上的数据对比研究了PEC的经度变化情形.研究结果表明:(1)PEC主要集中分布在磁赤道±45°之间的一个绕地球的环带状区域中;(2)PEC表现出以下的昼夜变化规律特征:白天时段之值高于夜间,约在12-16MLT之间达到最高峰值,而最小PEC值出现在日出前大约4-5MLT左右的时段;(3)相比其他季节月份而言,PEC在北半球夏季月份(5-8月)具有最小值;(4)PEC存在明显的经度变化,不同经度链上的PEC存在不同的季节变化特征. 相似文献
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(陈培善,肖磊,白彤霞,王溪莉)Theenvironmentshearstressfieldforthe1976Tangshanearthquakesequence¥Pei-ShanCHEN;LeiXIAO;Tong-XiaBAIandXi-LiWA... 相似文献