地磁低点时间与经度的相关性分析

地磁低点时间在空间分布上的主要特征是随着经度变化而变化。为了求出这种变化关系的解析式,首先使用国家地磁台网的数据计算甘肃省近三年13个地磁台站的低点时间序列和低点时间的期望,并绘制了低点时间序列的频次分布图和概率密度曲线;然后对低点时间与台站经度的关系做线性回归,并指出这个线性回归方程应无限趋近于“格林尼治时间-经度”关系式。文章第一次提出台站经度与地磁Z分量低点时间的关系式,并提出它的趋近方程。各台站低点时间的期望就是地磁低点时间的正常背景值,它是判定地磁低点时间异常与否的参考标准。本文的工作完善和发展了丁鉴海先生的地磁低点位移法。     

大跨度主-副桁架钢结构的地震反应探讨分析

桁架钢结构被广泛应用于大跨度建筑中,分析桁架钢结构的地震反应具有一定的现实意义。构建大跨度主-副桁架钢结构的有限元模型,以该模型作为研究对象,对其进行地震反应的探讨分析。采用自振特性分析方法在刚度和质量两个因素的基础上分析大跨度主-副桁架钢结构的自振特性;通过振型分解反应谱法分析大跨度主-副桁架钢结构的力学性能,利用桁架钢结构的力学性能分析其地震作用下的反应。模拟发现,大跨度主-副桁架钢结构刚度较好,其抗风柱柱脚连接处的受力最强且位移最大,为大跨度主-副桁架钢结构的地震反应研究提供参考,为其抗震设计提供初步依据。     

首都圈东部地区震群序列性质判定

采用传统方法和数字地震学方法（视应力）,对首都圈东部地区2009-2017年发生的震群序列性质进行分析,分析结果表明：①使用传统方法不能确定震群序列性质,可以利用视应力方法进一步分析,该方法能够反映每个震群应力场的变化特征,可以进行异常性质判别;②通过2种方法的对比分析,可以提高震群序列异常性质判定结果的科学性和可信度,为后续地震活动趋势提供有力的参考依据。对2种方法进行震例检验,可知后续地震一般为中等以上地震,在震群（具有异常性质）发生1-7个月后发震,发震位置在震源区附近。     

2017年九寨沟MS 7.0地震震源深度测定

为了更好地确定2017年8月8日九寨沟M_(S )7.0地震震源深度其发震机理,利用四川、甘肃和青海区域地震台网的观测波形数据,采用多种方法研究了此次地震的震源深度。首先,采用gCAP方法反演了九寨沟M_(S )7.0地震的震源机制解和矩心深度,结果显示,节面Ⅰ走向243°/倾角87°/滑动角-158°,节面Ⅱ走向151°/倾角68°/滑动角-3°,矩震级为M_(W )6.5,矩心深度为8 km;然后,采用ISOLA近震全波形方法反演了此次地震的震源机制解,反演结果与gCAP方法结果相差不大,矩心深度为7 km;最后,通过sPn震相与Pn震相之间的走时差测定此次地震初始破裂震源深度,结果显示深度约为12 km。研究表明,九寨沟M_(S )7.0地震的矩心深度为7—8 km,初始破裂深度约为12 km。     

地震活动性总体参量Rt在北京及邻区地震预测中的应用

采用地震活动性总体参量R_t方法,研究北京及邻区R_t值在中等地震前随时间的变化特征,分析跟踪地震发生前研究区域地震活动状态,探讨中等地震孕震过程的异常信息的变化特征。结果显示:当R_t值大于阈值0.84时,研究区域地震活动状态比较稳定,发生中等地震的可能性较小;反之,表明地震活动处于不稳定状态,具有发生中等地震的危险。检验R_t值的地震预测效能,预测效果比较理想,利用地震活动状态参量R_t研究北京及邻区地震活动状态,判定中等地震发生的风险性,具有一定预测意义。     

残余位移反应谱的参数影响研究

从PEER强震数据库中选取4类场地的320条地震动记录作为输入,采用BISPEC程序对非线性单自由度（SDOF）体系（周期T=0.05—5s）进行非线性时程分析,得到相应的残余位移反应谱（Dres）,进而研究地震动特性和恢复力模型动力参数对Dres的影响,得到如下结论:①Dres谱值随震级和PGA的增加而增大;其他设防烈度的Dres可由PGA_其他与PGA_基准之比调整基准烈度的Dres得到。②场地土较硬时,场地类型对Dres的影响较小;场地土较软时,Dres谱值随土质的变软而增大。③当位移延性比μ较小时,屈服后刚度比η对Dres的影响可忽略;但当μ较大时,Dres谱值随η的增加而减小。另外,Dres谱值还随阻尼比ξ的增加而减小。④随着T或μ的增大,Dres谱值均呈递增趋势;但当μ>3后,μ对Dres谱值的影响有所下降。     

离散Fréchet距离在强震台站场地分类中的应用

当强震台站场地资料不完整时,所收集到的强震数据因缺乏准确的场地类别信息而难以有效利用。为解决这一问题,本文提出一种基于离散Fréchet距离的强震台站场地分类方法。将获取到的664个KiK-net台站场地按照《建筑抗震设计规范（GB 50011—2010）》进行分类,并构建2个数据集。利用数据集1得到Ⅰ、Ⅱ、Ⅲ类场地标准谱比曲线,并结合离散Fréchet距离对数据集2中的台站进行场地分类,统计分类成功率与误判率。统计结果表明,本文方法能较准确地对场地进行分类,且误判率在可接受范围内。将本文方法分类统计结果与斯皮尔曼秩相关系数法分类的成功率与误判率进行对比,结合本文方法分类后得到的平均谱比曲线,均可表明应用本文方法进行强震台站场地分类具有合理性。     

Cyclical one-way continental rupture-drift in the Tethyan evolution: Subduction-driven plate tectonics

Numerous continents have rifted and drifted away from Gondwana to repeatedly open ocean basins over the past-500 millionyears.These Gondwana-derived continents drifted towards and collided with components of the Eurasian continent to successively close the preexisting oceans between the two.Plate tectonics satisfactorily describes the continental drift from Gondwana to Eurasia but does not define the geodynamic mechanism of continuously rifting to collisions of continents in the Tethy an Realm.After reappraisal of geological records of the rift,collision and subduction initiation from the surface and various geophysical observations from depth,we propose that Eurasia-directed subducting oceanic slabs would have driven Tethyan system in the Phanerozoic.The Eurasia-directed subduction would have dragged the passive Gondwana margin to rift and drift northwards,giving birth to new oceans since the Paleozoic.The closure of preexisting oceans between the Gondwana-derived continents and Eurasia led to continental collisions,which would have induced the initiation of oceanic subduction in the Tethyan Realm.Multiple episodic switches between collision-subduction-rift repeatedly led to the separation of continental fragments from Gondwana and dragged them to drift towards Eurasia.The final disappearance of Neo-Tethy s would have induced collision of the Gondwana-derived continents with the Eurasian continent,giving rise to the Cenozoic Alpine-Zagros-Himalayan collisional system.Therefore,the Eurasia-directed oceanic subduction would have acted as a 'one-way train' that successively transferred the ruptured Gondwana continental fragments in the south,into the terminal in the north.In this regard,the engine of this "Tethyan one-way train" is the negative buoyancy of subducting oceanic slabs.     

Quantitative simulation and verification of upgrade law of sustainable development in Beijing-Tianjin-Hebei urban agglomeration

The natural formation and development of urban agglomerations is a process in which core cities continue to unite their neighboring cities to enhance sustainability for their own sustainable development.The upgrade mechanism of sustainable development urban agglomeration is a nonlinear composite upgrade curve that is a function of time,increasing with the number of cities.In this paper,the sustainable upgrade function curve,upgrade rate,and upgrade speed of urban agglomerations were solved using a geometrical derivation,and the index system for measuring the upgrade capability of sustainable development of urban agglomerations was established.The dynamic change in economic sustainable upgrade capability,social sustainable upgrade capability,environmental sustainable upgrade capability,and comprehensive sustainable upgrade capability of a Beijing-Tianjin-Hebei urban agglomeration from 2000 to 2015 was measured by technique for order preference by similarity to an ideal solution and a grey correlation method,and a comprehensive,intercity unite strength model and a unite threshold calculation method for urban agglomerations were established.The research shows that the economic sustainable upgrade capability,social sustainable upgrade capability,environmental sustainable upgrade capability,and comprehensive sustainable upgrade capability of the Beijing-Tianjin-Hebei urban agglomeration all show a wave-like rising trend.The average annual upgrade speeds during 2000-2015 are,respectively,2.4%.1.67%,1.1%,and 1.74%,with the intercity comprehensive unite strength of urban agglomerations maintaining a general increase;but there is a limit to the joint threshold.From 2000 to 2015,as the core city of the Beijing-Tianjin-Hebei urban agglomeration,Beijing,to enhance its sustainable upgrade capability,jointly developed with Tianjin,Langfang,and Baoding before 2000,Tangshan in 2002,Cangzhou in 2009,Zhangjiakou and Shijiazhuang in 2012,and Chengde in 2014.By 2015,the comprehensive unite strength between Beijing and four cities(Handan,Qinhuangdao,Hengshui,and Xingtai) was still lower than the unite threshold of 6.14.These four cities are relatively far from Beijing,and offer no substantial contribution to the sustainable upgrade capability of Beijing.Through multiple fittings of the upgrade curve using the long-term sequence index of the comprehensive sustainable upgrade capability of Beijing(the core city of the Beijing-Tianjin-Hebei urban agglomeration) from 2000 to 2015,it was found that the simulated curve of the comprehensive sustainable upgrade function of the agglomeration was very similar to the curve of the comprehensive sustainable upgrade capability,which indicates that the simulation results are satisfactory.The future comprehensive sustainable upgrade capability of the agglomeration can be analyzed and predicted by the comprehensive sustainable upgrade function model.This study provides quantitative decision-supporting evidence for promoting the coordinated development of the Beijing-TianjinHebei urban agglomeration and provides theoretical guidance and algorithms for determining the number of cities joined with the sustainable development of national urban agglomerations.     

Tropical cyclones and multiscale climate variability: The active western North Pacific Typhoon season of 2018

The 2018 typhoon season in the western North Pacific(WNP) was highly active, with 26 named tropical cyclones(TCs) from June to November, which exceeded the climatological mean(22) and was the second busiest season over the past twenty years. More TCs formed in the eastern region of the WNP and the northern region of the South China Sea(SCS). More TCs took the northeast quadrant in the WNP, recurving from northwestward to northward and causing heavy damages in China's Mainland(69.73 billion yuan) in 2018. Multiscale climate variability is conducive to an active season via an enhanced monsoon trough and a weakened subtropical high in the WNP. The large-scale backgrounds in 2018 showed a favorable environment for TCs established by a developing central Pacific(CP) El Ni?o and positive Pacific meridional mode(PMM)episode on interannual timescales. The tropical central Pacific(TCP) SST forcing exhibits primary control on TCs in the WNP and large-scale circulations, which are insensitive to the PMM. During CP El Ni?o years, anomalous convection associated with the TCP warming leads to significantly increased anomalous cyclonic circulation in the WNP because of a Gill-type Rossby wave response. As a result, the weakened subtropical high and enhanced monsoon trough shift eastward and northward, which favor TC genesis and development. Although such increased TC activity in 2018 might be slightly suppressed by interdecadal climate variability, it was mostly attributed to the favorable interannual background. In addition, high-frequency climate signals,such as intraseasonal oscillations(ISOs) and synoptic-scale disturbances(SSDs), interacted with the enhanced monsoon trough and strongly modulated regional TC genesis and development in 2018.