强震临震微波动现象跟踪试验研究

强震临震微波动是强震临震阶段优势频率集中在11~16 Hz、频谱形态较为整齐的临震异常脉动记录,在汶川、玉树、青川等不同强震前有重现,可用于强震临震判定。为了对强震临震微波动现象进行跟踪检验,利用"兰州地脉动实时监控技术系统"分析2015—2016年间发生在青藏块体和新疆的4次5.5级以上地震震前3个月地脉动连续记录,通过临震微波动事件活动度异常幅度变化和持续时间验证临震微波动现象的重现性,跟踪检验结果符合杨立明等基于临震微波动提炼的震情跟踪指标。     

近场地震下竖向刚度不同的混合结构动力性能分析

近场地震的动力特性明显不同于远场地震,因此有必要对结构在近场地震作用下的动力性能展开研究。以上部钢结构-下部混凝土结构这类竖向刚度不同的加层混合结构为研究对象,对其在近场脉冲型地震、近场无脉冲型地震及远场地震作用下的动力响应进行研究。结果表明:在多遇、设防、罕遇地震作用下,近场脉冲型地震会使结构的层间位移角、层间剪力、加速度等动力响应均放大并出现超限的情况,而且都比罕遇地震作用下结构的响应增大更明显;在进行近场区加层混合框架结构的设计和建设时,近场脉冲效应会使结构存在不满足规范的情况,有必要对竖向刚度不同的加层混合结构在近场区的适用性进行深入研究。     

Subduction-zone peridotites and their records of crust-mantle interaction

Subduction is the core process of plate tectonics. The mantle wedge in subduction-zone systems represents a key tectonic unit, playing a significant role in material cycling and energy exchange between Earth's layers. This study summarizes research progresses in terms of subduction-related peridotite massifs, including supra-subduction zone(SSZ) ophiolites and mantle-wedge-type(MWT) orogenic peridotites. We also provide the relevant key scientific questions that need be solved in the future. The mantle sections of SSZ ophiolites and MWT orogenic peridotites represent the mantle fragments from oceanic and continental lithosphere in subduction zones, respectively. They are essential targets to study the crust-mantle interaction in subduction zones. The nature of this interaction is the complex chemical exchanges between the subducting slab and the mantle wedge under the major control of physical processes. The SSZ ophiolites can record melt/fluid-rock interaction, metamorphism,deformation, concentration of metallogenic elements and material exchange between crust and mantle, during the stages from the generation of oceanic lithosphere at spreading centers to the initiation, development, maturation and ending of oceanic subduction at continental margins. The MWT orogenic peridotites reveal the history of strong metamorphism and deformation during subduction, the multiple melt/fluid metasomatism(including silicatic melts, carbonatitic melts and silicate-bearing C-HO fluids/supercritical fluids), and the complex cycling of crust-mantle materials, during the subduction/collision and exhumation of continental plates. In order to further reveal the crust-mantle interaction using subduction-zone peridotites, it is necessary to utilize high-spatial-resolution and high-precision techniques to constrain the complex chemical metasomatism, metamorphism,deformation at micro scales, and to reveal their connections with spatial-temporal evolution in macro-scale tectonics.     

基于等效源的总强度磁异常非线性处理方法

总强度磁异常(ΔT1)常规处理方法通常将其近似当作磁异常矢量在地磁正常场方向上的投影(ΔT2).然而对于高磁环境如磁铁矿处的磁异常场幅值可达104 nT甚至更大的情况,上述近似假设则不再成立,如采用常规处理方法可能会带来明显的误差.本文针对该问题,提出一种基于等效源的总强度磁异常非线性处理方法;该方法根据总强度磁异常获取流程,直接反演实测地磁场总强度幅值与正常场强度幅值之差来求取等效场源.本文首先通过模型试验,分析ΔT1与ΔT2的差异;然后将ΔT1当作ΔT2采用常规处理方法以及ΔT1采用新方法得到的结果作对比分析,结果表明新方法处理结果与理论值的差异为常规方法处理结果的1/5甚至更小,充分说明了新方法的有效性;最后将该方法应用于铁矿实测总强度磁异常处理实例中来转换计算磁异常总模量,其实际应用效果进一步体现了高幅值总强度磁异常数据处理过程中采用新方法的必要性.     

行星际磁场B_y对弓激波影响的MHD结果

利用全球磁流体模拟的结果,本文研究了行星际磁场B_y对弓激波位型的影响.结果显示:随着行星际磁场B_y绝对值的增大,弓激波的日下点距离、旋转对称张角、南北非对称性以及旋转非对称性均随之增加.其中,B_y对弓激波日下点距离的影响可达5 RE左右.东向B_y和西向B_y对弓激波位型影响具有对称性,东向B_y和西向B_y大小相同时弓激波日下点距离、旋转对称张角以及旋转非对称性参数均相同,而南北非对称性参数大小相同正负相反.行星际磁场B_y占主导时弓激波尾部横截面在南北方向上拉伸,并且拉伸程度随着B_y绝对值的增大而增大,弓激波尾部横截面的拉伸现象与磁声波马赫数密切相关.     

扩孔螺栓连接型消能梁段的力学模型及参数研究

当前国家对建筑结构的抗震性能和震后功能恢复能力提出了更高要求。基于短剪切型消能梁段的受剪屈服特性和剪切扩孔型螺栓连接的受剪滑移性能,提出一种新型扩孔螺栓连接型消能梁段,可有效增大消能梁段的延性和耗能能力并同时减小消能梁段的损伤,使带扩孔螺栓连接型消能梁段的新型Y形偏心支撑结构更好地适应当前要求。采用有限元方法详细分析扩孔螺栓连接型消能梁段的滞回性能、破坏模式和耗能机理,由此得到其骨架曲线和力学模型,并阐述其力学模型的影响参数,为相应偏心支撑结构的设计和分析提供理论依据。     

Dynamic amplification factors for a system with multiple-degrees-of-freedom

It is well-known that the responses of a structure are different when subjected to a static load or a sudden step load. The dynamic amplification factor (DAF), which is defined as the ratio of the amplitude of the vibratory response to the static response, is normally used to depict the dynamic effect. For a single-degree-of-freedom system (SDOF) subjected to a sudden dynamic load, the maximum value of DAF is 2. Many design guidelines therefore use 2 as an upper bound to consider the dynamic effect. For a civil engineering structure, which is normally a multiple-degrees-of-freedom (MDOF) system, the DAF may exceed 2 in certain circumstances. The adoption of 2 as the upper bond as suggested by the design guidelines therefore may lead to unsafe structural design. Very limited studies systematically investigate the DAF of a MDOF system. This study theoretically investigates the DAF of a MDOF system when it is subjected to a step load based on the fundamental theory of structural dynamics. The condition on which the DAF may exceed 2 is defined. Two numerical examples and one experimental study of a cable-stayed bridge subjected to sudden cable loss are presented to illustrate the problem.     

Ground motion duration effect on responses of hydraulic shallow-buried tunnel under SV-waves excitations

Although intensive research of the influence of ground motion duration on structural cumulative damage has been carried out, the influence of dynamic responses in underground tunnels remains a heated debate. This study attempts to highlight the importance of the ground motion duration effect on hydraulic tunnels subjected to deep-focus earthquakes. In the study, a set of 18 recorded accelerograms with a wide-range of durations were employed. A spectrally equivalent method serves to distinguish the effect of duration from other ground motion features, and then the seismic input model was simulated using SV-wave excitation based on a viscous-spring boundary, which was verified by the time-domain waves analysis method. The nonlinear analysis results demonstrate that the risk of collapse of the hydraulic tunnel is higher under long-duration ground motion than that of short-duration ground motion of the same seismic intensity. In a low intensity earthquake, the ground motion duration has little effect on the damage energy consumption of a hydraulic tunnel lining, but in a high intensity earthquake, dissipation of the damage energy and damage index of concrete shows a nonlinear growth trend accompanied by the increase of ground motion duration, which has a great influence on the deformation and stress of hydraulic tunnels, and correlation analysis shows that the correlation coefficient is greater than 0.8. Therefore, the duration of ground motion should be taken into consideration except for its intensity and frequency content in the design of hydraulic tunnel, and evaluation of seismic risk.

     

Modeling the westward transversal current in the southern Yellow Sea entrance: a case study in winter 2007

Ocean Dynamics - The westward transversal current (TC) in the southern Yellow Sea entrance was investigated during winter 2007 using a numerical ocean model. The three-dimensional structures and...