2008年汶川大地震单侧破裂过程的动力学机制研究

2008年汶川大地震的破裂过程极其发杂,向东北方向的破裂距离长达300 km,而向西南方向的破裂长度很小,呈现出单侧破裂的主要特征.尽管汶川地震破裂呈单侧传播的现象引起许多地震学家的关注,但其物理机制至今还不是十分清楚.本文利用有限单元计算方法,模拟了汶川地震的破裂过程.模型中根据龙门山断裂带两侧（东南侧为四川盆地,西北侧为川西高原）实际的地震波速度来确定模型的介质物性参数,利用目前观测的应力环境来选定初始应力条件.模拟结果表明：破裂在汶川地震的震中处成核后,先向断层两侧自发传播,但向东北方向的传播距离明显大于向西南方向;断层面上的正应力在东北方向（破裂的正方向）随着传播距离的增大而不断减小,位错速率随着破裂的传播距离而越来越大,其脉冲变得越来越尖锐,即产生了Weertman脉冲.研究结果显示：由于这种脉冲的出现,破裂在正方向上（东北方向）能够自己放大、自己愈合、自行维持,摩擦热极小,所以破裂能够沿着东北方向一直传播,直到应力场方位发生变化,不利于破裂时才最后终止.但在西南方向,破裂过程中断层面上的正应力增大,阻碍破裂继续扩展.最后就出现了汶川地震中破裂朝东北方向单侧优势传播的基本格局.模拟结果还表明：若断层面两侧介质均匀,则破裂向两侧是对称传播,且破裂距离很短,因此这种情况无法产生像汶川大地震那样的特大地震.因此,文中的模拟结果表明龙门山断裂带两侧的物性差异是造成汶川大地震单侧传播的决定性因素.断层两侧物性差异（bimaterial contrast）影响断层破裂过程的研究对于深入认识地震动力学过程、地震灾害预测及评估等有重要的科学意义.     

A pseudo-coupled analytic fluid-structure interaction method for underwater implosion of cylindrical shells

Underwater implosion, the rapid collapse of a structure caused by hydrostatic pressure, is a fully coupled, highly dynamic and nonlinear fluid-structure interaction (FSI) problem. The primary motivation behind studying implosion is the short-duration, high-pressure pulse generated in the surrounding water. This paper presents a simplified analytic method to estimate the energy in the pressure pulse, based on potential flow theory. The method accounts for the varying fluid pressure and accompanying FSI. The focus is on long, thin, unstiffened metallic cylindrical shells that collapse in mode 2. The implosion pulse energy is shown to be equal to the maximum system kinetic energy developed during collapse. The kinetic energy is calculated using an energy balance approach and analytic solutions for plastic energy dissipation and energy required to compress the internal air. The time-varying fluid pressure, and subsequently the work done by the fluid on the cylinder, is found using a novel explicit time-stepping methodology. The result is a pseudo-coupled analytic solution for the fluid pressure time history and implosion pulse energy. Solutions for pulse energy agree with RANS numerical simulations within 5%.     

VLF/LF signal studies of the ionospheric response to strong seismic activity in the Far Eastern region combining the DEMETER and ground-based observations

The paper presents the results of a joint analysis of ground-based and satellite observations of very low-frequency and low-frequency (VLF/LF) signals during periods of strong seismic activity in the region of Kuril Islands and Japan in 2004–2010. Ground and satellite data was processed using a method based on the difference between the real signal in nighttime and that of a model. The results of the analysis show a good correlation between ground-based and satellite data for several cases of strong (M ⩾ 6.8) earthquakes.     

A model of the generation of electromagnetic emissions detected prior to earthquakes

Recent satellite and ground-based observations prove that during the formative period of earthquakes VLF/LF and ULF electromagnetic emissions are observed in seismogenic areas. This work offers an original model of self-generated electromagnetic oscillations of local segments of the lithospheric origins of the emissions. In the paper, the seismogenic area is considered to be an oscillatory-distributed system. This model simplifies physical analyses of the nonlinear effects and qualitatively explains the mechanisms that generate very low frequency electromagnetic waves in the period prior to an earthquake.     

电磁干扰对自动气象站的影响及防范措施

一般说来电磁干扰源分为两大类：自然干扰源和人为干扰源,不管那一种电磁干扰都可能会对自动气象站设备造成影响,甚至使自动气象设备发生故障。本文根据气象站实际使用中出现的情况,分析了产生电磁干扰的来源,提出了抑制电磁干扰的具体防范措施。     

Orientation and nature of active crustal stresses determined by electromagnetic measurements in the Patagonian segment of the South America Plate

Based on electromagnetic measurements we determined the current stress directions in the uppermost continental crust of Patagonia between the active plate margin of the Chilean Pacific coast and the Argentinean passive Atlantic margin. Regional variations of the observed stress pattern are giving details onto the acting tectonic processes. We distinguish five regional stress domains with different prevailing horizontal stress directions (S_H): 1. Southern Coastal Cordillera and Longitudinal Valley (S_H = SSW–NNE), 2. Chiloé Island (S_H = SW–NE), 3. Northern Patagonian Andes (S_H = WSW–ENE), 4. Argentinean Pampa and Atlantic margin (S_H = WNW–ESE) and 5. Southern Patagonian Andes (S_H = WNW–ESE). These stress regimes can be related to the geometry of the subducting Nazca- and Antarctic plates, to the transform fault between the South America and Scotia plates and to passive margin processes along the Atlantic coast. Absolute plate motion and rapid relative plate convergence control the subduction geometry and therefore the stress directions along the convergent margin of the South America Plate and the structural style within and landward of the Magmatic Arc. The knowledge of current local stress directions permits the characterisation of potential fault kinematics. By in situ measuring of electromagnetic emissions from rocks we determined the maximum horizontal stress orientation in the uppermost crust using a new geophysical tool. Our investigations on the orientation of the stress regimes also allow conclusions about the causative forces of either tectonic or gravitational origin in this part of the South-America Plate.     

基于线性放电法的多道脉冲幅度分析器设计

多道伽马能谱仪是天然、人工放射性核素测定的必备设备,多道脉冲幅度分析是多道伽马能谱仪的核心,它决定了对核素的分辨能力和分析精度.本文从线性放电法入手,首先介绍了基于线性放电法的多道脉冲幅度分析器的工作原理,给出了分析脉冲幅度和获取能谱道址的方法;其次围绕分析器的8个重要组成部分,详细描述了设计方法,给出了设计依据、设计...     

EMIC waves around the plasma-pause region

Electromagnetic ion-cyclotron (EMIC) instability has been studied using the general loss-cone distribution function by investigating the trajectories of charged particles and using the method of particle aspect analysis. A low β (ratio of plasma pressure to magnetic pressure) plasma consisting of resonant and non-resonant particles has been considered. It is assumed that the resonant particles participate in energy exchange with the wave, whereas non-resonant particles support the oscillatory motion of the wave. The wave is assumed to propagate parallel to the static magnetic field. The effects of steepness of loss-cone distribution with thermal anisotropy are discussed. The growth rate, perpendicular and parallel resonant energies of the particles and marginal instability condition are derived. The effect of general loss-cone distribution function is to enhance the growth rate of EMIC waves. The results are interpreted for the space plasma parameters appropriate to the plasma-pause region of the earth's magnetoplasma. The results of the work is consistent for EMIC emissions observation by SAMPEX and CRRES satellite around the plasma-pause region as reported by Bortnik et al. [Bortnik, J., Thorne, R.M., O’Brien, T.P., Green, J.C., Strongeway, R.J., Shprits, Y.Y., Baker, D.N., 2006. Observation of two distinct, rapid loss mechanisms during the 20 November 2003 radiation belt dropout event. J. Geophys. Res. 111, A12216, doi:10.1029/2006JA011802] and Xinlin et al. [Xinlin, Li., Baker, D.N., O’Brien, T.P., Xie, L., Zong, Q.G., 2006. Correlation between the inner edge of outer radiation belt electrons and the innermost plasmapause location. Geophys. Res. Lett. 33, L14107, doi:10.1029/2006GL026294].     

穿云飞机电磁噪声的实验分析

利用高灵敏度和高时空精度的三维雷电观测系统LMA(Lightning Mapping Array)分析穿云飞机的观测资料,发现这一系统在地面可探测到穿云飞机产生的60～66MHz带宽内的电磁辐射,其强度在1W～10kW之间,甚至更高,且与所探测到的辐射源数成线性反比,辐射是由飞机上的尖端放电产生的. 穿云飞机在10～12km高度上产生的辐射最强,且在靠近发生闪电的对流区比远离这一区域强. 飞机穿过不同云系时,辐射强度不同,其中穿过层状云系时,辐射最弱.     

泥浆脉冲式随钻测量系统在高位定向孔中的应用

近年来,煤矿井下随钻测量系统由于其效率高、精度准的优点,已被广泛应用于煤矿瓦斯治理、地质构造勘探及水害防治中。通过在山西临汾市德通煤业现场实际应用泥浆脉冲随钻测量系统,对比中心通缆式测量装置与泥浆脉冲测量装置的精度和效率,证实新型泥浆脉冲仪器钻进效率高、节约成本、工作稳定,具有高安全性和可靠性的特性。可在高位定向孔中推广应用。