Stochastic procedure for the simulation of synthetic main shock‐aftershock ground motion sequences

According to the current seismic codes, structures are designed to resist the first damaging earthquake during their service life. However, after a strong main shock, a structure may still face damaging aftershocks. The main shock‐aftershock sequence may result in major damage and eventually the collapse of a structure. Current studies on seismic hazard mainly focus on the modeling and simulation of main shocks. This paper proposes a 3‐step procedure to generate main shock‐aftershock sequences of pairs of horizontal components of a ground motion at a site of interest. The first step generates ground motions for the main shock using either a source‐based or site‐based model. The second step generates sequences of aftershocks' magnitudes, locations, and times of occurrence using either a fault‐based or seismicity‐based model. The third step simulates pairs of ground motion components using a new empirical model proposed in this paper. We develop prediction equations for the controlling parameters of a ground motion model, where the predictors are the site condition and the aftershock characteristics from the second step. The coefficients in the prediction equations and the correlation between the model parameters (of the 2 horizontal components of 1 record and of several records in 1 sequence) are estimated using a database of aftershock accelerograms. A backward stepwise deletion method is used to simplify the initial candidate prediction equations and avoid overfitting the data. The procedure, based on easily identifiable engineering parameters, is a useful tool to incorporate effects of aftershocks into seismic analysis and design.     

十足类甲壳动物多倍体育种进展

结合作者近期的研究,综述了近年来十足类甲壳动物多倍体育种的原理及诱导方法的进展,并对研究现状、存在问题和今后的发展方向进行了探讨。     

Urban shrinkage and growth: Measurement and determinants of economic resilience in the Pearl River Delta

Journal of Geographical Sciences - In the aftermath of the global financial crisis of 2008, China witnessed gradual shrinkage of cities in the Pearl River Delta (PRD). In this study, we introduce...     

Shock metamorphism in meteorites

Shock metamorphism resulting from hypervelocity collisions between planetary bodies, is a fundamental processes in the solar system. The term "shock metamorphism" is used to describe all changes in rocks and minerals resulting from the passage of shock waves. Most meteorites have experienced collisions and have a record of shock metamorphism, which includes brecciation, deformation, phase transformation, local melting and crystallization. The key to reading this record is to use the shock features to estimate the pressure and duration of shock event. In this paper, the history of the study of shock metamorphism is reviewed; basic knowledge of shock physics is discussed; recent 10 years' studies of shock-induced melt veins are summarized; and finally a short note to the shock metamorphism in general is given.     

Weathering, shock metamorphism and type distribution patterns of 98 ordinary chondrites from the Grove Mountains, Antarctica

Petrography and mineral chemistry of ninety-eight ordinary chondrites from Grove Mountains (GRV), Antarctica, were presented and their.weathering effect, shock metamorphism and type distribution patterns were discussed in this study. Among them, six are unequilibrated ordinary chondrites, including 3 H3 and 3 L3; and 92 meteorites are equilibrated ordinary chondrites, including 24 H-group (13 H4, 10 H5, 1 H6), 64 L-group (2 L4, 44 L5, 18 L6) and 4 LL-group (3 LL4, 1 LL5). Most GRV chondrites (>90%) displayed minor weathering effect (W1 and W2). About half of the meteorites experienced severe shock metamorphism. They commonly contain shock-induced melt veins and pockets. These heavily shocked meteorites provide us with natural samples for study of high-pressure polymorphs of minerals. In addition, the Grove Mountains collection seems to have more abundant unequilibrated and L group ordinary chondrites compared to the US Antarctic meteorite collection which were mainly found along the Transantarctic Mountains.     

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人工触发闪电通道的发光特征

利用成像率为１０００幅／秒的高速数字化摄像系统在３８０ｍ的极近距离对人工触发闪电通道的发光特征进行了观测的研究。人工引发闪电除了采用的火箭地带接地导线的触发方式外还发展导线下端不接地的空中触发闪电的新技术。结果表明,闪电通道的发光截面基本上呈对称型。     

走滑断裂型地震诱发的滑坡在断裂两盘的空间分布差异

以玉树地震滑坡为实例,选择高程、坡度、坡向、坡位、水系、地层岩性、同震地表破裂、地震动峰值加速度(PGA)8个因子,以地震滑坡面积百分比(LAP)与滑坡点密度(LND)为指标,研究走滑断裂型地震诱发滑坡在断裂两盘的空间分布差异。在分析这些影响因子的断裂两盘的差异的基础上,基于LAP与LND两个指标详细分析断裂两盘每个因子内部级别滑坡发育的情况。结果表明,总体上北盘的滑坡较南盘发育,除了个别因子级别内南北盘滑坡差别较大外,大部分表现为南北盘滑坡分布情况类似。总之,玉树地震滑坡在断裂两盘的空间分布基本类似,只是在某些因子分级内存在一定的差异。     

Shaking table test on the seismic failure characteristics of a subway station structure on liquefiable ground

In order to investigate the seismic failure characteristics of a structure on the liquefiable ground, a series of shaking table tests were conducted based on a plaster model of a three‐story and three‐span subway station. The dynamic responses of the structure and ground soil under main shock and aftershock ground motions were studied. The sand boils and waterspouts phenomena, ground surface cracks, and earthquake‐induced ground surface settlements were observed in the testing. For the structure, the upward movement, local damage and member cracking were obtained. Under the main shock, there appeared longer liquefaction duration for the ground soil while the pore pressure dissipated slowly. The acceleration amplification effect of the liquefied soil was weakened, and the soil showed a remarkable shock absorption and concentration effect with low frequency component of ground motion. However, under the aftershock, the dissipation of pore pressure in the ground soil became obvious. The peak acceleration of the structure reduced with the buried depth. Dynamic soil pressure on the side wall was smaller in the middle and larger at both ends. The interior column of the model structure was the weakest member. The peak strain and damage degree for both sides of the interior column exhibited an ‘S’ type distribution along the height. Moreover, the seismic response of both ground soil and subway station structure exhibited a remarkable spatial effect. The seismic damage development process and failure mechanism of the structure illustrated in this study can provide references for the engineers and researcher. Copyright © 2013 John Wiley & Sons, Ltd.