关于偶极法预报地震的试验研究

1982年6月到12月初在宁夏海原地区进行了偶极法连续观测试验。试验共布置了2条测线5个观测点,供电电流保持在70—100安培左右,观测精度约0.5%。人工电位差脉冲观测使用改装的小型仪器车每天流动定时测量一次,每次观测20组脉冲,观测精度在3%左右。观测结果表明:在8月14日海原北2.7级地震前(测区距震中17公里)各观测点地电阻率都明显出现异常,异常幅度8—20%不等。四极对称装置浅层探测异常幅度约1.5%。11月5日距震中区约110公里同心北3.3级地震前,赤道式装置的2个观测点有明显异常,异常幅度约7—9%。本文所观测到的前兆异常可用郭增建同志提出的地震前兆优显层的理论得到解释。     

Effect of nano-MgO on mechanical performance of cement stabilized silty clay

Abstract

A series of direct shear tests were performed on cement-admixed silty clay to investigate the effect of cement content and nano-magnesia (MgO) on its shear strength properties. For each normal stress, shear strength increased with cement content. However, an obvious increment in shear strength was achieved when the cement content was adjusted from 13% to 17%. Both cohesion and friction angle of cemented soil increased with cement content, and exponential function was adopted to correlate both the factors with cement content. For cement content of 10% investigated in this study, the optimum nano-MgO content was 10‰, wherein the cohesion could reach the peak value. The microstructure of the mixture revealed that the structure of the mixture was compacted for the optimum nano-MgO content. However, micro-cracks were formed when the amount of nano-MgO exceeded its optimum content.     

中国大陆中上地壳剪切波速结构

为使已获得的中国大陆中上地壳结构更为可靠,本文搜集了很多对浅部结构分辨率较好的短周期面波资料. 与传统面波层析成像反演方法不同,本文在第二步由面波频散得到剪切波速的过程中不再对每个结点进行一维波速模型分别反演,而是直接将所有结点上的区域化频散转换成三维波速结构的线性化约束,实现了直接的三维反演. 检测板测试结果显示该方法可以得到理想的反演结果. 本文得到的波速模型显示,中国大陆中上地壳的速度分布存在明显的横向变化和分区特征. 较低的波速异常很好地勾勒出我国主要的沉积盆地,波速异常在不同深度上的变化在一定程度上反映了各盆地结晶基底的深度. 以东经95deg;为界,特提斯构造域西部具有明显的低速异常,而东部基本没有低速异常. 基于油气资源多存在于沉积层中,而沉积层表现低速异常,我们推测特提斯构造域西部油气前景比东部好. 另外, 由于特提斯构造域西部低速非常明显,这可能也说明了其地壳温度较高. 兴安造山带的低速异常可能也说明了其地壳温度较高. 20 km深度上鄂尔多斯盆地西侧的弱低速带, 很好地勾勒出中国大陆近似沿105deg;经线的强震带的走势.      

Variability of East Asian Winter Monsoon in Quaternary Climatic Extremes in North China

In order to examine high-frequency variations of East Asian winter monsoon in Quaternary climatic extremes, two typical loess–paleosol sequences in the Chinese Loess Plateau were investigated. Sandy layers in the loess deposits, the “Upper sand” and “Lower sand” (layers L9 and L15, respectively), which represent a high-resolution record of paleomonsoon changes, have been sampled at intervals of 5–6 cm from sections at Luochuan and Xifeng. The grain size and magnetic susceptibility was measured for all samples. The grain-size results (a proxy of winter monsoon strength) indicate that the winter monsoon strength fluctuated on a millennial timescale during cold climatic extremes, with climatic events of a few hundred to a few thousand years. However, the winter monsoon was relatively stable during warm periods. The magnetic susceptibility signal (a proxy of summer monsoon intensity) is practically constant over the same period. This is tentatively explained by the assumption that the summer monsoon intensity was too low to be recorded in the magnetic susceptibility signal. The intensified winter monsoon events show periodicities in a range of 1000 to 2770 yr, with a dominant cycle of approximately 1450 yr. The detection of this oscillation in older glacial stages strongly suggests that it may be a pervasive cycle of the cold climatic phases of the Quaternary. Millennial-scale variations of the winter monsoon may be caused by instability of the westerly jet, which is determined by temperature differences between the polar and the equatorial regions.     

A new method for GLONASS inter-frequency bias estimation based on long baselines

GPS Solutions - Frequency division multiplexing of GLONASS signals causes inter-frequency bias (IFB) in receiving equipment. IFB significantly increases the difficulties of fixing GLONASS...     

Q estimation based on logarithmic spectral areas with different high and low frequencies

When a seismic wave propagates through subsurface viscoelastic media, the formation absorbs the high-frequency energy of the seismic wave more strongly than the...     

Effects of Concentrated Freshwater Discharge on Hydrography and Mesozooplankton Community in a Dammed Estuary

Ocean Science Journal - This study examines the different effects of high and low freshwater discharge on the water physical structure of the water column and plankton community in a tide-dominated...     

Model Test Study on Ice-Induced Vibrations of Compliant Multi-Cone Structures

For the study on the ice-induced vibration of a compliant mono-cone structure,a series of model tests were performed from 2004 to 2006.In these tests,the ice sheet before the compliant conical structure was found to be failed in two-time breaking.Based on this important finding,model tests study of the ice force on a compliant multi-cone structure were performed from 2006 to 2007.in these tests,the ice sheet broke before each single cone non-simultaneously.The exciting energy of the total ice force was found to be in a wide range of frequencies,and the structure can be easily excited with nonlinear resonance.     

Paleoclimatic significance of grain size of loess-palaeosol deposit in Chinese Loess Plateau

Particle size analysis for samples from three last glacial cycle loess-palaeosol profiles along a northwestsoutheast transection on the Chinese Loess Plateau has been carried out. The paleoclimatic significance of grain size indices has been obtained by analyzing the fraction content variations and their comparisons with global ice volume and solar radiation variations. The results show that (i) paleoclimatic significance of the grain size indices of loess-palaeosol deposit is different with grain size fraction content and sampling points in Chinese Loess Plateau; (ii) the sub-coarse grain fraction is a good proxy index of East Asia winter monsoon strength and therefore can be used to detect the global climate changes; (iii) the content of sub-fine and fine grain fractions is influenced by both the input of sub-coarse grain fraction and pedogenesis; (iv) the sub-coarse fraction exhibits a negative relationship with the sub-fine and fine fractlon. Project supported by the 9.5 major project of Chinese Academy of Sciences and the open grant of the State Key Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences.     

Investigation on strength and stability of jointed rock mass using three‐dimensional numerical manifold method

This paper proposes a numerical model for jointed rock masses within the 3‐D numerical manifold method (NMM) framework equipped with a customized contact algorithm. The strength of rock sample containing a few sets of discontinuities is first investigated. The results of models with simple geometries are compared with the available analytical solutions to verify the developed computer code, whereas models with complex geometries are simulated to better understand the fundamental behavior and failure mechanism of jointed rock mass. Furthermore, the stability of jointed rock mass in an underground excavation is studied, where rock failure process is determined by the 3‐D NMM simulation. The simulation results provide valuable guidance on excavation process design and stabilization design in rock engineering practice. Copyright © 2012 John Wiley & Sons, Ltd.