2013年3月11日阿图什5．2级地震灾害损失评估和房屋震害特征分析

2013年3月11日新疆阿图什发生慨5．2地震,震中烈度Ⅵ度,地震没有造成人员伤亡,个别民宅倒塌,造成直接经济损失2397万元。结合此次地震考察评估工作,分析此次地震造成经济损失的震害原因。从房屋破坏、房屋建筑场地条件和抗震安居工程三点,描述了此次地震的震害特征,与新疆伽师、莎车等具有相同地质条件的地区进行震后对比,并结合2009年4月22日发生的新疆阿图什Ms5．0地震,提出了对此次地震的认识与建议。     

新疆及哈萨克斯坦地下流体氦气震兆特征

分析新疆10泉、04泉及哈萨克斯坦卡帕尔—阿拉善4井、下卡姆卡井氦气(He)含量变化的源兆、场兆、远兆的映震特征,地震前兆异常表现为:上升(或下降)幅度、速率变化超出正常范围,具有较好的重复性,测值遵循背景值—趋势性上升(或突升)—恢复至背景值;趋势性下降(或突降)—恢复至背景值的变化过程.各监测点氦气异常形态、异常持续时间、异常幅度同源兆、场兆、大震远兆没有明显的关系;由于各观测点的水文地质条件和地球化学环境不同,不同监测点氦气映震能力有较大差异,其中新10号泉和卡帕尔—阿拉善4井氦气的映震能力较强.     

Soil bentonite wall protects foundation from thrust faulting: analyses and experiment

When seismic thrust faults emerge on the ground surface,they are particularly damaging to buildings,bridges and lifelines that lie on the rupture path.To protect a structure founded on a rigid raft,a thick diaphragm-type soil bentonite wall(SBW) is installed in front of and near the foundation,at sufficient depth to intercept the propagating fault rupture.Extensive numerical analyses,verified against reduced–scale(1 g) split box physical model tests,reveal that such a wall,thanks to its high deformability and low shear resistance,"absorbs" the compressive thrust of the fault and forces the rupture to deviate upwards along its length.As a consequence,the foundation is left essentially intact.The effectiveness of SBW is demonstrated to depend on the exact location of the emerging fault and the magnitude of the fault offset.When the latter is large,the unprotected foundation experiences intolerable rigid-body rotation even if the foundation structural distress is not substantial.     

Dominant pulse simulation of near fault ground motions

In this study, a new mathematical model is developed composed of two parts, including harmonic and polynomial expressions for simulating the dominant velocity pulse of near fault ground motions. Based on a proposed velocity function, the corresponding expressions for the ground acceleration and displacement time histories are also derived. The proposed model is then fitted using some selected pulse-like near fault ground motions in the Next Generation Attenuation (NGA) project library. The new model is not only simple in form but also simulates the long-period portion of actual velocity near fault records with a high level of precision. It is shown that the proposed model-based elastic response spectra are compatible with the near fault records in the neighborhood of the prevailing frequency of the pulse. The results indicate that the proposed model adequately simulates the components of the time histories. Finally, the energy of the proposed pulse was compared with the energy of the actual record to confirm the compatibility.     

Frost heave control of fine round gravel fillings in deep seasonal frozen regions

Fine round gravel soil is widely employed in the subgrade of high speed railways in cold regions to prevent frost heaving and thawing. The lower the fines content in fine round gravel soil, the smaller the quantities of frost heaving and thawing, but compaction difficulty increases. This study is to obtain the optimum fines content and limited frost heaving and thawing. The fine round gravel soil filling (FRGSF) used in the Harbin-Qiqihaer Passenger Dedicated Line is taken as the study object. Influence of fines content on optimum water content, maximum dry density and frost heaving properties of FRGSF were studied by means of compaction and frost heaving tests. Results show that the maximum dry density of the FRGSF increases first and then decreases with an increase of fines content, namely there is an optimum fines content for easy compaction. The method of surface-vibratory instrument is fit for coarse-grained soils, and wet state of coarse-grained soil is in favor of compaction. Considering the relationship of fines content with maximum dry density and the frost heaving ratio of FRGSF, the fines content should be limited to within the range of 9%-10%, so that the frost heaving ratio is less than 1%, and the FRGSF is easily compacted. Water supply is proved to be an important factor influencing the amount of frost heaving of FRGSF. We also conclude that in the field, it is imperative to control waterproofing and drainage measures.     

Lake Area Changes and the main causes in the hinterland of Badain Jaran Desert during 1973–2010, China

Lake area information in the Badain Jaran Desert in 1973, 1990, 2000, and 2010 was obtained by visual interpretation and water index analysis of remote sensing images, based on the spatial and temporal characteristics of lake area changes during 37 years. Results indicated that the number of lakes declined from 94 to 82 and the total surface area was reduced by 3.69 km² during 1973–2010. The desert lake area reduced by different degrees in different periods, but this occurred most rapidly during 1973–1990. According to the statistics of lake area changes, lake area decreases mainly occurred in the lakes with areas less than 0.2 km², while the areas of lakes greater than 0.9 km² only fluctuated. The changes of lake areas were probably due to changes in the quantity of underground water supplies rather than the effects of local climate change or human factors.     

Response to climate change of different tree species and NDVI variation since 1923 in the middle arid region of Ningxia, China

The normalized difference vegetation index (NDVI) is used extensively to describe vegetation cover and ecological environment change. The purpose of this study was to contrast the response of different tree species growing in the same habitat to climate change and retrieve past NDVI using tree-ring width data from tree cores collected from the transitional zone of Pinus tabulaeformis and Picea crassifolia in the Luoshan Mountains in the middle arid region of Ningxia. Correlation analysis indicated that radial growth of P. tabulaeformis is more sensitive to precipitation and temperature change than that of P. crassifolia. Natural factors such as water availability and heat at this elevation are more suited to the growth of P. crassifolia, and are more advantageous to its renewal and succession. P. crassifolia is probably the better of the two species for protecting the forest ecosystem and conserving water in the Luoshan desertification area. Ring width of P. crassifolia correlates significantly with average NDVI for April–May (r =0.641, p <0.01), and both of them are influenced positively by precipitation in April–May. The reconstructed NDVI for 1923–2007 shows the relatively low vegetation cover occurred in the 1920s–1930s, the 1960s–1970s, and the early 21st century. The reconstructed NDVI better reflected the drought climate in the study area.     

The aboveground biomass of desert steppe and its spatiotemporal variation in western Inner Mongolia

A precise understanding of the aboveground biomass of desert steppe and its spatio-temporal variation is important to understand how arid ecosystems respond to climate change and to ensure that scarce grassland resources are used rationally. On the basis of 756 ground survey quadrats sampled in western Inner Mongolia steppe in 2005–2011 and remote sensing data from the Moderate Resolution Imaging Spectroradiometer (MODIS)—the normalized difference vegetation index (NDVI) dataset for the period of 2001–2011—we developed a statistical model to estimate the aboveground biomass of the desert steppe and further explored the relationships between aboveground biomass and climate factors. The conclusions are as follows: (1) the aboveground biomass of the steppe in the research area was 5.27 Tg (1 Tg=10¹² g) on average over 11 years; between 2001 and 2011, the aboveground biomass of the western Inner Mongolia steppe exhibited fluctuations, with no significant trend over time; (2) the aboveground biomass of the steppe in the research area exhibits distinct spatial variation and generally decreases gradually from southeast to northwest; and (3) the important factor causing interannual variations in aboveground biomass is precipitation during the period from January to July, but we did not find a significant relationship between the aboveground biomass and the corresponding temperature changes. The precipitation in this period is also an important factor influencing the spatial distribution of aboveground biomass (R²=0.39, P<0.001), while the temperature might be a minor factor (R²=0.12, P<0.01). The uncertainties in our estimate are primarily due to uncertainty in converting the fresh grass yield estimates to dry weight, underestimates of the biomass of shrubs, and error in remote sensing dataset.     

大地震多发于俯冲带和洋底断裂带的交叠区

全世界的大地震都发生在俯冲带,因为在俯冲带中,一个构造板块在另一个之下滑动.但是,俯冲区的哪些地方最有可能发生大地震呢?澳大利亚悉尼大学的科学家研究发现,海底断裂带与俯冲带的交叠区域发生大地震的风险高于其他区域.该项研究成果于2012年12月发表在欧洲地球科学联合会(EGU)的开放获取期刊Solid Earth上.