九寨沟M_S7.0地震的前兆异常时空演化特征及其分析

以2017年8月8日九寨沟MS7.0地震震中为中心,对震前不同震中距前兆异常的时空演化过程进行分析。研究表明,震中距100km范围内无前兆异常,前兆异常主要分布在震中距100～500km范围内。震前2年新增前兆异常开始逐渐增多;不同震中距范围内的新增异常测项所占比例在震前1.5年左右达到最大,在震前又降低。在震中距300km范围内的异常测项所占比例相对较高。前兆异常时空演化过程存在3个不同的变化阶段,即α阶段(前兆异常的早期阶段,包括α_1和α_2,震前1000天以上)的异常主要分布在震中东北方向和西南方向,异常具有向外扩展的特征;β阶段(前兆异常的中期阶段,震前500～1000天)的异常表现为大范围出现异常;γ阶段(前兆异常的短期阶段,包括γ_1和γ_2,震前500天内)的异常分布在震中的东北方向,表现为远源区的异常向震中收缩过程(γ_1)和近源区的异常向外扩展的过程(γ_2)。通过与其他震例对比分析发现,前兆异常的3个阶段现象可能是大震前的共性特征,大震前前兆异常的显著增加对发震时间的预测具有一定的指示意义。     

Effect of thickness of planar nozzles on erosion depth of levee soils subjected to plunging water

In this study, the effect of the thickness of a planar jet on the erosion depth when the jet impinges on a surface composed of cohesive soil was analytically and numerically evaluated. The results showed that the erosion depth was practically independent of the nozzle thickness for erosion depths shallower than the potential core length (i.e. the region of the jet in which the central flow velocity is the same as the nozzle velocity). The relation between nozzle thickness and erosion depth was non-linear with continuously variable slope for erosion depths deeper than the potential core length. Finally, the relation was approximately linear when the erosion depth converged to the equilibrium erosion depth. The findings of this study indicate that direct and fast prediction of the erosion depth in the field is possible using the data from a small scale soil erosion test with similar flow velocities.     

2017年6月3日阿拉善左旗5.0级地震震源深度测定

2017年6月3日18时11分内蒙古阿拉善左旗（37.99° N,103.56° E）发生5.0级地震,利用近震深度震相sPL测定法、CAP波形反演法、sPn与Pn震相走时差法,进行震源深度精确测定。研究结果表明,3种方法测得的该地震震源深度基本一致,分布范围为8.5—11 km,表明该地震发生在上地壳。     

2016年射阳MS 4.4地震前后重力场变化

利用江苏重力测网2014-2017年重力场观测资料,采用绝对重力控制与相对重力联测相结合的平差方法,获取2016年射阳M_S 4.4地震前后重力场变化图。根据射阳M_S 4.4地震前后射阳地区各测线重力段差变化特点,绘制重力场等值线并进行对比分析,结合相关机理,探讨重力场变化与该地震的内在联系。同震观测数据显示：射阳M_S 4.4地震发生在重力异常值高梯度带附近,发震时震中地区位于NS挤压正异常、EW张拉负异常状态,震后区域重力梯度变化量开始减小,是一种典型的重力异常调整现象。     

部分预制型钢混凝土梁抗震性能试验研究

为探究部分预制型钢混凝土梁的抗震性能,进行了7个部分预制型钢混凝土梁试件的拟静力试验,研究了试件的裂缝开展过程、破坏形态、承载能力、延性、耗能能力和刚度退化情况,探究预制截面模式、剪跨比和后浇混凝土强度等对其抗震能力的影响。结果表明:地震作用下,该7个试件力学性能较好,剪跨比是影响试件抗震性能的首要要素,剪跨比大的试件耗能能力强,型钢约束部分混凝土可以提高试件的耗能能力,截面模式和后浇混凝土强度对抗震性能影响不大。     

Conductivity model for pyrite-bearing laminated and dispersed shaly sands based on a differential equation and the generalized Archie equation

The conductance of pyrite-bearing laminated and dispersed shaly sands is not well understood and resistivity models for pyrite-bearing shaly sands are nonexistent. Thus, we first synthesize clean pyrite-matrix samples, and quartz-matrix samples with variable laminated shale, dispersed shale, and pyrite content and then perform petrophysics experiments to assess the effect of pyrite content on the conductivity of pyrite-bearing shaly sands. Second, based on the differences in conductivity and conduction pathways and geometries because of the variable composition of the pyrite-bearing laminated and dispersed shaly sands, we divide the shaly sands into their components, i.e., laminated shale, quartz grains, pyrite grains, hydrocarbon, dispersed shale, microscopic capillary water, and mobile water. A generalized resistivity model is proposed to describe the conductivity of pyrite-bearing laminated and dispersed shaly sands, based on the combined conductivity differential equation and generalized Archie equation. In the generalized resistivity model, the conductivity differential equation is used to describe the conductivity of dispersed inclusions in a host, whereas the generalized Archie equation is used to describe the conductivity of two conducting phases. Moreover, parallel conductance theory is used to describe the conductivity of dispersed shaly sands and laminated shale. Theoretical analysis suggests that the proposed model satisfies the physical constraints and the model and experimental results agree. The resistivity and resistivity index of shaly sands decrease with increasing conductivity and pyrite. Finally, the accuracy of the resistivity model is assessed based on experimental data from 46 synthetic core samples with different oil saturation. The model can describe the conductivity of clean pyrite-matrix samples, and quartz-matrix samples with different volumes of laminated shale, dispersed shale, and pyrite. An accurate saturation model of pyrite-bearing laminated and dispersed shaly sands is thus obtained and the log data interpretation in complex shaly sands can improve with the proposed model.     

Regeneration and utilization of nutrients during collapse of a <Emphasis Type="Italic">Mesodinium rubrum</Emphasis> red tide and its influence on phytoplankton species composition

High-biomass red tides occur frequently in some semi-enclosed bays of Hong Kong where ambient nutrients are not high enough to support such a high phytoplankton biomass. These high-biomass red tides release massive inorganic nutrients into local waters during their collapse. We hypothesized that the massive inorganic nutrients released from the collapse of red tides would fuel growth of other phytoplankton species. This could influence phytoplankton species composition. We tested the hypothesis using a red tide event caused by Mesodinium rubrum (M. rubrum) in a semi-enclosed bay, Port Shelter. The red tide patch had a cell density as high as 5.0×10⁵ cells L^?1, and high chlorophyll a (63.71 μg L^?1). Ambient inorganic nutrients (nitrate: \(\rm{NO}_3^-\), ammonium: \(\rm{NH}_4^+\), phosphate: \(\rm{PO}_4^{3-}\), silicate: \(\rm{SiO}_4^{3-}\)) were low both in the red tide patch and the non-red-tide patch (clear waters outside the red tide patch). Nutrient addition experiments were conducted by adding all the inorganic nutrients to water samples from the two patches followed by incubation for 9 days. The results showed that the addition of inorganic nutrients did not sustain high M. rubrum cell density, which collapsed after day 1, and did not drive M. rubrum in the non-red-tide patch sample to the same high-cell density in the red tide patch sample. This confirmed that nutrients were not the driving factor for the formation of this red tide event, or for its collapse. The death of M. rubrum after day 1 released high concentrations of \(\rm{NO}_3^-\), \(\rm{PO}_4^{3-}\), \(\rm{SiO}_4^{3-}\), \(\rm{NH}_4^+\), and urea. Bacterial abundance and heterotrophic activity increased, reaching the highest on day 3 or 4, and decreased as cell density of M. rubrum declined. The released nutrients stimulated growth of diatoms, such as Chaetoceros affinis var. circinalis, Thalassiothrix frauenfeldii, and Nitzschia sp., particularly with additions of \(\rm{SiO}_4^{3-}\) treatments, and other species. These results demonstrated that initiation of M. rubrum red tides in the bay was not directly driven by nutrients. However, the massive inorganic nutrients released from the collapse of the red tide could induce a second bloom in low-ambient nutrient water, influencing phytoplankton species composition.     

Spatial variations of terrain and their impacts on landscape patterns in the transition zone from mountains to plains—A case study of Qihe River Basin in the Taihang Mountains

Terrain plays a key role in landscape pattern formation, particularly in the transition zones from mountains to plains. Exploring the relationships between terrain characteristics and landscape types in terrain-complex areas can help reveal the mechanisms underlying the relationships. In this study, Qihe River Basin, situated in the transition zone from the Taihang Mountains to the North-China Plain, was selected as a case study area. First, the spatial variations in the relief amplitudes (i.e., high-amplitude terrain undulations) were analyzed. Second, the effects of relief amplitudes on the landscape patterns were indepth investigated from the perspectives of both landscape types and landscape indices. Finally, a logistic regression model was employed to examine the relationships between the landscape patterns and the influencing factors (natural and human) at different relief amplitudes. The results show that with increasing relief amplitude, anthropogenic landscapes gradually give in to natural landscapes. Specifically, human factors normally dominate the gentle areas (e.g., flat areas) in influencing the distribution of landscape types, and natural factors normally dominate the highly-undulating areas (e.g., moderate relief areas). As for the intermediately undulating areas (i.e., medium relief amplitudes), a combined influence of natural and human factors result in the highest varieties of landscape types. The results also show that in micro-relief areas and small relief areas where natural factors and human factors are more or less equally active, landscape types are affected by a combination of natural and human factors. The combination leads to a high fragmentation and a high diversity of landscape patterns. It seems that appropriate human interferences in these areas can be conducive to enhancing landscape diversity and that inappropriate human interferences can aggravate the problems of landscape fragmentation.     

罗斯海难言岛地区近地面层风场特征分析及数值模拟

本文介绍了中国第3座南极常年考察站新站址候选地——罗斯海难言岛的基本信息。通过对设在其上的自动气象站的观测数据分析表明,近地面风场主要由下降风控制,西-西北风是6级以上大风的主要风向,最大风力可达12级以上,1月、11月、12月是平均风力较小的三个月份。通过分析基于CFSR海冰资料的Polar-WRF模式模拟结果发现:Polar-WRF模式能模拟出和实测资料十分一致的下降风风场,分辨率越高越能更好的模拟出下降风的特点。难言岛附近强劲的西-西北向下降风是地形强迫的结果;来自Reeves冰川的气流是下降风的主要来源。大风的水平分布范围约为50 km。海拔1 400—300 m为下降风的加速关键区,风速最大的地方在海拔300 m高度的陡坡附近,下降风在抵达难言岛时,由于地面摩擦作用,风力已经有一定的衰减。模拟风场可以对观测资料做出有益的补充。     

Water quality assessment of the Huaihe River segment of Bengbu (China) using multivariate statistical techniques

In the study, multivariate statistical methods including principal component analysis (PCA)/factor analysis (FA) and cluster analysis (CA) were applied to analyze surface water quality data sets obtained from the Huaihe River segment of Bengbu (HRSB) and generated during 2 years (2011–2012) monitoring of 19 parameters at 7 sampling sites. The results of PCA for 7 sampling sites revealed that the first four components of PCA showed 94.89% of the total variance in the data sets of HRSB. The Principal components (Factors) obtained from FA indicated that the parameters for water quality variations were mainly related to heavy metals (Pb, Mn, Zn and Fe) and organic related parameters (COD, PI and DO). The results revealed that the major causes of water quality deterioration were related to inflow of industrial, domestic and agricultural effluents into the Huaihe River. Three significant sampling locations—(sites 2, 3 and 4), (sites 1 and 5) and (sites 6 and 7)—were detected on the basis of similarity of their water quality. Thus, these methods were believed to be valuable to help water resources managers understand complex nature of water quality issues and determine the priorities to improve water quality.