地震活动因子A值在川滇地区Ms≥6地震中短期预报中的应用

对 1971— 2 0 0 0年间川滇地区 ML≥ 2 .5地震资料进行地震活动因子 A值的空间扫描 ,结果表明 :川滇地区 80 %的 MS≥ 6地震前 1— 2年 ,在未来震中周围有 A值异常出现。用 R值对其进行评分 ,可以通过检验。通过与华北地区的部分结果进行比较 ,对两个区域地震孕育过程中的差异进行了讨论     

川滇地区GL值动态演化特征与强震预测

用地震活动非均匀度CL值作参数,使用1971～2000年期间川滇地区M≥2.5级地震资料进行了GL值的空间扫描.结果表明,川滇地区72%的M≥6级地震前1～2 a,在未来震中周围均有GL值异常出现,用R值对其进行评分,可以通过检验.由典型震例图像给出了异常的主要特征.     

川滇地区b值空间分布特征及其与震源类型关系的初步探讨

本文利用川滇地区1980—2013年震级M2.2—5.9的12924条地震资料,对该地区进行了精细b值计算;利用川滇地区321个M≥4.7的中强地震震源机制解资料,结合b值的空间分布特征,划分震源区,并探讨了不同类型震源区b值的变化规律。研究结果显示:川滇地区b值分布存在较大差异,川滇菱形块体的东边界和西南边界的低b值范围较大,菱形块体内部高b值区域相对集中,研究区内其余地区的b值分布较为零散;结合我国现行的地震区带划分方案,b值分布没有表现出带内的一致性;结合地震的震源机制,倾滑断层型的地震表现出逆断型震源区地震的b值低于正断型震源区内同类型地震的b值。这将为b值统计单元的划分提供有益的参考。     

2008年汶川8.0级地震前川滇地区6级以上地震平静异常

2008年5月12日四川汶川8.0级地震前,川滇地区出现了显著的地震平静异常:M≥6.0、M≥6.5和M≥7.0地震平静时间分别达3.63年、8.29年和12.27年。通过对1900年以来川滇地区M≥6.0、M≥6.5和M≥7.0地震时间分布特征的统计分析,发现这些平静异常现象在川滇地区近100年来的地震活动性中是非常显著的。在M≥7.0地震平静时间大于5年的条件下,M≥6.0(1.0σ以上)和M≥6.5地震(1.5σ以上)平静异常在统计上具有显著性和重现性,可能是这类7级地震前一个重要或典型的异常现象。     

川滇地区M_S≥7.0地震时空对称特征及趋势判断

地震时空趋势判断对于防灾、减灾有重要意义.选取1900年以来川滇地区M_S≥7.0地震序列数据,采用可公度计算、蝴蝶结构图和可公度结构系方法研究川滇地区M_S≥7.0地震时间对称特征及趋势;分析地震震中经纬度迁移,结合川滇地区地质构造和地震危险性判断准则研究川滇地区M_S≥7.0地震空间对称特征及趋势.研究结果显示:(1)川滇地区M_S≥7.0地震具有明显时间对称特征,2017年发震信号最强.(2)川滇地区M_S≥7.0地震具有明显空间对称特征,存在主、次对称轴带和对称中心,未来鲜水河—小江断裂带中段安宁河断裂带发震水平最高.     

前言

近年较多研究指出,本世纪第五强震活跃幕内四川西部地区及川滇藏交界地区未来强震(M≥7)危险地段为南北向构造系的川滇断块东西边界地带的部分地段。这是近年地震势态研究中的重要认识之一。1989年度全国地震趋势会商报告提出划分重点监视区的原则,即有重要异常出现,被分析判定为有发生较大地震,我国西部6级以上,东部5级以上的危险地区;具有监视价值和社会经济效益的地震危险区。我省将川滇断(?)东边界的乾宁—康定—泸定—石     

川滇藏交界地区M≥7地震记载的起始年代与资料完整性分析

地震资料是地震活动性分析、地震危险性分析及地震预测等研究的基础数据。川滇藏交界地区是中国地震活动强烈的地区之一,分析该地区地震资料的完整性有助于进行相关断层的危险性评价及区域地震活动趋势分析。文中通过查阅川滇藏交界地区44个县的地方志,了解各县的建制沿革,由川滇进藏通道的演化明确了川滇藏交界地区的关键交通枢纽与节点,结合历史地震目录、地震史料及前人对该地区地震资料完整性的研究成果,综合分析了鲜水河地区与三江并流区7级以上强震不会被漏记的可靠年代及6级以上地震应被记载的起始年代。同时,根据历史地震等烈度线长、短轴数据拟合得到的川滇菱形块体烈度衰减关系,在空间上分析6、 7级地震的影响范围。结果表明,1719—1736年为鲜水河地区M_S≥7地震资料完整的起始年代,1719—1728年为三江并流区M_S≥7地震资料完整的可能起始年代,上述年代同样可以作为2个地区6级以上地震应记载的起始年代。     

缅甸弧强震对川滇地区主要断裂的应力影响

收集并分析了1969—2018年缅甸弧地区共170次地震的震源机制解,发现浅源地震主要分布在缅甸弧西侧和实皆断裂,且震源机制解以走滑为主;逆冲型地震主要位于缅甸弧中部,且以中源地震为主;正断型地震主要分布在缅甸弧南侧。基于缅甸弧至川滇地区粘弹性介质模型,以川滇地区51条主要断裂、129个断层段、2 112个断层离散点作为接收断层模型,分别计算了缅甸弧单次地震模型和1969—2018年所有M_W≥6.0地震在川滇地区产生的静态和累积库仑应力。结果表明:缅甸弧中源地震对川滇地区库仑应力影响较小,一般情况下可忽略不计;浅源地震在川滇地区产生的库仑应力大小明显高于中源地震;1969—2018年缅甸弧所有M_W≥6.0地震对川滇地区的最大累积库仑应力小于0.1 bar,应力加载作用最强的区域集中在小滇西—滇西北附近地区。     

川滇强震前地震活动空间扫描短期特征

对比分析了川滇地区近30年强震活跃段地震活动因子A值和空间集中度C值的全时空扫描结果.结果表明,川滇地区大地震孕育进入短期阶段时,震中周围地区的中小地震活动在A值和C值出现不同程度的变化,而且选取地震活动因子A值可更好地表征川滇地区的地震活动在时、空、强方面短期的综合特征.     

川滇地区Ms≥7.0地震时间对称特征及其周期解释

通过地震时间对称特征进行地震趋势判断的研究,对于地震防灾、减灾有重要意义。为验证地震时间对称性研究方法,揭示地震时间对称特征的机理,采用可公度计算、蝴蝶结构图和可公度结构系方法研究川滇地区MS≥7.0地震时间对称特征及趋势;然后利用小波分析所提取的川滇地区MS≥5.0地震能量释放周期和日月活动周期,对川滇地区MS≥7.0地震时间对称特征进行解释。研究结果显示:(1)川滇地区MS≥7.0地震具有明显时间对称特征,2017年发震信号最强,其随机概率为65.5%。(2)川滇地区MS≥7.0地震时间对称特征是地震能量释放周期更直观的表达。(3)川滇地区MS≥7.0地震时间对称特征是月球赤纬角周期和太阳黑子周期组合叠加的结果,月球赤纬角极值是强震的主要触发因素。     

Changes in sediment transport in the Kuye River in the Loess Plateau in China

In this paper, the changes in sediment transport over 51 years from 1955 to 2006 in the Kuye River in the Loess Plateau in China are assessed. Key factors affecting sediment yield and sediment transport, such as precipitation depth, discharge, and human activities are studied. To investigate the changes in sediment yield in this watershed, a trend analysis on sediment concentration, precipitation depth, and discharge is conducted. Precipitation depths at 2 Climate Stations （CSs）, as well as discharge and sediment transport at 3 Gauging Stations （GSs） are used to assess the features of sediment transport in the Kuye River. The rtmoff modulus （defined as the annual average discharge per unit area, L/（s·km^2）） and the sediment transport modulus （defined as the annual suspended sediment transport per unit area, t/（yr km^2）） are introduced in this study to assess the changes in runoff and sediment yield for this watershed. The results show that the highest average monthly discharge during the study period in the Kuye River is 66.23 m^3/s in August with an average monthly sediment concentration of 88.9 kg/m^3. However, the highest average monthly sediment concentration during the study period in the Kuye River is 125.34 kg/m^3 and occurs in July, which has an average discharge of 42.6 m^3/s that is much less than the average monthly discharge in August. It is found that both the runoff modulus and sediment transport modulus at Wenjiachuan GS on the Kuye River has a clear downward trend. During the summer season from July to August, the sediment transport modulus at Wenjiachuan GS is much higher than those at Toudaoguai and Longmen GSs on the Yellow River. The easily erodible loess in the Kuye River watershed and the sparse vegetation are responsible for the extremely high sediment yield from the Kuye River watershed. The analyses of the grain size distribution of suspended load in the Kuye River are presented. The average monthly median grain size of suspended load in the Kuye River is largest in February and then decreases until June. In July, the average monthly median grain size of suspended load approaches another peak and decreases until September. Then, the median grain size of suspended load starts to increase until February of the following year. However, the average monthly median grain size of suspended load in the Yellow River at Toudaoguai and Longmen GSs is the smallest between early summer and late fall The median grain size in the Yellow River starts to increase in November and approaches the largest size in January.     

TritiogenicHe in groundwater in Takaoka

³He/⁴He ratios up to 3.5 times the ratio of atmospheric He were found in groundwater samples. The³He enrichment can be attributed to radiogenic³He produced by in-situ beta-decay of³H. This shows that tritiogenic³He is accumulating in confined waters. From tritiogenic³He and³H concentrations, ages of groundwaters can be calculated. Detection of tritiogenic³He gives a tool to trace a tritium contamination which occurred in the past and cannot be assessed only by the³H counting method.     

Variations in trace gas concentrations in different environments in India

Observations of trace gases (SO₂, NH₃, NO₂ and O₃) were made during the period 1981 to 1984 at 6 different locations representative of urban industrial, urban, nonurban, thermal power plant and marine environment. Diurnal variations of the trace gases were studied in an urban environment. Except in the urban industrial environment, the concentration of NH₃ was found in the range of background values. Also, the average concentrations of NO₂ and O₃ at the different environments were in the order of background values. However, the concentrations of SO₂ were substantially higher by about 7 times, in urban industrial and thermal power plant environments. The diurnal variations of SO₂, NH₃ and NO₂ showed anitphase relationship with surface temperature at the urban environment station which is relatively free of industrial pollution. Discussion is centred on trace gas variations in different environments in India together with the values reported for various countries in the world.     

Projected changes in flood indices in selected catchments in Poland in the 21st century

The aim of this study is to estimate likely changes in flood indices under a future climate and to assess the uncertainty in these estimates for selected catchments in Poland. Precipitation and temperature time series from climate simulations from the EURO-CORDEX initiative for the periods 1971–2000, 2021–2050 and 2071–2100 following the RCP4.5 and RCP8.5 emission scenarios have been used to produce hydrological simulations based on the HBV hydrological model. As the climate model outputs for Poland are highly biased, post processing in the form of bias correction was first performed so that the climate time series could be applied in hydrological simulations at a catchment-scale. The results indicate that bias correction significantly improves flow simulations and estimated flood indices based on comparisons with simulations from observed climate data for the control period. The estimated changes in the mean annual flood and in flood quantiles under a future climate indicate a large spread in the estimates both within and between the catchments. An ANOVA analysis was used to assess the relative contributions of the 2 emission scenarios, the 7 climate models and the 4 bias correction methods to the total spread in the projected changes in extreme river flow indices for each catchment. The analysis indicates that the differences between climate models generally make the largest contribution to the spread in the ensemble of the three factors considered. The results for bias corrected data show small differences between the four bias correction methods considered, and, in contrast with the results for uncorrected simulations, project increases in flood indices for most catchments under a future climate.     

Copper in natural waters in Transbaikalia

Cu concentrations in surface (river and lake) and subsurface waters are determined. The geographic pattern of Cu distribution in natural water is identified. This pattern is controlled by the difference between its concentrations in drained rocks and soils and the geochemical redox conditions of its migration. Territories with low, medium, and elevated Cu concentrations in natural waters are identified. The concentrations of Cu in natural waters of the region are found to be generally lower than the Clarke values.     

Changes in thermal extremes in Poland

Changes in thermal extremes of the climate of Poland in 1951–2010 are examined. Warm extremes have become more frequent, while cold extremes have become less frequent. In the warming climate of Poland, the increase in the number of extremely warm days in a year and the decrease in the number of extremely cold days in a year have been observed. Also the increase of the maximum number of consecutive hot days in a year and the decrease of the maximum number of consecutive very cold and extremely cold days in a year have been observed. However, the trends are not of ubiquitous statistic significance, as the natural variability is strong.     

Hydrological changes in the Ganges system in Bangladesh in the post-Farakka period

Abstract

The basin area of the Ganges River in Bangladesh is extremely dependent on a regular water supply from upstream to meet requirements for agriculture, fisheries, navigation, salinity control, and domestic and industrial sectors. In 1975, India commissioned a barrage on the Ganges River at Farakka to divert a significant portion of the dry season flow in order to make the Calcutta Port navigable. Statistical analyses of discharge and water level data have been carried out to determine if significant changes have occurred in the hydrology of the Ganges system in Bangladesh in the post-Farakka period. Siltation of the Gorai River (an offtake of the Ganges River) has also been examined using the stage-discharge relationship and regression analysis. The analyses show that the diversion has caused considerable hydrological changes in the Ganges system in Bangladesh. The water supply in the dry season has been reduced substantially, while siltation of the Gorai River has increased significantly.     

Advances in ground motion studies in China

This paper briefly summarizes the works in the processing of strong ground motion data, the factors affecting strong ground motion, the modeling of strong ground motion and the calculating of broad-band response spectrum which have been done recent years by engineering seismologists and seismologists of China. In addition, we think back to the international cooperation in strong ground motion of the recent years and make some expectations for the future.