2021年漾濞MS6.4地震前后重力场动态特征分析

基于2015年以来南北地震带南段相对重力和绝对重力观测资料,系统分析了区域重力场动态变化及其与2021年5月21日漾濞M_S6.4地震的关系.结果表明:(1)区域重力场变化与维西—乔后断裂关系密切,反映了2015—2021年期间该断裂活动引起了地表重力场变化;(2)与漾濞地震孕育有关的重力场经历了“弱变化—区域性异常—局部异常—四象限分布异常—大范围的正异常—反向变化发震”的演化过程;(3)重力场累积变化和差分变化图像均反映出漾濞震前两年出现显著的重力异常变化,地震发生在重力变化梯度带、四象限中心和零等值线拐弯附近;(4)重力场动态演化图像较好地反映了漾濞M_S6.4地震孕育发生过程中出现的中期前兆现象,并基于该现象在漾濞M_S6.4地震前作过一定程度的中期预测,尤其是强震地点判定.     

应用GPS连续观测和流动重力资料分析新疆洛浦MS6.0地震的前兆特征

对2012年3月9日新疆洛浦MS6.0地震前陆态网络GPS连续跟踪站数据与喀什—伽师2010年7月～2012年3月期间重力复测数据进行计算分析。结果表明：（1）断层两端运动速率不同,为应力积累创造条件;（2）地震发生前监测区出现区域性的重力异常变化高值区,区域重力场等值线与发震断裂走向平行;震前区域重力场出现增强—减弱—增强过程。     

应用GPS连续观测和流动重力资料分析新疆洛浦MS6.0地震的前兆特征

对2012年3月9日新疆洛浦Ms6.0地震前陆态网络GPS连续跟踪站数据与喀什—伽师2010年7月～2012年3月期间重力复测数据进行计算分析.结果表明：（1）断层两端运动速率不同,为应力积累创造了条件;（2）地震发生前监测区出现区域性的重力异常变化高值区,区域重力场等值线与发震断裂走向平行;震前区域重力场出现增强—减弱—增强过程.     

2020年伽师MS6.4地震重力与地壳形变综合分析

2020年1月19日新疆维吾尔自治区伽师县发生M_S6.4地震,此次地震为N倾逆冲兼少量走滑型地震,地震的发震构造是南天山柯坪塔格逆冲推覆体最南缘的柯坪断裂,伽师地震的震中位于喀什-伽师流动重力观测网和中国大陆构造环境监测网络GNSS观测网监测区域内。文中选取2015—2021年的流动重力和GNSS观测资料开展分析。采用绝对重力点约束流动重力数据,并进行全网经典平差计算,进而获得重力场变化图像;基于GNSS数据通过GAMIT/GLOBK软件解算获得研究区的运动速率,借助位移与应变的偏导关系获取水平视应变场分布图。之后,分别研究了孕震区的重力场和应变场的变化特征,并综合探讨了孕震区的重力场、 GNSS形变场特征与伽师M_S6.4地震孕震过程的关系。研究表明：1)一年时间尺度的重力场时变图像较好地反映了伽师M_S6.4地震附近区域重力场的系统演化过程,重力变化零等值线拐弯处及“四象限”特征可为地震预报提供有益参考。2)重力场累积变化反映出伽师M_S6.4地震前的重力场变化受到区域大断裂的控制,研究区一系列中强震...     

河北唐山古冶5.1级地震前的重力变化

利用京津冀地区2018—2020年5月的流动重力观测资料,分析了2020年7月12日河北唐山古冶5.1级地震前不同时间尺度重力场变化.结果表明:0.5年尺度重力场变化图像较好地反映了此次地震"震前一年,重力场持续上升(正)变化→震前反向变化→在重力变化梯度带零等值线附近发震"的演化过程;震前0.5年和1年年尺度重力场均...     

2012年宁蒗—盐源5.7级地震前的重力变化

利用2010年7月~2012年3月四川省和云南省的流动重力观测数据,对2012年6月24日宁蒗—盐源5.7级地震孕育和发生过程中的重力场动态演化情况进行分析。结果显示:地震孕育阶段震中区域重力场出现大面积的重力正值变化高值异常区域,并形成密集的正值变化梯度带;震前震中区域呈重力正变化低值状态,处于重力变化0值线附近且等值线稀疏;震前与发震有关的断裂带的跨断层重力测段段差值变化明显。     

唐山老震区中强地震流动重力异常研究

选取唐山老震区1992—2014年的流动重力,绘制重力场测值空间变化等值线和时序变化曲线,结合唐山地区4次M≥5.0地震进行异常分析。发现震前有如下特征:(1)流动重力观测资料均有较为明显的前兆异常反应;(2)地震均发生在重力变化的"0"等值线附近。     

日本MW9.0地震震区及其周缘2002—2015年卫星重力变化时空特征

本文在考虑全球陆面数据同化系统陆地水储量变化影响后,利用2002年4月—2015年4月GRACE卫星RL05月重力场模型获取了2011年日本M_W9.0地震震中及其周边区域的重力场信息;然后给出了日本及其周边2003—2015年的年度累积重力变化和差分重力变化,并且利用经验正态函数方法深入分析了该地震过程中同震重力变化对区域重力场的贡献. 结果显示:日本M_W9.0地震前研究区域出现了幅值高达2×10-8 m/s2的异常重力变化,其同震效应的时间和空间特征均出现在第一模态,且同震重力变化和震后区域重力场变化特征显著,这充分表明该地震对区域重力场的影响显著.      

2022年芦山6.1级地震和马尔康6.0级地震前的重力变化特征

地震孕育过程中的地表重力值会发生相应的变化,利用四川地区2018年3月—2022年4月的流动重力观测数据得到重力场等值线变化图,研究2022年芦山6.1级地震和马尔康6.0级地震前的重力变化特征。结果表明：(1)芦山6.1级地震和马尔康6.0级地震震前约一年半进入重力变化显著时期;(2)芦山6.1级地震对马尔康6.0级地震的发生有促进作用;(3)芦山6.1级地震和马尔康6.0级地震前震区重力变化等值线出现类似于四象限区域的分布特征,显示该处应力高度集中;(4)芦山6.1级地震和马尔康6.0级地震震中区处于零值线附近且零值线在此处转折弧度较大,是构造带易发震的薄弱位置。     

广西北流Ms5.2地震区域重力场变化

利用广西及邻区2016—2019年流动重力观测资料,系统分析区域重力场变化及其与广西北流M_S5.2地震的关系。结果表明:①北流M_S5.2地震前,震区附近重力异常变化与主干断裂关系密切,反映沿控震断裂在2016—2019年间发生了引起地表重力变化效应的地壳变形和构造活动;②差分重力图像表明北流M_S5.2地震前震中附近的重力变化是一个"局部重力异常→重力反向变化→重力变化平缓后发震"过程;③近期重力场累积动态图像表明玉林—岑溪—苍梧一带为重力变化剧烈区域,有利于应力的高度积累而孕育地震。     

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.