连续波形:数字地震台网的新前沿

21世纪以来,连续波形的自动处理成为数字地震台网的一个新的前沿领域。本文通过深低频脉动(LFT,Low Frequency Tremor)、噪声相关函数(NCF,Noise Correlation Function)、"重复地震"等3个方面,指出在这一新的前沿领域中,中国数字地震观测系统正面临巨大的发展机遇。与此相应,在中国地震台网的下一步发展中,应重视连续波形的记录,并将连续波形的自动处理作为一个发展重点来考虑。     

固体潮观测中的震颤异常波

在地震与固体潮台站的日常监测中,常发现有一些异常"脉动"信号叠加在固体潮曲线上.这些异常"脉动"与宽频带数字地震计的观测在时间上同步、一致,其中的一部分由发生在西太平洋上的热带气旋引起,而其他的则大多与强地震相伴随,统称为震颤异常波.本文介绍了华中科技大学的地震与固体潮观测台站(HUST)的概况,报道了该台应用 DZW重力仪和VS-1倾斜仪观测记录到的大量震颤异常波事例.大量观测事实表明:中国固体潮台站记录的震颤异常波,绝大多数只在DZW重力仪和VS-1倾斜仪的低通滤波1 通道(LP1)出现,而在其低通滤波2通道(LP2)和其他固体潮仪器中则罕有发现;震颤异常波的包络线大多呈"纺锤状"或"尾巴状",持续时间多为1~3天. 通过对震颤异常波和固体潮观测仪器的分析研究,得到以下结论:震颤异常波实际上就是一种来源复杂的地球脉动信号,响应范围广泛,可被宽频带数字地震计和固体潮仪器记录.由西太平洋上的热带气旋引起的震颤异常波的主要周期在3~7 s范围,而强震前的震颤异常波则除此外,还包含10~60 s及更长周期的信号.固体潮仪器对震颤异常波响应的差异是因为仪器的传递函数不同和特性所致. DZW重力仪和VS-1倾斜仪分钟值采样数据中的震颤异常波,只是真实信号的一种"混叠"或映射.强震前的震颤异常波是否与地震有关？是否是震兆？尚需做更深入细致的分析和研究.     

苏门答腊Ms8.7级大震前的地脉动预警信息

介绍了辽宁数字台网运行的脉动异常跟踪系统(RTTS),叙述了这个系统在2004年12月26日08时58分55.2秒印尼苏门答腊西北近海(北纬3.9,东经95.9)8.7级地震前,营口、锦州台地脉动波形的幅度和周期明显异常的情况。并展现了利用RTTS系统进行地脉动研究的前景。     

应对巨大地震的应急流动观测系统

通过“十五”数字地震观测网络项目建设,目前。我国的地震观测系统和地震观测信号传输几乎完全依赖于公共通讯网络。但是,大地震常常严重破坏公共通讯系统,应对巨大地震的流动观测系统就提到迫切的日程。2007年,通过采用无线竞带接入技术,结合中国地震局数字地震观测网络技术,初步建成了应对巨大地震的应急流动观测系统,并在汶川地震现场观测初期发挥了重要作用。     

新一代中国数字地震台网(NCDSN)数据的应用

中美地震科技合作至今已20多年了,通过中美地震科技合作建成的中国数字地震台网(CDSN)在我国已运行了16个年头,它为我国数字地震观测技术的发展提供了借鉴,也促进了我国数字地震学的研究和地震预报工作开展。 第2代数字地震观测系统不仅具有远程数据快速传输的能力,而且具有动态范围更大,记录频带更宽的特点。从STS-1地震计中滤波出来的UH信号,能观测地球的自由振荡信     

基于地脉动噪声的呼伦贝尔地区监测能力研究

基于地脉动噪声计算方法,以呼伦贝尔市地震台网8个台站连续波形资料为基础,对地震观测台网监测能力进行评估,同时开展台网优化和科学布局研究。通过累计的历史噪声数据,用来评估台站观测环境的变迁,及时掌握地震监测能力的变化。该成果将为地震速报、重点地震危险区震情跟踪、强震后现场应急提供科学参考。     

中国数字地震台网的建设与发展

ldquo;十五rdquo;（2001——2005年）期间,中国地震观测系统得到了迅速的发展,中国地震局完成了ldquo;中国数字地震观测网络rdquo;项目建设,将所有模拟地震观测系统全部进行了数字化改造,并新建了一些数字化地震台站,标志着中国的地震观测已进入数字时代. 本文介绍了新一代国家数字地震台网、区域数字地震台网、火山数字地震台网和流动数字地震台网的规模、布局原则和主要功能.      

前言

"新疆数字地震观测网络"建设项目是我国"十五"期间"中国数字地震观测网络"重点工程项目的一部分,由新疆数字前兆台网、数字测震台网、数字强震动台网、乌鲁木齐城市活断层探测与地震危险性评价、地震应急指挥技术系统和地震信息服务系统6个子项目组成.该项目自2002～2003年开始初步设计和勘选,2004～2005年铺开建设,2006年进行仪器安装调试,2007年全面进入试运行和分项验收阶段,从项目立项到通过验收,历时6年,建成了一批高质量的地震观测台站和相关技术系统,部分功能指标优于设计要求,并有所创新.项目的完成,标志着新疆地震观测科学、地震预测研究、抗震救灾指挥和地震信息服务等进入网络化的信息时代,对新疆防震减灾工作的深入和社会可持续发展起到了积极的推动作用.     

中国地震台网观测系统特性分析与资料应用研究

正2000年以来我国地震观测系统得到了迅速的发展,目前已建成了由国家数字地震台网、区域数字地震台网、火山数字地震台网和流动数字地震台网组成的新一代中国数字地震台网。中国地震台网中心每天汇集的数据量达到40GB,可以说,我国地震台网产出的观测数据积累到了一定程度,如此海量的地震波形数据为地震监测与研究提供了丰富的原始资料,     

新疆喀什地区地震前地磁脉动异常分析

1996年11月17日至29日在新疆喀什地区发生8次地震,震前均观测到地磁脉动异常．文中对未发生地震期间地磁脉动观测的背景环境以及喀什台常见的地磁脉动进行分析,然后对地震前地磁脉动异常现象进行研究,并初步探讨这种震前地磁脉动异常的产生机制．这种震前发生的地磁脉动异常在地震的短期预报上可能有广泛的应用前景．     

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.     

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.     

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.     

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.     

Resistivity methods in geothermal prospecting in Iceland

Resistivity techniques have been used successfully to identify and delineate geothermal resources in Iceland. The most frequently used techniques include Schlumberger, central loop TEM and head-on profiling. Geothermal systems in Iceland are located both within and outsite the active volcanic regions. Outsite the active volcanic regions the temperature in the upper most kilometer of the geothermal systems is below 150° C whereas the temperature in the geothermal fields within the active volcanic regions exceeds 200° C. The resistivity of the rock in geothermal fields located outside the active volcanic regions ranges from about 10 m to some hundreds of m, and are characterized by considerably lower resistivity than of the surrounding rocks. Most of the geothermal systems within the active volcanic regions, show common resistivity structure with low resistivity of 1–5 m surrounding an inner core of higher resistivity. This increasing resistivity with depth is associated with a change in the conduction mechanism, from interface conduction to electrolyte conduction due to a change in alteration minerals at about 240° C. Examples of resistivity surveys of geothermal fields from both outsite and within the active volcanic regions are discussed.