Sediment fingerprinting in fluvial systems： review of tracers,sediment sources and mixing models   总被引：3，自引：0，他引：3  

Arman HADDADCHI  Darren S. RYDER  Olivier EVRARD  Jon OLLEY 《国际泥沙研究》2013,28(4):560-578

Suspended sediments in fluvial systems originate from a myriad of diffuse and point sources, with the relative contribution from each source varying over time and space. The process of sediment fingerprinting focuses on developing methods that enable discrete sediment sources to be identified from a composite sample of suspended material. This review identifies existing methodological steps for sediment fingerprinting including fluvial and source sampling, and critically compares biogeochemical and physical tracers used in fingerprinting studies. Implications of applying different mixing models to the same source data are explored using data from 41 catchments across Europe, Africa, Australia, Asia, and North and South America. The application of seven commonly used mixing models to two case studies from the US （North Fork Broad River watershed） and France （Bldone watershed） with local and global （genetic algorithm） optimization methods identified all outputs remained in the acceptable range of error defined by the original authors. We propose future sediment fingerprinting studies use models that combine the best explanatory parameters provided by the modified Collins （using correction factors） and Hughes （relying on iterations involving all data, and not only their mean values） models with optimization using genetic algorithms to best predict the relative contribution of sediment sources to fluvial systems.  相似文献   

Petrography of alluvial sands as a past and present environmental indicator: Case of the Loire River (France)     

Jean-Jacques MACAIRE  Isabelle GAY-OVEJERO  Michel BACCHI  Constantin COCIRTA  Luc PATRYL  Stéphane RODRIGUES 《国际泥沙研究》2013,28(3):285-303

Four sample sets of the Upper and Middle Loire river sands were analyzed in order to study the impact of natural and anthropogenic factors on their petrographic composition in space (on an 800 km stretch) and time. Composition was determined by modal analysis of three sand-size fractions using a polarizing optical microscope and calculated for each sample (“standard sand” = Sst). The watershed is composed mainly of endogenic (Massif Central) and sedimentary (southern Parisian Basin) rocks. B-set sands collected in channels for different water flows in 1996 show that Sst compositions vary by only 5 %. Present-day sands in the Upper Loire and Middle Loire have very high petrographic immaturity comparing to others worldwide fluvial sands, although bio-climatic conditions favor sand maturation by source-rock weathering in the watershed. This shows the strong impact of the Massif Central on sediment yield due to relief rejuvenation as a consequence of the formation of the Alps during the Quaternary. Fluvial sands stored during the Weichselian and the Holocene in the Middle Loire floodplain, although partly weathered since their deposition, show higher inputs from the endogenic rocks of the Massif Central than present-day deposits. This can be explained by Weichselian periglacial conditions and the development of crop farming since the Neolithic, which favored mechanical erosion, particularly in the Massif Central which is characterized by a cold, humid climate and steep slopes. The upstream-downstream change in the composition of presently deposited sand is low in the diked area. It shows however that basalt and some heavy mineral grains are vulnerable to abrasion during transport and indicates a marked sediment yield from ancient sediment stored in the floodplain. This is in line with the high incision of the river bed over the last 150 years partly due to dam construction and aggregate mining.  相似文献   

Comparison of the time-domain electromagnetic field from an infinitesimal point charge and dipole source   总被引：2，自引：0，他引：2  

Zhou Nan-Nan  Xue Guo-Giang  Wang He-Yuan 《应用地球物理》2013,10(3):349-356

An electromagnetic field is generated through the accelerating movement of two equal but opposite charges of a single dipole. An electromagnetic field can also be generated by a time-varying infinitesimal point charge. In this study, a comparison between the electromagnetic fields of an infinitesimal point charge and a dipole has been presented. First, the time-domain potential function of a point source in a 3D conductive medium is derived. Then the electric and magnetic fields in a 3D homogeneous lossless space are derived via the relation between the potential and field. The field differences between the infinitesimal point charge and the dipole in the step-off time, far-source, and near-source zones are analyzed, and the accuracy of the solutions from these sources is investigated. It is also shown that the field of the infinitesimal point charge in the near-source zone is different from that of the dipole, whereas the far-source zone fields of these two sources are identical. The comparison of real and simulated data shows that the infinitesimal point charge represents the real source better than the dipole source.  相似文献   

电性源时域地空电磁数据小波去噪方法研究   总被引：4，自引：2，他引：2       下载免费PDF全文

李肃义  林君  阳贵红  田培培  王远  于生宝  嵇艳鞠 《地球物理学报》2013,56(9):3145-3152

基于飞艇的时间域地空电磁探测系统,具有勘探深度大、效率高、空间分辨率高、飞行控制容易等优势.但在低空飞行测量过程中,飞艇飞行高度、航迹、姿态等受风向、大气气流、地形、地面局部温度场变化等影响而发生变化,导致固定在艇囊前端的接收线圈发生运动,切割大地磁场,产生了电磁噪声、运动噪声、基线漂移等,从而影响电磁数据的电阻率成像质量.因此,研究地空电磁信号中多种噪声的去除方法,对数据的反演解释非常重要.由于地空电磁信号中有效信号频带与部分噪声频带相重叠,使用传统滤波或消噪方法具有一定局限性.因此,本文提出一种综合小波去噪法:根据地空电磁信号的特点,采用sym8小波基;基于小波多分辨率分析原理,利用小波高尺度近似分量估计基线漂移,以校正电磁数据中的基线;基于小波阈值收缩原理,采用5层小波分解、极小极大阈值配合硬收缩函数的消噪方法,来压制数据中的其余噪声.最后,通过异常环模型的理论响应和实测数据进行算法的验证,结果表明这种综合消噪法对多种噪声均有很好的抑制作用,是一种实用有效的时间域地空电磁数据消噪方法.  相似文献   

利用井中低频偶极横波进行声波远探测的新方法   总被引：2，自引：1，他引：1       下载免费PDF全文

魏周拓  唐晓明  苏远大  谭宝 《地球物理学报》2013,56(10):3572-3580

为了突破目前声波远探测技术存在的局限性,提出了一种新的偶极横波远探测方法,即利用井中偶极子产生的井中弯曲波存在低频截止频率的现象,在声源截止频率以下激发偶极声波.通过对比分析井中偶极声源分别在截止频率上、下激发时,井孔内外产生的辐射声场,明确了截止频率以下井中偶极声源的远场辐射特征和低频截止频率激发偶极横波的优势,结合数值模拟,进一步对其反射声场进行了分析.结果表明,该方法可以避免艾里相的巨大振幅对数据量化产生的"饱和"效应,相比传统的远探测测井方式更具优势,常规源距即可满足专门的远探测测井仪器需求.  相似文献   

日本Mw9.0地震前的舒曼谐振异常分析          下载免费PDF全文

周洪娟  于海雁  曹丙霞  乔晓林 《地震学报》2013,35(3)

2011年3月11日日本本州岛东海岸附近海域发生了Mw9.0地震.基于中国云南的舒曼谐振(SR)观测站的磁场观测数据,分析了与该次地震有关的SR疑似异常现象.分析表明,震前3 4天低阶谐振开始出现比较明显的幅度增强现象,以2011年3月8日(北京时间)这一天的现象最明显,南北向在7:00-10:00和12:00-15:00异常比较明显,而东西向只在12:00-15:00异常相对比较强.根据对2011年3月1-11日及对应每天前后各15天共41天的数据的联合分析,3月8日部分时间段的低阶谐振磁场差明显高于一倍甚至两倍标准差;相比而言,正常的一天内各阶磁场差要明显低于一倍标准差.最后,根据一些日本地震学者提出的SR异常机理,进一步分析了在云南观测站能观测到日本地震异常的可能性.结果表明,在永胜观测站可以观测到日本地震引起的一阶到三阶SR异常,与发现的异常主要集中在低阶的现象比较吻合.  相似文献   

云南中小地震矩震级的测定   总被引：4，自引：0，他引：4  

杨晶琼  刘丽芳  杨周胜 《地震研究》2013,36(3)

利用云南省测震台网的数字地震波形资料,反演了2008年1月至2012年9月675个中小地震的震源波谱参数,并计算了这些地震的地震矩M0和矩震级Mw,最后利用回归分析方法得到了近震震级ML和Mw之间的关系式.  相似文献   

芦山地震有限断层混合震源模型模拟     

孙晓丹  王罡  刘成清 《地震工程与工程振动》2013,33(4)

建立了基于有限断层的芦山地震的混合震源模型,突出破裂面上滑动量分布中凹凸体的主导作用,同时借助k平方模型表达对震源复杂性认识尚不够深入所带来的随机性.混合震源模型中全局震源参数均值与局部震源参数均值的确定,主要依据统计的半经验标定公式,进一步借助截断正态分布将区域地震、地质构造、地震活动性提供的参数限值结合起来,生成最终的震源参数值.基于上述思路,本文共建立了30组芦山地震混合震源模型,进而以芦山地震8个近场观测台站为试算点,借助地震动反应谱残差评价的方法,从30组模型中选定了表达“平均”特征的混合震源模型.  相似文献   

Spatial and temporal dust source variability in northern China identified using advanced remote sensing analysis   总被引：1，自引：0，他引：1  

A. Taramelli  M. Pasqui  J. Barbour  D. Kirschbaum  L. Bottai  C. Busillo  F. Calastrini  F. Guarnieri  C. Small 《地球表面变化过程与地形》2013,38(8):793-809

The aim of this research is to provide a detailed characterization of spatial patterns and temporal trends in the regional and local dust source areas within the desert of the Alashan Prefecture (Inner Mongolia, China). This problem was approached through multi‐scale remote sensing analysis of vegetation changes. The primary requirements for this regional analysis are high spatial and spectral resolution data, accurate spectral calibration and good temporal resolution with a suitable temporal baseline. Landsat analysis and field validation along with the low spatial resolution classifications from MODIS and AVHRR are combined to provide a reliable characterization of the different potential dust‐producing sources. The representation of intra‐annual and inter‐annual Normalized Difference Vegetation Index (NDVI) trend to assess land cover discrimination for mapping potential dust source using MODIS and AVHRR at larger scale is enhanced by Landsat Spectral Mixing Analysis (SMA). The combined methodology is to determine the extent to which Landsat can distinguish important soils types in order to better understand how soil reflectance behaves at seasonal and inter‐annual timescales. As a final result mapping soil surface properties using SMA is representative of responses of different land and soil cover previously identified by NDVI trend. The results could be used in dust emission models even if they are not reflecting aggregate formation, soil stability or particle coatings showing to be critical for accurately represent dust source over different regional and local emitting areas. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

震源动力学破裂过程数值模拟研究   总被引：2，自引：1，他引：1  

张丽芬  姚运生 《地震学报》2013,35(4):604-615

首先阐述了震源动力学过程研究的重要意义, 在此基础上, 研究了复杂的断层几何形态及介质模型对动力学破裂过程的影响, 并对常用的有限元方法、 离散元方法、 有限差分方法和边界积分方程方法等进行了相应介绍. 讨论了这些数值模拟方法各自的优缺点, 建议在方法的选择上应视具体问题及计算的精度而定. 最后对动力学数值模拟的关键部分, 滑动摩擦准则进行了论述. 常用的滑动摩擦准则有滑动弱化准则、 速率弱化准则和速率-状态依赖摩擦准则. 在单纯考虑某个地震的动力学破裂传播过程时, 滑动弱化准则较为常用, 其中滑动弱化距离的选取至关重要. 但若考虑整个地震循环, 速率-状态依赖摩擦准则更为合适.   相似文献