Identifying causes of ground-penetrating radar reflections using time-domain reflectometry and sedimentological analyses   总被引：5，自引：0，他引：5  

Remke L. Van Dam  & Wolfgang Schlager 《Sedimentology》2000,47(2):435-449

Ground-penetrating radar (GPR) is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves. However, little is known about the exact cause of GPR reflections because few studies have coupled wave theory to petrophysical data. In this study, a 100- and 200-MHz GPR survey was conducted on aeolian deposits in a quarry. Time-domain reflectometry (TDR) was used to obtain detailed information on the product of relative permittivity (ɛ_r) and relative magnetic permeability (μ_r), which mainly controls the GPR contrast parameter in the subsurface. Combining TDR data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and ɛ_rμ_r. Synthetic radar traces, constructed using the TDR logs and sedimentological data from the lacquer peels, were compared with the actual GPR sections. Numerous peaks in ɛ_rμ_r, which are superimposed on a baseline value of 4 for dry sand, are caused by potential GPR reflectors. These increases in ɛ_rμ_r coincide with the presence of either organic material, having a higher water content and relative permittivity than the surrounding sediment, or iron oxide bands, enhancing relative magnetic permeability and causing water to stagnate on top of them. Sedimentary structures, as reflected in textural change, only result in possible GPR reflections when the volumetric water content exceeds 0·055. The synthetic radar traces provide an improved insight into the behaviour of radar waves and show that GPR results may be ambiguous because of multiples and interference.  相似文献   

类锂离子C^3 光电离过程的研究     

冯向华  马轩文 《测绘学院学报》2000,17(2):152-153,156

使用Ｒ－矩阵方法,采用三态密耦图像计算了类锂离子Ｃ＾３＋激发态１ｓ＾２２ｐ＾２Ｐ的光电离截面,并给出了不同过程及不同分波的截面。计算结果揭示了光电离过程中的Ｒｙｄｂｅｒｇ系列共振。  相似文献   

长江中下游第四纪沉积物发育土壤磁性增强的环境磁学机制   总被引：25，自引：2，他引：23  

卢升高  俞劲炎  章明奎  俞立中  张卫国 《沉积学报》2000,18(3):336-340

对长江中下游第四纪沉积物 (Q₃ 黄土,Q₂ 红土和Q₃ 红土 )发育土壤的磁性增强现象及其物理机制进行了讨论。结果表明 :(1)铁磁性矿物是土壤磁性的主要载体,它们是成土过程中形成的稳定单畴 (SSD)和超顺磁性 (SP)态的次生磁性矿物,没有显示重要的反铁磁性矿物的贡献;(2 )土壤磁化率 (χ)的高低与成土过程产生的稳定单畴和超顺磁性颗粒呈极显著正相关,指示了风化成土作用的强度,磁化率可作为反映成土环境变化的代用指标;(3)频率磁化率 (χfd) 5 %可作为土壤中的超顺磁性颗粒存在与否的临界值,土壤 χfd值的高低同样反映了风化成土作用的强度,可用作研究第四纪环境变化的有用工具之一。  相似文献   

地基-非线性结构相互作用体系的主共振与分叉   总被引：2，自引：1，他引：1  

姜忻良  谷岩 《地震工程与工程振动》2000,20(3):22-27

本文考虑上部结构的恢复力为双线型模型,地基上简化为集中参数模型,运用平均法研究相互作用体系的主共振,得到主共振的定数解并讨论其稳定性。文中导出相互作用体系的分叉方程,并根据厅异性理论给出开折参数平面下的分叉图和转迁集,讨论不同物理参数域内系统的振动行为并通过算例得到一些定性的结论。  相似文献   

对保靖——慈利逆冲断裂带的一些认识   总被引：2，自引：0，他引：2  

袁照令  李大明 《地质与勘探》2000,36(5):59-61

以物探、地质资料为依据,对保靖－慈利逆冲断裂带的具体位置及推覆运动的方向提出了一些新的认识。  相似文献   

重磁数据计算机处理技术在莺子山地区地质研究中的应用     

姚超美  杨泽元 《地质与勘探》2000,36(6):66-69

对莺子山地区１：１万重磁资料进行了计算机处理,根据处理结果,推断了数条断裂构造,其方向主要为ＮＮＥ向和ＮＷ向,分析了构造重向上的变化,认为深部构造以ＮＮＥ向为主,ＮＷ向构造减少;圈定了莺子山岩体的范围,其面积约为５ｋｍ＾２。根据重磁数据处理与解译,综合前人工作成果,对莺子山地区进行了硫铁矿成矿预测,提出了４个硫铁矿远景区。  相似文献   

Determination of High Field Strength Elements, Rb, Sr, Mo, Sb, Cs, Tl and Bi at ng g⁻¹ Levels in Geological Reference Materials by Magnetic Sector ICP-MS after HF/HClO₄ High Pressure Digestion     

Zongshou Yu  Philip Robinson  Ashley T. Townsend  Carsten Mnker  Anthony J. Crawford 《Geostandards and Geoanalytical Research》2000,24(1):39-50

Six low abundance rock reference materials (basalt BIR-1, dunite DTS-1, dolerite DNC-1, peridotite PCC-1, serpentine UB-N and basalt TAFAHI) have been analysed for high field strength elements (Zr, Nb, Hf, Ta, Th and U), Rb, Sr, Mo, Sb, Cs, Tl and Bi at ng g⁻¹ levels (in rock) by magnetic sector inductively coupled plasma-mass spectrometry after HF/HClO₄ high pressure decomposition. The adopted method uses only indium as an internal standard. Detection limits were found to be in the range of 0.08 to 16.2 pg ml⁻¹ in solution (equivalent to 0.08 to 16.2 ng g⁻¹ in rock). Our data for high field strength elements, Rb, Sr, Mo, Sb, Cs, Tl and Bi for the six selected low abundance geological reference materials show general agreement with previously published data. Our Ta values in DTS-1 and PCC-1 (1.3 and 0.5 ng g⁻¹) are lower than in previously published studies, providing smooth primitive mantle distribution patterns. Lower values were also found for Tl in BIR-1, DTS-1 and PCC-1 (2, 0.4 and 0.8 ng g⁻¹). Compared with quadrupole ICP-MS studies, the proposed magnetic sector ICP-MS method can generally provide better detection limits, so that the measurement of high field strength elements, Rb, Sr, Mo, Sb, Cs, Tl and Bi at ng g⁻¹ levels can be achieved without pre-concentration, ion exchange separation or other specialised techniques.  相似文献   

发挥高精度磁测作用的几个实例   总被引：3，自引：0，他引：3  

张立军  高飞 《地质与资源》2001,10(3):184-189

简要介绍了高精度磁测的应用现状.通过金厂沟金矿区辽河群大石桥岩组与盖县组接触界限的划分,以及阜新建设花岗岩与长英质糜棱岩边界的划分等实例,说明得用高精度磁测结果,在配合地质填图、划分地质界线、圈定矿体和寻找古墓及古坑道等地质问题方面的优越性.用于隐伏区地质填图时,不仅能确定强磁性岩石边界,而且还能确定弱磁性岩石边界.在提高信息密度的前提下,根据磁化率K值和剩余磁化强度J_r值的不同,在典型成矿区能直接圈定弱磁性矿体.  相似文献   

Complex site effects and building codes: Making the leap   总被引：1，自引：0，他引：1  

Francisco J. Chávez-García  Ezio Faccioli 《Journal of Seismology》2000,4(1):23-40

The engineering community is aware of the importance of site effects, but it lags behind seismological studies when it comes to incorporating site effect considerations in design spectra for seismic norms. This lag is reflected in the conspicuous fact that current building codes make allowance for 1D site effects but ignore complex site effects. The purpose of this paper is to explore a way for including complex site effects in a building code environment. We take as example Eurocode 8, which is a modern code that exemplifies the current approach to site effect consideration. We examine the restrictions that we have imposed to make the problem of a feasible size and discuss the approach we have taken. We propose a strategy to incorporate a class of complex site effects in a design elastic spectrum.  相似文献   

兰州台地磁观测常见故障的判断与排除     

燕明芝  辛长江 《高原地震》2000,12(4):42-46

在地磁观测中,当绝对观测磁力仪,相对记录磁变仪,辅助设备等发生故障以及观测所得不准或其它问题时,将如何快速判别及排除,作了较详细的叙述。  相似文献