Mineral fibres and environmental monitoring:A comparison of different analytical strategies in New Caledonia     

Jasmine Rita Petriglieri  Christine Laporte-Magoni  Peggy Gunkel-Grillon  Mario Tribaudino  Danilo Bersani  Orietta Sala  Monika Le Mestre  Ruggero Vigliaturo  Nicola Bursi Gandolfi  Emma Salvioli-Mariani 《地学前缘(英文版)》2020,11(1):189-202

Covered by ultrabasic units for more than a third of its surface,the New Caledonia(South West Pacific)is one of the largest world producers of Ni-ore from lateritic deposits.Almost all outcrops of geological units and open mines contain serpentine and amphibole,also as asbestos varieties.In this geological context,in which weathering processes had a great contribution in the production and dispersion of mineral fibres into the environment,the development of a routinely analytical strategy,able to discriminate an asbestiform fibre from a non-harmful particle,is a pivotal requisite.However,the acquisition of all these parameters is necessary for determining the risk associated to fibres exposition.A multidisciplinary routinely approach,based on the use of complementary simply-to-use but reliable analytical methods is the only possible strategy.In addition,the instrumental apparatus must be easily transportable on the field,directly on the mining site.The employment of specialized tools such as Polarized Light Microscopy associated to Dispersion Staining method(PLM/DS)and portable Raman spectroscopy for identification of environmental asbestos,are proved extremely effective in the improvement of the performance and rapidity of data acquisition and interpretation.Both PLM/DS and handheld Raman devices confirmed to be discriminant in the detection and characterization of asbestos fibres for both serpentine and amphibole.Furthermore,these techniques proved extremely effective even in the presence of strongly fibrous and altered samples.  相似文献   

南海地区地震背景噪声成像与壳幔深部结构          下载免费PDF全文

赵建忠  李志伟  林建民  郝天珧  包丰  谢军  王嘹亮  涂广红 《地球物理学报》2019,62(6):2070-2087

利用南海地区28个陆地地震台站和2个布设于太平岛和东沙岛的新增海岛地震台站2011—2016年间的连续地震背景噪声波形数据,使用互相关方法计算得到了台站间的互相关函数,并提取出Rayleigh面波群速度和相速度频散曲线.采用快速行进和子空间方法反演获得了南海及周边地区12～40s周期的Rayleigh面波群速度和相速度图像,并联合反演得到了研究区深至60km的三维S波速度结构.考虑到南海数千米厚海水层对于面波频散反演的严重影响,本文在反演模型中加入了水层,显著提高了反演结果的可靠性.成像结果表明:南海及周边地区地壳上地幔顶部S波速度结构存在显著的横向不均匀性,并与这一区域的主要构造单元具有较好的空间对应关系.在5～10km深度,莺歌海—宋红盆地区的低速异常特征可能与盆地较厚的沉积层有关.在5～15km深度,海域高速异常区与海盆空间位置具有高度一致性,推测与海盆区地壳厚度相对陆缘区明显偏薄有关.当深度从20km增加至30km,海盆区的高速特征扩展至了陆缘地区,反映了地壳厚度从海盆至陆缘逐渐增厚的趋势,与OBS(海底地震仪)深地震剖面给出的地壳精细结构结果一致.至35～60km深度,海盆的高速异常特征依然明显,且速度值随深度增加整体呈现上升的趋势,推测南海海盆区的岩石圈厚度应该大于60km.  相似文献   

含小断层煤层Rayleigh型槽波波场和频散分析   总被引：1，自引：0，他引：1       下载免费PDF全文

乔勇虎  滕吉文  皮娇龙 《地球物理学报》2018,61(12):4976-4987

煤层隐伏小断层在煤田地质勘探期间能否查明，是影响煤矿安全生产的主要地质因素.煤层中传播的地震槽波，非常适用于探测煤田异常构造.本文利用谱元法模拟计算了含断层模型Rayleigh型地震槽波的产生、传播过程，对于直达槽波、反射槽波、透射槽波进行了波场特征分析，频散特征分析，频谱特征分析.根据不同小落差断层模型（垂直断距分别为1/4、1/2、3/4、1个煤厚；断层倾角分别为90°、60°、45°），分析了Rayleigh型槽波传播过程中断层对反射槽波、透射槽波能量、频谱的影响效应.基于以上分析，对于小断层模型中的Rayleigh型地震槽波取得了一些规律性认识，并对Rayleigh型地震槽波的勘探应用做了一些探讨.  相似文献   

煤层厚度变化时地震槽波理论频散曲线计算方法及频散特征分析   总被引：1，自引：0，他引：1       下载免费PDF全文

乔勇虎  滕吉文 《地球物理学报》2018,61(8):3374-3384

槽波地震勘探利用槽波的频散特性反演煤层的结构特征，故理论频散曲线的计算是一个重要方面.使用水平层状模型假设下的面波频散曲线计算方法能够计算煤层厚度恒定模型地震槽波频散曲线；但当煤层厚度变化时该方法不再适用.基于前人水平层状均匀介质模型的面波理论频散曲线计算方法，对于含煤三层模型，本文发展了煤层厚度变化情况下的地震槽波理论频散曲线计算方法，并使用该方法计算分析了不同厚度函数模型的频散曲线形态特征.研究表明：与稳定厚度煤层相比，煤层厚度变化使得地震槽波群速度成为与频率及传播射线在水平面投影路径相关的二元函数；射线路径上煤层厚度的变化使得频散曲线在群速度方向上压缩，群速度变化范围变小，且使处于最小值位置的埃里相群速度增大；而煤层厚度的线性变化模型频散曲线只与射线首、尾处的煤层厚度有关，与煤层厚度恒定模型相比，曲线形态不发生改变；煤层厚度呈非线性变化时，频散曲线形态上可能发生改变.  相似文献   

Frequency-dependent PP and PS reflection coefficients in fractured media     

Shuo Pang  Alexey Stovas 《Geophysical Prospecting》2020,68(3):926-940

When a porous layer is permeated by mesoscale fractures, wave-induced fluid flow between pores and fractures can cause significant attenuation and dispersion of velocities and anisotropy parameters in the seismic frequency band. This intrinsic dispersion due to fracturing can create frequency-dependent reflection coefficients in the layered medium. In this study, we derive the frequency-dependent PP and PS reflection coefficients versus incidence angle in the fractured medium. We consider a two-layer vertical transverse isotropy model constituted by an elastic shale layer and an anelastic sand layer. Using Chapman's theory, we introduce the intrinsic dispersion due to fracturing in the sand layer. Based on the series coefficients that control the behaviour of velocity and anisotropy parameters in the fractured medium at low frequencies, we extend the conventional amplitude-versus-offset equations into frequency domain and derive frequency-dependent amplitude-versus-offset equations at the elastic–anelastic surface. Increase in fracture length or fracture density can enlarge the frequency dependence of amplitude-versus-offset attributes of PP and PS waves. Also, the frequency dependence of magnitude and phase angle of PP and PS reflection coefficients increases as fracture length or fracture density increases. Amplitude-versus-offset type of PP and PS reflection varies with fracture parameters and frequency. What is more, fracture length shows little impact on the frequency-dependent critical phase angle, while the frequency dependence of the critical phase angle increases with fracture density.  相似文献   

多极子阵列声波测井数据的纵横波慢度联合反演方法          下载免费PDF全文

江灿  庄春喜  李盛清  苏远大  唐晓明 《地球物理学报》2019,62(6):2294-2302

多极子阵列声波测井仪器采集的单极和偶极数据受到地层、井孔、仪器测量系统的影响.在处理实际声波测井数据时,必须考虑多极子模式波的频散效应,以及测井仪器在其中的影响.根据仪器等效理论和相位匹配方法,本文提出了一种从多极子阵列声波测井数据中同时获得纵、横波慢度的联合反演方法.这种方法的关键在于利用相同仪器-地层模型计算多极子模式波频散曲线,以此来匹配频域内纵波与横波数据的相位.相对于将泄漏纵波和弯曲波频散效应分开处理的其他方法,该方法不仅可以减少纵横波速度反演的不确定性,而且还避免了从声波数据中提取频散数据的繁琐过程.通过理论分析和现场数据处理证明了本文联合反演方法的准确性和有效性.  相似文献   

Wave-ice interaction in the North-West Barents Sea     

《Applied Ocean Research》2019

The results of field work on drift ice during wave propagation are analyzed and presented. The field work was performed in the Barents Sea, and the main focus of the paper is on wave processes in the MIZ. A model of wave damping in broken ice is formulated and applied to interpret the field work results. It is confirmed that waves of higher frequencies are subjected to stronger damping when they propagate below the ice. This reduces the frequency of most energetic wave with increasing distance from the ice edge. Difference of wave spectra measured in two relatively close locations within the MIZ is discussed. The complicated geometry and dynamics of the MIZ in the North-West Barents Sea allow waves from the Atlantic Ocean and south regions of the Barents Sea to penetrate into different locations of the MIZ.  相似文献   

基于频变AVO反演的页岩储层含气性地震识别技术          下载免费PDF全文

逄硕  刘财  郭智奇  刘喜武  刘宇巍 《地球物理学报》2018,61(11):4613-4624

结合地震岩石物理技术，研究了叠前频变AVO反演在四川盆地龙马溪组页岩储层含气性识别中的应用.首先，应用Backus平均理论将测井数据粗化为地震尺度储层模型，应用传播矩阵理论进行高精度地震正演及井震标定，分析页岩气储层地震响应特征.其次，基于岩心观测结果，应用Chapman多尺度裂缝理论设计页岩气储层理论模型，研究储层衰减、频散以及对应的地震反射特征.应用该理论模型测试频变AVO反演方法，计算结果表明：对于研究区地层结构和地震数据，区分流体类型的优势频率不是地震子波的主频，还受层间调谐干涉等储层结构因素控制，也进一步说明理论模型测试和标定的重要性.最后，将频变AVO反演技术应用到四川盆地龙马溪组页岩地层，计算得到的频散属性为页岩气储层含气性识别提供依据.  相似文献   

Analysis of macrodispersion through volume-averaging: Moment equations     

P. K. Kitanidis 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(1):5-25

Macrodispersion is spreading of a substance induced by spatial variations in local advective velocity at field scales. Consider the case that the steady-state seepage velocity and the local dispersion coefficients in a heterogeneous formation may be modeled as periodic in all directions in an unbounded domain. The equations satisfied by the first two spatial moments of the concentration are derived for the case of a conservative non-reacting solute. It is shown that the moments can be calculated from the solution of well-defined deterministic boundary value problems. Then, it is described how the rate of increase of the first two moments can be calculated at large times using a Taylor-Aris analysis as generalized by Brenner. It is demonstrated that the second-order tensor of macrodispersion (or effective dispersion) can be computed through the solution of steady-state boundary-value problems followed by the determination of volume averages. The analysis is based solely on volume averaging and is not limited by the assumption that the fluctuations are small. The large-time results are valid when the system is in a form of equilibrium in which a tagged particle samples all locations in an appropriately defined phase space with equal probability.  相似文献   

横向非均匀介质多道瑞雷波频散曲线正演     

胡书凡  赵永辉  吴健生  葛双成 《地球物理学报》2021,64(5):1699-1709

作为近地表横波速度结构成像的主要手段之一,面波多道分析法的正问题研究对现场观测系统设计及后续反演计算具有重要意义.目前面波频散曲线的正演主要分为两类:一是对水平层状介质中面波的本征值问题进行求解,该类方法计算效率高但较难考虑地下介质在横向上的不均匀性;二是基于波动方程的全波场模拟,该类方法在理论上可考虑任意复杂的地质模型但计算成本相对较高.本文基于振幅归一化加权的聚束分析,提出了一种适用于横向非均匀介质模型的多道瑞雷波频散曲线正演方法.首先,基于聚束分析的计算公式推导得到了经振幅归一化加权后输出功率谱中相速度与局部相速度之间的关系,然后通过黄金分割极值搜索算法计算得到了多道瑞雷波数据的理论频散曲线.数值分析结果表明,该算法能够快速地实现横向非均匀介质中多道瑞雷波频散曲线的正演计算,所求取的频散曲线与采用二维弹性波时间域有限差分模拟分析得到的结果误差较小,这在一定程度上说明了该计算方法的可靠性,从而可为面波多道分析法中的观测系统快速优化设计以及横向非均匀介质中频散曲线的反演解释提供理论支撑.  相似文献