地震走时层析成像方法及在陨石坑探测中的应用

地震走时层析成像是地球物理反演中成熟的方法之一,已在许多领域得到广泛应用,并取得了良好的效果。本文介绍的地震层析成像方法包括模型参数化、射线追踪和理论走时计算、非线性方程组的线性化、线性化方程组的求解以及解的评价。观测数据使用了中国地震局地球物理勘探中心在岫岩陨石坑取得的浅层地震折射资料,反演得到两条近垂直交叉剖面的P波速度结构。结果表明,该坑为一简单坑,直接撞击形成的区域为直径约1．8km、深度约700m的坑体;坑中心深度约700m周围以及向下出现的7．0km／s以上的高波速可能是陨石撞击时所产生的高温高压使表层岩石达到熔融状态,改变了围岩的性质,致使围岩速度升高。     

三维非均匀地质模型中的逐段迭代射线追踪

地震射线追踪是地震定位、层析成像、偏移等领域的重要正演环节.随着这些领域研究的深入,针对传统的网格结构和层状结构在描述复杂地质模型遇到的很大困难,我们采用大小不等、形状各异的地质块组成的集合体来描述三维复杂地质模型,并用三角形面片来描述地质块之间的物性间断面,理论上可以描述任意复杂的地质模型.为适应任意非均匀速度分布的地质模型,基于费马原理,本文发展了与之相适应的逐段迭代射线追踪方法.该方法属于弯曲法范畴,对路径点采用一阶显式增量修正,相对于传统的迭代法,高效省时.数值试验表明,联合逐段迭代法和伪弯曲法的射线追踪扰动修正方案在三维复杂非均匀块状模型中有适用性和高效性.     

电离层人工调制激发的VLF波在磁层的传播特性及应用研究

电离层人工调制可以激发甚低频（VLF）波,其中向上传播进入磁层的VLF波,不但能够用来研究磁层中的各种物理现象,且具有人工沉降高能粒子,消除辐射带等实际用途.本文使用射线追踪方法,模拟电离层调制激发的VLF波在磁层的传播路径,分析激发纬度和调制频率对传播路径和传播特性的影响;并基于低频波的色散方程和波粒共振条件,分析VLF波传播路径上与磁层高能粒子的最低共振能及其分布.研究表明,VLF波通过在磁层来回反射向更高的L-shell传播,最终稳定在某一L-shell附近.以较低的调制频率或者从较高的纬度激发的VLF波能够传播到更高的L-shell,但是,当激发纬度过高时,低频波也可能不发生磁层反射而直接进入电离层和大气层.低频波在磁层的传播过程中,在较高的纬度或者较低的L-shell能够与较高能量的电子发生共振相互作用,在较高的L-shell并且低纬地区,能够与较低能量的电子发生共振相互作用.共振谐数越高,能发生波粒共振的电子能量越高.     

Sediment routing hypothesis for pool‐riffle maintenance

This paper provides comprehensive evidence that sediment routing around pools is a key mechanism for pool‐riffle maintenance in sinuous upland gravel‐bed streams. The findings suggest that pools do not require a reversal in energy for them to scour out any accumulated sediments, if little or no sediments are fed into them. A combination of clast tracing using passive integrated transponder (PIT) tagging and bedload traps (positioned along the thalweg on the upstream riffle, pool entrance, pool exit and downstream riffle) are used to provide information on clast pathways and sediment sorting through a single pool‐riffle unit. Computational fluid dynamics (CFD) is also used to explore hydraulic variability and flow pathways. Clast tracing results provide a strong indication that clasts are not fed through pools, rather they are transported across point bar surfaces, or around bar edges (depending upon previous clast position, clast size, and event magnitude). Spatial variations in bedload transport were found throughout the pool‐riffle unit. The pool entrance bedload trap was often found to be empty, when the others had filled, further supporting the notion that little or no sediment was fed into the pool. The pool exit slope trap would occasionally fill with sediment, thought to be sourced from the eroding outer bank. CFD results demonstrate higher pool shear stresses (τ ≈ 140 N m^–2) in a localized zone adjacent to an eroding outer bank, compared to the upstream and downstream riffles (τ ≈ 60 N m^–2) at flows of 6 · 2 m³ s^–1 (≈ 60% of the bankfull discharge) and above. There was marginal evidence for near‐bed velocity reversal. Near‐bed streamlines, produced from velocity vectors indicate that flow paths are diverted over the bar top rather than being fed through the thalweg. Some streamlines appear to brush the outer edge of the pool for the 4 · 9 m³ s^–1 to 7 · 8 m³ s^–1 (between 50 and 80% of the bankfull discharge) simulations, however complete avoidance was found for discharges greater than this. Copyright © 2013 John Wiley & Sons, Ltd.     

Nonlinearities and Linearities in Internal Gravity Waves of the Atmosphere and Oceans

The spectrum of internal gravity waves in the atmosphere and oceans is sufficiently intense that nonlinear interactions must occur, if these waves are analyzed in Eulerian coordinates as is usually done. As it happens, however, if these waves are analyzed in Lagrangian coordinates the most important nonlinearity can be entirely avoided: it is an Eulerian mathematical construct only, not a physical process. The mathematical basis for this assertion is developed here, and some of its consequences are discussed. Among the latter is a questioning of the validity of standard Eulerian eikonal methods of calculating ray paths and related functions in a multiwave environment, discussed in an appendix.     

Estimation of viscoelastic attenuation of real seismic data by use of ray tracing software: Application to the detection of gas hydrates and free gas

Analysis of P wave velocity profiles and seismic data recorded over the 2002 Hydratech cruise conducted in the Storegga region, North of Norway, has shown the existence of anomalies (a velocity decrease) in some layers of the medium. An elastic propagation model is not sufficient to explain clearly these anomalies, since the viscoelastic attenuation, represented by the quality factor Q_P, is sensitive to physical phenomena of geological media. The combination of the quality factor profile with the velocity profile leads to realistic explanations of these anomalies. In this article, we explain the procedure which we developed for determining the Q_P profile from the P wave velocity profile and the seismic data recorded during Hydratech cruise. Both the Q_P and velocity profiles indicate anomalies in the same layers. Based on previous studies, we interpret that these anomalies are being due to existence of gas hydrates and free gas within these layers.     

东胜煤田锡尼布拉格勘查区煤层对比

东胜煤田锡尼布拉格勘查区主要含煤地层为中侏罗统延安组,含煤层层数较多,且钻孔间距较大,煤层对比难度较大。根据区内勘查成果结合区域资料,采用煤层组合宏观结构、沉积旋回、地震波阻抗追索、测井曲线特征、标志层、煤层间距及煤层结构对比法等综合手段进行煤层对比,使3-1、4-1、4-2、5-1、5-2主要可采煤层达到对比可靠,3-2、3-3、4-1下等次要可采煤层和不可采煤层达到对比基本可靠的程度。     

基于大炮初至的近地表层析反演方法研究及应用

详细研究了射线追踪、层析反演方法原理以及层析反演数值求解算法,提出了利用大炮初至直接建立初始地震模型,由小折射和微测井进行约束的层析反演近地表速度模型的处理流程,提出了基于多次回溯的高精度快速射线追踪算法和层析反演数值求解算法。采用双重网格技术提高正演模拟计算精度和层析反演的成像质量,另外,充分考虑多种质量控制方案,确保最终的反演速度模型精确。设计了10种不同地表地质条件的理论模型,进行模型试算,并在实际生产中应用,理论模型试算和实际资料反演结果证明了本文方法的正确性。     

地下水温度示踪理论与方法研究进展

对地下水温度示踪理论与方法的相关研究做了评述,介绍了当前地质体中温度场与渗流场耦合作用模型、数值模拟技术和渗流参数反演方法,并从温度示踪方法的两个主要应用领域:地表水与地下水交换和工程地下水渗漏探测(以堤坝为例),说明地下水温度示踪的应用研究.在地质体中温度场与渗流场耦合模型方面,裂隙介质、非饱和带、复杂边界条件和非D...     

黄海绿潮应急溯源数值模拟初步研究

基于三维全动力POM 海洋模式, 根据2008 年6 月1 日海监飞机监测绿潮所在位置, 采用拉格朗日粒子追踪法反向积分, 追溯绿潮来源。数值模拟结果显示, 回溯至5 月中旬, 绿潮主要来源于黄海南部江苏连云港和盐城近海海域。黄海绿潮溯源数值模拟, 为政府相关部门了解绿潮的源头, 并采取相应的措施提供依据, 进而为保护生态环境、防灾减灾做贡献。