Flexible spectral methods for the generation of random fields with power-law semivariograms

Random field generators serve as a tool to model heterogeneous media for applications in hydrocarbon recovery and groundwater flow. Random fields with a power-law variogram structure, also termed fractional Brownian motion (fBm) fields, are of interest to study scale dependent heterogeneity effects on one-phase and two-phase flow. We show that such fields generated by the spectral method and the Inverse Fast Fourier Transform (IFFT) have an incorrect variogram structure and variance. To illustrate this we derive the prefactor of the fBm spectral density function, which is required to generate the fBm fields. We propose a new method to generate fBm fields that introduces weighting functions into the spectral method. It leads to a flexible and efficient algorithm. The flexibility permits an optimal choice of summation points (that is points in frequency space at which the weighting function is calculated) specific for the autocovariance structure of the field. As an illustration of the method, comparisons between estimated and expected statistics of fields with an exponential variogram and of fBm fields are presented. For power-law semivariograms, the proposed spectral method with a cylindrical distribution of the summation points gives optimal results.     

Pore-water geochemistry in methane-seep sediments of the Makran accretionary wedge off Pakistan: Possible link to subsurface methane hydrate

Cold seeps are pervasive along the continental margin worldwide,and are recognized as hotspots for elemental cycling pathway on Earth.In this study,analyses of pore water geochemical compositions of one-400 cm piston core(S3) and the application of a mass balance model are conducted to assess methane-associated biogeochemical reactions and uncover the relationship of methane in shallow sediment with gas hydrate reservoir at the Makran accretionary wedge off Pakistan.The results revealed that approximately 77% of sulfate is consumed by the predominant biogeochemical process of anaerobic oxidation of methane.However,the estimated sulfate-methane interface depth is-400 cm below sea floor with the methane diffusive flux of 0.039 mol/(m~2·a),suggesting the activity of methane seepage.Based on the δ~(13)C_(DIC) mass balance model combined with the contribution proportion of different dissolved inorganic carbon sources,this study calculated the δ~(13)C of the exogenous methane to be-57.9‰,indicating that the exogenous methane may be a mixture source,including thermogenic and biogenic methane.The study of pore water geochemistry at Makran accretionary wedge off Pakistan may have considerable implications for understanding the specific details on the dynamics of methane in cold seeps and provide important evidence for the potential occurrence of subsurface gas hydrate in this area.     

数字与模拟地震台网记录的震相特征与地震参数对比分析

本文对辽宁数字与模拟地震台网从1998年12月至1999年5月记录到震波特征、地震参数进行初步的比较与分析。     

The effectiveness of a pseudo-inverse extended Born operator to handle lateral heterogeneity for imaging and velocity analysis applications

Wave equation–based migration velocity analysis techniques aim to construct a kinematically accurate velocity model for imaging or as an initial model for full waveform inversion applications. The most popular wave equation–based migration velocity analysis method is differential semblance optimization, where the velocity model is iteratively updated by minimizing the unfocused energy in an extended image volume. However, differential semblance optimization suffers from artefacts, courtesy of the adjoint operator used in imaging, leading to poor convergence. Recent findings show that true amplitude imaging plays a significant role in enhancing the differential semblance optimization's gradient and reducing the artefacts. Here, we focus on a pseudo-inverse operator to the horizontally extended Born as a true amplitude imaging operator. For laterally inhomogeneous models, the operator required a derivative with respect to a vertical shift. Extending the image vertically to evaluate such a derivative is costly and impractical. The inverse operator can be simplified in laterally homogeneous models. We derive an extension of the approach to apply the full inverse formula and evaluate the derivative efficiently. We simplified the implementation by applying the derivative to the imaging condition and utilize the relationship between the source and receiver wavefields and the vertical shift. Specifically, we verify the effectiveness of the approach using the Marmousi model and show that the term required for the lateral inhomogeneity treatment has a relatively small impact on the results for many cases. We then apply the operator in differential semblance optimization and invert for an accurate macro-velocity model, which can serve as an initial velocity model for full waveform inversion.     

Feature Construction and Identification of Convective Wind from Doppler Radar Data

Convective wind is one of the common types of severe convective weather. Identification and Forecasting of con- vective wind are essential. In this paper, five ...     

基于扩展Lagrange乘子的Clough接触面模型及应用

双曲线接触面本构模型能比较真实地模拟堆石材料与混凝土面板间的接触关系,扩展Lagrange乘子法能比较精确地计算接触面间接触状态。在吸取Clough双曲线接触面本构关系应用于无厚度的Goodman单元和有厚度的Desai薄层单元的成功经验的基础上,将Clough双曲线接触面模型引入扩展Lagrange乘子法进行摩擦接触问题的求解。介绍了基于扩展Lagrange乘子法的序列二次规划法（SQP）提法,详细推导了在扩展Lagrange算法的非线性接触计算中引入Clough双曲线接触面本构关系的数值列式和实施步骤。数值算例和工程实例的计算结果证明该方法是成功的,能够比较真实地模拟堆石-混凝土墙（混凝土面板）之间的接触状态。     

在CTMAB存在下应用苯基萤光酮分光光度法测定岩矿中微量锡

本文研究了在ＣＴＭＡＢ存在下，应用苯基萤光酮分光光度法测定微量锡的条件。该法灵敏度高，操作简便，可用于测定岩矿样品中的微量锡。     

对中国地震预报现状与未来的思考

本文是作者根据自己多年从事地震预报的经历与实践,将我国地震预报的38年历史分为四个阶段,概括了我国地震预报的主要进展和成就,指出地震预报的难点及我国地震预报的思路和技术上存在的几个问题,最后对我国地震预报发展战略提出思考。作者的观点和建议可供地震主管部门的领导和地震分析预报人员参考     

冲填土固结特性与变形沉降规律研究

应用室内模型试验的方法对上海地区冲填土的固结特性进行了研究,冲填土从水力吹填开始到固结完成,经历了三个阶段,即沉积阶段、土体颗粒接触阶段与土体固结阶段; 固结时有效应力的增长分为快速增长和缓慢增长两个时期,土体固结沉降主要发生在固结前期,沉降量与有效应力呈正比关系; 排水及荷载条件对冲填土的固结特性与强度有较大影响。本文通过双面排水自重固结、单面排水加载固结及单面排水自重固结三组对照试验,揭示了冲结、变形与沉降量之间的关系,为冲填土地区地面沉降的预测和地基变形的计算提供了有价值的参考。     

新月形沙丘迎风坡形态及沉积物对表面气流的响应

对孤立新月形沙丘迎风坡风速的野外实测和计算表明,沙丘迎风坡表面风速廓线呈非对数关系,近地面剪切风速和输沙强度由坡脚至丘顶总体呈递增趋势,但同时随断面坡度的增减而发生相应的变化;沿断面输沙率的变化导致蚀积强度的改变,表现为沙丘迎风坡坡度变缓的部位沉积大于侵蚀,其它部位侵蚀大于沉积,其中丘顶输沙率和侵蚀强度最大。在沙丘形态上,表现为坡度减缓的部位沉积变凸、其它部位因侵蚀变凹以及坡脚和丘顶的前移。变凸和变凹部位反过来又制约着表面剪切风速的相应变化。粒度分析也表明,沙丘迎风坡表面粒度特征主要取决于表面蚀积状况,同断面形态表现出密切的相关性。