岩石非均匀性对震级—频度关系的影响的数值模拟

无论是从天然地展的统计分析还是实验室岩石破裂实验，由于测试设备的限制、观测台站或测试位置的影响，目前有关地展展级-频度关系和G—R关系式及b值的研究都不可能保证数据资料的独立性和完整性。充分利用RFPA^20数值模拟软件，克服漏记、精度低和人为的限定资料范围等不利因素的影响，在充分考虑岩石的非均匀性的基础上，研究了岩石破裂过程中微震系列震级-频度关系及b值随岩石均质度的变化规律。     

Horizontal Scale of Roughness Variations for Realistic Landscapes

A method is described to infer the horizontal scale of roughness variations from land-use maps, for use in flux aggregation schemes designed to account for sub-grid scale terrain heterogeneity in numerical models of the atmosphere. Based on simple statistical-geometrical considerations, it is shown that this horizontal scale is inversely proportional to edge density, which can be readily derived from high-resolution land-use maps. The method is demonstrated for a highly heterogeneous landscape in northern Belgium, the resulting length scale values approximately ranging between 200 and 1500 m. Finally, the extension towards satellite imagery and coarse land-use data is discussed.     

艾比湖地区土壤异质性及其对植物群落生态分布的影响

艾比湖水域萎缩、湖区旱化和人类活动频繁严重影响了当地生态环境和社会经济发展。本文通过对艾比湖地区不同类型土壤的理化性状分析和植物群落样方调查统计及其分布的规律研究，讨论了土壤质地、盐分、pH、养分、水分等自然综合体空间异质性对植物群落生态分布的影响，为该区生态环境恢复和重建提供了参考。     

Origine du matériel altéré et hétérogénéité du matériel originel de la météorite Foum Tatahouine (Tunisie) : éléments traces et isotopes du SrOrigin of altered material and heterogeneity of original material in the Foum Tatahouine meteorite (Tunisia): Trace elements and Sr isotopes

Foum Tatahouine is one of the rare meteorites that allow studying weathering effects since their fall on Earth. The comparison between clasts collected the very day of the fall (1931) and in 1994 showed some chemical modifications. We report data obtained on samples collected in 2000. The purpose of this study is: (1) to define (REE, Sr isotopes) the terrestrial weathering origin that is to be found in soil carbonates, (2) to show (Sr, Rb, REE) that the weathering effects are small on centimetre-sized samples, and (3) to emphasise (HREE) Foum Tatahouine samples heterogeneity. To cite this article: Y. Bentahila et al., C. R. Geoscience 334 (2002) 267–272.     

由含断层岩石非均匀性产生的地震前兆的数值模拟研究

使用新开发岩石破裂过程分析软件(RFPA2D)，通过一系列模型实验，研究岩石中预制断层面几何特征和力学非均匀性对地震前兆产生的影响。模型使用5个具有不同均质度的岩石样本进行数值模拟研究。数值模拟结果表明，不同均质度岩石破坏在地壳中会产生不同的地震前兆现象。在一些区域，可以观测到明显的前兆，而在另一些地区却很难观测到明显的前兆现象。模拟结果与实验观测和自然界实际观测结果由很好的一致性。     

LES Study of the Energy Imbalance Problem with Eddy Covariance Fluxes

The spatial representativeness of heat fluxes on the basis of single-tower measurements, and the mechanism of the so-called energy imbalance problem, are investigated through numerical experiments using large-eddy simulation (LES). LES experiments are done for the daytime atmospheric boundary layer heated over a flat surface, as a best-case scenario completely free of sensor errors and the uncertainties of field conditions. Imbalance is defined as the deviation of the `turbulent' heat flux at a grid point from the horizontally averaged `total' heat flux. Both the theoretical and numerical results of the present study suggest the limitation of single-tower measurements and the necessity of horizontally-distributed observation networks.The temporally averaged `turbulent' flux based on a point measurement systematically underestimates the `total' flux (negative imbalance). This is attributed to local advection effects caused by the existence of turbulent organized structures (TOS), whose time scale is much longer than that of thermal plumes. The temporal and spatial change of TOS patterns causes low-frequency trends in the velocity and temperature data resulting in large scatter of the flux estimates. The influences of geostrophic wind speed, averaging time, observation height, computational domain size and resolution on tower-measured fluxes are also discussed. Finally, it is suggested that a weak inhomogenity in surface heating may reduce the negative bias of flux estimates.     

Mechanical stratigraphy as a factor controlling the development of a sandbox transfer zone: a three-dimensional analysis

In thrust belts, fold–fault terminations are common features of the structural architecture and can pose complicated problems to unravel, in particular when two or more terminations are in close proximity. Such terminations usually reflect pre-existing attributes. Amongst the many factors, lateral variations in the mechanical stratigraphy can control along-strike geometry and kinematics of fault-related folds.A displacement transfer zone was produced in a compressional sandbox model by means of two adjacent, mechanically different stratigraphic domains. The experiment allowed two discrete chains to develop in the different domains, so that a complex structural setting occurred in the connecting area. Periclinal folds, oblique thrust fronts and oblique ramps developed in the resulting transfer zone. The interaction between periclines in the transfer zone produced lateral culminations in the folded structures. The analysis of displacement across the structural domains revealed that a significant loss of slip along the faults occurred in the relay zone. In this area, imbricate faulting was partially replaced by layer-parallel shortening. A linear relationship appears to exist between the bed length of the thrust sheet and the related fault slip.     

Three-Dimensional Numerical Method of Moments for Linear Equilibrium-Adsorbing Solute Transport in Physically and Chemically Nonstationary Formations

A Lagrangian perturbation method is applied to develop a method of moments for reactive solute flux through a three-dimensional, nonstationary flow field. The flow nonstationarity may stem from medium nonstationarity, finite domain boundaries, and/or fluid pumping and injecting. The reactive solute flux is described as a space–time process where time refers to the solute flux breakthrough in a control plane at some distance downstream of the solute source and space refers to the transverse displacement distribution at the control plane. The analytically derived moments equations for solute transport in a nonstationary flow field are too complicated to solve analytically; therefore, a numerical finite difference method is implemented to obtain the solutions. This approach combines the stochastic model with the flexibility of the numerical method to boundary and initial conditions. The approach provides a tool to apply stochastic theory to reactive solute transport in complex subsurface environments. Several case studies have been conducted to investigate the influence of the physical and chemical heterogeneity of a medium on the reactive solute flux prediction in nonstationary flow field. It is found that both physical and chemical heterogeneity significantly affect solute transport behavior in a nonstationary flow field. The developed method is also applied to an environmental project for predicting solute flux in the saturated zone below the Yucca Mountain Project area, demonstrating the applicability of the method in practical environmental projects.     

渭北旱塬土壤水分空间变异性

渭北旱塬是陕西省重要的苹果生产基地，探讨该区不同土地利用的土壤水分时空变异特征，对农业生产布局、种植业结构调整和减少径流、控制侵蚀具有特殊的现实意义。本文用地统计学的理论和方法，分析了渭北旱塬区3种主要土地利用类型农地、苹果地和苜蓿地3个土层深度(0～20cm、60～80cm、280～300cm)的土壤水分空间变化趋势。变异函数分析结果表明，3种土地利用类型的土壤水分具有明显的空间变异特性。在0～20cm土层，空间变异性尺度为9～16m，60-80cm土层为5～12m，280-300cm土层深为5～10m，空间变异性程度随尺度变化。自相关尺度为1～17m，自相关部分的空间变异性在0～20cm、60～80cm和280-300cm分别占总空间变异性的90．0％～94．0％、84．0％～98．0％和85．0％～94．0％，明显大于随机部分的空间变异性。从苜蓿地、苹果地到农地，空间自相关的尺度逐渐增大。各向异性分析表明，农地和苜蓿地在表层(0～20cm)具有明显的各向异性，而苹果地的土壤水分含量接近各向同性。