Application of space analysis of electromagnetic fields to investigation of the geoelectrical structure of the Earth

Lateral composition inhomogeneities of the Earth's deep geoelectric structure require special consideration for any conductivity evaluation of a region. This paper presents a review of some theoretical techniques for determining both the vertical and horizontal conductivity profiles of a region using a spatial distribution of observed electromagnetic fields at the Earth's surface. Effects of shallow positioned anomalies upon a deep conductivity determination are also considered. An application of the procedure is illustrated by a conductivity study in the Soviet Carpathians.     

海底淤泥层对海洋工程地震作用环境的影响问题

本提出了海底淤泥的流变性质对海洋工程的地震 作用环境的影响问题,并进行了有关的讨论。     

Influence of the topography of the surface of the Earth on vertical sounding of the temperature profile

Atmospheric temperature and humidity fields as well as information on other meteorological parameters are nowadays retrieved from radiance measurements recorded by operational meteorological satellites. Up to now, the inversion procedures used only take into account crude information on the topography of the Earth’s surface. However, the applied radiative transfer codes have to consider the Earth’s surface as the lower boundary of the atmospheric model and, therefore, need a more precise mean elevation and a classification of the roughness of the Earth’s surface. The influence of the topography of the Earth surface on retrieved temperature profiles is studied by using a physico-statistical inversion method. An objective analysis is made of the more precise mean elevation and derivation of roughness parameters using a new high-resolution digital elevation model (DEM) with a resolution of 500 m×500 m. By means of a geomorphological process and a newly developed topography rejection test, areas with a high surface roughness are localized and singled out. The influence of topography on the retrieved temperature profiles is illustrated by case studies. Changes are found predominantly in areas with a high variation of topography. Using the new high-resolution DEM and the topography rejection test, the geographical position of the calculated temperature profiles tends to be shifted towards areas with a small vertical variation of topography. The mean elevation determined by the new elevation model better characterizes the area observed. Hence, the temperature profiles can be calculated down to lower atmospheric levels. Furthermore, a guess profile better describing the atmospheric situation is selected by the more precise elevation. In addition, the temperature profiles obtained near the coast are improved considerably by the more precise determination of the surface property ‘sea’ and ‘land,’ respectively. Integration of an independent physical information such as topography leads, on average, to a slight improvement of the results of the physico-statistical inversion procedure. In some cases, however, significant improvements have been achieved regarding the desired accuracy of temperature profiles of the order of 1 K. In future, the spatial resolution of new high-resolution sounding instrumentation on the next generation of operational meteorological satellites will be increased. To exploit the resolving power of this new instrumentation, the different variation of the topography of the Earth surface, especially in regions with a high variation of topography, can be taken into account more precisely by using a high-resolution DEM.     

Computation of spectra of some simple functions using various types of Windows

Summary In the introductory part of the paper, a method of computing spectra by computer is described, which cuts down the computer time required without using the Fast Fourier Transformation. Windows which can be used to adjust the resultant spectrum are described. The spectra of a constant, a linear function, a sine function, of the superposition of two sine functions and of the superposition of a sine function with a constant and linear function are described in detail and it is demonstrated how these spectra change when different types of windows are used. The suitability of the separate windows for various purposes is discussed. Finally, in the case of the superposition of two sine oscillations it is shown under what conditions the two frequency components can be distinguished.     

Quantification of the stability of river flow regimes

Abstract

An important characteristic of a river flow regime type is the time of year when high and low flows are likely to occur. How likely is it, however, to observe an identified seasonal pattern each individual year? Stability is an often neglected property of a flow regime, though shifts in the seasonal behaviour of flows affect both environmental and economic activities. An approach to characterize objectively the stability of a flow regime type, based on the concept of entropy, is presented. The stabilities of river flow maxima and minima are studied separately to investigate their respective contributions to the stability character of a particular regime type. A quantitative “instability index” permits a study of the development of a flow regime's stability in time, especially important in the context of a possible climate change. The method is presented using the example of a quantitative flow regime classification developed for Scandinavia and western Europe.     

Origin of the Velocity-Strengthening Nature of Granular Friction

A simple theory for a constitutive law for steady state dynamic friction in granular matter is presented. Starting from the energy balance equation together with the kinetics of grains, the energy dissipation rate is estimated, which directly leads to a constitutive law. The result indicates that a system of lower density is stronger than a system of higher density, albeit somewhat counterintuitive. This is a consequence of the fact that the grain rearrangement, which causes energy dissipation, is more frequent in a system of lower density. Thus, the velocity-strengthening nature of granular friction is naturally explained by the negative shear-rate dependence of the density. The present theory also qualitatively explains the experimental observation that a system of smaller layer thickness tends to be velocity-weakening.     

A micromechanical analysis of the effect of fabric on low-strain stiffness of granular soils

The effect of fabric on low-strain shear stiffness properties of granular soils was assessed using Discrete Element simulations. These soils were idealized as a collection of non-spherical particles that interact according to Hertz׳s contact law. Different fabrics of the same soil were obtained by extracting particles from the weak or strong interparticle force networks. The associated stiffness properties were evaluated for various levels of isotropic triaxial confining stress conditions. The conducted analyses showed that a soil with a given void ratio and level of confining stress may have various fabrics associated with noticeably different low-strain shear moduli. The mechanical coordination number and particle shape were found to be the main factors that dictate the low-strain stiffness properties of a certain granular soil (with a specific contact law). For a defined level of confining stress, the shear stiffness of a particular soil is shown to be linked to the mechanical coordination number by a unique relation.     

山西地震综合数据处理系统

《山西地震综合数据处理系统》是遵循《国家地震局数据库技术规范》,以PDP-11/23~+小型机与IBM/PC联机为硬件支撑,以网状型数据库为核心,含前期处理、库管理、数据检索、科学计算、分析会商5个子系统的较大型应用软件系统。具有对数据进行收集、录入、预处理、存储、管理、加工及应用等功能。整个系统通过总控菜单程序实现了异种机间上百个模块的调度,使查询-处理一体化。该系统把地震数据库、日常监测数据处理、专家地震预报系统有机地衔接于一体,可直接服务于地震科研和震情会商。该系统的建设是山西省重大科技攻关项目,也是国家地震局的合同制项目。     

Development of solar flares and features of the fine structure of solar radio emission

The reason for the occurrence of different elements of the fine structure of solar radio bursts in the decimeter and centimeter wavelength ranges has been determined based on all available data from terrestrial and satellite observations. In some phenomena, fast pulsations, a zebra structre, fiber bursts, and spikes have been observed almost simultaneously. Two phenomena have been selected to show that the pulsations of radio emission are caused by particles accelerated in the magnetic reconnection region and that the zebra structure is excited in a source, such as a magnetic trap for fast particles. The complex combination of unusual fiber bursts, zebra structure, and spikes in the phenomenon on December 1, 2004, is associated with a single source, a magnetic island formed after a coronal mass ejection.     

Theory of the drift of asymmetrically-heated lithospheric plates

An approximate solution to the problem of the drift of a raft formed of two parallel wires, differentially heated, rigidly coupled and floating in a fluid of finite thickness and with linear viscosity, has been obtained and is shown to agree well with experiment up to a multiplicative constant. In addition, the solution to the problem of the drift of a solid raft with a suspended single-wire heater also shows good agreement with experiment up to a multiplicative constant. In both cases, the rafts drift with constant velocity. For small amounts of heat, the drift velocity is proportional to the first power of the heat input; for large amounts of heat, the drift velocity is proportional to the square root of the heat input. Within imponderable factors of an order of magnitude, the drift velocities are appropriate for drift of lithospheric plates containing both an oceanic and a continental part.     

Assessment of the reliability of 2D inversion of apparent resistivity data

The reliability of inversion of apparent resistivity pseudosection data to determine accurately the true resistivity distribution over 2D structures has been investigated, using a common inversion scheme based on a smoothness‐constrained non‐linear least‐squares optimization, for the Wenner array. This involved calculation of synthetic apparent resistivity pseudosection data, which were then inverted and the model estimated from the inversion was compared with the original 2D model. The models examined include (i) horizontal layering, (ii) a vertical fault, (iii) a low‐resistivity fill within a high‐resistivity basement, and (iv) an upfaulted basement block beneath a conductive overburden. Over vertical structures, the resistivity models obtained from inversion are usually much sharper than the measured data. However, the inverted resistivities can be smaller than the lowest, or greater than the highest, true model resistivity. The substantial reduction generally recorded in the data misfit during the least‐squares inversion of 2D apparent resistivity data is not always accompanied by any noticeable reduction in the model misfit. Conversely, the model misfit may, for all practical purposes, remain invariant for successive iterations. It can also increase with the iteration number, especially where the resistivity contrast at the bedrock interface exceeds a factor of about 10; in such instances, the optimum model estimated from inversion is attained at a very low iteration number. The largest model misfit is encountered in the zone adjacent to a contact where there is a large change in the resistivity contrast. It is concluded that smooth inversion can provide only an approximate guide to the true geometry and true formation resistivity.     

Propagation of Rayleigh waves in a model of the cross-section of a mountain and its root

Summary This study deals with the theoretical investigation of a model of a mountain and its root. A Gaussian function with a set of constants is used to represent the surface of a mountain and a Gaussian with a different set of constants approximates the root i.e. the crust-mantle boundary underneath the mountain. The expressions for the amplitudes of the components of strain are obtained. Also the period equation as a function of distance (x) for the propagation of Rayleigh waves is derived here.     

Basic characteristics of active tectonics of China

Active tectonics is inferred to all the structures which have been active since the late Pleisto-cene, 100—120 ka B.P., are still active recently, and will be active in a certain time period in the future, such as active faults, active folds, active basi…     

Laboratory study of seismic free-field response of sand

This paper describes a new soil-structure interaction test box for use on a moderately large shaking table. The test box is designed to replicate, as nearly as possible, the free-field seismic response of a soil layer overlying a rigid base. Results from shaking table testing are presented which demonstrate the ability of the test box to serve as a large-scale shear device. The test box is unique in its ability to determine dynamic shear modulus for both high- and low-amplitude shear strain, and also to study the dynamic response of sand under low levels of confining stress. Dynamic shear modulus for standard Ottawa sand was measured over a wide range of shear strain amplitude and compared with data from the existing literature. Finally, based on results from the test box, a constitutive model is proposed which describes the free field response of a sand layer overlying bedrock and subjected to vertically propagating SH waves. The model is simple in form with a single parameter uniquely related to the friction angle of the sand.     

Laboratory-scale study of field of view and the seismic interpretation of fracture specific stiffness

The effects of the scale of measurement, i.e., the field of view, on the interpretation of fracture properties from seismic wave propagation was investigated using an acoustic lens system to produce a pseudo-collimated wavefront. The incident wavefront had a controllable beam diameter that set the field of view at 15 mm, 30 mm and 60 mm. On a smaller scale, traditional acoustic scans were used to probe the fracture in 2 mm increments. This laboratory approach was applied to two limestone samples, each containing a single induced fracture and compared to an acrylic control sample. From the analysis of the average coherent sum of the signals measured on each scale, we observed that the scale of the field of view affected the interpretation of the fracture specific stiffness. Many small-scale measurements of the seismic response of a fracture, when summed, did not predict the large-scale response of the fracture. The change from a frequency-independent to frequency-dependent fracture stiffness occurs when the scale of the field of view exceeds the spatial correlation length associated with fracture geometry. A frequency-independent fracture specific stiffness is not sufficient to classify a fracture as homogeneous. A nonuniform spatial distribution of fracture specific stiffness and overlapping geometric scales in a fracture cause a scale-dependent seismic response, which requires measurements at different field of views to fully characterize the fracture.     

Prediction of eruption of Hawaiian volcanoes

Prediction of Hawaiian volcanic eruptions depends primarily on the interpretation of records of earthquakes and tumescence of the volcano. Recent work byJ. P. Eaton of the U. S. Geological Survey appears to demonstrate the presence of two distinct groups of earthquakes. One group originates at a depth of 40 to 60 km, within the earth’s mantle, and is thought to mark the zone of origin of the magma. The other group is of shallower origin and results from change of shape and size of the volcanic edifice. Earthquakes of the deep group occur from time to time, often in swarms, between eruptions and are not useful in predicting an outbreak. Those of the shallow group may accompany the swelling and splitting open of the volcano preceding eruption, but they may also accompany shrinking of the volcano and sinking of the mountain top that appears to result from withdrawal of magma beneath the volcano without surface eruption. Determining whether the quakes result from swelling of shrinking of the volcano depends largely on measurements of tilting of the ground surface. If the volcano is in a swollen condition and continues to swell, a large number of earthquakes of shallow origin is highly suggestive, if not definitely indicative, of imminent eruption. The place of origin of the quakes indicates, sometimes very closely, the location of the coming eruption. It is not yet possible, however, to predict the time of outbreak except in a rather general manner. Sometimes it can be predicted within a few days. At times there may be an oscillation of ground tilting directly preceding the eruption, suggesting a pulsation of magmatic pressure at depth, but this is not yet certain. There appears to be some indication that summit eruptions of either Mauna Loa or Kilauea are preceded by a less definite earthquake pattern, and are therefore less readily predictable, than flank eruptions. No cycle of activity of any great value in predicting activity has been recognized in Hawaii. Intervals between eruptions of Mauna Loa have ranged from a few months to more than 9 years, and Kilauea has been even more variable. In the case of Mauna Loa there has been a rough alternation between summit and flank eruptions, but with many exceptions to this general sequence. Astronomical and tidal cycles have been studied in relation to both time of outbreak and strength of eruption, but without demonstration of any very definite relationship. Eruptions have occurred in every month of the year, but there is a slight tendency for them to cluster just before and after solstice, particularly winter solstice.     

一种反演滤波器设计方法研究

该文针对在地震数据采集器中，使用最小相位滤波器而带来的波形畸变，提出了波形反演的概念，讨论了用逆滤波器直接反演可能出现的问题，并给出了一种反演滤波器的设计方法，经实验模拟证明，该方法是可行的。     

Statistical characterization of temporal structure of storms

The authors present a statistical procedure to estimate the probability distributions of storm characteristics. The approach uses recent advances in stochastic hydrological modeling. The temporal dynamics of rainfall are modeled via a reward alternating renewal process that describes wet and dry phases of storms. In particular, the wet phase is modeled as a rectangular pulse process with dependent random duration and intensity; the global dependence structure is described using multidimensional copulas. The marginal distributions are described by Generalized Pareto laws. The authors derive both the storm volume statistics and the rainfall volume distribution within a fixed temporal window preceding a storm. Based on these results, they calculate the antecedent moisture conditions. The paper includes a thorough discussion of the validity of the assumptions and approximations introduced, and an application to actual rainfall data. The models presented here have important implications for improved design procedures of water resources and hydrologic systems.     

Fractal generation of surface area of porous media

Many natural porous geological rock formations, as well as engineered porous structures, have fractal properties, i.e., they are self-similar over several length scales. While there have been many experimental and theoretical studies on how to quantify a fractal porous medium and on how to determine its fractal dimension, the numerical generation of a fractal pore structure with predefined statistical and scaling properties is somewhat scarcer. In the present paper a new numerical method for generating a three-dimensional porous medium with any desired probability density function (PDF) and autocorrelation function (ACF) is presented. The well-known Turning Bands Method (TBM) is modified to generate three-dimensional synthetic isotropic and anisotropic porous media with a Gaussian PDF and exponential-decay ACF. Porous media with other PDF's and ACF's are constructed with a nonlinear, iterative PDF and ACF transformation, whereby the arbitrary PDF is converted to an equivalent Gaussian PDF which is then simulated with the classical TBM. Employing a new method for the estimation of the surface area for a given porosity, the fractal dimensions of the surface area of the synthetic porous media generated in this way are then measured by classical fractal perimeter/area relationships. Different 3D porous media are simulated by varying the porosity and the correlation structure of the random field. The performance of the simulations is evaluated by checking the ensemble statistics, the mean, variance and ACF of the simulated random field. For a porous medium with Gaussian PDF, an average fractal dimension of approximately 2.76 is obtained which is in the range of values of actually measured fractal dimensions of molecular surfaces. For a porous medium with a non-Gaussian quadratic PDF the calculated fractal dimension appears to be consistently higher and averages 2.82. The results also show that the fractal dimension is neither strongly dependent of the porosity nor of the degree of anisotropy assumed.