Flares Unaccompanied by Interplanetary Coronal Mass Ejections and Solar Proton Events

Geomagnetism and Aeronomy - For a coronal mass ejection (CME) to occur, the magnetic pressure of the overlying layers must be lower than that of the underlying layers, and the corresponding...     

日本东京城区四个场地的土层放大效应分析(英文)

本文用统计一经验格林函数法合成１９２３年关东地震近场加速度时程，对比分析东京城区四个相近场地的土层放大效应，说明在结构抗震分析中考虑土层放大效应的重要性。     

层状介质井中电测数值计算及其应用研究

采用Gauss Laguerre求积公式对层状介质井中电测地-井方式的ΔV1（电位梯度）、ρa参数进行了理论计算.大量的正演数据揭示在层状介质情况下,井中电测地-井方式观测可以获得台阶异常,与相应的地电层相对应;低阻覆盖层和中间低阻层对井中电测影响很大,厚层覆盖区对地-井方式观测不利;水槽模拟和应用实例表明,分析实测资料时,要考虑层状介质ΔV1、ρa的正常场特征,对实测数据进行正常场改正,分析正常场改正后的ΔV″1异常效果较好.     

On the parameters of absorbing layers for shallow water models

Absorbing/sponge layers used as boundary conditions for ocean/marine models are examined in the context of the shallow water equations with the aim to minimize the reflection of outgoing waves at the boundary of the computational domain. The optimization of the absorption coefficient is not an issue in continuous models, for the reflection coefficient of outgoing waves can then be made as small as we please by increasing the absorption coefficient. The optimization of the parameters of absorbing layers is therefore a purely discrete problem. A balance must be found between the efficient damping of outgoing waves and the limited spatial resolution with which the resulting spatial gradients must be described. Using a one-dimensional model as a test case, the performances of various spatial distributions of the absorption coefficient are compared. Two shifted hyperbolic distributions of the absorption coefficient are derived from theoretical considerations for a pure propagative and a pure advective problems. These distribution show good performances. Their free parameter has a well-defined interpretation and can therefore be determined on a physical basis. The properties of the two shifted hyperbolas are illustrated using the classical two-dimensional problems of the collapse of a Gaussian-shaped mound of water and of its advection by a mean current. The good behavior of the resulting boundary scheme remains when a full non-linear dynamics is taken into account.     

Slope flows governed by diffusion effects in seas, lakes, and reservoirs

The hydrodynamics of slope flows governed by heat and salt diffusion near a rigid sloping impermeable boundary in stratified water bodies is studied. The physics of this phenomenon consists in that, because of the impermeability of the shore slope, the fluxes of heat and salt normal to the slope surface must be zero. Since the background stratification does not meet this condition, diffusion boundary layers appear along the shore slope. It is shown that, depending on the ratio between diffusion coefficients of heat and salt and the parameters of stratification by temperature and salinity, of convection the slope flows can be either ascending or descending. Moreover, under some conditions, a finger-type regime can form in boundary layers, though the background stratification is stable. The appearing slope flows, though they are local, initiate global transverse ventilation of water in the entire water body.     

On particular ignimbrites of the Island of Pantelleria (channel of sicily)

On the Island of Pantelleria (Channel of Sicily) several layers of particular ignimbrites have been found. Their properties can be explained only by admitting a great fluidity of the deposited material. Such a low viscosity is abnormal for sodarhyolitic or sodatrachytic melts and demonstrates that the temperature must have been exceptionally high, as it is possible only in the case of contact anatexis.     

Where Can Seismic Anisotropy Be Detected in the Earth’s Mantle? In Boundary Layers...

—During the last 30 years, considerable evidence of seismic anisotropy has accumulated demonstrating that it is present at all scales, but not in all depth ranges. We detail which conditions are necessary to detect large-scale seismic anisotropy. Firstly, minerals must display a strong anisotropy at the microscopic scale, and/or the medium must be finely layered. Secondly, the relative orientations of symmetry axes in the different crystals must not counteract in destroying the intrinsic anisotropy of each mineral, and there must be efficient mechanisms of orientation of minerals and aggregates. Finally, the strain field must be coherent at large scale in order to preserve long wavelength anisotropy. Part of shallow anisotropy can be related to the past strain field (frozen-in anisotropy), however the deep anisotropy is due to the present strain field. All these conditions are fulfilled only in boundary layers of convective mantle.¶We review in this paper, the seismic data sets which provide insight into the location at depth of large-scale anisotropy from the D"-layer up to the lithosphere. In addition to the well-documented seismic anisotropy in the lithosphere and asthenosphere, there is new evidence of seismic anisotropy in the upper (400–660 km) and lower (660–900 km) transition zones and in the D"-layer. Nonetheless the bulk of the lower mantle seems close to isotropy. If we assume the hypothesis that seismic anisotropy is associated with boundary layers in convective systems, these observations strongly suggest that the transition zone is a boundary layer which makes the pasage of matter between the upper and the lower mantle difficult. However, this general statement does not rule out flow circulation between the upper and lower mantles. Finally, the geophysical, mineral physics and geological applications are briefly reviewed. An intercomparison between surface wave anisotropy and body-wave anisotropy data sets is presented. We discuss the scientific potential of seismic anisotropy and how it makes it possible to gain more insight into continental root, deformation and geodynamics processes.     

FINITE-ELEMENT ANALYSIS OF SHALLOW TEMPERATURE ANOMALIES*

Finite-element analysis has been used in calculating shallow temperature anomalies due to both the presence of salt domes and near-surface faults. The results of the numerical analysis are in good agreement with field observations reported earlier by Poley and van Steveninck. The calculations show how surface emissivity must be responsible for the pronounced temperature anomalies above salt domes. Faulting is a mechanism that disorders the layering sequence of sedimentary deposits. If the disordered sedimentary layers show notable differences in heat conductivity, the layers are thick enough and the displacements along the fault plane large enough, temperature anomalies close to the free surface may be apparent because of the surface-emissivity mechanism. In order to explain certain characteristic temperature anomalies where a fault reaches or approaches the free surface, an additional mechanism has to be assumed; namely a distortion of texture, and consequently a change in the heat conductivity of the rock material surrounding the fault plane. The consequences of both a reduced and an increased heat conductivity of the surroundings of a near-surface fault have been calculated, and they show remarkable agreement with temperature anomalies observed in various parts of the world.     

RESISTIVITY SOUNDING ON A MULTI-LAYERED EARTH WITH TRANSITIONAL LAYERS. PART I: THEORY*

The electrical potential generated by a point source of current on the ground surface is studied for a multi-layered earth formed by layers alternatively characterized by a constant conductivity value and by conductivity varying linearly with depth. The problem is accounted for by solving a Laplace's differential equation for the uniform layers and a Poisson's differential equation for the transitional layers. Then, by a simple algorithm and by the introduction of a suitable kernel function, the general expression of the apparent resistivity for a Schlumberger array placed on the surface is obtained. Moreover some details are given for the solution of particular cases as 1) the presence of a infinitely resistive basement, 2) the absence of any one or more uniform layers, and 3) the absence of any one or more transitional layers. The new theory proves to be rather general, as it includes that for uniform layers with sharp boundaries as a particular case. Some mathematical properties of the kernel function are studied in view of the application of a direct system of quantitative interpretation. Two steps are considered for the solution of the direct problem: (i) The determination of the kernel function from the field measurements of the apparent resistivity. Owing to the identical mathematical formalism of the old with this new resistivity theory, the procedures there developed for the execution of the first step are here as well applicable without any change. Thus, some graphical and numerical procedures, already published, are recalled. (ii) The determination of the layer distribution from the kernel function. A recurrent procedure is proposed and studied in detail. This recurrent procedure follows the principle of the reduction to a lower boundary plane, as originally suggested by Koefoed for the old geoelectrical theory. Here the method differs mainly for the presence of reduction coefficients, which must be calculated each time when passing to a reduced earth section.     

Liquid collection in sidewall crystallization of magma: A comment on “liquid fractionation. Part I”, by A.R. McBirney, B.H. Baker and R.H. Nilson

The term liquid fractionation is inappropriate for a process driven by crystallization; liquid collection is proposed instead. The amount of evolved residual liquid produced by sidewall crystallization is not greater than that produced by any perfect fractional crystallization process and the fractionation products must be balanced somewhere by less evolved crystal deposits. There is no free lunch in petrology. Sidewall heating limits the local duration of liquid collection and the complementary crystal products should be sought in conduits. Flux ratios rather than diffusivities control the differences between thermal and chemical boundary layers.     

Matrix impedance in the problem of the calculation of synthetic seismograms for a layered-homogeneous isotropic elastic medium

A new method is proposed for calculating synthetic seismograms caused by a force in a plane-parallel medium consisting of homogeneous elastic isotropic layers. The matrix impedance, i.e., the matrix function of depth, by which motion vector must be multiplied in order to obtain the stress vector, is introduced for solving a system of ordinary differential equations with respect to the motion-stress vector, which appears during the separation of variables. An independent nonlinear equation is obtained for the impedance. The propagator for the motion vector is constructed with the aid of the impedance. The closed analytical formulas, which do not contain any exponents with positive indices, are obtained both for the impedance and for the motionvector propagator. The algorithm for the calculation of seismograms, free of limitations on the number and thickness of layers, as well as on the frequency range of interest, is constructed on the basis of these formulas. The algorithm is tested with the aid of an analytical solution.     

Evaluation of infrared emission spectra of aircraft exhaust with the FitFas software

A Fourier transform spectrometer was used to measure infrared spectra of the exhaust gas of an aircraft’s jet engine. The measured spectra were modelled by use of the program FASCODE. For this simulation, the inhomogeneous gas mixture is divided into several homogenous layers which are characterized by their geometrical extents, temperatures, pressures and chemical compositions. To obtain values for the temperatures and the CO, NO, H₂O and CO₂ concentrations of the layers a nonlinear least-squares algorithm was implemented. The program (FITFAS) not only changes the parameters to find the minimum of the squared differences between measurement and calculation; it also provides the variances and covariances of the parameters. Thus information is obtained to which parameters (besides the interesting ones) must be fitted (or be accurately known). It also tells us whether or not another spectral interval is more suitable for the determination of a specific parameter.     

Processes and modes of permafrost degradation on the Qinghai-Tibet Plateau

Climate warming must lead the mainly air temperature controlled permafrost to degrade.Based on the numerical simulation,the process of permafrost degradation can be divided into five stages,i.e.,starting stage,temperature rising stage,zero geothermal gradient stage,talic layers stage,and disappearing stage,according to the shape of ground temperature profile.Permafrost on the Qinghai-Tibet Plateau (QTP) is generally considered a relic from late Pleistocene,and has been degenerating as a whole during Holocen...     

Seismites in the Dasheng Group: New evidence of strong tectonic and earthquake activities of the Tanlu Fault Zone

More than 80 layers of seismites were recognized from the Early Cretaceous Dasheng Group in the Mazhan and Tancheng graben basins in the Tanlu Fault Zone, eastern China. The responsible seismic events took place about 110–100 Ma in the Early Cretaceous. The fault zone was affected at the time by strong tectonics, due to tension-related stretching and scattered squeezing by strike-slip faults. These tectonic activities induced a series of strong earthquakes with Richter magnitudes(M) of 5–8.5. The earthquakes affected saturated or semi-consolidated flood and lake sediments, and produced intra-layer deformations by several processes, including liquefaction, thixotropy, drop, faulting, cracking, filling and folding, which resulted in the formation of various soft-sediment deformation structures, such as dikes and veins of liquefied sand, liquefied breccias, liquefied homogeneous layers, load structures, flame structures, ball-and-pillow structures, boudinage, diapirs, fissure infillings, a giant conglomerate wedge, and syn-sedimentary faults. The seismites are new evidence of tectonic and seismic activities in the Tanlu Fault Zone during the Early Cretaceous; the series of strong seismic events that can be deduced from them must be considered as a response to the destruction of the North China Craton.     

Multiple origins and interpretations of the magnetic susceptibility signal in Chinese wind-blown sediments

In most Chinese loess–paleosol sequences, high magnetic susceptibility values are found in the soil horizons, with low values in the loess layers. The susceptibility signal has been widely used as a proxy climatic indicator. However, both the causes and mechanisms which control susceptibility still remain controversial. Our recent studies challenge some earlier interpretations of the magnetic susceptibility signal in Chinese wind-blown sediments. First, the prevailing hypothesis of pedogenic origin cannot totally account for the susceptibility variations in many sections. Second, in some cases, the principal carrier of the magnetization seems not to be the ultrafine pedogenic minerals, rather coarse lithogenic magnetic minerals derived from local sources can also contribute significantly to the susceptibility signal. Finally, not all the Chinese soils have higher susceptibility values than that of loess or sand layers, opposite relationships do exist. It is concluded that the source and causes of susceptibility may be different from site to site or even at different times at a given site. Any single hypothesis cannot completely account for the susceptibility variations in the Chinese Loess Plateau and its surrounding regions. Besides the previous explanations of carbonate leaching, pedogenic processes and organic decomposition, the contribution of source materials to magnetic susceptibility must also be taken into account.     

Validity of the long-wave approximation in periodically layered media

In seismic modelling, a stack of thin layers is often replaced by an effective equivalent anisotropic homogeneous slab. For waves with finite wavelength, this is an approximation, and the error thus introduced can be quantified by considering the relative error in the phase velocity between the layer stack and the effective medium. For periodic layering, the relative phase-velocity error can be expressed in closed form as a function of wavelength, reflection coefficients and layer thicknesses. By comparing the relative phase-velocity error with laboratory measurements and numerical simulations, we find that the difference in seismic response between a periodic layer stack and an equivalent effective medium depends not only on wavelength, but it also depends significantly on reflection coefficients and the ratio between layer thicknesses. For a 1% relative error in the phase velocity, and if all layers have the same thickness measured in vertical traveltime, we find that the wavelength must be larger than approximately three times the layer period for a reflection coefficient of 0.1, but this increases to 13 times the layer period for a reflection coefficient of 0.9, which is highly unrealistic in a geological setting.     

我国几个大地震地区地壳与上地幔顶部结构关系的初步分析

本文根据我国境内及邻近地区地壳结构的分布特征,特别是近年来我国发生的几个大地震所处的深部地壳构造背景,讨论了地震孕育与发生的可能构造模式。结果表明,近代地震活动地带均为地壳厚度急剧变化的地带和地壳构造的转折交汇部位。在深部构造上又为上地幔顶部局部的隆起地区及邻近隆起地带的边缘或斜坡上。此外,地震发生的深部部位与重力场、磁力场的高梯度变化以及地壳中的低电阻层、低速层和高速层的分布密切相关。这种与地震有关的深部构造背景与地球物理场特征,是今后地震预报和地震成因研究必须十分重视的。     

我国西北地区地壳中的高速夹层

在我国西北地区的柴达木盆地东部和甘肃地区,在距离炮点40互100公里处,能够接收到不少能量较强的地壳深界面反射波。另外还发现一种与一般反射波性质不同的波,其视速度特大,视速度随距离的变化不大,而且有较明显的终点;其吋距曲线与一般深界面反射波的时距曲线相交。根据它的特征可以判断地壳中存在具有速度梯度的高速夹层.求得的夹层参数为: 甘肃地区柴达木盆地东部覆盖层厚度 18.8公里 30.5公里覆盖层平均速度 5.5公里/秒 5.3公里/秒夹层厚度 6.0公里 3.2公里夹层速度 7.5-8.5公里/秒 7.5-8.0公里/秒夹层的上下界面均为强反射面,可以产生多次反射波。分別利用相邻两个反射波可以求得各层参数,并能避免射线折射的影响。甘肃地区和柴达木盆地东部的地壳厚度分別为51和52公里。地壳中有高速夹层的存在,可以更好地说明P~*速度分散的原因,而且也能够解释Lg波的传播机制。     

近地表高频补偿技术在三维地震勘探中的应用研究

近地表的滤波作用不仅会引起地震波高频成分的快速衰减,还会引起地震子波相位的畸变,在高分辨率地震资料处理中,必须对这些由近地表引起的衰减和频散进行补偿.文中研究了近地表吸收规律,应用微测井资料求出了表层的吸收衰减因子,补偿了近地表高频成分,给出了针对三维地震资料的近地表高频补偿方法,对大庆齐家北工区的地震资料进行了实际应用,同时还应用属性分析技术对应用效果进行了分析评价,结果表明,该方法是可行的.     

Two-level magnetovariational measurements for the determination of underground resistivity distributions1

We investigate, from a theoretical point of view, the possibility of performing marine two-level magnetovariational measurements. An apparent resistivity function is denned and calculated after solving the differential equation governing the behaviour of the natural magnetic field variations inside a one-dimensional earth. In order to generalize the problem, a frequency-dependent resistivity is assumed to characterize the layers and the distortions caused by the polarization effects are carefully analysed. The computation of three-layer amplitude and phase diagrams for the apparent resistivity function shows that, in the case of an intermediate polarizable layer, sandwiched between a non-dispersive overburden and substratum, the H-type sequence results are the most affected by the dispersion phenomenon as it occurs in magnetotellurics. Finally we consider the problem of the sensitivity of the method, since, in practice, it requires top and bottom sensors separated by a vertical finite distance. It is found that in the higher-frequency range, due to the strong attenuation of the relative components of the field, the depth of the bottom sensor must be small enough to guarantee detectable signals, well above the full-scale resolution of the acquisition system. Conversely, in the lower-frequency range such a depth must be large enough to allow the difference between the top and bottom signals to be above the same recording sensitivity threshold.