Difficulties in determining electrical anisotropy in subsurface investigations

Surface electrical and electromagnetic methods have a limited resolution capability for determining the conductivity structure of the earth. In one-dimensional modelling a collection of many thin layers is frequently considered as one composite layer, which is then macro-anisotropic. Neither galvanic methods nor inductive methods alone can resolve the anisotropy of the ground, but a joint inversion of galvanic and inductive data may do so. The necessity of including the coefficient of anisotropy in the joint inversion of galvanic and inductive sounding data is demonstrated. An analysis is made of the combined use of geoelectrical and transient soundings to resolve the coefficient of anisotropy of a subsurface layer for varying thickness, resistivity and coefficient of anisotropy. It is found that the coefficient of anisotropy is well resolved only for layers that are many times thicker than the overburden and for coefficients of anisotropy that are not too small. The ability of the joint inversion of geoelectrical and transient sounding data to resolve macro-anisotropic layers is tested using realistic earth models determined from electrical logs.     

The dispersive flux in transport phenomena in porous media

Employing the principles of continuum mechanics and a volumetric averaging approach to the derivation of the macroscopic balance equation of an extensive quantity of a fluid phase in a porous medium, the paper derives a macroscopic expression for the dispersive flux that appears in the latter as a result of averaging. It is shown that the dispersive flux obeys a Fickian type law, i.e., it is proportional to the macroscopic density gradient of the considered extensive quantity. The nature of the coefficient of dispersion that appears in the expression of the dispersive flux is analyzed and interpreted.     

Recent progress in estimating uncertainty in geomagnetic field modeling

Abstract

Recent work pertaining to estimating error and accuracies in geomagnetic field modeling is reviewed from a unified viewpoint and illustrated with examples. The formulation of a finite dimensional approximation to the underlying infinite dimensional problem is developed. Central to the formulation is an inner product and norm in the solution space through which a priori information can be brought to bear on the problem. Such information is crucial to estimation of the effects of higher degree fields at the Core-Mantle boundary (CMB) because the behavior of higher degree fields is masked in our measurements by the presence of the field from the Earth's crust. Contributions to the errors in predicting geophysical quantities based on the approximate model are separated into three categories: (1) the usual error from the measurement noise; (2) the error from unmodeled fields, i.e. from sources in the crust, ionosphere, etc.; and (3) the error from truncating to a finite dimensioned solution and prediction space. The combination of the first two is termed low degree error while the third is referred to as truncation error.

The error analysis problem consists of “characterizing” the difference δz = z—z, where z is some quantity depending on the magnetic field and z is the estimate of z resulting from our model. Two approaches are discussed. The method of Confidence Set Inference (CSI) seeks to find an upper bound for |z—?|. Statistical methods, i.e. Bayesian or Stochastic Estimation, seek to estimate E(δz² ), where E is the expectation value. Estimation of both the truncation error and low degree error is discussed for both approaches. Expressions are found for an upper bound for |δz| and for E(δz² ). Of particular interest is the computation of the radial field, B., at the CMB for which error estimates are made as examples of the methods. Estimated accuracies of the Gauss coefficients are given for the various methods. In general, the lowest error estimates result when the greatest amount of a priori information is available and, indeed, the estimates for truncation error are completely dependent upon the nature of the a priori information assumed. For the most conservative approach, the error in computing point values of B_r at the CMB is unbounded and one must be content with, e.g., averages over some large area. The various assumptions about a priori information are reviewed. Work is needed to extend and develop this information. In particular, information regarding the truncated fields is needed to determine if the pessimistic bounds presently available are realistic or if there is a real physical basis for lower error estimates. Characterization of crustal fields for degree greater than 50 is needed as is more rigorous characterization of the external fields.     

Potentiometrische Fluoridbestimmung in Trinkwasser

The measurement is carried out after addition of perchloric acid up to a concentration of 0.45 M perchloric acid, and the results are compared with those obtained in 0.16 M sodium citrate as well as with a gas-chromatographic determination, and they show a good agreement, The detection limit is 0.002 mg/l F^?, the coefficient of variation is nearly 0.01 at 0.85 mg/l F^?, independently of whether a direct measurement or a measurement with a standard addition is carried out. The measurement is disturbed by aluminium(III)- and Iron(III)-ions.     

Soil-pile interaction in vertical vibration

The interaction between a soil layer and an end bearing pile is theoretically investigated. The pile is assumed to be vertical and elastic, the soil is considered as a linear visco-elastic layer with hysteretic type damping. The layer alone is solved first and the wave modes of the layer are used in the analysis of the pile response. The pile response to a harmonic load is obtained in a closed form and used to define stiffness and damping at the level of the pile head. The dimensionless parameters of the problem are identified. A parametric study is conducted to determine the main features of the response and of the equivalent stiffness and damping. The validity of equivalent viscous damping is examined. A comparison is made with the simpler plane strain theory used previously and its accuracy is assessed.     

Internal waves in a rotating stratified fluid in an arbitrary gravitational field

Abstract

Small amplitude oscillations of a uniformly rotating, density stratified, Boussinesq, non-dissipative fluid are examined. A mathematical model is constructed to describe timedependent motions which are small deviations from an initial state that is motionless with respect to the rotating frame of reference. The basic stable density distribution is allowed to be an arbitrary prescribed function of the gravitational potential. The problem is considered for a wide class of gravitational fields. General properties of the eigenvalues and eigenfunctions of square integrable oscillations are demonstrated, and a bound is obtained for the magnitude of the frequencies. The modal solutions are classified as to type. The eigenfunctions for the pressure field are shown to satisfy a second-order partial differential equation of mixed type, and the equation is obtained for the critical surfaces which delineate the elliptic and hyperbolic regions. The nature of the problem is examined in detail for certain specific gravitational fields, e.g., a radially symmetric field. Where appropriate, results are compared with those of other investigations of waves in a rotating fluid of spherical configuration and the novel aspects of the present treatment are emphasized. Explicit modal solutions are obtained in the specific example of a fluid contained in a rigid cylinder, stratified in the presence of vertical gravity, with the buoyancy frequency N being an arbitrary prescribed function of depth.     

随机子空间识别方法计算效率的改进

参数识别是结构健康监测领域研究中的重点。随机子空间法是近年来发展起来的一种线性系统辩识方法,可以有效地从环境激励的结构响应中获取模态参数。该方法的基本原理是将“将来”数据向“过去”数据进行垂直投影,进而根据该投影计算出可观测矩阵和一个Kalman滤波状态序列。而Kalman滤波序列是“过去”输出信号的线性组合,即“过去”输出和“将来”状态估计建立了关系。而从Hankel矩阵的组成来看,由于要使得该矩阵具有单无限的条件,所需的计算时间也比较长。据此对随机子空间方法进行了改进。改进的基本思想是采用一个测点的信号作为“过去”作为输出信号代替全部测点的信号。这样就减少了计算量。最后用一数值模拟算例进行了验证,结果良好。     

Advances in noctilucent cloud research in the space era

A summary of NLC research in the last two decades is presented. Results of NLC studies from the near-Earth space are discussed. It is shown that NLC can cover much larger territories than those estimated earlier and that there exists asymmetry in the coverage and also in the physical properties of NLC in the Northern and Southern Hemispheres. The mesopause often reveals a compelx multilayered structure. The pilot program of NLC research is discussed as a subprogram of the Middle Atmosphere Program and some vistas in NLC research are discussed.     

Response variability in structural dynamics

This paper presents a technique for treating uncertainties in the dynamic models of a structural system. The formulation of the method is presented for a simple case of a single-degree-of-freedom linear oscillator. The uncertainties are modelled as random variables and are assumed to be time-independent. The solution is expanded as a series involving the random terms, and a system of linear ordinary differential equations for the unknowns of the problem is derived using the weighted residual method. The system of equations is then integrated in time and the response variability is computed. Validation calculations show that the results from the method agree well with those obtained by other solution techniques. Finally, some possible applications and extensions of the present work are discussed.     

Issues in characterizing heterogeneity and connectivity in non-multiGaussian media

The performances of kriging, stochastic simulations and sequential self-calibration inversion are assessed when characterizing a non-multiGaussian synthetic 2D braided channel aquifer. The comparison is based on a series of criteria such as the reproduction of the original reference transmissivity or head fields, but also in terms of accuracy of flow and transport (capture zone) forecasts when the flow conditions are modified. We observe that the errors remain large even for a dense data network. In addition some unexpected behaviours are observed when large transmissivity datasets are used. In particular, we observe an increase of the bias with the number of transmissivity data and an increasing uncertainty with the number of head data. This is interpreted as a consequence of the use of an inadequate multiGaussian stochastic model that is not able to reproduce the connectivity of the original field.     

Atmospheric anomalies in summer 1908: Water in the atmosphere

A gigantic noctilucent cloud field was formed and different solar halos were observed after the Tunguska catastrophe. To explain these anomalous phenomena, it is necessary to assume that a large quantity of water was carried into the atmosphere, which indicates that the Tunguska cosmic body was of a comet origin. According to rough estimates, the quantity of water that is released into the atmosphere as a result of a cosmic body’s destruction is more than 10¹⁰ kg. The observation of a flying object in an area with a radius of ≥700 km makes it possible to state that the Tunguska cosmic body looked like a luminous coma with a diameter not smaller than ≥10 km and became visible at heights of >500 km. The assumption that the Tunguska cosmic body started disintegrating at a height of ∼1000 km explains the formation of an area where its mater diffused and formed a luminous area above Europe.     

唐山地区近十年地震的重定位研究

分别运用双差定位法、结合波形互相关的双差定位法和结合波形互相关的双差层析成像法,对唐山地区2010年1月至2020年7月河北地震台网记录的4874个地震事件进行重定位.结果表明:结合波形互相关的双差层析成像法的定位精度高于其它两种方法,地震走时均方根残差由初始的0.71降至0.27;重定位后的震中分布更加集中,线性分布...     

银川盆地西大滩隐伏断层晚第四纪活动特征

西大滩隐伏断层位于银川盆地北部,是石嘴山市活断层探测项目的目标断层之一。在浅层地震勘探的基础上,通过钻孔联合剖面探测和钻孔样品年龄测试,获得断层上断点埋深、主要标志层断距及沉积年龄等数据,估算了晚第四纪不同时段断层的滑动速率,结合地层变形情况探讨了该断层晚第四纪的活动特征。结果表明,西大滩隐伏断层自12 275±45aB.P.以来没有发生明显活动,属晚更新世末活动断层;晚更新世以来断层活动偏弱,平均滑动速率为0.024mm/a;除断层活动外,伴随着地层倾斜变形;两者均具间歇活动的特点,最小间隔约6 600a,最大间隔期12 275a。     

Short-term changes in global cloud cover and in cosmic radiation

Galactic cosmic rays (GCR) have been suggested as a possible contributory mechanism to cloud formation. If these are significant then, in addition to the similarity between long-term (years) changes in GCR and cloud cover, there should also be a similarity over shorter (days) time scales. This paper reports an analysis of changes in global cloud cover and GCR recorded at 3 hourly intervals over 22 years. There is a significant correlation between short-term changes in low cloud cover over northern and southern hemispheres, consistent with about 3% of the variation arising from common factors. However, GCR is not a major factor responsible for cloud cover changes. There is an association between short-term changes in low cloud cover and galactic cosmic radiation over a period of several days. This could arise if approximately 3% of the variations in cloud cover resulted from GCR.     

Two large earthquakes in western Switzerland in the sixteenth century: 1524 in Ardon (VS) and 1584 in Aigle (VD)

The Valais is the most seismically active region of Switzerland. Strong damaging events occurred in 1755, 1855, and 1946. Based on historical documents, we discuss two known damaging events in the sixteenth century: the 1524 Ardon and the 1584 Aigle earthquakes. For the 1524, a document describes damage in Ardon, Plan-Conthey, and Savièse, and a stone tablet at the new bell tower of the Ardon church confirms the reconstruction of the bell tower after the earthquake. Additionally, a significant construction activity in the Upper Valais churches during the second quarter of the sixteenth century is discussed that however cannot be clearly related to this event. The assessed moment magnitude Mw of the 1524 event is 5.8, with an error of about 0.5 units corresponding to one standard deviation. The epicenter is at 46.27 N, 7.27 E with a high uncertainty of about 50 km corresponding to one standard deviation. The assessed moment magnitude Mw of the 1584 main shock is 5.9, with an error of about 0.25 units corresponding to one standard deviation. The epicenter is at 46.33 N and 6.97 E with an uncertainty of about 25 km corresponding to one standard deviation. Exceptional movements in the Lake Geneva wreaked havoc along the shore of the Rhone delta. The large dimension of the induced damage can be explained by an expanded subaquatic slide with resultant tsunami and seiche in Lake Geneva. The strongest of the aftershocks occurred on March 14 with magnitude 5.4 and triggered a destructive landslide covering the villages Corbeyrier and Yvorne, VD.     

Experimental catchments in the Pampa biome: Database on hydrology in grasslands and eucalyptus plantations in subtropical Brazil

The introduction of exotic, fast-growing forest species in the Pampa biome (Southern Grasslands) is a controversial topic, considering the potential effect on water and soil resources. This repository contains hydrologic data (rainfall, discharge and turbidity) collected since 2011 in three small (≤1.1 km²), paired experimental catchments of the “Ponta da Canas” site, in the Pampa biome in subtropical Brazil. Two catchments are predominantly covered with eucalyptus plantations, and one with livestock-grazing degraded grassland. For each catchment, the collected data include 10-min resolution rainfall, streamflow, and turbidity (except for one of the eucalyptus catchments), automatically recorded in 10-min intervals. In each catchment, rainfall is measured with an automatic tipping-bucket rain gauge; stream depth is determined with a pressure transducer at the spillway, and a rating curve is used to estimate discharge; and turbidity is measured with a turbidimeter. The collected data are being used to understand water balance and sediment production under the distinct land uses, to improve forest management, and comply with State legislation.     

藏南宁金抗沙西麓断裂晚第四纪活动特征

宁金抗沙西麓断裂位于亚东-谷露裂谷系南部.本文利用15 m分辨率的ETM 遥感影像和20 m分辨率的数字高程模型,结合野外地质考察,重点研究了该断裂的详细结构和晚第四纪以来的活动习性.依据与热隆盆地的关系,该断裂主要分为三段,热隆盆地以北为北段,热隆盆地边界断裂为中段,热隆盆地以南为南段.该断裂在强烈正断的同时兼具有左旋走滑运动,自中更新世以来,主要有三期活动,活动开始时间分别为384 ka1、08 ka和34 ka,累积水平活动速率分别为4.8 mm/a5、.5 mm/a和6.4 mm/a.断裂自中更新中期以来的垂直断错速率为1 mm/a.     

ESW在磁尾磁场重联耗散区分形线附近的观测特性及其作用

磁场重联是空间能量释放和转换的重要机制.静电孤立波(ESW)虽然在空间中有广泛观测,但在磁场重联附近少有直接观测,对它在磁场重联附近的特性了解甚少.通过Geotail卫星对一个磁场重联事件的观测,仔细分析了其边界层上观测到的静电孤立波的特性,并讨论了它对磁场重联的影响.研究表明,亚暴期间在磁尾发生磁场重联,重联区域的分形线附近观测到了大量的静电孤立波,其特性与在其他地方观测到的并没有显著差别,但具有更明显的非线性和孤立性的特征.它们对电子加速和能量耗散有促进作用,加速磁场重联的进程.