地球主磁场电磁转矩导致的地球差异旋转

为探索驱动地球系统差异旋转的力源,选择整个地球作为研究对象,应用经典电磁学理论,分析地球固体介质中的电荷在地球主磁场中的运动特点,发现存在一个与地球自转方向相反的切向洛伦兹力.通过电荷与介质间的相互作用,切向洛伦兹力传递至介质迫使介质西漂.为探索地球差异旋转的规律,建立了地球薄圆筒圈层模型.应用经典物理学理论和方法推导出了地球主磁场电磁转矩及其产生的角加速度公式.研究得到四点主要结论:1)作用于半径不同的地球薄圆筒圈层的地球主磁场电磁转矩及其产生的角加速度绝对值不同:地轴及赤道附近圈层的小,其自转相对较快;半径等于3～(1/2)倍地球半径的薄圆筒圈层及其相邻圈层的大,其自转相对较慢.2)同一薄圆筒圈层中的差异旋转缘于介质的介电常数、阻力系数及质量密度的差异.3)地球差异旋转缘于地球的自转、正负电荷的非对等分布及介质的介电常数、阻力系数、质量密度的差异.4)地球差异旋转导致地壳运动,孕育地震,地球主磁场是地球差异旋转和地震孕育的敏感因子.     

The electrical state of the earth's interior and the origin of the earth's main magnetic field

Summary From the standpoint of the electrical state of the earth's interior as inferred from both geophysical and physical researches, the possibility ofElsasser-Bullard's theory is discussed. The electromagnetic shielding within the earth's mantle is also taken into account. It is of interest that the theory seems to well harmonize with the electrical state considered.     

The intensity of the earth's magnetic field in the past derived from the archaeomagnetic data

a n¶rt;u¶rt; amuu amua uuu anmuaum n a n¶rt;u 8500 m nm um au aam m uuu m naama. ¶rt;u u ¶rt;a ¶rt; u ¶rt; m¶rt; mumu auu nau nuu aau mama [1–3] (Puc. 1.B). nma aau auau (Puc.2) mnaua m m m¶rt;a, ¶rt; au n¶rt; amu u, m n¶rt;u 2- ma m, mmu naa auu nu¶rt; n¶rt;a 1000 m u 350 m, au a aumu, mmm 80%- mmu. am au ¶rt;a u anmu ¶rt; m¶rt; mumu (mum) naa auu u¶rt; ma u ¶rt; m naama[5] (Puc. 3). uma a mam nma aaua naaa auu nu¶rt; n¶rt;a 750 m, 200 m u a — 300 m. (Puc. 4.) nmu u ¶rt;a nma amua an¶rt;u n¶rt;u n u ma m (au) auumu m ¶rt;m m (Puc. 5). aa a m¶rt;m nu naamaum n aam ¶rt;uu mu au, anum¶rt;a m uua nm m¶rt;a.

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Dedicated to Academician Alois Zátopek on His 65th Birthday     

The relative stabilities of the reverse and normal polarity states of the earth's magnetic field

Recent analyses of the geomagnetic reversal sequence have led to different conclusions regarding the important question of whether there is a discernible difference between the properties of the two polarity states. The main differences between the two most recent studies are the statistical analyses and the possibility of an additional 57 reversal events in the Cenozoic. These additional events occur predominantly during reverse polarity time, but it is unlikely that all of them represent true reversal events. Nevertheless the question of the relative stabilities of the polarity states is examined in detail, both for the case when all 57 “events” are included in the reversal chronology and when they are all excluded. It is found that there is not a discernible difference between the stabilities of the two polarity states in either case. Inclusion of these short events does, however, change the structure of the non-stationarity in reversal rate, but still allows a smooth non-stationarity. Only 7 of the 57 short events are pre-38 Ma, but the evidence suggests that this is a real geomagnetic phenomenon rather than degradation of the magnetic recording or a bias in observation. This could be tested by detailed magnetostratigraphic and oceanic magnetic surveys of the Paleogene and Late Cretaceous. Overall it would appear that the present geomagnetic polarity timescale for 0–160 Ma is probably a very good representation of the actual history, and that different timescales and additional events now represent only changes in detail.     

An overview of the external magnetic field with regard to magnetic surveys

Surveys in Geophysics -     

Multi-channel surface NMR instrumentation and software for 1D/2D groundwater investigations

Multi-channel surface nuclear magnetic resonance (NMR) instrumentation and software, developed in the United States, has been applied to investigate 1D and 2D hydrology at various locations in the Western US. The GeoMRI instrument offers several practical improvements over the previous state of the art in surface NMR instrumentation, including a multi-channel transmit/receive capability, a significantly shorter measurement dead-time of 10 ms, and an ultra-low receiver input noise density of less than 0.4 nV/sqrt (Hz). Two multi-channel NMR processing techniques, reference coil-based noise cancellation and integrated FID imaging, are shown to increase effective signal to noise ratios by an order of magnitude or more. These effective SNR gains enable multi-coil surface NMR to produce useful and reliable images when the post-averaged SNR is less than 1. We also suggest an alternate approach to imaging, in which NMR signals are initially isolated in the space domain, and then NMR parameter estimation is applied in the time domain. Experimental results are presented for recent surface NMR groundwater investigations conducted in Nebraska and Texas, USA.     

Multi-channel surface NMR instrumentation and software for 1D/2D groundwater investigations

Multi-channel surface nuclear magnetic resonance (NMR) instrumentation and software, developed in the United States, has been applied to investigate 1D and 2D hydrology at various locations in the Western US. The GeoMRI instrument offers several practical improvements over the previous state of the art in surface NMR instrumentation, including a multi-channel transmit/receive capability, a significantly shorter measurement dead-time of 10 ms, and an ultra-low receiver input noise density of less than 0.4 nV/sqrt (Hz). Two multi-channel NMR processing techniques, reference coil-based noise cancellation and integrated FID imaging, are shown to increase effective signal to noise ratios by an order of magnitude or more. These effective SNR gains enable multi-coil surface NMR to produce useful and reliable images when the post-averaged SNR is less than 1. We also suggest an alternate approach to imaging, in which NMR signals are initially isolated in the space domain, and then NMR parameter estimation is applied in the time domain. Experimental results are presented for recent surface NMR groundwater investigations conducted in Nebraska and Texas, USA.     

Inviscid,frozen-flux velocity components at the top of earth's core from magnetic observations at earth's surface: Part 1. A new methodology

Abstract

Two alternative methods are described for obtaining inviscid velocity components at the surface of earth's liquid core, assumed perfectly conducting, given perfect and complete measurements of the geomagnetic main field and secular variation at earth's surface. The mantle is treated as a spherically-symmetric insulator for purposes of extrapolation to the core. Both methods utilize the vertical component of the induction equation and require one-dimensional interpolation along special curves on the core surface as the initial step. For the next step, the first method then utilizes the two horizontal components of the induction equation, whereas the second method relies on the horizontal components of Ohm's law. Both methods work within the confines of the ambiguity elucidated by Backus (1968) but nonetheless can still yield results of value, because the two horizontal velocity components are determined separately and at distinct locations. A brief comparison of the two methods suggests that the one, based in part on Ohm's law, should be superior from a practical viewpoint.     

The use of the cooling-history of thick intrusive sheets for the study of the secular variation of the earth's magnetic field

Summary Numerical results are given which show the way in which thc Curie temperature moves inwards from the margin during the cooling of a thick intrusive sheet. The time taken to move from the margin to the centre varies as the square of the thickness of the sheet, being about 6500 years for a sheet 1000 m thick on reasonable assumptions as to the thermal properties of the material. This implies that the secular variation of the Earth's magnetic field over periods of time of 1000 years or more may be studied by measuring the directions of magnetisation at a series of points across the thickness of such a sheet.Some measurements on a Tasmanian sill about 430 m thick of Jurassic or Cretaceous age suggest a change from maximum to minimum inclination in a time of about 200 years. Since the margins of the sill are not available this figure may be considerably in error but the results suggest the general practicability of the method.     

Paleointensity of the earth's magnetic field during the Laschamp excursion and its geomagnetic implications

The reversed paleomagnetic direction of the Laschamp and Olby flows represents a specific feature of the geomagnetic field. This is supported by paleomagnetic evidence, showing that the same anomalous direction was recorded at several distinct sites, including scoria of the Laschamp volcano. To examine this anomalous geomagnetic fluctuation, we studied the paleointensity of the Laschamp and Olby flows, using the Thellier method. Twenty-five samples were selected for the paleointensity experiments, and from seven we obtained reliable results. Because the paleointensity results of the Olby and Laschamp flows as well as Laschamp scoria are very similar, they can be represented by a single mean paleointensity,F = 7.7 μT. Considering that this low paleointensity is less than 1/6 of the present geomagnetic field and is more characteristic of transitional behavior, our results suggest that the paleomagnetic directions of the Laschamp and Olby flows were not acquired during a stable reversed polarity interval. A more likely explanation is that the Laschamp excursion represents an unsuccessful or aborted reversal.     

Displacements of the earth's surface in seismic regions

am amuuma u mua u nmu a a¶rt;uau nu, an u aua u -a.     

核磁共振测井探测岩石内部磁场梯度的方法

岩石内部磁场梯度对核磁共振测井横向弛豫T2分布有较大的影响.本文提出了一种利用自旋回波脉冲序列探测岩石内部磁场梯度的二维核磁共振方法,发展了相应的反演方法,得到了含顺磁性物质的饱和水砂岩和泥质砂岩的内部磁场梯度分布规律.结果表明,随顺磁物质含量的增加,岩石内部磁场梯度增大.含顺磁物质的饱和水砂岩颗粒均匀,不含粘土矿物,内部磁场梯度呈单峰分布特征.含绿泥石粘土矿物的饱和水泥质砂岩,T2分布呈双峰特征,束缚水峰明显,小孔短T2对应的梯度值大于大孔长T2对应的梯度值.当绿泥石含量小于15%时,随绿泥石含量的增加,对应束缚水峰的短T2组分明显增多,T2分布展宽;当绿泥石含量大于15%以后,较大的岩石内部磁场梯度使短弛豫信息衰减迅速,表现出随绿泥石含量的增加,短T2组分减少,T2分布变窄.     

位场曲化平的插值-迭代法

将起伏曲面B上的位场向下延拓至曲面最低点的平面A的插值-迭代法步骤是：1）将曲面B上的场值放置在水平面A上具有相同水平坐标的点上,作为A上的初值;2）用若干水平面切割B,从A的初值,用快速傅里叶变换法(FFT)向上延拓出这些平面的场值,用插值的方法从这些平面的场值计算曲面B的场值;3）根据B上的实测值与计算值的差值,对A上的值进行加权改正;4）重复步骤2）和3）,直到B上的差值小到可以忽略.这种插值-迭代法具有高的计算速度,比通常的FFT法延拓得更深,可以超过10倍点距.文中给出计算实例.     

Magnetic variations excited by a radial magnetic dipole located in the earth's core

Summary Theoretical formulae are derived for computing a variable magnetic field, excited by a harmonically oscillating radial magnetic dipole (RMD), located eccentrically at the surface of the Earth's core. By numerical computations, using a three-layered conductivity model of the Earth, it is proved that the field due to this source, computed for the surface of the Earth, is relatively weak in comparison to the field of a stationary magnetic dipole, provided the period of the changes is less than 500 years. The zone of influence of the RMD at the Earth's surface is also determined and on its basis a number of conclusions were drawn with respect to representing the non-dipole part of the geomagnetic field by means of the RMD system in the Earth's core.Dedicated to RNDr. Jan Pícha, CSc., on his 60th Birthday     

Quaternary vertical movements of the earth's surface in East-Central Europe

Fluvial terraces in mountain territories and granulometric cycles in fluvial sediment complexes show 300–400 m uplifts in mountain regions and about the same sized subsidences in major East-Central European basins during the Quaternary (−2.4 Ma). The vertical movements are not at all regular and equal in the mountains nor in the great basins. The number of the terraces is different in the valleys and their mutual proportions also differ. Similarly, some local Quaternary basins were developed deeper in the peripheries of the large basins while the central parts are shallow. There are also some stable blocks between the mountains and the lowlands, which did not move essentially during the last two and a half million years.The course and velocity of Pliocene and Quaternary subsidence were proved in a local sub-basin of the Carpathian mountain arch by paleomagnetic measurements of cores from two deep boreholes. In the Körös Basin, filled with fine-grained fluvial sediment, the sedimentation rate was 0.16–0.19 mm/y in the last 700.000 years; 0.15–0.16 mm/y during the proceding one million years; and 0.22–0.28 mm/y during the Pliocene (from −5.2 to −2.4 Ma).In sub-basins filled with coarse-grained sediments, the sedimentation rate was 0.3–0.4 mm/y during the Quaternary.     

磁屏蔽室内磁性样品所产生干扰磁场的探讨

磁屏蔽室内岩石和各种沉积物样品所受的地磁场影响可以被有效地压制,然而磁性样品本身也会产生次级干扰磁场.本文通过理论模拟计算,定量评估了这种次级干扰磁场的影响.结果发现无论是单个还是聚集在一起的磁性样品,其产生的干扰磁场一般都低于磁屏蔽室的本底值(～300 nT).因此,弱磁性样品的相互影响可以忽略不计.这为进一步理解古...     

Current stabilizer for the magnetic field of a mass spectrograph

Summary A new automatic current stabilizer is constructed, which can be used for a magnetic field of a mass spectrograph. A stability of the order of 10^–6 is attained for relatively long intervals. The dependence of the magnetic field constancy on the different parameters of the stabilizer is investigated by methods of servomechanism.     

Upward continuation of potential fields from a polyhedral surface1

An equivalent source procedure is derived for upward continuation of unevenly spaced gravity and magnetic data. The dipole layer is placed on a topographic relief approximated by a polyhedral surface, the stations being the vertices of the triangular faces. The dipoles have linear magnitudes, being directed along the normal vector over each triangle. The unknown values of the dipole magnitudes at each station are obtained by a suitable modification of the usual integral equation considering the discontinuity of the normal vector at each vertex of the dipole surface. Profile data processing is also studied. A numerical test outlines the accuracy and the limitations of the model for the case of a magnetic field significantly perturbed by a rough topographic relief.     

频率域偶层位曲面位场处理和转换方法研究

在空间域偶层位法的基础上,研究了完整的频率域偶层位曲面位场处理和转换方法.该法可应用于平面或曲面、规则网或非规则网的位场数据处理和转换.通过对偶层面z坐标和计算面z坐标平移不同的量来加速正演快速收敛和保证反演稳定、快速收敛;提出了适合于不规则网曲面处理和转换的核心算法——单点快速Fourier变换;提出了频率域不规则网曲面处理和转换方法技术.通过以上技术措施解决了大数据量特别是曲面不规则网的位场处理和转换问题,模型试算以及实际资料处理验证了该方法的应用效果.