三维非均匀地幔中深源电场和磁场的谱理论(Ⅱ)——横向缓变摄动和极型场快速扩散

It is one of the classical problems in Earth′s electromagnetism that continuation of the observatory data of magnetic field into the conducting region. This paper built the coupling vector equations governing the poloidal, toroidal and potential fields in 3-D inhomogeneous conducting mantle. Considering the limitation on variable scale of inhomogeneities in global mantle from study of the Earth′s deep interior, a perturbation　theory of gradually lateral variation was presented. It is unnecessary that the 1-D spherical symmetric distribution of electric conductivity as zero-degree approximation. Serving as a example of solvability of the zero-degree approximation, it was demonstrated how the gradually lateral variation of electric conductivity effect on anti-diffusive problem of poloidal field in Earth′s mantel.     

三维非均匀地幔中深源电场和磁场的谱理论（Ⅱ）──-横向缓变摄动和极型场快速扩散

把磁场观测数据向导电区域延拓,是地球电磁学的经典问题之一．从准静态近似和非零矢势规范的电磁场方程出发,依据矢量的球面分解唯一性定理,本文建立支配三维非均匀电寻率分布全球地慢中的环型场、极型场和电位势场的耦合方程组烤虑地球深部研究对认识全球地幔非均匀性横向变化尺度的限制,提出横向缓变意义下三维非均匀地幔中电场和磁场的摄动理论,其零级近似不要求电导率分布一维球对称．作为零级近似可解的例证,研究了地幔深源极型场的反扩散问题,在利用地面磁场观测反演到核幔边界时,可以考虑地幄横向非均匀性影响．     

Electromagnetic studies of global geodynamic processes

The deep electromagnetic sounding (DES) technique is one of the few geophysical methods, along with seismology, gravity, heat flow, which may be use to probe the structure of the Earth's mantle directly. The interpretation of the DESs may provide electrical conductivity profiles down to the upper part of the lower mantle. The electrical conductivity is extremely sensitive to most of the thermodynamic processes we believe are acting in the Earth's mantle (temperature increases, partial melting, phase transition and to a lesser extent pressure). Therefore, in principle, results from DES along with laboratory measurements could be used to constrain models of these processes.The DES technique is reviewed in the light of recent results obtained in a variety of domains: data acquisition and analysis, global induction modeling and data inversion and interpretation.The mechanisms and the importance of surface distortions of the DES data are reviewed and techniques to model them are discussed. The recent results in terms of the conductivity distribution in the mantle from local and global DES are presented and a tentative synthesis is proposed.The geodynamic interpretations of the deep conductivity structures are reviewed. The existence of mantle lateral heterogeneities in conductivity at all scales and depths for which electromagnetic data are available is now well documented. A comparison with global results from seismology is presented.     

全球地壳、上地幔电导率经向分布特征

计算了对应于各个ＵＴ小时的２４个经度带的Ｓ_q地下感应场对外部施感场的响应函数，应用Ｓｃｈｍｕｃｋｅｒ＇ｓＡｐｐｒｏｘｉｍａｔｅＥｕｒｉｓｔｉｃ反演方法，计算了这些经度带的地下等效层及其电导率分布，得到了地壳－上地幔电导率经向分布的大致图案。对该结果的分析研究得出，全球电导率经向分布存在着极大的不均匀性，在０－４００ｋｍ深度范围内，太平洋和大西洋为低导区；欧亚大陆与美洲大陆为高导区。电导率分布特征与岩石层结构有明显的相关性：在俯冲带，低导区由海洋向大陆下插入；在大洋中脊表现为高导电性。反演结果与地震层析成像结果的比较表明，地下高电导区和低电导区的位置分别对应于地震波低速区和高速区。     

兰州地区深部电性结构的初步研究

利用兰州地区现有的大地电磁资料，对该区的深部电性结构进行了初步研究。结果表明，兰州地区各地质构造单元的电性差异较明显，与区域构造有较好的对应性。     

Cauchy integral analogues for the separation and continuation of electromagnetic fields within conducting matter

The main results in the theory of the interpretation of geopotential fields are generalized to the case of arbitrary variable electromagnetic fields by means of elaborating electrodynamic analogues for the integral of the Cauchy type.The generalized Kertz method for separating a variable electromagnetic field into parts related to the sources located in different regions of space is elaborated on the basis of this technique. The generalized Kertz method allows the selection of external and internal, normal and anomalous parts of the geomagnetic field, as well as the separation of geomagnetic anomalies into the surface and deep components caused by conductivity inhomogeneities in the Earth's crust and upper mantle.The theory of analytical continuation of variable electromagnetic fields in a conducting medium is also developed in the present work using the technique of analogues for the integral of the Cauchy type. It is shown that analytical continuation of a field downwards permits the determination of the location and form of deep geoelectric inhomogeneities according to the configuration of the isolines of flux functions for magnetic and electric fields.     

The effect of the electric conductivity of the Earth's mantle on the Ekman-Hartman hydromagnetic boundary layer and on the magnetic diffusion region

Summary The effect of the electrical conductivity of the Earth's mantle on the non-stationary Ekman-Hartman hydromagnetic boundary layer is investigated under the conditions in the Earth's core. It is shown that under an impulsive change of rotation of the mantle Alfvén waves can only be excited if the Ekman-Hartman hydromagnetic boundary layer is in a non-stationary state, i.e. at a time when its structure is developing. The intensity of the Alfvén waves is very small, because the excitation is more of a mechanic nature than magnetic.     

本州M_W9.1地震前破裂区内地震与地球自转之间的相关现象

强震发生前震源系统可能处于不稳定状态,在这种情况下,震中附近地区的地震活动或许会对微小的应力变化敏感.地球自转会在震源断层面上引起应力,地球自转速率变化也会在震源断层面上引起应力变化.由于地球自转速率变化非常微小,在震源断层面上引起应力变化也非常微弱,如果震源区处于极不稳定状态,这种微弱的应力变化或许会激发一些地震活动.这些被激发的地震活动将会表现出与地球自转速率变化的显著相关性.为了考察2011年3月11日日本本州9.1地震发生前震中附近地区是否存在与地球自转速率变化显著相关的地震活动,选取2000年1月-2011年2月M≥5.0地震集中活动区域为研究区域,根据USGS发布的1991年1月-2011年2月的地震目录,利用舒斯特(Schuster)统计检验方法,研究了地球自转与本州M_W9.1地震前发生的地震活动之间的相关性.检验结果用P值来评估,P值越低表示相关性越显著.结果如下:在研究区内5.4≤M≤6.9地震的P值的时间变化显示本州M_W9.1地震前从2009年6月-2010年1月存在低于0.5%的P值.当P值达最低值时,约82%的5.4≤M≤6.9地震发生在地球自转速率季节性变化的加速期,显示出了地震活动与地球自转速率加速之间的显著相关性.取3°×3°的空间窗,以0.1°的步长沿经度和纬度滑动对P值进行空间扫描,可以得到P值的空间分布.扫描区域远大于研究区,经纬度范围为(33°N-43°N,138°E-147°E).在P值的空间分布图上,可发现在P值处于最低值期间,低于0.5%的P值集中分布在研究区的北部,本州M_W9.1地震震中位于这个低P值区的边缘.因此,本州M_W9.1地震前在其破裂区内存在显著的与地球自转相关的地震活动现象,说明破裂区内存在非常不稳定的地区.     

The local geodynamic test area of CLG-organization and first results of leveling measurement

In 1982, the Central Laboratory for Geodesy (CLG) started a long-term study of the recent crustal movements in a local test area in a mobile region located southwards of Sofia.The recent geodynamic conditions and the deep structure of the Earth's crust in this region are described.Data on the local network of precise leveling are given-the scheme and characteristics of the loops, benchmarks and their monumentation. A first geodynamic analysis of the results of the first and third cycles of measurements is made, a map of the module of horizontal gradient of vertical velocity has been elaborated. The results obtained corroborate the reasons for the selection of this geodynamic test area.     

The types of the earth's crust

For the comprehensive mapping of the deep structure of the Earth's crust a determination of the general types of the crust based on its most essential structural parameters is attempted. Three parameters are considered as most informative, and are accepted as basic for this purpose: thickness of the Earth's curst, thickness of the sedimentary layer, and average velocities of compressional waves in the consolidated parts of the crust. Six types of the crust are recognized. A more detailed division of the crust into sub-types has also been worked out.     

Comparative analysis of hypotheses of the geoelectric structure of the Transcaucasian region from magnetotelluric data

Various hypotheses of the geoelectric structure of the Transcaucasian region reflecting a priori geological and geophysical information and data from profile magnetotelluric (MT) soundings are analyzed. These hypotheses are used to construct simplified 3-D models of electrical conductivity differing in the patterns of the shallow and deep structure of the region. Numerical modeling of MT fields is performed. Comparative analysis of its results indicates that the most probable conductivity model consistent with the available data is a model involving a high-conductivity channel connecting the Black and Caspian seas.     

地震层析成像板块构造及地幔演化动力学

地震层析成像技术的飞速发展给人类提供了一个探测地球内部结构的强有力的工具，也给人类展示了一片新的天地，使人类更加清晰地在两个层次之上（地球的层圈构造和内部横向不均匀性）了解地球内部，特别是对幔内部非均匀结构，从全球和区域的尺度上揭示出地球内部特别是地壳和上地幔横向不均匀结构。呈现出全新的地球，特别是地幔结构的三维图像框架，很容易理解，这一基本框架正是地幔演化热动力学过程的现代表现，如此，我们可以利用该框架去追溯、探讨全球构造特别是地幔构造演化的历史，从而深化对于我们这个星球演化过程的理解。     

Caldera formation by magma withdrawal from a reservoir beneath a volcanic edifice

Caldera formation has been explained by magma withdrawal from a crustal reservoir, but little is known about the conditions that lead to the critical reservoir pressure for collapse. During an eruption, the reservoir pressure is constrained to lie within a finite range: it cannot exceed the threshold value for eruption, and cannot decrease below another threshold value such that feeder dykes get shut by the confining pressure, which stops the eruption. For caldera collapse to occur, the critical reservoir pressure for roof failure must therefore be within this operating range. We use an analytical elastic model to evaluate the changes of reservoir pressure that are required for failure of roof rocks above the reservoir with and without a volcanic edifice at Earth's surface. With no edifice at Earth's surface, faulting in the roof region can only occur in the initial phase of reservoir inflation and affects a very small part of the focal area. Such conditions do not allow caldera collapse. With a volcanic edifice, large tensile stresses develop in the roof region, whose magnitude increase as the reservoir deflates during an eruption. The edifice size must exceed a threshold value for failure of the roof region before the end of eruption. The largest tensile stresses are reached at Earth's surface, indicating that faulting starts there. Failure affects an area whose horizontal dimensions depend on edifice and chamber dimensions. For small and deep reservoirs, failure conditions cannot be achieved even if the edifice is very large. Quantitative predictions are consistent with observations on a number of volcanoes.     

井间电磁成像的迭代反演算法

提出一种基于逐次逼近解法的选代反演算法,对并间地层电导率的构造进行成像．该方法用一阶Ｂｏｒｎ近似将积分方程线性化,得到对电导率分布的初始估计,在选代反演中用高阶Ｂｏｒｎ近似对井间地层电导率构造进行更精确的估计．应用该方法还可以对井间电子率分布进行二次成像,从而使成像分辨率更为准确．数值计算结果表明,这种迭代反演算法与基于Ｂｏｒｎ近似、二阶Ｂｏｒｎ近似和扩展Ｂｏｒｎ近似的反演算法相比提高了成像分辨率,且计算效率相当．     

Induction studies with satellite data

The natural variations of the Earth's magnetic field of periods spanning from milliseconds to decades can be used to infer the conductivity-depth profile of the Earth's interior. Satellites provide a good spatial coverage of magnetic measurements, and forthcoming missions will probably allow for observations lasting several years, which helps to reduce the statistical error of the estimated response functions.Two methods are used to study the electrical conductivity of the Earth's mantle in the period range from hours to months. In the first, known as the potential method, a spherical harmonic analysis of the geomagnetic field is performed, and the Q-response, which is the transfer function between the internal (induced) and the external (inducing) expansion coefficients is determined for a specific frequency. In the second approach, known as the geomagnetic depth sounding method, the C-response, which is the transfer function between the magnetic vertical component and the horizontal derivative of the horizontal components, is determined. If one of these transfer functions is known for several frequencies, models of the electrical conductivity in the Earth's interior can be constructed.This paper reviews and discusses the possibilities for induction studies using high-precision magnetic measurements from low-altitude satellites. The different methods and various transfer functions are presented, with special emphasis on the differences in analysing data from ground stations and from satellites. The results of several induction studies with scalar satellite data (from the POGO satellites) and with vector data (from the Magsat mission) demonstrate the ability to probe the Earth's conductivity from space. However, compared to the results obtained with ground data the satellite results are much noisier, which presumably is due to the shorter time series of the satellite studies.The results of a new analysis of data from the Magsat satellite indicate higher resistivity in oceanic areas than in continental areas. However, since this holds for the whole range of periods between 2 and 20 days, this difference probably is not caused purely by differences in mantle conductivity (for which one would expect less difference for the longer periods). Further studies with data from recently launched and future satellites are needed.     

水平层状对称各向异性介质的大地电磁资料反演

论述了某些条件下地球介质呈现出明显的电导率各向异性的情形，研讨了均匀水平层状对称各向异性介质大地电磁正、反演有关问题，试验表明所给出的反演方法是适用和有效的．给出了利用大地电磁资料了解地壳应力状态及研究膨胀各向异性地震前兆的一种途径．     

Magnetic torque and convection in the earth's core

Summary The problem of expressing analytically the magnetic torque, acting on the electrically conducting part of the Earth's mantle, is treated as a function of the system of convection on the surface of the core. The changes of velocities in the system of convection are estimated for decadic changes of the Earth's rotation and for the perturbation of the Earth's rotation in 1897. As regards the decadic changes of the Earth's rotation a change of velocity in the system of convection at the surface of the core of the order of 10^–4 m/s corresponds, and as regards the perturbation of the Earth's rotation in 1897 (10^–3 s/year) a change of velocity of 10^–3 m/s reduced to the whole surface of the core corresponds, and 10^–2 m/s corresponds for the region of the focus of the world geomagnetic anomaly (dimension of this region is 10⁶ m).     

地球内部结构探测研究——以华北克拉通为例

本文立足对地球物理学科发展态势的分析认识,通过解剖华北克拉通研究实例,对地球内部结构探测研究,特别对壳幔结构的地震学探测研究,对中国近20多年的发展做了回顾;探讨了从区域问题认识全球构造的研究思路.     

The electrical conductivity of the Moon

Investigations of the lunar electrical conductivity were described in excellent reviews by Sonett (1974) and Dyalet al. (1976). In this paper we will try to consider some new aspects of this problem in comparison with the Earth's data.     

地球转速率变化主要中短周期的分析

利用新的世界时高精度观测资料序列分析讨论了地球自转速率的变化特征，采用最大熵谱分析的方法得到这一运动中主要中短周期的参数，而利用小波分析的方法发现某些周期具有明显的时变特征，是值得深入研究的。