Research on the relationship between Earth’s variable rotation and global seismic activity

Based on the time series of observational variations of the length of day (LOD) and seismic data in the world, the relations of the decadal fluctuation and seasonal variation in the Earth’s rotation with global seismic activity are studied in this paper. The results suggest that there are overall correlations on temporal scale and regional discrepancy on spatial scale between global seismic activity and the Earth’s variable rotation, especially the seismic activity in the Eurasian seismic zone (not including southeast Asia) and the Lower California-Eastern Alaska seismic zone correlating well with the Earth’s variable rotation. According to the relations mentioned above, the observational data of the Earth’s rotation might provide a referential basis for monitoring global seismic activity.     

On the application of fiber optic gyroscopes for detection of seismic rotations

In recent years, the measurement of rotational components of earthquake-induced ground motion became a reality due to high-resolution ring laser gyroscopes. As a consequence of the fact that they exploit the Sagnac effect, these devices are entirely insensitive to translational motion and are able to measure the rotation rate with high linearity and accuracy over a wide frequency band. During the last decade, a substantial number of earthquakes were recorded by the large ring lasers located in Germany, New Zealand, and USA, and the subsequent data analysis demonstrated reliability and consistency of the results with respect to theoretical models. However, most of the observations recorded teleseismic events in the far-field. The substantial mass and the size of these active interferometers make their near-field application difficult. Therefore, the passive counterparts of ring lasers, the fiber optic gyros can be used for seismic applications where the mobility is more important than extreme precision. These sensors provide reasonable accuracy and are small in size, which makes them perfect candidates for strong motion applications. The other advantage of fiber optic gyroscopes is that if the earthquake is local and shallow (like one occurred early this year at Canterbury, New Zealand), the large ring lasers simply do not have the dynamic range??the effect is far too large for these instruments. In this paper, we analyze a typical commercially available tactical grade fiber optic gyroscope (VG-951) with respect to the seismic rotation measurement requirements. The initial test results including translation and upper bounds of seismic rotation sensitivity are presented. The advantages and limitations of tactical grade fiber optic gyroscope as seismic rotation sensor are discussed.     

内核地球自转动力学理论的研究进展(Ⅰ)

地球固体内核（SIC）和地球其余部分之间的引力和压力的耦合作用引起了一个力矩，从而对地球的章动运动产生影响.由于SIC的转动惯量和整体地球转动惯量相比是非常小的，因此可以认为SIC的动力学效应只是导致一个新的章动本征模，其频率与自由核章动（FCN）相差不太远，且对地球章动产生了一个微弱的共振影响.本文在文献〔1〕理论的基础上，对内核地球自转动力学理论进行了更加深入和详细的研究，顾及到高阶引潮力位的影响，介绍了研究内核地球自转的基本假设和定义，引潮力位的复数球函数表示，复数矢量球函数的基本理论等.     

内核地球自转动力学理论的研究进展(Ⅴ)——地球自转耦合运动方程组

本文是序列文章的第五篇,其内容包括：基于连续介质力学的基本理论,在考虑到地球的自引力、液核对核幔边界的压力和外部引潮力的作用下,严格地给出了地幔的角动量方程.利用前文的有关结论,进而给出了整体地球自转的动力学方程和内核地球模型的地球自转耦合运动学方程组.本文顾及了高阶岁差章动力矩对地球自转的影响,因而在理论上扩展了文献〔1〕给出的理论模型.本文的理论对进一步研究在高阶岁差章动力矩作用下的内核地球章动是非常有意义的.     

全球强震与地球自转角加速度变化过程关系统计研究

统计分析了1962—2017年全球强震活动与地球自转角加速度变化过程的关系, 结果显示, 全球8级以上地震发生在地球自转角加速度下降期的概率相对自然概率高出12%, 达到64%, 统计结果具有显著性, 但7.5级和7.8级以上地震的统计结果没有显著性。 分区统计结果表明, 全球强震活动具有明显的区域性特征: 在地球自转角加速度上升期, 高于自然概率的强震主要分布在阿尔卑斯带中西段、 环太平洋地震带的琉球—菲律宾地区以及中国东部; 在地球自转角加速度下降期, 高于自然概率的强震主要分布在环太平洋地震带、 阿尔卑斯带中段(喜马拉雅弧)、 阿尔卑斯带东段(印尼岛弧海沟)以及中亚大陆地区。 分析认为地球自转角加速度变化过程与全球区域地震活动之间存在较强的相关性, 可能与地球自转角加速度变化引起板块间相互作用的强弱有关。     

Manifestation of solar and geodynamic activity in the dynamics of the Earth’s rotation

The relationships between different manifestations of solar and geomagnetic activity and the structural peculiarities of the dynamics of the pole wobble and irregularities in the Earth??s rotation are studied using singular spectrum analysis. There are two close major peaks and several lower ones in the same frequency range (1.1?C1.3 years) in the Chandler wobble (CW) spectrum. Components in the geomagnetic activity were distinguished in the same frequency band (by the Dst and Ap indices). Six- to seven-year oscillations in the Earth??s rotation rate with a complex dynamics of amplitude variations are shown in variations in geomagnetic activity. It is revealed that secular (decade) variations in the Earth??s rotation rate on average repeat global variations in the secular trend of the Earth??s geomagnetic field with a delay of eight years during the whole observation period.     

Complex demodulation in VLBI estimation of high frequency Earth rotation components

The spectrum of high frequency Earth rotation variations contains strong harmonic signal components mainly excited by ocean tides along with much weaker non-harmonic fluctuations driven by irregular processes like the diurnal thermal tides in the atmosphere and oceans. In order to properly investigate non-harmonic phenomena a representation in time domain is inevitable. We present a method, operating in time domain, which is easily applicable within Earth rotation estimation from Very Long Baseline Interferometry (VLBI). It enables the determination of diurnal and subdiurnal variations, and is still effective with merely diurnal parameter sampling. The features of complex demodulation are used in an extended parameterization of polar motion and universal time which was implemented into a dedicated version of the Vienna VLBI Software VieVS. The functionality of the approach was evaluated by comparing amplitudes and phases of harmonic variations at tidal periods (diurnal/semidiurnal), derived from demodulated Earth rotation parameters (ERP), estimated from hourly resolved VLBI ERP time series and taken from a recently published VLBI ERP model to the terms of the conventional model for ocean tidal effects in Earth rotation recommended by the International Earth Rotation and Reference System Service (IERS). The three sets of tidal terms derived from VLBI observations extensively agree among each other within the three-sigma level of the demodulation approach, which is below 6 μas for polar motion and universal time. They also coincide in terms of differences to the IERS model, where significant deviations primarily for several major tidal terms are apparent. An additional spectral analysis of the as well estimated demodulated ERP series of the ter- and quarterdiurnal frequency bands did not reveal any significant signal structure. The complex demodulation applied in VLBI parameter estimation could be demonstrated a suitable procedure for the reliable reproduction of high frequency Earth rotation components and thus represents a qualified tool for future studies of irregular geophysical signals in ERP measured by space geodetic techniques.     

Magnetorotational instability in the Earth’s core

The anisotropy of the convection in the Earth’s core can act as a cause of its nonsolid rotation. In the case of differential rotation, the magneto-rotational instability (the Velikhov instability) can arise in the liquid core. It is shown that the development of the magneto-rotational instability of the hydromagnetic flows in the liquid core of the Earth can generate variations in the geomagnetic field observed on the Earth’s surface.     

Cyclic variations in the Earth’s flattening and questions of seismotectonics

For more than a decade, the global network of GPS stations whose measurements are part of the International GPS Service (IGS) have been recording cyclic variations in the radius vector of the geodetic ellipsoid with a period of one year and amplitude of ~10 mm. The analysis of the figure of the Earth carried out by us shows that the observed variations in the vertical component of the Earth’s surface displacements can induce small changes in the flattening of the Earth’s figure which are, in turn, caused by the instability of the Earth’s rotation. The variations in the angular velocity and flattening of the Earth change the kinetic energy of the Earth’s rotation. The additional energy is ~10²¹ J. The emerging variations in the flattening of the Earth’s ellipsoid lead to changes in the surface area of the Earth’s figure, cause the development of deformations in rocks, accumulation of damage, activation of seismotectonic processes, and preparation of earthquakes. It is shown that earthquakes can be caused by the instability of the Earth’s rotation which induces pulsations in the shape of the Earth and leads to the development of alternating-sign deformations in the Earth’s solid shell.     

On the theory of the geomagnetic dynamo based on mean field electrodynamics

A survey is given on the present state of the geomagnetic dynamo theory which is based on the electrodynamics of mean fields in electrically conducting turbulent media. Models of both the ²-type and the ω-type are taken into consideration, i.e. models where the -effect alone, or together with a differential rotation, gives rise to the regeneration of magnetic fields. Results of special investigations are given and discussed. Models of the ²-type apply to the Earth provided that it shows no noticeable differential rotation. It is pointed out that such models can explain not only the generation of a magnetic field with an axisymmetric dipole-like structure, but also the occurrence of non-axisymmetric components and their westward drift. If, however, a noticeable differential rotation exists, models of the ω-type have to be envisaged. Such models also allow an understanding of the existence of a magnetic field with an axisymmetric dipole-like structure, but they do not provide for a straightforward interpretation of the occurrence and behaviour of the non-axisymmetric components.     

地球自转与北半球中纬度地面温度的年代际关系及其可能物理过程分析

利用地球日长（LOD）资料和美国环境预报中心/国家大气研究中心（NCEP/NCAR）的气象要素资料,统计分析发现1962-2010年LOD的变化和北半球中纬度地面温度均存在明显的十年以上的波动周期.相关分析、合成分析等统计方法均检测到LOD与中纬度地面温度的显著负相关关系,当地球自转速率加快时,北半球中纬度地面增温;反之,中纬度地面降温.小波功率谱和交叉谱分析则确定二者的相互关系属于准20年周期尺度上的年代际变化联系,并且LOD的变化超前于地面温度的变化大概3~4年.平均而言,LOD的变化可带来中纬度地面温度0.2℃的降温（或增温）.通过对大气相对角动量、纬向风场、海平面气压场的年代际合成分析,揭示了LOD与地面温度的年代际联系形成的具体物理过程.当地球自转加速时,北半球高低纬度经向温差梯度减弱,热带地区向极地扩展,造成北半球中纬度地区地面增温;地球自转减速时段相反,经向温差梯度增强,热带地区向赤道收缩,中纬度地区地面降温.     

On the frequency variations in the Earth’s rotation caused by unstable flows in the liquid core

The correlation between frequency variations in the Earth’s rotation and geomagnetic jerks is analyzed on the interval from 1900 to 2008. It is found that jerks precede changes in the rate of the Earth’s rotation frequency in the interval of periods ranging from 5 to 8 years. A mechanism of jerks generation is suggested in which the jerks are considered as the result of the excitation of magnetorotational instability in the Earth’s core with the subsequent generation of torsional oscillations causing a change in the Earth’s rotation frequency.     

地球自转及其和地球物理现象的联系：Ⅰ日长变化

本文回顾了近十年来的研究进展，分各个时间尺度讨论了日长变化及其地球物理激发原因，并评估未来十年内地球自转运动可能的研究方向及课题。     

地球自转及其和地球物理现象的联系：：Ⅱ.地极运动

地球自转运动包括岁差和章动，极移和日长的变化，极移指自转轴相对地壳的运动。其主要激发原因是地球上物质分布的变化。因而，对极移的观测和研究必然为全球性的地球物理现象提供着信息。     

Effects of Earth's rotation on convection in magma chambers

The rotation of the Earth is predicted to have a strong influence on the convective motions in basaltic magmas which cool at high and intermediate latitudes on the Earth's surface. Convection in layers greater than 100 m deep is characterised by large Taylor numbers and small Rossby numbers, for which laboratory experiments provide evidence of strong rotationally-induced flows. In the case of convection driven by either thermal or compositional buoyancy fluxes from horizontal top or bottom boundaries Coriolis forces induced by the Earth's rotation are expected to cause the turbulent convective motions to form into intense vortices whose axes tend to be close to the vertical. These vortices should be tall and thin, be very unsteady, and have rapid vertical motion in their cores. Earth's rotation is likely to have little or no effects on convection in very shallow convecting layers ( < 100 m) of basaltic magmas or in chambers of more viscous (granitic) magmas. When convection is driven by horizontal density differences (such as those produced by cooling or crystallization at sloping or vertical walls or by simple lateral variation of layer depth) in basaltic chambers of order 10 km or greater in width the rotation of the Earth may cause relatively rapid horizontal (geostrophic) circulation over the lateral scales of the chamber. These predictions involve some extrapolation of fluid dynamical principles from laboratory to magma chamber conditions. Speculative comments on some possible petrological implications are included.     

The effect of the earth's rotation on ground water motion

The average pore velocity of ground water according to Darcy's law is a function of the fluid pressure gradient and the gravitational force (per unit volume of ground water) and of aquifer properties. There is also an acceleration exerted on ground water that arises from the Earth's rotation. The magnitude and direction of this rotation-induced force are determined in exact mathematical form in this article. It is calculated that the gravitational force is at least 300 times larger than the largest rotation-induced force anywhere on Earth, the latter force being maximal along the equator and approximately equal to 34 N/m(3) there. This compares with a gravitational force of approximately 10(4) N/m(3).     

内核地球自转动力学理论的研究进展(Ⅳ)——内核自转动力学方程

本文是序列文章的第四篇,其内容包括：基于连续介质力学的基本理论,给出了固体外核（SIC）自转的动力学方程,考虑了地球的自引力、液核对内核边界的压力和二阶外部引潮力位对SIC自转的影响,并在O(mε)的量级上给出了其实用的表达式.本文的理论推导更加严密和细致,改正了文献〔1〕在推导过程中的某些错误（例如：（B39）、（B44）和（B59c）式）.本文的工作是对文献〔1〕有关理论的扩展和改进,对进一步研究内核地球自转的动力学理论是非常重要的.     

内核地球的自转运动和地球固定参考系的研究

本文研究了内核地球模型下的地球表面的旋转运动和地球形变场的复数矢量球函数表示,以及外壳固定参考架、地球参考系的理论定义和它们之间等价性的理论证明.同时给出了液体外核（FOC）、固体内核（SIC）和整体地球的转动惯量张量和角动量的具体表达式.在考虑到引潮力位对地球形变场的影响下,研究了地幔相对角动量的具体表述.本文的工作是对前人有关理论的扩展和改进,对进一步研究内核地球自转的动力学理论是非常重要的.