Long-Period Variations in Oscillations of the Earth’s Pole due to Lunar Perturbations

A numerical–analytical approach is used to investigate irregular effects in oscillations of the Earth’s pole related to variations in the Chandler and annual components. An approach to studying oscillations in the motion of the Earth’s pole based on a joint analysis of the Chandler and annual components of this motion is proposed. A transformation to a new coordinate system in which the motion of the pole is synchronous with the precession of the lunar orbit can be found in this approach. Estimates of the precision of predictions of the coordinates of the Earth’s pole taking into account additional terms due to lunar perturbations are presented.

     

Rotational-oscillatory variations in the Earth rotation parameters within short time intervals

A mathematical model for rotational-oscillatory motions of the Earth is constructed by applying celestial mechanics to the spatial problem of the Earth-Moon system subject to the Sun’s gravitation. Some basic phenomena associated with tidal irregularity in the Earth’s axial rotation and the polar oscillations are studied. It is shown that the perturbing component of the gravitational-tidal forces orthogonal to the plane of the lunar orbit is responsible for some short-term perturbations in the Moon’s motion. The constructed model for the rotational-oscillatory motions of the deformable Earth includes both the main high-amplitude perturbations and more complex small-scale motions attributed to short-term lunar perturbations with combinational frequencies. Numerical modeling (interpolation and forecasting) of the Earth rotation parameters within various time intervals based on astrometric data obtained by the International Earth Rotation Service is presented.     

In-phase Variations in the Parameters of the Earth’s Pole Motion and the Lunar Orbit Precession

Astronomy Reports - We found an oscillatory process of the Earth’s pole associated with the precession motion of the Moon’s orbit using numerical processing a series C01 of...     

Seismicity modulation by external stress perturbations in plate boundary vs. stable plate interior

Characterization of critically stressed seismogenic fault systems in diverse tectonic settings can be used to explore the stress/frictional condition of faults, along with its sensitivity for seismicity modulation by periodic stress perturbation. However, the process of seismicity modulation in response to external stress perturbation remains debated. In this paper, the characteristic difference in the seismicity modulation due to resonance destabilization phenomenon governed by rate-and-state friction is presented and validated with the globally reported cases of seismicity modulation in diverse tectonic settings. The relatively faster-moving plate boundary regions are equally susceptible for both shorter-period (e.g., semi-diurnal, diurnal, and other small tidal constituents) and long-period (e.g., semi-annual, annual, pole tide and pole wobble) seismicity modulation processes in response to stress perturbations from natural harmonic forcing, including tidal, semi-annual, annual, or multi-annual time scales. In contrast, slowly deforming stable plate interior regions and diffuse deformation zones appear to be more sensitive for long-period seismicity modulation of semi-annual, annual, or even multi-annual time scales but less sensitive for short-period seismicity modulation. This finding is also supported by the theoretical model predictions from the resonance destabilization process and worldwide documented natural observations of seismicity modulation in diverse types of tectonic settings.     

A Model for the polar motion of the deformable Earth adequate for astrometric data

Refined analytical expressions for the frequencies corresponding to the Chandler motion of the pole and the diurnal rotation of the deformable Earth are derived. Numerical estimates of the period and amplitude of the polar oscillations are presented. The trajectory of the Chandler polar motion derived via numerical modeling is in qualitative and quantitative agreement with experimental data from the International Earth Rotation Service (IERS). An evolutionary model describing slow variations in the Earth’s rotation parameters under the action of the dissipative moments of the tidal gravitational forces on time scales considerably longer than the precession period of the Earth’s axis is constructed. The axis of the Earth’s figure tends to approach the angular momentum vector of the proper rotation.     

A multidimensional analysis and the chronologic structure of the Earth’s geodynamic activity

An attempt has been undertaken to examine time series of volcanic and seismic events in a multidimensional reference system related to the parameters of the Earth’s orbital motion. Volcanic eruptions and strong (M > 5) earthquakes (a sample from the USGS/NEIC seismological database: Significant Worldwide Earthquakes) [18] were analyzed within the fields of the JPL Planetary and Lunar Ephemerides, (DE-406) astronomical indicators [19]: the Earth-Moon distance, Earth-Sun distance, ecliptic latitude of the Moon, and the differences between the geocentric longitudes of the Moon and Sun, Venus and Sun, and Mars and Sun. Distribution spectra were obtained and normalization was performed taking the nonuniform motion of celestial bodies into consideration, and the values of multidimensional diurnal probability were calculated. As a result, the statistically reliable drift in the distribution of geoevents was calculated relative to the duration of the intervals of multidimensional diurnal probability, which indicates distribution regions where more geoevents can take place during shorter intervals (and vice versa). Linear relationships between the multidimensional diurnal probability and diurnal probability of geoevents were found. All these results and the astronomic ephemerides were used as a base for computing the probabilities of volcanic and seismic activity of the Earth for the period of 2005–2007. The spatial structure of volcanic and seismic processes was examined, which allowed the revelation of probabilistic parameters of the spatiotemporal structure of Earth’s geodynamic activity and outlining an approximate algorithm for its monitoring.     

中国地壳运动观测网络在地球科学研究中的应用前景

简要地介绍了中国地壳运动观测网络的概况和目前的进展,论述了地壳运动观测网络在地球科学研究中的重要作用和应用前景。其应用潜力主要体现在:①在中国地壳运动监测研究中发挥重要作用,成为中国地震预测预报研究的重要基础;②为地球动力学研究提供重要的依据;③建立维持ITRF地球参考框架、研究地球自转、极移和章动及变化;④精化、加密全国大地网和大地水准面;⑤在气象学中的应用;⑥研究电离层电子浓度及其变化规律;⑦提供精密近实时的GPS轨道参数;⑧为广域差分定位奠定基础。     

Buoyancy‐driven deformation and contemporary tectonic stress in the lithosphere beneath Central Italy

We studied the continental deformation and modelled the contemporary flow and stress distribution in the lithosphere beneath Central Italy. We made use of a revisited crust and uppermost mantle Earth structure that supports delamination processes. The model behaviour is primarily determined by the thick high density lithospheric root to the east and the low‐viscosity shallow mantle wedge to the west. The rate of the modeled crustal motion is in agreement with GPS data and the pattern of lithospheric flow explains the heat flux, the regional geology and provides a new background for the genesis and age of the recent Tuscan magmatism. The modelled stress in the lithosphere is spatially correlated with the prevailing stress field and the gravitational potential energy patterns and shows that buoyancy forces, solely, can explain the coexisting regional contraction and extension and the unusual sub‐crustal seismicity.     

Intrayear irregularities of the Earth’s rotation

The methods of celestial mechanics can be used to construct a mathematical model for the perturbed rotational motions of the deformable Earth that can adequately describe the astrometric measurements of the International Earth Rotation Service (IERS). This model describes the gravitational and tidal influences of the Sun and Moon. Fine resonant interactions of long-period zonal tides (annual, semiannual, monthly, and biweekly) with the diurnal and semidiurnal tides are revealed. These interactions can be reliably confirmed via a spectral analysis of the IERS data. Numerical modeling of tidal irregularities of the Earth’s axial rotation was carried out, focusing on the analysis and forecasting of variations of the day length occurring within short time intervals of a year or shorter (intrayear variations).     

Study of the crust and mantle using magnetic surveys by Magsat and other satellites

Among the first measurements made from near-Earth orbiting satellites were measurements of the magnetic field. The sources of that field lie both within the Earth, in its core and crust, and in the surrounding ionosphere and magnetosphere. This article summarizes some of the methodology and results for studies of the Earth’s mantle and crust. Mantle conductivity studies can be made either by studying signals impressed on the Earth from outside, e.g., the ionosphere or magnetosphere, or by studying signals originating in the core and transmitted through the mantle. Crustal field studies begin with a careful selection of the data and subsequent removal of core and external fields by some sort of filtering. Average maps from different local times sometimes differ, presumably due to the remaining presence of fields of external origin. Several techniques for further filtering are discussed. Where large-area aeromagnetic maps are available, crustal maps derived from satellite data can be compared with upward continued data. In general, the comparisons show agreement, with some differences, particularly in and near the auroral belts. The satellite data are further reduced by various methods of inverse and forward modelling, sometimes including reduction to the pole (RTP). These techniques are generally unstable at the equator. Common methods of stabilizing the inversions include principle components analysis and ridge regression. Because of the presence of the core field, the entire crustal contribution from the field is not known. Also, there is a basic nonuniqueness to the inverse solutions. Nevertheless, magnetizations that are interpretable can be derived.     

A study of seismic reflection imaging using microearthquake sources

We present a method for processing three-component digital recordings of microearthquakes to obtain near-vertical reflection profiles in regions of shallow seismicity. The processing includes magnitude and focal depth normalization and event stacking, where stacking is by small localized groups, with ray theoretical time and distance corrections applied to compensate for varying focal depths. In areas with high seismicity, this procedure allows earthquakes to be treated as “controlled” sources to probe layered structures of the deep crust and upper mantle.The validity of our approach is examined using aftershocks of the Borah Peak, Idaho earthquake (M_s = 7.3). Several thousand events occurred in a NNW-trending zone about 10 km wide, 75 km long, and 15 km deep. A small (~ 10 ×10 km) array of nine University of Wisconsin three-component triggered short-period digital seismographs was installed in the region of aftershock activity. Over a 10-day period, about 1000 useable events were recorded, of which about 120 have been used for this study. Hypocenters have been computed using both P- and S-wave arrivals, the latter being essential for stable solutions of events outside the network.The Borah Peak data have been processed to obtain shear-wave reflection profiles for the central station (Station 8) of the digital station array. The stacked shear wave (transverse) record sections reveal coherent reflections from horizons at mid-crustal to Moho depths. The most prominent reflections are from crustal discontinuities in the depth range 18–28 km. Coherent reflections can be obtained only through stacking, which is necessary to improve the signal to noise ratio. The major sources of data scatter, as manifested by “smearing” of reflections on the stacked records, are crustal heterogeneity and errors in the determination of focal depth and origin time.     

古地磁场研究:挑战与机遇

地磁场源于地核流体的运动,至少已有约35亿年历史。地磁场的起源及演化一直是地球科学研究的前沿领域之一,这是因为它既是地球宜居环境的重要保障,也是探究地球系统各圈层联系的重要途径。本文重点围绕保留在岩石中的"深时"古地磁场记录,分析在地球内部磁场的形成与维持、地磁场极性倒转、以及地磁场强度变化等古地磁场研究三个方面的主要进展及面临的挑战。同时,结合古地磁测试技术的革新,磁发电机实验和超算模拟的应用,生物磁学的发展,阐述古地磁与地质学多学科交叉研究有望在揭示古地磁场变化及其对生物演化方面的贡献。对古地磁场变化的研究不仅有助于理解地磁场的起源与演化规律,也对认识地球的早期演化,甚至其它行星的演化有重要意义。     

俯冲物质深地幔循环——地球动力学研究的一个新方向

地球上发生的各种地壳运动,大规模的火山喷发,不同深度不同规模的地震活动,规模宏大的山脉和高原的形成,以及地球历史上发生的大陆漂移运动,都被认为与板块构造活动密切相关。但这些运动的动力源究竟来自何方?如何去发现和证明它们的存在以及从理论上去认识和解释,是当今地球科学面临的巨大挑战,也是今后很长一段时间内地球科学的前沿和热点问题。近些年,人们通过各种方法,试图从更深部寻找板块作用动力学的证据。首先是地震层析研究取得了很大进展,获得了许多区域性和全球的高分辨率3-D地震地幔波速结构,使得我们得以认识地球深部的结构,探讨地幔的物质组成,流体的作用和动力学过程。证据显示,板块俯冲不仅可以到达地幔过渡带深度,而且可达到下地幔底部,堆积在核幔边界的上部,成为核幔边界产生的地幔柱的重要物质组成。其次是开展了大量的实验岩石学研究,模拟了一系列地球深部的高温高压矿物组合,被认为可能代表了地幔过渡带和下地幔的矿物组合,甚至核幔边界的含水矿物组合。另一方面,计算机模拟实验揭示了冷的大洋岩石圈发生深俯冲是可行的。尤为重要的是,许多来自地幔过渡带甚至下地幔深度的高压矿物已经在自然界陆续被发现,证明其中一些矿物是源...     

The great sulfur depletion of Earth’s mantle is not a signature of mantle–core equilibration

The extreme depletion of the Earth’s mantle in sulfur is commonly seen as a signature of metal segregation from Earth’s mantle to Earth’s core. However, in addition to S, the mantle contains other elements as volatile as S that are hardly depleted relative to the lithophile volatility trend although they are potentially as siderophile as sulfur. We report experiments in metal-sulfide–silicate systems to show that the CI normalized abundances of S, Pb, and Sn in Earth’s mantle cannot be reproduced by element partitioning in Fe ± S–silicate systems, neither at low nor at high pressure. Much of the volatile inventory of the Earth’s mantle must have been added late in the accretion history, when metal melt segregation to the core had become largely inactive. The great depletion in S is attributed to the selective segregation of a late sulfide matte from an oxidized and largely crystalline mantle. Apparently, the volatile abundances of Earth’s mantle are not in redox equilibrium with Earth’s core.     

Effects of Crustal Structure for Estimation of Vertical Load Deformation on the Solid Earth Using GRACE in China Mainland

When the inversion of vertical load deformation on Earth’s surface using GRACE (Gravity Recovery and Climate Experiment) data, the load Love numbers based on PREM (Preliminary Reference Earth Model) are commonly used. But the crustal structure under China mainland especially under Tibet Plateau is quite different from that given by PREM Earth model. New load Love numbers were calculated based on a modified Earth model which accounted for regional crustal structure in China mainland. And the effect of regional crustal structure in China mainland for estimation of vertical load deformation on Earth’s surface using GRACE RL05 data was investigated in this paper. It is found that the effect of crustal difference is very prominent. The relative difference of load Love numbers for vertical deformation can reach about 11% at degree 90. The extreme value of difference in vertical load deformation below 90 degree of spherical harmonic coefficients located at the southeastern Tibet Plateau and the maximum relative difference reaches 10%. The relative difference of the root mean square is about 4%. It is suggesting that an Earth model with a more realistic crustal structue instead of PREM should be used for the estimation of vertical load deformation in China mainland espacially in Tibet Plateau.     

A correlation model for oscillations of the Earth’s pole with parametric perturbations

A differential correlation model for oscillations of the Earth’s pole is constructed. The model has gravitational-tidal, additive and parametric, slowly varying, harmonic (at the Chandler frequency and double this frequency), and random Gaussian, broadband perturbations. Special attention is paid to the analysis of trends and the amplitude-frequency characteristics of stochastic oscillations of the Earth’s pole. Numerical simulations show that first-approximation equations can be used to estimate the correlation characteristics of oscillations of the Earth’s pole to within 10%. The results of the model are compared with the results of statistical modeling of oscillations at the Chandler frequency. The model represents a base of informational resources for analytical modeling of the motion of the Earth’s pole over intervals of three to five years.     

Migration of crustal deformation

Observations on the migration rates of crustal deformation, as recently discovered in several tectonic areas, such as the south Kanto and central Tohoku districts, Japan and the West Cordillera Mts., Peru, has opened up a new opportunity for the study of crustal dynamics. Briefly, these examples from coastal areas are characterized by migration landwards with a velocity of about 10–100 km/yr. This agrees well with the velocity of mIgration of seismicity as previously known. Dispersion and dissipation of the deformation waveform are also noted as characteristics.Simple extrapolation of the migration path back toward the ocean may locate a possible origin of the event. In the case of the south Kanto district, for example, the deformation front seems to have originated in the early 1950s from the vicinity of the junction of the Japan and Izu—Mariana trenches. The deformation front in the central Tohoku district, on the other hand, is thought to have originated in the northern part of the Japan Trench in the late 1960s. One may suppose that either a repeated irregular aseismic plate motion generates the deformation events, or that it results from a periodic seismic slip at a plate boundary. In the latter case, the 1953 Boso-oki and the 1968 Tokachi-oki earthquakes might be suspected of generating the deformation fronts in the south Kanto and central Tohoku districts respectively.As Scholz speculated, the migration of a deformation front might trigger earthquakes, if it hits areas of high seismic potential. Studies of migration events can contribute significantly to earthquake prediction studies.     

Plate tectonics,flood basalts and the evolution of Earth’s oceans

The chemical composition of the bulk silicate Earth (BSE) indicates that the present‐day thermal budget of Earth is likely to be characterized by a significant excess of surface heat loss over internal heat generation, indicating an important role of secular cooling in Earth’s history. When combined with petrological constraints on the degree of secular cooling, this thermal budget places a tight constraint on permissible heat‐flow scaling for mantle convection, along with implications for the operation of plate tectonics on Earth, the history of mantle plumes and flood basalt magmatism, and the origin and evolution of Earth’s oceans. In the presence of plate tectonics, hotter mantle may have convected more slowly because it generates thicker dehydrated lithosphere, which could slow down subduction. The intervals of globally synchronous orogenies are consistent with the predicted variation of plate velocity for the last 3.6 Gyr. Hotter mantle also produces thicker, buoyant basaltic crust, and the subductability of oceanic lithosphere is a critical factor regarding the emergence of plate tectonics before the Proterozoic. Moreover, sluggish convection in the past is equivalent to reduced secular cooling, thus suggesting a more minor role of mantle plumes in the early Earth. Finally, deeper ocean basins are possible with slower plate motion in the past, and Earth’s oceans in the Archean is suggested to have had about twice as much water as today, and the mantle may have started as dry and have been gradually hydrated by subduction. The global water cycle may thus be dominated by regassing, rather than degassing, pointing towards the impact origin of Earth’s oceans, which is shown to be supported by the revised composition of the BSE.     

胶辽吉地区古元古代早期花岗岩的侵位模式及其与隆滑构造的关系

通过对胶辽吉地区古元古代裂谷带的深入研究，提出了伸展构造环境下中深部地壳花岗质岩浆侵位的一种模式，即花岗质岩浆沿基底与盖层之间的拆离滑脱带多次贯入，形成岩席，之后随着地壳拉伸（或伸展）作用，这些岩席逐渐远离侵位中心，发生侧向迁移。这种大陆壳内中深部花岗质岩浆的侵位和地壳的侧向伸展的模式，与有些学者提出的大洋中脊玄武质岩浆的侵位和洋壳扩张的模式是基本相似的。这一模式也是大陆地壳快速生长加厚的一种有效机制。由于花岗质岩浆的上涌引起上覆盖层因重力失稳形成一系列顺层滑脱构造组合。它们与花岗岩和基底共同构成中深构造层次岩浆隆起－顺层分层滑脱构造系     

Deep mantle roots and continental emergence: implications for whole-Earth elemental cycling,long-term climate,and the Cambrian explosion

Elevations on Earth are dominantly controlled by crustal buoyancy, primarily through variations in crustal thickness: continents ride higher than ocean basins because they are underlain by thicker crust. Mountain building, where crust is magmatically or tectonically thickened, is thus key to making continents. However, most of the continents have long passed their mountain building origins, having since subsided back to near sea level. The elevations of the old, stable continents are lower than that expected for their crustal thicknesses, requiring a subcrustal component of negative buoyancy that develops after mountain building. While initial subsidence is driven by crustal erosion, thermal relaxation through growth of a cold thermal boundary layer provides the negative buoyancy that causes continents to subside further. The maximum thickness of this thermal boundary layer is controlled by the thickness of a chemically and rheologically distinct continental mantle root, formed during large-scale mantle melting billions of years ago. The final resting elevation of a stabilized continent is controlled by the thickness of this thermal boundary layer and the temperature of the Earth’s mantle, such that continents ride higher in a cooler mantle and lower in a hot mantle. Constrained by the thermal history of the Earth, continents are predicted to have been mostly below sea level for most of Earth’s history, with areas of land being confined to narrow strips of active mountain building. Large-scale emergence of stable continents occurred late in Earth’s history (Neoproterozoic) over a 100–300 million year transition, irreversibly altering the surface of the Earth in terms of weathering, climate, biogeochemical cycling and the evolution of life. Climate during the transition would be expected to be unstable, swinging back and forth between icehouse and greenhouse states as higher order fluctuations in mantle dynamics would cause the Earth to fluctuate rapidly between water and terrestrial worlds.