Experimental earth tidal models in considering nearly diurnal free wobble of the Earth''''s liquid core

Based on the 28 series of the high precision and high minute sampling tidal gravity observations at 20 stations in Global Geodynamics Project (GGP) network, the resonant parameters of the Earth's nearly diurnal free wobble (including the eigenperiods, resonant strengths and quality factots) are precisely determined. The discrepancy of the eigenperiod between observed and theoretical values is studied, the important conclusion that the real dynamic ellipticity of the liquid core is about 5% larger than the one under the static equilibrium assumption is approved by using our gravity technique. The experimental Earth's tidal gravity models with considering the nearly diurnal free wobble of the Earth's liquid core are constructed in this study. The numerical results show that the difference among three experimental models is less than 0.1%, and the largest discrepancy compared to those widely used nowdays given by Dehant (1999) and Mathews (2001) is only about 0.4%. It can provide with the most recent real     

Characteristics of tidal gravity changes in Lhasa, Tibet, China

Tidal gravity changes arise from the response of the solid Earth to the tidal forces of the Sun,Moon and planets close to the Earth,and are a comprehensive reflection of the structure and distribution of physical properties of the Earth’s interior.As a result,observations of tidal gravity changes are the basis of studies on other global and/or regional dynamic processes.The characteristics of tidal gravity changes in the region of the Tibetan Plateau were investigated through continuous gravity measurements recorded with a superconducting gravimeter (SG) installed in Lhasa over a year.Through contrast measurements with a spring gravimeter LaCoste-Romberg ET20 at the same site,the gravity observations in Lhasa were scaled to the international tidal gravity reference in Wuhan.Meanwhile,the scale factor of the SG was determined accurately as-777.358 ± 0.136 nm s-2V-1,which is about 2.2% less than the value provided by the manufacturer.The results indicate that the precision of the tidal gravity observations made with the SG in Lhasa was very high.The standard deviation was 0.459 nm s-2,and the uncertainties of for the four main tidal waves (i.e.O 1,K 1,M 2 and S 2) were better than 0.006%.In addition,the observations of the diurnal gravity tides had an obvious pattern of nearly diurnal resonance.As a result,it is affirmed that the Lhasa station can provide a local tidal gravity reference for gravity measurements on the Tibetan Plateau and its surrounding regions.The loading effects of oceanic tides on tidal gravity observations in Lhasa are so weak that the resulting perturbations in the gravimetric factors are less than 0.6%.However,the loading effects of the local atmosphere on either the tidal or nontidal gravity observations are significant,although no seasonal variations were found.After removal of the atmospheric effects,the standard deviation of the SG observations in Lhasa decreased obviously from 2.009 to 0.459 nm s-2.Having removed the loading effects of oceanic tides and local atmosphere,it was found that the tidal gravity observations made with the SG in Lhasa significantly differed by about 1% from those expected theoretically,which may be related to active tectonic movement and the extremely thick crust in the region of the Tibetan Plateau.A more-certain conclusion requires longer accumulation of SG data and further associated theoretical studies.     

Detection of the translational oscillations of the Earth＇s solid inner core based on the international superconducting gravimeter observations

Based on the 21 series of the high precision tidal gravity observations recorded using superconducting gravimeters (SG) at 14 stations distributed globally (in to-tally about 86 years), the translational oscillations of the Earth抯 solid inner core (ESIC) is detected in this paper. All observations are divided into two groups with G-Ⅰ group (8 relatively longer observational series) and G-Ⅱ group (13 relatively shorter observational series). The detailed correc-tions to minute original observations for each station are carried out, the error data due to the earthquakes, power supply impulses and some perturbations as change in at-mospheric pressure and so on are carefully deleted for the first step, the gravity residuals are obtained after removing further synthetic tidal gravity signals. The Fast Fourier Transform analysis is carried out for each residual series, the estimations of the product spectral densities in the sub-tidal band are obtained by using a multi-station staking technique. The 8 common peaks are found after further removing the remaining frequency dependent pressure signals. The eigen-periods, quality factors and resonant strengths for these peaks are simulated. The numerical results show that the discrepancies of the eigenperiods for 3 of 8 peaks, compared to those of theoretical computation given by Smith, are only 0.4%, -0.4% and 1.0%. This coincidence signifies that the dynamical phenomenon of the Earths solid inner core can be detected by using high precision ground gravity observations. The reliability of the numerical computation is also checked, the spectral peak splitting phenomenon induced by Earths rotation and ellipticity is preliminary discussed in this paper.     

Detection of the special gravity signals in sub-tidal band by using wavelet technique

With the rapid increase of the requirements to geo-dynamics of the Earth’s deep interior in global basic sciences and space techniques, the theoretical study and experimental detection of the geodynamic phenomena in Earth’s liquid core (ELC) and Earth’…     

Experimental detection of the inner core translational triplet

The translational oscillation of the solid inner core is one of the Earth’s fundamental normal modes, which is also called Slichter mode. The normal mode should be split to form a triplet due to the Earth’s rotation and ellipticity. In this study, according to the splitting pattern of Slichter mode, an attempt has been made to detect the possibility of Slichter triplet’s existence by using the product spectra of the long-term continuous gravity measurements from the superconducting gravimeters (SG) at 6 glo...     

Evidence for tritium production in the Earth’s interior

We have made a new investigation on the vertical profiles of tritium and helium isotopes in Lakes Van and Nemrut （Eastern Turkey）, using experimental data from the reference by Kipfer et al. for study of long-term vertical mixing and deep water renewal in Lake Van. Lakes Van and Nemrut are crater lakes. Lake Nemrut is at the western border of Lake Van. The ^3He and ^4He are injected at the bottom of Lakes Van and Nemrut, and the both helium isotopes are confirmed from the mantle source. From ^3H （tritium） data in Lakes Van and Nemrut, we have observed ＂^3H anomaly＂ at the vertical profile of ^3H concentrations in Lake Nemrut. The ^3H concentration at the lake bottom is 10% higher than at the surface. The difference of ^3H concentrations between surface and bottom is about 3.7±1.2 TU. This excess ^3H should be injected from the lake bottom. An investigation on the origin of the injected tritium has been made. The results show the conventional origins are excluded, such as residence of precipitation tritium from nuclear testing in the early 1950s--1960s and tritium from known nuclear reactions. Based on the correlation of excess ^3H with ^3He and heat flow in Lake Nemrut, we infer that the ^3He and ^3H might be all from the mantle source, and produced by the supposed natural-nuclear-fusion, which might occur in an environment rich in water （H） and （U ＋ Th） at high temperature and high pressure in the deep Earth. Detection of tritium in the Earth＇s interior is a key evidence for exploration of natural nuclear fusion in the deep Earth. Based on the published data, we have found that the excess ^3He and ^3H injected at the bottom of Lake Laacher （Germany） were also released from the mantle source. The present work will be helpful to the further study of mechanism of natural nuclear fusion in the Earth＇s interior.     

Biomechanical behavior study of dog‘s small intestines

The biomechanical behavior of dog‘s duodenum and jejunum were studied and a formulation of the stress-strain relation is presented in this paper,The results obtained indicated that the exponential coefficient α and the incremental duodenum of the elastic modulus are both larger than those of the jejunum.It means that the duodenum is more deformabel than the jejunum.The experimental results of this work provide basal data for kinematics study of a robotic endoscope.     

Effect of the free surface on the earthquake energy: A case study of reverse faulting

Based on the representation theorem of seismic energy radiation, in this study, we have quantitatively investigated the effect of free surface on the radiation energy distribution due to a coupling interaction between free surface and near surface finite fault for the reverse earthquake faulting. Corresponding to the finite faulting, a 2-D pseudostatic-reverse-fault-dislocation solution has been used in the calculation of the work done by the seismic response against free surface. The results indicate that, due to a strong coupling interaction between the free surface and near surface fault, the total radiated seismic energy ER is much larger than that radiated only from the fault itself （EF）, especially for the shallow reverse faulting. In convention, EF is commonly used in the estimation of earthquake energy radiation. However, when the fault depth H, the distance between the free surface and top of fault location, increases, the effect of the coupling interaction between the fault and free surface decreases gradually. Therefore, the total radiated energy ER approaches to the EF when the depth H is about 2 times the fault length L The current study could provide us a partial explanation of the apparent stress discrepancy observed at the far field and near field in the recent large earthquake. Moreover, the current study also has a significant implication of how to quantitatively describe the near fault strong ground motion and associated seismic hazard from the earthquake source energy point of view.     

Comparison of Some Methods on Prediction of Activity Interaction Coefficient

Based on Miedema's semiempirical formation enthalpy model for binary alloys, free volume theory and a general solution model, a new model for prediction of activity interaction coefficient ε₁1 is proposed. The calculated results are better in agreement with the experimental values than the two previous models. The related theories and models are discussed according to the degree of agreement with experimental values.     

Study on characteristics of long-term gravity changes at Wuhan station

We consider the characteristics of long-term changes in non-tidal gravity and their implication to the local perturbations in barometric pressure and water storage and to the local vertical crustal movement using the long-term continuous gravity observations from a superconducting gravimeter （SG） at Wuhan station, together with the co-site measurements from a Global Positioning System （GPS） receiver and an absolute gravimeter FG5. The observation results indicate that there are obvious seasonal variations in the long-term gravity changes measured with the SG. About 70 percent of the whole seasonal changes come from the contribution of the local disturbances in air pressure and water storage, while over 95 percent of the annual changes are attributed to the loading effects of these environmental perturbations. Due to the absence of direct measurements of the local water storage, especially those of the underground water, the global assimilating models of land water LaD （Land Dynamics） and GLDAS （Global Land Data Assimilation System） cannot virtually describe the real hydrologic disturbances around the station. The resulting gravity changes, which are simulated theoretically by means of convolution integration of the loading Green＇s functions and water models LaD and GLDAS, show significantly time delay of about 55 days from those measured with the SG. Compared with the measurements of the absolute gravity with the FG5, the long-term drift rate of the SG is determined as about 17.13 nms^-2/a. From the co-site GPS measurements, it is found that the local crust is slowly subsiding at a rate of 3.71±0.16 mm/a, and the related gravity variation is estimated as 13.88±0.22 nms^-2/a. In other words, the ratio of the changes in gravity and altitude related to the local vertical crustal movement is about -37.41 nms^-2/cm. It implies that a considerable mass adjustment may be associated with the local vertical crustal movement, and its dynamic mechanism should be investigated further.     

Comprehensive comparison and analysis of the tidal gravity observations obtained with superconducting gravimeters at stations in China, Belgium and France

The long-term tidal gravity observations of about 27 a obtained with superconducting gravimeters (SG) at stations in Wuhan (China), Brussels (Belgium) and Strasbourg (France) are analyzed comprehensively. The quality factors of these observations at various stations are obtained and the tidal parameters are determined accurately. The efficiency when using various procedures on improving accuracy of the tidal parameters is discussed. The loading corrections on tidal parameters are carried out based on the global ocean tidal models. The correlations between the observed residuals and air pressure change are studied, the atmospheric gravity admittances in both temporal and frequency domains are determined, and the possible reasons of inducing the discrepancy between the observed tidal parameters and those in the standard tidal models are studied.     

Tidal dissipation and the strength of the Earth's internal magnetic field

Magnetic fields at the Earth's surface represent only a fraction of the field inside the core. The strength and structure of the internal field are poorly known, yet the details are important for our understanding of the geodynamo. Here I obtain an indirect estimate for the field strength from measurements of tidal dissipation. Tidally driven flow in the Earth's liquid core develops internal shear layers, which distort the internal magnetic field and generate electric currents. Ohmic losses damp the tidal motions and produce detectable signatures in the Earth's nutations. Previously reported evidence of anomalous dissipation in nutations can be explained with a core-averaged field of 2.5?mT, eliminating the need for high fluid viscosity or a stronger magnetic field at the inner-core boundary. Estimates for the internal field constrain the power required for the geodynamo.     

Evidence for an oxygen-depleted liquid outer core of the Earth

On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth's liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of light elements. Although the concentrations of the light elements are small, they nevertheless affect the Earth's core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo. Several light elements-including sulphur, oxygen, silicon, carbon and hydrogen-have been suggested, but the precise identity of the light elements in the Earth's core is still unclear. Oxygen has been proposed as a major light element in the core on the basis of cosmochemical arguments and chemical reactions during accretion. Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe-S-O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major light element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.     

Seismological evidence for mosaic structure of the surface of the Earth's inner core

The transition from the Earth's solid inner core to liquid outer core is the location where the inner core grows and from which compositional convection in the outer core originates. Most seismological models of the Earth describe the inner-core boundary as sharp and simple, although experimental data requiring the presence of a thin transition layer at the bottom of the outer core have been reported. The density jump at the inner-core boundary--an important parameter determining gravitational energy release and constraining the compositional difference between the inner and outer core-is also not well known. Estimates of this density jump obtained using free-oscillation eigenfrequencies give low values of 0.25-1.0 g cm(-3), whereas a method using the amplitude ratio of core-reflected phases yielded values of 0.6-1.8 g cm(-3) (refs 14, 15, 16-17). Here we analyse properties of waves precritically reflected from the Earth's inner core (PKiKP phases) that show significant variability in amplitude, consistent high-frequency content and stable travel times with respect to a standard Earth model. We infer that the data are best explained by a mosaic structure of the inner core's surface. Such a mosaic may be composed of patches in which the transition from solid inner to liquid outer core includes a thin partially liquid layer interspersed with patches containing a sharp transition.     

Geochemistry: does U-Pb date Earth's core formation?

Constraining the timing of the formation of Earth's core, which defines the birth of our planet, is essential for understanding the early evolution of Earth-like planets. Wood and Halliday and Halliday discuss the apparent discrepancy between the U-Pb (60-80 Myr) and Hf-W clocks (30 Myr) in determining the timescale of Earth's accretion and core formation. We find that the information the authors present is at times contradictory (for example, compare Fig. 1 in ref. 1 with Fig. 1 in ref. 2) and confusing and could suggest that the U-Pb clock constrains core formation better than the Hf-W system. Here we point out the limitations of the U-Pb system and show that the U-Pb age cannot be used to argue for protracted accretion and/or core formation (>50 Myr) because this clock only records the processes that occurred during the last 1% of Earth's accretion and core formation in the Wood and Halliday mechanism.     

自由Poincaré行星模型的动力学分析

本文讨论了由一个刚性慢和一个液体核组成的行星的自转运动。得到了三组平衡解,并对其进行了详细的讨论。探讨了平衡解附近的运动,特别研究了两种极限情况。得到了由于液核的存在角动量轴趋向于形状轴的结论。分析表明行星核的大小及其动力学扁率决定了自由摆动的频率。     

一种GPS海拔高度测量系统的实现方法

介绍GPS高程转换的基本原理,着重讨论了顾及地球重力场模型EIGEN-CG03C的移除-恢复法,并将此算法模型用程序实现固化在以ARM7为核的微处理器内,用硬件实现了海拔高的转换,速度快,精度高,实用性好。