Oscillations Of Earth Research Articles

小径管に対応した空気圧駆動式イモムシ型ロボット

This paper describes development of an in-pipe mobile robot driven by pneumatic pressures. Town gas is supplied to houses through polyethylene pipes laid under the road. It is necessary to inspect these pipes regularly caused by the gas leak owing to earth load and oscillation for driving cars on the road. So we manufactured in-pipe mobile robot driven by pneumatic pressures on the model of a green caterpillar. The robot is structured by three somites, four suction brakes and ten air supply tubes. In this work, we researched best diameter of suction brake to move in-pipe, robot's moving speed, movable minimum tube inner diameter and traction force. As a result, the diameter of suction brake was 18 mm, the speed was 9.7 mm/s, the inner diameter was 34mm and the force was 4.2 N.

OS1220 小径管に対応したイモムシ型管内走行ロボットの試作

This paper describes development of an in-pipe mobile robot driven by pneumatic pressures. Town gas is supplied to houses through polyethylene pipes laid under the road. It is necessary to inspect these pipes regularly caused by the gas leak owing to earth load and oscillation for driving cars on the road. So we manufactured in-pipe mobile robot driven by pneumatic pressures on the model of a green caterpillar. The robot is structured by three somite and four suction brakes. In this work, we researched best diameter of suction brake to move in-pipe, robot's moving speed and traction force. As a result, the diameter of suction was 18 mm, the speed was 9.7 mm/s and the force was 4.2 N.

Attenuation of free spheroidal oscillations of the Earth after the M = 9 Earthquake in Sumatra and the super-deep Earthquake in the Sea of Okhotsk: I. the Admissible Q-factor range for the fundamental mode and overtones of the free spheroidal oscillations

The problem of reconstructing the depth distribution of density and the depth and frequency dependences of the mechanical Q-factor in the Earth’s mantle from the entire set of the present-day seismic and astrometric data on the travel times and periods of seismic waves and the amplitudes and phases of forced nutations is considered. The solution of the problem is refined by including the new data about the attenuation of the free oscillations of the Earth excited by the Sumatra earthquake (M = 9) and super-deep earthquake in the Sea of Okhotsk. The actual accuracy of the Q-factor is studied in the first part of the paper. To this end, we analyze (1) the convergence of the Q-factor estimated from the time series of different length shifted along the time axis and (2) the convergence of the results based on the different data. Since the accuracy of identifying all the periods and attenuation factors for the free oscillations from the Sumatra earthquake is significantly higher than for the earthquake with M = 9 in Japan, the data are only compared for the Sumatra and Okhotsk events. The signal-to-noise ratio (SNR) is analyzed based on the records from different Global Seismographic Network (GSN) stations including the station in Obninsk, the Kurchatov station in Kazakhstan, and the main ERM and MAJO stations in Japan. It is found that the highest SNR was observed in Obninsk. The inverse problem of reconstructing the density and Q-factor is solved for the frequency dependent real parts of the shear moduli with allowance for the most accurate data about the attenuation factors for the fundamental spheroidal modes of the free oscillations of the Earth.

A Method for Oscillation Errors Restriction of SINS Based on Forecasted Time Series.

Continuity, real-time, and accuracy are the key technical indexes of evaluating comprehensive performance of a strapdown inertial navigation system (SINS). However, Schuler, Foucault, and Earth periodic oscillation errors significantly cut down the real-time accuracy of SINS. A method for oscillation error restriction of SINS based on forecasted time series is proposed by analyzing the characteristics of periodic oscillation errors. The innovative method gains multiple sets of navigation solutions with different phase delays in virtue of the forecasted time series acquired through the measurement data of the inertial measurement unit (IMU). With the help of curve-fitting based on least square method, the forecasted time series is obtained while distinguishing and removing small angular motion interference in the process of initial alignment. Finally, the periodic oscillation errors are restricted on account of the principle of eliminating the periodic oscillation signal with a half-wave delay by mean value. Simulation and test results show that the method has good performance in restricting the Schuler, Foucault, and Earth oscillation errors of SINS.

The density and Q-factor models based on the new data on the nutations and overtones of the free oscillations of the earth: 2. The results of the numerical modeling of the solution of the inverse problem

In the first part of the paper, we obtained the refined estimates for the periods and Q-factors of the fundamental modes and overtones of spherical and toroidal oscillations with periods longer than 3 min from the data on the free oscillations of the Earth, which were excited by the earthquakes with magnitude 9 that occurred in Sumatra, Japan, and the Sea of Okhotsk. In (Molodenskii et al., 2013), we analyzed the limits of the admissible density distributions in the mantle and liquid core of the Earth, using the data on the amplitudes and phases of the forced nutations, as well as the periods and attenuation factors of the fundamental modes of the free spheroidal and toroidal oscillations of the Earth. These studies were conducted with the fixed values of the total mass and total moment of inertia of the Earth and the fixed distributions of the body seismic waves in the mantle and in the core. The solution was obtained by orthogonalizing the kernels of the integral equations that link the residuals of the observed frequencies and attenuation factors of the free oscillations, as well as the amplitudes and phases of the forced nutations, with the sought densities and Q-factors of the mantle and liquid core. Below, we present the solution of the same problem with allowance for the results obtained in the first part of this paper, namely, the new data on the periods and attenuation factors of the fundamental modes of free oscillations of the Earth and on the periods of the first four overtones of the free spheroidal and toroidal oscillations. Despite the involvement of the new data on the overtones, which have not been considered in our calculations, the weighted root mean square deviations of the theoretical predictions from the observed periods and attenuation factors of the free oscillations, as well as the amplitudes and phases of the forced nutations, have significantly decreased. This is due to (1) the noticeable reduction of the real errors in estimating the parameters of the free oscillations described in the first part of the paper and (2) the inclusion of the quantities determining the depth- and frequency dependences of the Q-factor in the mantle in the set of the independently varied parameters.

Constraining the gravitational wave energy density of the Universe using Earth’s ring

The search for gravitational waves is one of today's major scientific endeavors. A gravitational wave can interact with matter by exciting vibrations of elastic bodies. Earth itself is a large elastic body whose so-called normal-mode oscillations ring up when a gravitational wave passes. Therefore, precise measurement of vibration amplitudes can be used to search for the elusive gravitational-wave signals. Earth's free oscillations that can be observed after high-magnitude earthquakes have been studied extensively with gravimeters and low-frequency seismometers over many decades leading to invaluable insight into Earth's structure. Making use of our detailed understanding of Earth's normal modes, numerical models are employed for the first time to accurately calculate Earth's gravitational-wave response, and thereby turn a network of sensors that so far has served to improve our understanding of Earth, into an astrophysical observatory exploring our Universe. In this paper, we constrain the energy density of gravitational waves to values in the range 0.035--0.15 normalized by the critical energy density of the Universe at frequencies between 0.3 and 5 mHz, using ten years of data from the gravimeter network of the Global Geodynamics Project that continuously monitors Earth's oscillations. This work is the first step towards a systematic investigation of the sensitivity of gravimeter networks to gravitational waves. Further advances in gravimeter technology could improve sensitivity of these networks and possibly lead to gravitational-wave detection.

Dynamic processes in earth’s rotation parameters and tidal deformations on a rotating geoid

Amplitude-frequency analysis of the Earth's rotaryoscillatory motion due to lunisolar gravita� tional and tidal perturbing torques is performed using methods of classical mechanics. Dynamic processes that occur in Earth's rotation parameters (ERP) and Earth's potential due to tidal deformations lead to distortions in Earth's shape and fluctuations in the gravitational field (1, 2). The results of the numerical modeling of oscillatory processes in the Earth's pole motion and variations in the second zonal harmonic δc20 of the geopotential are discussed. The amplitude and phase of oscillations of the Earth's pole are determined using the dynamic Euler-Liou� ville equations. The power spectral densities of the time series of Earth's polar coordinates are compared with those of δc20 variations in the geopotential. This harmonic is found to be a function of the amplitude and phase of the oscillatory process of the Earth's pole. 1. The study of temporal variations in the geopo� tential (2, 3) due to Earth's rotaryoscillatory motion is of scientific and practical interest. The observed ERP variations and variations in the Earth's gravita� tional field are highly interrelated; dynamic processes that lead to appreciable changes in both ERPs and geophysical phenomena have acquired the most detailed reflection in diurnal oscillations (4). The refinement of the Earth's gravitational field involves replacing the statistical geoid by a geoid that corresponds to the deformable shape of the Earth (due to oceanic and rigidbody tides and other factors). Due to increasing demands on the accuracy of the coordinatetime maintenance of navigation systems, investigations related to the refinement of the gravita� tional field and the shape of the Earth have developed intensively (2). Note that the modeling of tidal deformations on a rotating geoid can be used to reach high characteristics of atomic clock synchronization (the stability of atomic frequency is 10 -14 ) for objects that are located on different continents of the globe. Differential equations of the Earth's rotaryoscilla� tory motions with allowance for the harmonic struc� ture of the tidal coefficients were derived from the dynamic Euler-Liouville equations in the problem considering "a deformable Earth-Moon" system in the solar gravitational field (4):

Statistical analysis of laser-interferometric detector Dylkin-1 data and data on seismic activity

This work presents statistical analysis of data collected from laser interferometric detector "Dylkin-1" and nearby seismic stations. The final goal of Dylkin project consists in creating detector of theoretically predicted gravitational waves produced by binary relativistic astrophysical objects. Currently, works are underway to improve sensitivity of detector by 2-3 orders. The goals of this research were to test isolation of detector from noise caused by seismic waves and to find out whether it is sensitive to variations in the gradient of gravitational potential (acceleration of free fall) caused by free Earth oscillations. Noise isolation has been tested by comparing energy of signals during significant seismic events. Sensitivity to variations in acceleration of free fall has been tested by means of cross-spectral analysis.

Direct observation of an interaction in magnetosphere

Researchers have now directly observed an interaction between poloidal waves, a type of ultralow‐frequency oscillation of the Earth's geomagnetic fields, and ions in the ring current, a band of charged particles drifting around Earth in the magnetosphere above the equator. This so‐called drift resonance wave‐particle interaction has been studied theoretically, and some modes of the interaction (in particular the second harmonics, similar to higher‐frequency vibrations of a vibrating string) have been reported in spacecraft observations, but the first fundamental mode resonances of this interaction had not been clearly observed.

Potential Gravitational - Solar Electromagnetic Spectral Radiance Interaction as the Source of the Earth’s Background Free Oscillations

The origins of the continuous free oscillations of the whole earth have been attributed to coupling between the solid earth and atmosphere primarily through the fundamental spheroidal mode 0S29 oscillation of ~3.7 mHz. The origins of these interference patterns have been attributed to an excitation source just above the Earth’s surface. However, comparable surface oscillations have been measured in the Sun’s photosphere. The cube root of the product of the gravitational constant, the spectral radiance of the sun, and the square of the frequency produced an acceleration value that was identical to the measured amplitude of the free Earth oscillations (~0.4∙10-11 m∙s-2). The quantitative convergence suggests these narrow-band accelerations may emerge within the Sun-Earth system as it moves through galactic space.

Potential Gravitational - Solar Electromagnetic Spectral Radiance Interaction as the Source of the Earth’s Background Free Oscillations

The origins of the continuous free oscillations of the whole earth have been attributed to coupling between the solid earth and atmosphere primarily through the fundamental spheroidal mode 0S29 oscillation of ~3.7 mHz. The origins of these interference patterns have been attributed to an excitation source just above the Earth’s surface. However, comparable surface oscillations have been measured in the Sun’s photosphere. The cube root of the product of the gravitational constant, the spectral radiance of the sun, and the square of the frequency produced an acceleration value that was identical to the measured amplitude of the free Earth oscillations (~0.4∙10-11 m∙s-2). The quantitative convergence suggests these narrow-band accelerations may emerge within the Sun-Earth system as it moves through galactic space.

On the admissible range for the mass and inertia moments of the liquid core: I. Solving the inverse problem of nutations and free oscillations of the Earth by decomposition of mechanical parameters in an orthogonalized basis

The results of solving the inverse problem of forced nutations and free oscillations of the Earth by decomposing the Q-factor and small depth variations in density in a system of orthogonal functions are considered. These functions are determined by orthogonalization of the functional derivatives of the observed parameters with respect to the depth distributions of the sought parameters (assuming there are no distributions of the velocities of body seismic waves Vp and VS with depth and unchanged total mass M and inertia moments I of the Earth). The examples are presented to illustrate the numerical solution of the inverse problem on finding the density distributions in the mantle and core of the Earth using orthogonalization of the integral constraints for the probable depth distributions of density describing the conditions of unchanged M and I, as well as the constraints posed by the data on the periods of the free low-order oscillations of the Earth.

Carbon Cycle Makeover

Enhanced levels of anaerobic respiration processes may explain oscillations in Earth's carbon cycle. [Also see Research Article by Schrag et al. ]

Formation of Glaciation Epochs

The effect of Earth precession angle on a climate is presented here. It is shown that the glaciation epochs occurred only when the precession angle was low. After the continental glaciation formed in the Northern hemisphere, Earth’s spherecal symmetry was disrupted and its precession angle increased drastically. As a result, a drastic and rapid climate warm-up occurred, the glaciers melted down and an interglacial stadial1 began. Subsequently, affected by the Lunar-Solar gravity pull on the Earth’s equatorial swelling, the precession angle gradually decreased and a new cooling-down phase occurred. As a result, there was nonlinear oscillation of Earth’s climate with periods on the order of 100 - 120 MY.

Comparative Analysis on the Characteristics of Low‐Frequency Energy Released by the Wenchuan Earthquake and Kunlun Mountains Earthquake

AbstractThe Mw7.9 Wenchuan earthquake of 12 May 2008 and Mw7.8 Kunlun Mountain earthquake of 14 November 2001 have equivalent energy magnitudes. However, the characteristics of the fault rupture processes and the geographical positions of these two great earthquakes are very different, and the damage and the public attention of the Kunlun Mountain earthquake are far less than the Wenchuan earthquake. The seismic wave energy information generated by great earthquakes is very rich. High‐frequency energy of a big quake decays quickly within short time in a small scope, while low‐frequency energy especially very low‐frequency energy decays slowly, and can spread many laps around the Earth before consumed. We employ the spectral element method incorporated with large‐scale parallel computing technology to investigate the characteristics of seismic wave propagation excited by the two great earthquakes. The transverse isotropic PREM (Preliminary Reference Earth Model) model is employed as a prototype for the numerical global Earth model. The Crust2.0 and S20RTS models are taken into consideration. These wave propagation processes are simulated by solving three‐dimensional elastic wave governing equations. The visualization of the numerical results displays the profile with three components of the seismic wave propagation. Our calculation displays the thrusting and strike‐slip of the source rupture processes of the Wenchuan earthquake and the left‐lateral strike‐slip of the source rupture process of the Kunlun Mountain earthquake, respectively. Comparison of low‐frequency energy information of synthetic seismograms excited by the two earthquakes shows that the energy at low‐frequency oscillation modes is broadly equivalent, but the energy of the Kunlun Mountain earthquake is slightly smaller than that of the Wenchuan event. The results also demonstrate that the frequency components are almost the same at low‐frequency displacement amplitude spectra recorded at different stations between the two great earthquakes, but the energy is obviously different. These can further reveal that the characteristics of Earth's oscillation triggered by large earthquakes with different source ruptures are different, and the characteristics of Earth's oscillations recorded by different stations are also different.

The admissible interval for the Q factor in the solid inner core: Constraints from new data on the nutation and free oscillations of the earth

The models of the mechanical Q factor of the inner solid core of the Earth are reconstructed from the amplitudes and phases of forced nutation and the periods and damping constants of the high-order overtones of free radial modes. The admissible range of the Q-factor in the solid core is estimated and the stability of the obtained distributions is analyzed. The real accuracy of the obtained model distributions is estimated on the basis of the previous conclusions concerning the uncertainty in the solution of the inverse problem of reconstructing the internal structure of the Earth in the low-frequency range.

Saturn's equatorial oscillation: Evidence of descending thermal structure from Cassini radio occultations

[1] A series of near-equatorial radio occultations of Cassini by Saturn occurred in 2005 and again in 2009–2010. Comparison of the temperature-pressure profiles obtained from the two sets of occultations shows evidence of a descending pattern in the stratosphere that is similar to those associated with equatorial oscillations in Earth's middle atmosphere. This is the first time that this descent has been observed in another planetary atmosphere. If absorption of upwardly propagating waves drives the descent, the implied absorbed flux is 0.05 m2 s−2, at least as large if not greater than on Earth.

The Application of Quasi-Mean-Element-Method to LEO under Additional Perturbation due to Change of Coordinate System

The perturbation caused by the oscillation of Earth's equator plane must be taken into account when working on the motion of satellite on a low Earth orbit (LEO) in the geocentric celestial coordinate system. Since 1960 s, an intermediate orbit coordinate system using true equator and mean equinox (TEME) is introduced. It effectively solves the problem and has been widely used in various applications till today. But this traditional reference frame is purely conceptual and has always been a headache when performing the transition between these systems especially for those who are unfamiliar with celestial frames. As proved in a previous paper, it is possible to avoid the intermediate TEME frame, and conversions between osculating elements and mean elements can be completed in a consistent geocentric celestial coordinate system where only short-period terms are required. In this paper, after including the improved secular and long-period terms, the quasi-mean-element-method is available to predict the orbit analytically, reaching the accuracy of 10 −6 in Earth's radius. And all these can be done in the same celestial frame. The results suggest that the celestial coordinate system (J2000.0 nowadays) can be used throughout any applications without having to introduce TEME system as intermediate frame any more.

Spherical Oscillations of the Earth*

Summary Frequencies of spheroidal free oscillations OSO to OS41 observed at UCLA due to the 1964 March 27 Alaskan quake are listed. For the modes of lower degree the values are generally an order of magnitude more precise than those customarily reported. Several circumstances contribute to this precision–(a) the presence of two improved instruments, (b) the use of interpolation formulae for determining the peak frequencies, (c) computation of the spectra by two methods, and (d) in some instances, the use of energy considerations concerning the identification and relative excitation of the fine structure multiplets. Some of the overtones are also listed. In the case of OSO and OS20 the precision seems to be especially high, with the several determinations differing respectively by 3 in 100000, and 1.5 in 10000. The mode OSO and its first overtone 1S 0 are well observed. Q values for some of the observed spheroidal modes are also presented.

Some Recent Work on Earth Models, with Special Reference to Core Structure

Summary The earlier part of the paper gives background, relating to a sequence of Earth models A, HB1, B2, HB2 and HBs, from which we have inferred that various past interpretations of certain seismic PKP precursor readings in terms of regular ray theory are unsatisfactory. As a consequence, one of us (R.A.H.) has proposed a new interpretation of the precursors in terms of scattering near the mantle4ore boundary. The later part of the paper gives details of the new interpretation and discusses some of the preliminary findings. On this interpretation, a simple two-layer core can satisfy the entire body of data, including free Earth oscillation data, on the structure of the core, and the difficulties of arriving at a satisfactory overall Earth model appear to have been much reduced. 1. Introductioll The Earth models to be considered will be spherically symmetrical (apart from the scattering effects to be discussed) and concerned with distributions of the density p, incompressibility k, rigidity p, and related variables such as the P and S velocities a and 8, the pressure p, and gravitational intensity g. The symbols T and A will denote travel times along seismic paths (not necessarily rays) and the angles subtended by the paths at the Earth's centre. The problem of securing a completely satisfactory model has been lately complicated by difficulties in interpreting seismic data for the core. The present paper outlines a section of the writers' work on Earth models, tracing the sequence of events leading one of us (R.A.H.) to his latest interpretation of core bodily-wave data. 2. The model HBl