Models of density and mechanical <Emphasis Type="Italic">Q</Emphasis>-factor distributions according to new data on the nutations and free oscillations of the Earth: 2. Comparison with astrometric data

In the first part of the paper [Molodenskii, 2011], we considered the problem of ambiguity in the solution of the inverse problem of retrieval of density distribution in the Earth’s core and mantle and determination of the Q factors in the mantle from the entire set of modern data on seismic velocities (V _p and V _S ), the frequencies f _i and quality factors Q _i of free oscillations of the Earth, and the amplitudes and phases of its forced nutations. We have constructed the model distributions of these parameters, in which the root-meansquared (rms) deviations of all observed values from the predicted ones are much smaller than in the PREM model. Below, we compare the observed amplitudes of the forced nutation with the values predicted by our model. In order to understand how rigid are the constraints imposed by the amplitudes of forced nutation, we not only calculate the deviations of the observed amplitudes of nutation from the predictions by our model but also estimate the changes in these deviations caused by small variations in several parameters of the model. To the parameters to be varied we refer those which have no or barely any effect on the periods and damping constants of free oscillations but have a pronounced effect on the amplitudes of forced nutation. These parameters include (1) the rheological properties of the mantle in the interval of periods from an hour to a day; (2) the dynamical flattening of the liquid core; (3) the dynamic flattening of the solid inner core; (4) the viscosity of the liquid core; and (5) the moment of inertia of the solid inner core. In addition, we estimate the effects of variations in the moment of inertia of the liquid core to be small (±0.2%) and not to affect, within the observation error, the periods of free oscillations. We show that the uncertainty in the model depth distributions of density considerably decreases when the new data on the amplitudes and phases of the forced nutation of the Earth are taken into account. With these data, it is possible to estimate the creep function for the lower mantle in a wide range of periods from a second to a day.     

土层特性变异性对场地传递函数的影响

选取日本Kik-Net强震数据库中软（FKSH14）、硬（FKSH12）两类场地,建立场地概率模型。应用Monte Carlo技术随机生成50组场地剖面,分别计算场地的传递函数STF及STF标准差,讨论场地土层厚度、剪切波速,以及两者组合工况对场地传递函数的标准差的影响。结果显示：对于硬土场地,场地特征频率标准差相对于软土场地较大,且剪切波速变异性的影响略大于土层厚度变异性的,两者组合工况的影响最大;而对于软土场地,土层厚度、剪切波速变化工况下,场地特征频率的标准差相当,略低于两者组合工况;对于软、硬两类场地,土层厚度与剪切波速两者组合工况下的STF标准差略大于单一量变化工况,但3种工况下的场地STF标准差相差不明显;场地STF标准差在场地自振频率附近的频率段取值较大,极值点与场地STF的极值点相对应;基于实际地震记录的场地传递函数标准差高于模拟的结果,但是两者极值点对应的频率范围吻合。     

DETERMINATION OF ELECTRIC ROCK PARAMETERS FROM THE FIELD STRUCTURE OF A MAGNETIC DIPOLE*

In the theoretical part of the present paper, formulas have been analyzed for a magnetic dipole in a homogeneous and unbounded medium. The magnetic field is elliptically polarized in the region between the quasistatic zone and the far field. Since the position and the shape of the polarization ellipses depend on the complex wave number, k, it is possible to determine k by measuring the polarization ellipses. From k, the conductivity and the dielectric constant of the medium are easily calculated. The functions required for the measuring method have been computed and plotted in graphs. In the experimental part it was examined how far the theory may be applied to measurements of propagation through rock at frequencies ranging from 100-1000 kHz. These measurements showed that reasonably defined mean values of rock parameters can be given only if the deviations of the field from the theoretically expected field are not too high. These deviations have been named field distortions and have been examined by means of statistical methods (variance ratio tests). Gallery cavity and inhomogeneity or anisotropy of the medium account for these distortions.     

Numerical evaluation of the damping‐solvent extraction method in the frequency domain

The damping‐solvent extraction method for the analysis of unbounded visco‐elastic media is evaluated numerically in the frequency domain in order to investigate the influence of the computational parameters—domain size, amount of artificial damping, and mesh density—on the accuracy of results. An analytical estimate of this influence is presented, and specific questions regarding the influence of the parameters on the results are answered using the analytical estimate and numerical results for two classical problems: the rigid strip and rigid disc footings on a visco‐elastic half‐space with constant hysteretic material damping. As the domain size is increased, the results become more accurate only at lower frequencies, but are essentially unaffected at higher frequencies. Choosing the domain size to ensure that the static stiffness is computed accurately leads to an unnecessarily large domain for analysis at higher frequencies. The results improve by increasing artificial damping but at a slower rate as the total (material plus artificial) damping ratio ζ_t gets closer to 0.866. However, the results do not deteriorate significantly for the larger amounts of artificial damping, suggesting that ζ_t≈0.6 is appropriate; a larger value is not likely to influence the accuracy of results. Presented results do not support the earlier suggestion that similar accuracy can be achieved by a large bounded domain with small damping or by a small domain with larger damping. Copyright © 2002 John Wiley & Sons, Ltd.     

Parametric decay of beam-driven Langmuir wave and enhanced ion-acoustic fluctuations in the ionosphere: a weak turbulence approach

We present a model that describes the decay of beam generated Langmuir waves into ion-acoustic waves in the topside ionosphere. This calculation is done within the frame of the weak turbulence approximation. We study the spectral signature of such a process as seen by a VHF incoherent scatter radar. An incoherent scatter (IS) spectrum is characterized by two maxima at k_radar and −k_radar, the right and left ion lines respectively. It is shown that, for reasonable beam parameters, the parametric decay of beam-generated Langmuir waves can enhance either the right, the left or both ion lines simultaneously. The shape of the spectrum can change drastically on time scale of about 0.1 to 1 s. The role of the beam parameter as well as the ionospheric parameters is also investigated. For a given beam number density, the beam energy or the background density are important to trigger either the left or the right ion line. A large energy spread of the beam or low electron collision frequencies can explain the simultaneous observations of the left and the right ion line. The importance of the electron collision frequency can explain the altitude distribution of the coherent echoes observed by incoherent scatter radars.     

Inversion of swell frequency from a 1-year HF radar dataset collected in Brittany (France)

This article presents long period ocean wave (swell) frequencies inverted from a 13-month dataset of high-frequency (HF) phased array radars and an assessment of these estimates by comparison with WAVEWATCH III model data. The method of swell frequency inversion from high-frequency radar sea echo Doppler spectra is described. Radar data were collected from a two-site HF Wellen Radar (WERA) radar system on the west coast of Brittany (France) operating at 12 MHz. A standard beam-forming processing technique has been used to obtain Doppler spectra of processed radar cells. Swell frequencies are obtained from the frequencies of particular spectral peaks of the second-order continuum in hourly averaged Doppler spectra. The data coverage of effective Doppler spectra considered for swell frequency estimates shows the influence of islands and shallow water effects. Swell estimates from both radar stations are in good agreement. The comparison of radar-derived results to WAVEWATCH III (WW3) estimates shows that radar measurements agree quite well with model results. The bias and standard deviation between two estimates are very small for swells with frequency less than 0.09 Hz (period >11 s), whereas radar estimates are generally lower than model estimates for shorter swells, along with higher standard deviation. Statistical analysis suggests that radar measurement uncertainty explains most of the difference between radar and model estimates. For each swell event, time series of frequency exhibits a quasi-linear frequency increase which is associated with the dispersive property of wave phase velocity. The use of swell frequency estimates from both radars on common radar cells only slightly increases the accuracy of swell frequency measurement.     

τ-p SEISMIC DATA FOR VISCOELASTIC MEDIA - PART 2: LINEARIZED INVERSION1

An approach to extraction of viscoelastic parameters from seismic data is implemented and succesfully tested. Viscoelastic inversion is performed using adaptive damping factors to control the sensitivity of the viscoelastic parameters in relation to the τ-p seismic data. A priori information is incorporated through the damping factors as standard deviations of the data and of the viscoelastic model parameters. The stability of the inversion process is controlled by the variation of the damping factors as a function of the residual errors and parameter updates at each iteration. Tests on synthetic and real data show that P- and S-wave quality factors, Q_p and Q_s, in addition to P- and S-wave velocities and density C_p, C_s and p, can be extracted from τ-p seismic information. Singular value decomposition analysis demonstrates that estimated Q_p and Q_s values are more affected by the presence of data inaccuracies and noise than are those of C_p and p. C_s and Q_s are not uniquely recovered due to the limited contribution of P-S converted waves. Knowledge of the viscoelastic parameters is of particular importance in accurately describing petrophysical properties of rocks and pore fluids existing in the subsurface; this is demonstrated with real data from the Gulf of Mexico.     

Internal waves in a rotating stratified fluid in an arbitrary gravitational field

Abstract

Small amplitude oscillations of a uniformly rotating, density stratified, Boussinesq, non-dissipative fluid are examined. A mathematical model is constructed to describe timedependent motions which are small deviations from an initial state that is motionless with respect to the rotating frame of reference. The basic stable density distribution is allowed to be an arbitrary prescribed function of the gravitational potential. The problem is considered for a wide class of gravitational fields. General properties of the eigenvalues and eigenfunctions of square integrable oscillations are demonstrated, and a bound is obtained for the magnitude of the frequencies. The modal solutions are classified as to type. The eigenfunctions for the pressure field are shown to satisfy a second-order partial differential equation of mixed type, and the equation is obtained for the critical surfaces which delineate the elliptic and hyperbolic regions. The nature of the problem is examined in detail for certain specific gravitational fields, e.g., a radially symmetric field. Where appropriate, results are compared with those of other investigations of waves in a rotating fluid of spherical configuration and the novel aspects of the present treatment are emphasized. Explicit modal solutions are obtained in the specific example of a fluid contained in a rigid cylinder, stratified in the presence of vertical gravity, with the buoyancy frequency N being an arbitrary prescribed function of depth.     

Theoretical analysis of resonance conditions in magnetized plasmas when the plasma/gyro frequency ratio is close to an integer

We study cylindrical oscillations of electrons in a plasma where the background magnetic field is parallel to the axis of a cylinder and the ion background is taken to have a constant positive density. Assuming self-similarity, we reduce the problem to two second order nonlinear differential equations, relating fluctuations of electron density and fluctuations of magnetic field. The system studied is shown to have two fundamental frequencies. In the linear domain, these frequencies correspond to the Z and X cold plasma wave cutoff frequencies (R = 0 and L = 0 conditions in the notation of Stix (1992), respectively). Thus they differ by the gyrofrequency. In the nonlinear domain, these frequencies change and resonances at harmonics and at the sum and difference frequencies appear. When the plasma/gyro frequency ratio is close to an integer, our results indicate special resonance conditions which are characterized by an increase of the amplitude and a narrowing of the fundamental resonances.     

High-frequency filtering of strong-motion records

The influence of noise in strong-motion records is most problematic at low and high frequencies where the signal to noise ratio is commonly low compared to that in the mid-spectrum. The impact of low-frequency noise (<1 Hz) on strong-motion intensity parameters such as ground velocities, displacements and response spectral ordinates can be dramatic and consequentially it has become standard practice to low-cut (high-pass) filter strong-motion data with corner frequencies often chosen based on the shape of Fourier amplitude spectra and the signal-to-noise ratio. It has been shown that response spectral ordinates should not be used beyond some fraction of the corner period (reciprocal of the corner frequency) of the low-cut filter. This article examines the effect of high-frequency noise (>5 Hz) on computed pseudo-absolute response spectral accelerations (PSAs). In contrast to the case of low-frequency noise our analysis shows that filtering to remove high-frequency noise is only necessary in certain situations and that PSAs can often be used up to 100 Hz even if much lower high-cut corner frequencies are required to remove the noise. This apparent contradiction can be explained by the fact that PSAs are often controlled by ground accelerations associated with much lower frequencies than the natural frequency of the oscillator because path and site attenuation (often modelled by Q and κ, respectively) have removed the highest frequencies. We demonstrate that if high-cut filters are to be used, then their corner frequencies should be selected on an individual basis, as has been done in a few recent studies.     

Permanent deformation estimates of dynamic equipment foundations: Application to a gas turbine in granular soils

Permanent displacements of a gas turbine founded on a fine, poorly graded, and medium density sand are studied. The amplitudes and modes of vibration are computed using Barkan´s formulation, and the “High-Cycle Accumulation” (HCA) model is employed to account for accumulated deformations due to the high number of cycles. The methodology is simple: it can be easily incorporated into standard mathematical software, and HCA model parameters can be estimated based on granulometry and index properties. Special attention is devoted to ‘transient’ situations at equipment´s start-up, during which a range of frequencies – including frequencies that could be similar to the natural frequencies of the ground – is traversed. Results show that such transient situations could be more restrictive than stationary situations corresponding to normal operation. Therefore, checking the stationary situation only might not be enough, and studying the influence of transient situations on computed permanent displacements is needed to produce a proper foundation design.     

GSM-19T质子旋进磁力仪比测实验分析

为了检测GSM-19T质子旋进磁力仪主要技术指标及参数的性能,2019年10月17—21日河北省地震局红山基准台以GSM-19W Overhauser磁力仪为标准仪器,对40台GSM-19T质子旋进磁力仪地磁总强度F,通过同步连续采样观测和仪器差进行了比测,计算其差值和均方差。结果表明,大部分测量仪器与标准仪器具有较好的一致性和稳定性,地磁总强度F均方差和仪器差均较小,各项技术指标参数符合大纲测试要求,测量仪器比测合格,可为基站观测和野外流动观测提供准确可靠的数据和仪器保障;小部分测量仪器有漂移,地磁总强度F均方差稍大。     

Nonlinear Three-dimensional Inversion of Low-frequency Scattered Elastic Waves

—We investigate a new nonlinear inversion method for low frequencies to determine the bulk and shear modulus as well as the material density and the location of subsurface inhomogeneities. The solution is a direct exact nonlinear inversion of single scattered waves containing near- and far-field terms for incident P and scattered P and S waves, allowing for inversion of parameters in the vicinity and at distance from the sources and receivers. Because the approach is based on single scattering theory, the range of application includes single strong scattering anomalies of various sizes like magma chambers, gas- or fluid-filled cavities, or buried near-surface obstacles. The replacement of the material properties by a new set of parameters, referred to as scattering factors, allows the inverse problem to be solved analytically. The nonlinear nature of the scattering problem is investigated and implications for the inversion process are discussed. The deviations in the elastic parameters as a function of the scattering factors show a strong asymmetry about zero, and therefore linearized approximations will perform differently, depending on the sign of the perturbation. Based on the low frequency (Rayleigh) approximation, we introduce and evaluate a pair of approximations (Mie) derived by numerical and analytical integration of the Rayleigh approximation. Both approximations are based on the underlying principle of subdividing the inhomogeneities into a number of small noninteracting parts and subsequent integration over the total volume, thus increasing the Rayleigh limit and producing better resolution of the parameter estimates during the inversion. The two Mie approximations, when evaluated as a function of scattering angle and distance, produce similar results in the mid- and far-field of the inhomogeneity and reveal better resolution than the Rayleigh approximation. For three anomalies of ± 50% in bulk modulus, shear modulus, and density, the relative error between the exact solution and the two Mie approximations remains below 10%, 20%, and 30%, respectively, for values of k _p R < 3.0, where R is the radius of the heterogeneity. However, smaller errors for individual cases are found for values up to k _p R≈ 4.5. The performance of the inversion based on the analytically and the numerically integrated Mie approximation is tested for single parameter perturbations, revealing reliable and stable inversion results for the bulk and the shear modulus, reasonable results for the density, and crosstalk between the shear modulus and the density. The results show well-defined locations of the anomalies and slight deviations in the estimates of their magnitudes, which can be explained by amplitude and phase deviations between the analytical solution used for forward modeling and the approximations used for the inversion. The analytical Mie approximation provides a fast means to estimate elastic parameters compared to the more time consuming numerically integrated approximation, while the latter can be applied to more arbitrarily shaped inhomogeneities.     

Tidal variations in the high-latitude E- and F-region observed by EISCAT

During the MLTCS (Mesosphere-Lower Thermosphere Coupling Study) campaign the EISCAT UHF radar was continuously operated over 7 days (30 July-5 August 1992) in the CP-1 mode. The long time series obtained of the fundamental ionospheric parameters field-aligned ion velocity (V_i), ion and electron temperature (T and T_e), and electron density (N_e) are useful in investigating tidal variations in the E- and F-region since the geomagnetic activity was particularly low during the time of measurement. Maximum entropy spectra of the parameters were calculated for the relatively quiet interval from 1 August to 4 August 1992 and indicated dominant variations with harmonics of 24 hours. In the electron density spectrum especially, harmonics up to the sixth order (4-h period) are clearly visible. The phase and amplitude height profiles (100-450 km) of the diurnal, semidiurnal, and terdiurnal variations were determined by Fourier transform for a 24-h data set beginning at 12:00 UT on 3 August 1992 when the contaminating influences of electric fields were negligible. The tidal variations of the ion temperatures are compared with the corresponding variations of the neutral temperature predicted by the MSISE-90 model. A remarkable result is the dominance of terdiurnal temperature oscillations at E-region heights on 3–4 August 1992, while the measured diurnal and semidiurnal variations were negligible. The finding was confirmed by the analysis of further EISCAT data (2-3 August 1989, 2–3 July 1990, 31 March- 1 April 1992) which also showed a dominant terdiurnal temperature tide in the E-region. This is different from numerous observations of tides in the E-region at mid-latitudes where the diurnal and especially the semidiurnal temperature oscillations were dominant.     

Characterisation of Fulvic Acids and Glycyrrhizic Acid by Time‐of‐Flight Secondary Ion Mass Spectrometry

Fulvic acids of different origin, spray deposited on polished silicon after dissolution in high‐purity water without any additives, were analysed by time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) in combination with oblique 24...36 keV SF₅⁺ ion bombardment. The observed, highly reproducible mass spectra cover more than five orders of magnitude in dynamic range, without background subtraction. Apart from lines due to atomic ions and low‐mass ion fragments, the mass spectra exhibit broad maxima between m/z 200...350, mainly due to a beat‐like superposition of lines at every single mass number, up to at least m/z 400. In the negative ion spectra the beats have a spacing of m/z 14, corresponding to a CH₂‐unit. The high‐mass tails of the spectra extend well beyond m/z 5000, with similar slopes in the positive and the negative ion mass spectra. The negative spectra appear to be less affected by fragmentation products than the positive spectra. Fulvic acids (FAs) of different origin show distinctly different spectra, with mean masses ranging between m/z ≈ 450 and 580 (for a low‐mass cut‐off m/z 150). To further verify the ability of TOF‐SIMS to detect molecules and clusters with masses significantly above the maxima of the FA spectra, samples of glycyrrhizic acid (GA, as GA ammonium salt with molecular weight 840) were also analysed. Parent ions as well as multimers (GA)_n were observed as positive and negative ions, up to n = 4 (m/z 3320). The results are compared with spectra recently obtained by other mass spectrometric techniques.     

Polar mesosphere summer echoes (PMSE) studied at Bragg wavelengths of 2.8 m, 67 cm,and 16 cm

We present observations of radar volume reflectivities under conditions of polar mesosphere summer echoes (PMSE) at three frequencies, i.e., 53.5, 224, and 930 MHz corresponding to Bragg wavelengths of 2.8, 0.67, and 0.16 m. These measurements were made with the ALWIN radar in Andenes and the EISCAT VHF and UHF radars in Tromsø. Contributions to the signal at 930 MHz by incoherent scatter are used to estimate electron number densities and their gradient at PMSE altitudes, and spectral width measurements of Doppler spectra recorded at 224 MHz are used to estimate the turbulent energy dissipation rate. We further derive a theoretical expression for the radar volume reflectivity for the case of turbulent scatter aided by a large Schmidt number (i.e., the current standard theory of PMSE) and show that our observations quantitatively agree with this theory if Schmidt numbers between 2500 and 5000 are assumed. We then show that these Schmidt numbers correspond to ice particles with radii in the range 20–30 nm which should frequently occur in the polar summer mesopause region. In addition, we show that for the short period when PMSE was observed at UHF frequencies the volume reflectivity is proportional to a factor determined by the turbulent energy dissipation rate, electron number density, and the electron number density gradient in agreement with theory. We consider our findings as strong support that PMSE at all considered frequencies is indeed created by turbulent scatter in the presence of a large Schmidt number. We finally highlight that ultimate proof of this concept will require the direct measurement of ice particle sizes in a PMSE environment probed by radars covering frequencies between 50 MHz and 1 GHz.     

Low-frequency scaling applied to stochastic finite-fault modeling

Stochastic finite-fault modeling is an important tool for simulating moderate to large earthquakes. It has proven to be useful in applications that require a reliable estimation of ground motions, mostly in the spectral frequency range of 1 to 10 Hz, which is the range of most interest to engineers. However, since there can be little resemblance between the low-frequency spectra of large and small earthquakes, this portion can be difficult to simulate using stochastic finite-fault techniques. This paper introduces two different methods to scale low-frequency spectra for stochastic finite-fault modeling. One method multiplies the subfault source spectrum by an empirical function. This function has three parameters to scale the low-frequency spectra: the level of scaling and the start and end frequencies of the taper. This empirical function adjusts the earthquake spectra only between the desired frequencies, conserving seismic moment in the simulated spectra. The other method is an empirical low-frequency coefficient that is added to the subfault corner frequency. This new parameter changes the ratio between high and low frequencies. For each simulation, the entire earthquake spectra is adjusted, which may result in the seismic moment not being conserved for a simulated earthquake. These low-frequency scaling methods were used to reproduce recorded earthquake spectra from several earthquakes recorded in the Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation Models (NGA) database. There were two methods of determining the stochastic parameters of best fit for each earthquake: a general residual analysis and an earthquake-specific residual analysis. Both methods resulted in comparable values for stress drop and the low-frequency scaling parameters; however, the earthquake-specific residual analysis obtained a more accurate distribution of the averaged residuals.     

Correlation of atmospheric occurences over the United States with some physical and chemical parameters. Part I: Frequences of thunderstorms

Summary A multiple regression analysis has been carried out to obtain some approximate insight into conditions which might favour the occurence of thunderstorms, in terms of certain parameters measured on the ground. It is thought that annual thunderstorm frequencies may largely depend on local temperature parameters and deviations of precipitable water vapour from equilibrium values.Contribution of the «Centro Nucleazione Aerosoli» of the National Research Council of Italy, Via Vettore 4 (Monte Sacro),Roma.     

Acoustic reflection logging for open and cased holes

In the present work, the waveforms of reflected wave sonic log for open and cased boreholes are calculated. Calculations are performed for a borehole containing an acoustic multipole source (monopole, dipole, or quadrupole). A reflected wave is more efficiently excited at resonant frequencies. These frequencies for all source types are close to the frequencies of oscillations of a fluid column located in an absolutely rigid hollow cylinder. It is shown that the acoustic reverberation is controlled by the acoustic impedance of the rock Z = V_p ρ_s for fixed parameters of the borehole fluid, where V_p is the compressional wave velocity in the rock, and ρ_s is the rock density. This result is correct for all types of acoustic sources (monopole, dipole, or quadrupole). Methods of the waveform processing for determining parameters characterizing the reflected wave are discussed.     

A new analytical method for quantifying of sterane and hopane biomarkers

An analytical method for quantifying biomarker compounds of the sterane and the hopane existing in saturated hydrocarbons has been established by using comprehensive two-dimensional gas chromatography-flame ionization detector (GC×GC-FID) with optimized operating parameters. The new method achieves the quantification by using a GC×GC-FID system which is able to completely separate steranes from hopanes. The data obtained by the new method are of good repeatability and reliability. Compared with the original data, the relative standard deviations (RSDs) of 12 reference compounds are less than 5%. The RSDs of the quantitative results of the biomarkers based on seven separate analyses are also less than 5%. Compared with the traditional method of gas chromatography-mass spectrometry (GC-MS), the new method has a number of advantages, such as common internal standards (ISs), high resolution, no co-eluting peak, and no interference caused by diagnostic ion peaks. The new method provides petroleum geologists with an effective and scientific means in future researches.