A. P. Mironov

Deformation Processes in the Lithosphere Related to the Nonuniformity of the Earth's Rotation

The series of observations conducted at the Baksan and Protvino deformation stations in the Northern Caucasus and the Central Russian Plain, respectively, and the length-of-day (LOD) data describing the variable rate of the Earth’s rotation are used to study the relation between the deformation processes in the lithosphere and the global geodynamics of the Earth over short time intervals. The methods applied are based on high-resolution spectral analysis, analysis of the coherence of the studied processes, and correlation analysis. A significant (95%) correlation is revealed between the local deformation fields at two remote observation stations, which proves the existence of a global component in the Earth’s deformation field that manifests itself at characteristic time intervals of up to 3–4 weeks. At the same level of significance, the correlation between the local deformation fields and variations in the rate of the Earth’s rotation has also been identified. It is shown that the found correlations in the tidal low-frequency range are caused by the direct impact of the long-period tidal loading (Mf and Mtm waves) on the lithosphere and the length-of-the-day (LOD). The global mechanisms giving rise to the correlation of these processes in the nontidal range require further study.

Observations of crustal tide strains in the Elbrus area

Results of observations of tidal strains of the crust in the tectonically active Elbrus area of the Northern Caucasus carried out with the use of the Baksan SSAI laser interferometer strainmeter over the period from 2003 through 2006 are presented. Harmonic analysis is performed with the help of the ETERNA software package. Statistically significant time variations in the amplitudes of the main tidal waves M2 and O1 are revealed. The influence of the topography on tidal strains in the Baksan gorge is estimated at 22% (an increase in the measured strain values). The reduced amplitude factors of the main diurnal (O1) and semidiurnal (M2) waves are underestimated. Numerical modeling of tidal anomalies produced by regional heterogeneous inclusions is performed in a 2-D approximation. The observed anomaly of the M2 wave (12%) is shown to be due to the influence of the main magma-controlling fault associated with the deep magma source of the Elbrus dormant volcano.

The free oscillations of the earth excited by three strongest earthquakes of the past decade according to deformation observations

Based on the deformation data provided by the Baksan laser interferometer-strainmeter measurements, the free oscillations of the Earth (FOE) excited by the three strongest earthquakes of the past decade are analyzed. These seismic events include the Great Sumatra-Andaman earthquake that occurred in 2004 in the Indian Ocean, the Mauli earthquake of 2010 in Chile, and the Great Tohoku earthquake of March 2011 in Japan. The frequency-time structure of the free oscillations is studied, and the pattern of interaction between the modes with close frequencies (cross-coupling effect) is explored. For each earthquake, the correspondence of the observed FOE modes to the model predictions by the PREM model is investigated. A reliable consistent shift towards the high frequency of the toroidal modes with angular degree l = 12–19 is revealed. The maximal energy density of the toroidal oscillations is concentrated in the upper mantle of the Earth. Therefore, the established effect corresponds to the higher velocity of the shear waves in the upper mantle than it is predicted by the PREM model.

Velocities of contemporary movements of the Northern Caucasus estimated from GPS observations

The velocity field of the Northern Caucasus based on the results of observations at the Northern Caucasus Geodetic Network (NCGN) stations is represented in the paper. Appreciable horizontal displacement to the northeast with velocity of 26–28 mm/yr relative to the International Terrestrial Reference Frame (ITRF2008) is established. General shortening of the region at a rate of 1–2 mm/yr relative to fixed Eurasia is a source of the contemporary geological and seismic activity in the boundary zone between the Caucasus and the East European Platform.

The Contemporary GPS-Derived Horizontal Motions of the Main Elements of Tectonic Structure in the Ossetian Segment of Greater Caucasus

The Greater Caucasus overall and its Ossetian segment are parts of the neotectonically active Alpine-Himalaya mobile belt. This region, complex from the geodynamical standpoint, is traditionally treated as resulting from interaction between two large lithospheric plates, the Eurasian and Arabian ones. In 2010, a geodetic network for periodical repeated measurements by the mobile GPS instruments was deployed in this region. In addition to the survey-mode sites, three permanent GPS base stations were installed. In this paper, we describe the data processing procedure and results of GPS measurements carried out in 2010–2013. The horizontal GPS velocities are estimated in three reference systems: in global ITRF2008 coordinates (International Terrestrial Reference System), with respect to the fixed Eurasia, and in the local reference frame fixed to the ARDN base station. The analysis revealed a general submeridional drift of the region driven by the convergence of the Eurasian and Arabian plates. This pattern of motion is complicated by the specific tectonic features most probably associated with the ongoing local processes forming the tectonic structure of the region.

Status of the experiments on measurement of the Newtonian gravitational constant

Due to the weakness of gravity, the accuracy of the Newtonian gravitational constant G is essentially below the accuracy of other fundamental constants. The current value of G, recommended by CODATA in 2006, based on all results available at the end of 2006, is G = (6.67428 ± 0.00067) × 10−11 m3 kg−1 s−2 with a relative error of 100 ppm. The accuracy of the best experimental results is 15–40 ppm, although the scatter of the results is large enough. Therefore new experiments at a level of accuracy of 10–30 ppm are rather topical. One of the problems of improving accuracy of G is a precision measurement of the period of eigen oscillations of a torsion balance. The nonlinear behavior of the torsion balance with five degrees of freedom has been studied. It was shown that swing modes are excited by the acting environmental noise. A coupling of the swing modes to the torsional mode has been revealed. Methods of suppressing the effect of mode couplings have been considered.

Oceanic Loading and Local Distortions at the Baksan, Russia, and Gran Sasso, Italy, Strain Stations

Reliable use of strain data in geophysical studies requires their preliminary correction for ocean loading and various local distortions. These effects, in turn, can be estimated from the tidal records which are contributed by solid and oceanic loading. In this work, we estimate the oceanic tidal loading at two European strain stations (Baksan, Russia, and Gran Sasso, Italy) by analyzing the results obtained with the different Earth and ocean models. The influence of local distortions on the strain measurements at the two stations is estimated.

Velocities of Present-Day Horizontal Movements in the Central Sector of the Greater Caucasus according to GPS Observations and Their Relation to Tectonics and the Deep Structure of the Earth’s Crust

The results of the first GPS measurements along the geophysical profile that intersects all major geological structures of the Osetiya region of the Greater Caucasus are presented. The results of the measurements are interpreted in comparison with those of neotectonic studies and data on the deep structure.

Satellite geodetic monitoring of the Vladikavkaz active fault zone: First results

A geodetic network of Global Satellite Navigation System (GNSS) observation sites was organized in 2014–2015 for studying the contemporary crustal motions in the zone of the Vladikavkaz deep fault (Milyukov et al., 2014; 2015). The measurements were conducted and the first velocity estimates obtained testifying to the consistency of crustal motions in the Vladikavkaz fault zone and the Ossetian region overall in the ITRG2008 system. The first results show that the velocities and directions of horizontal motions do not change upon the transition of the fault zone. In correspondence with the northeastern orientation of the site displacement vectors and sublatitudinal trend of the disjunctive zone, the presence of left-lateral strike-slip displacements along the branches of an active fault should be expected. However, the signs pointing to the activation of motion in the fault zone are absent. Besides, even the manifestation of weak seismicity has not been observed within the high-magnitude seismogenic Vladikavkaz zone associated with this fault for more than 25 years. This suggests the passive present state of this structure, one of the largest disjunctive structures of the Northern Caucasus. In order to verify this conclusion and revealing the kinematic pattern of the displacements associated with the fault structure it is reasonable to continue the measurements.

Numerical modeling of the motion of a torsion balance in the problem of measuring the Newtonian gravitational constant

The motion of a torsion balance with five degrees of freedom has been numerically simulated. It has been shown that the oscillations along the swing degrees of freedom are excited by the random noise of the seismic origin and their amplitude varies with time. It has been shown also that the nonlinear couplings between the swing and torsion degrees of freedom result in the appearance of combination oscillations. The methods for effectively suppressing these combination oscillations have been considered.