A. V. Myasnikov

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.

Baksan laser interferometer

A description is given of the construction and technical parameters of a long-base (75m) laser interferometer made at the Shternberg State Astronomical Institute of Moscow State University and introduced into continuous operation in the Northern Caucasus. The purpose of the interferometer is to investigate lithospheric deformations in a wide frequency range (up to 103 Hz). An estimate of the spectral density of deformations has been obtained from the results of observations over a ten-month period.

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.

Observation of Luni-Solar Tides by the Long Base Laser Interferometer

Results of observations of tidal strains of the crust in the tectonically active region of the Northern Caucasus (the Elbrus mountain area) carried out with the use of the Baksan 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 Baksan canyon topography on tidal strains 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 magmacontrolling fault associated with the deep magma source of the Elbrus dormant volcano.

Monitoring the State of the Magmatic Structures of Elbrus Volcano Based on Observation of Lithosphere Strains

An analysis of crustal strain recorded by the Baksan laser interferometer revealed a shallow magma chamber in the structure of Elbrus Volcano (The Northern Caucasus, Russia). The analysis is based on estimation of parameters of magmatic structures resonant modes excited by teleseismic signals. The resonance parameters we have found were interpreted in the framework of contemporary models of magma resonators. The depth and dimension of the magma chamber, as well as the properties of the magma fluid were estimated. It was suggested the changing the magma state due to rising the intrachamber pressure.

Wideband laser interferometer for monitoring the Earth strains

The wide-band laser interferometer with a measurable armlength of 75 m has been installed in an underground tunnel (the North Caucasus), in one of the most active in geodynamic respect region of Russia. The optical scheme of the interferometer is the two passes (N equals 2) Michelson- type interferometer with unequal arms working in regime of space separated beams which is realized by use of the corner reflectors. The mirrors, the beam-splitter and the optical passes are placed in vacuum (5 X 10-5 mbar). The long-term monitoring strains of the Earth is provided in two frequency bands: below 0.1 Hz and in the bandwidth of 0.5 Hz around frequency of 1.62 kHz (the monitoring of quadrature components). The sensitivity in the high frequency band is about 10-15 Hz-1/2. In the regime of long- term monitoring the Earth strains the interferometer is operating from the beginning of 1993. The observation data, thanks to the unique capabilities of the laser interferometer with respect to both the frequency and the dynamic ranges, are used for studying some geophysical and astrophysical problems.