Nodia Institute of Geophysics

Tbilisi, Georgia

Nodia Institute of Geophysics

Tbilisi, Georgia
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Agency: European Commission | Branch: FP7 | Program: CP-CSA-Infra | Phase: INFRA-2008-1.1.1 | Award Amount: 4.00M | Year: 2009

The recently finished FP6 RI Black Sea SCENE project has established a Black Sea Scientific Network of leading environmental and socio-economic research institutes, universities and NGOs from the countries around the Black Sea and has developed a distributed virtual data and information infrastructure that is populated and maintained by these organisations to improve the identification, access, exchange, quality indication and use of their data and information about the Black Sea. The Black Sea SCENE research infrastructure stimulates scientific cooperation, exchange of knowledge and expertise, and strengthens the regional capacity and performance of marine environmental data and information management, underpins harmonization with European marine data quality control/assessment procedures and adoption of international meta-data standards and data-management practices, providing improved data & information delivery services for the Black Sea region at a European level. The Up-Grade of Black Sea SCENE project aims: a) to extend the existing research infrastructure with 19 marine environmental institutes/organizations from the 6 Black Sea countries, b) to implement the results of the Joint Research Activities of the FP6 RI SeaDataNet project (common communication standards and adapted technologies to ensure the datacenters interoperability), c) to network the existing and new Black Sea datacenters, active in data collection, and provide integrated databases of standardized quality on-line, d) to realize and improve on-line access to in-situ and remote sensing data, meta-data and products and e) to adopt standardized methodologies for data quality checking to ensure the quality, compatibility and coherence of the data issuing from so many sources. The Up-Grade Black Sea SCENE project is undertaken by 51 partners of which 43 are located in the Black Sea countries.

Jandieri G.V.,Georgian Technical University | Zhukova N.N.,Nodia Institute of Geophysics
2017 IEEE International Conference on Computational Electromagnetics, ICCEM 2017 | Year: 2017

Paper considers some aspects of the relationship between scintillation level of scattered radiation and anisotropic plasma irregularities in the collision turbulent magnetized plasma. Analytical calculations have been carried out using modify smooth perturbation method taking into account both diffraction effects and polarization coefficients of both ordinary and extraordinary waves. Scintillation level has been analyzed for different parameters characterizing anisotropic irregularities. © 2017 IEEE.

Eftaxias K.,National and Kapodistrian University of Athens | Potirakis S.M.,Technological Educational Institute of Piraeus | Chelidze T.,Nodia Institute of Geophysics
Natural Hazards and Earth System Sciences | Year: 2013

It has been suggested that fracture-induced MHz-kHz electromagnetic emissions (EME), which emerge from a few days up to a few hours before the main seismic shock occurrence permit a real-time monitoring of the damage process during the last stages of earthquake preparation, as it happens at the laboratory scale. Despite fairly abundant evidence, electromagnetic (EM) precursors have not been adequately accepted as credible physical phenomena. These negative views are enhanced by the fact that certain "puzzling features" are repetitively observed in candidate fracture-induced pre-seismic EME. More precisely, EM silence in all frequency bands appears before the main seismic shock occurrence, as well as during the aftershock period. Actually, the view that "acceptance of "precursive" EM signals without convincing co-seismic signals should not be expected" seems to be reasonable. In this work we focus on this point. We examine whether the aforementioned features of EM silence are really puzzling ones or, instead, reflect well-documented characteristic features of the fracture process, in terms of universal structural patterns of the fracture process, recent laboratory experiments, numerical and theoretical studies of fracture dynamics, critical phenomena, percolation theory, and micromechanics of granular materials. Our analysis shows that these features should not be considered puzzling. © 2013 Author(s).

Telesca L.,CNR Institute of Methodologies for Environmental analysis | Matcharasvili T.,Nodia Institute of Geophysics | Chelidze T.,Nodia Institute of Geophysics | Zhukova N.,Nodia Institute of Geophysics
Natural Hazards and Earth System Science | Year: 2012

The declustered seismic catalog from 1965 to 2010 around the Enguri high dam reservoir in western Georgia was analyzed using the singular spectrum analysis (SSA) technique in order to investigate the relationship of local seis-micity with the reservoir water variations. In particular, the seismic activity was analyzed in two periods: a "reference" period, from 1965 to 1970, before the start of dam building in 1971; and an "active" period, from 1978 to 2010, in which the influence of the reservoir was significantly effective on the seismic activity (since the first flooding of the dam occurred in 1978). The SSA was applied to both the monthly number of earthquakes and the time series of the monthly mean of the water level. The first four reconstructed components explained most of the total variance in both seismic-ity and water level. Clear signatures of the annual oscillation linked with the loading/unloading operations of the dam are present in the periodogram of the second and the third reconstructed components of the seismic activity during the "active" period. Such annual cycle is absent in the periodogram of the reconstructed components of the seismic activity during the "reference" period. This is a clear indication of the reservoir-induced character of the seismicity around the En-guri dam. © Author(s) 2012. CC Attribution 3.0 License.

Telesca L.,CNR Institute of Methodologies for Environmental analysis | Matcharashvili T.,Nodia Institute of Geophysics | Chelidze T.,Nodia Institute of Geophysics
Natural Hazards and Earth System Science | Year: 2012

The time-clustering behaviour of the seismicity of the Caucasus spanning from 1960 to 2010 was investigated. The analysis was performed on the whole and aftershock-depleted catalogues by means of the method of Allan Factor, which permits the identification and quantification of time-clustering in point processes. The whole sequence is featured by two scaling regimes with the scaling exponent at intermediate timescales lower than that at high timescales, and a crossover that could be probably linked with aftershock time activiation. The aftershock-depleted sequence is characterized by higher time-clustering degree and the presence of a periodicity probably correlated with the cyclic earth surface load variations on regional and local scales, e.g. with snow melting in Caucasian mountains and large Enguri dam operations. The obtained results were corroborated by the application of two surrogate methods: the random shuffling and the generation of Poissonian sequences. © 2012 Author(s).

Mamatsashvili G.R.,Tbilisi State University | Chagelishvili G.D.,Ilia State University | Chagelishvili G.D.,Nodia Institute of Geophysics | Bodo G.,National institute for astrophysics | Rossi P.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2013

We investigate the linear dynamics of non-axisymmetric perturbations in incompressible, vertically stratified Keplerian discs threaded by a weak non-zero net vertical magnetic field in the local shearing box approximation. Perturbations are decomposed into shearing waves or spatial harmonics whose temporal evolution is then followed via numerical integration of the linearized ideal magnetohydrodynamic equations of the shearing box. There are two basic modes in the system - inertia-gravity waves and magnetic mode, which displays the magnetorotational instability (MRI). Distinct from previous related studies, we introduce 'eigenvariables' characterizing each (counter-propagating) component of the inertia-gravity and magnetic modes, which are governed by a set of four first-order coupled ordinary differential equations. This allows us to identify a new process of linear coupling of the two above nonaxisymmetric modes due to the disc's differential rotation. We also carry out a comparative analysis of the dynamics of non-axisymmetric and axisymmetric magnetic mode perturbations. It is demonstrated that the growth of 'optimal' and close-to-optimal non-axisymmetric harmonics of this mode, having transient nature, can prevail over the exponential growth of axisymmetric ones (i.e. over the axisymmetric MRI) during dynamical time. A possible implication of this result for axisymmetric channel solutions emerging in numerical simulations is discussed. In particular, the formation of the (axisymmetric) channel may be affected/impeded by non-axisymmetric modes already at the early linear stage leading to its untimely disruption - the outcome strongly depends on the amplitude and spectrum of initial perturbation. Thus, this competition may result in an uncertainty in the magnetic mode's non-linear dynamics. Even so, we consider that incompressible perturbations, in the final part, speculate on the dynamics in the compressible case. It is shown that a maximum growth of non-axisymmetric magnetic mode occurs at vertical wavelengths close to the disc scaleheight, for which compressibility effects are important. This indirectly suggests that compressibility plays a role in the dynamics of the non-axisymmetric MRI and, ultimately, in the resulting turbulent state. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Chelidze T.,Nodia Institute of Geophysics | Varamashvili N.,Nodia Institute of Geophysics
GeoPlanet: Earth and Planetary Sciences | Year: 2010

The modern concept of seismic processes relays mainly on the model of frictional instability, which develops on the preexisting tectonic fault, in contrast to the earlier assumptions on the brittle fracture of the crust material attaining the critical stress. The Ditrich-Ruina equation for shear stress describes almost all main features of slip, obtained in numerous experiments: it shows that the frictional force is not a constant, but is time-dependent and undergoes complex evolution during the slip event. The equation is nonlinear, and consequently the slip process should manifest such properties as high sensitivity to weak external forcing, hysteresis effect, etc. It is quite natural that the instabilities of friction excite vibrations, including acoustic emission (AE). The AE is expected to occur during slips and be absent during stick phase. We presume that acoustic measurements may reveal the fine details of friction mechanism, which are beyond the reach of direct displacement-measuring techniques. The additional forcing, which can be much smaller than the main driving force, may provoke triggering and synchronization during stick-slip process, which means that these phenomena are invoked by nonlinear interaction of objects. An attempt to compile and analyze the rate- and state slip equation taking into account the periodic forcing is made. © Springer-Verlag Berlin Heidelberg 2010.

Matcharashvili T.,Nodia Institute of Geophysics | Chelidze T.,Nodia Institute of Geophysics | Zhukova N.,Nodia Institute of Geophysics
Physica A: Statistical Mechanics and its Applications | Year: 2015

In the present study, we investigated the interevent time interval distribution of earthquakes in Southern California. We analyzed and compared datasets of waiting times between consecutive earthquakes and time structure-distorted datasets. The aim of this study was to determine the proportion of waiting time values in the original catalogue that can be regarded as statistically distinguishable or indistinguishable from the baseline time intervals datasets where the original structure of the temporal distribution of earthquakes was disrupted. We compiled two types of time structure-distorted baseline sequences, which comprised mean values of: (a) shuffled original interevent data and (b) interevent times data from time-randomized catalogues. To compare the dynamical characteristics of the original and time structure-distorted baseline sequences, we used several data analysis methods such as power spectrum regression, detrended fluctuation, and multifractal detrended fluctuation analysis. We also tested the nonlinear structure of the original and baseline sequences using the magnitude and sign scaling analysis method. We calculated theZscore in order to assess whether the interevent time values in the original dataset shared statistical similarity or dissimilarity with the time structure-distorted baseline interevent data sequence. We compared the interevent time values in the original dataset with the mean baseline interevent times computed for two types of time structure-distorted sequences. The results showed that about 30% of the original interevent times were statistically indistinguishable from the mean of the shuffled dataset and 10% from the mean of the time structure-distorted baseline interevent dataset. We performed similar analyses for other catalogues obtained from different parts of the world. According to the results of this analysis, the proportion of events in the original catalogues that were indistinguishable from sequences with disturbed time structure did not contradict the results obtained for the Southern California catalogue. © 2015 Elsevier B.V.

Kordzadze A.A.,Nodia Institute of Geophysics | Demetrashvili D.I.,Nodia Institute of Geophysics
Ocean Science | Year: 2011

One of the parts of the Black Sea Nowcasting/Forecasting System is the regional forecasting system for the easternmost part of the Black Sea (including the Georgian water area), which has been developed within the context of the EU International projects ARENA and ECOOP. A core of the regional system is a high-resolution baroclinic regional model of the Black Sea dynamics developed at M. Nodia Institute of Geophysics (RM-IG). This model is nested in the basin-scale model of Marine Hydrophysical Institute (MHI, Sevastopol/Ukraine). The regional area is limited to the Caucasian and Turkish coastal lines and the western liquid boundary coinciding with the meridian 39.36 E. Since June 2010 we have regularly been computing 3 days' forecasts of current, temperature and salinity for the easternmost part of the Black Sea with 1 km spacing. In this study the results of two forecasts are presented. The first forecast corresponds to summer season and covers the prognostic interval from 00:00 h, 6 August to 00:00 h, 9 August 2010. The second one corresponds to autumn season and covers the prognostic interval from 00:00 h, 26 October to 00:00 h, 29 October 2010. Data needed for the forecasts-the initial and prognostic hydrophysical fields on the open boundary, also 2-D prognostic meteorological fields at the sea surface-wind stress, heat fluxes, evaporation and precipitation rates for our regional area are being placed on the MHI server every day and we are available to use these data operatively. Prognostic hydrophysical fields are results of forecast by the basin-scale model of MHI and 2-D meteorological boundary fields represent the results of forecast by regional atmospheric model ALADIN. All these fields are given on the grid of basin-scale model with 5 km spacing and with one-hour time step frequency for the integration period. The analysis of predicted fields shows that to use the model with high resolution is very important factor for identification of nearshore eddies of small sizes. It should be noted the very different character of regional circulation in summer and autumn seasons in the easternmost part of the Black Sea. © 2013 Author(s).

Kordzadze A.A.,Nodia Institute of Geophysics | Demetrashvili D.I.,Nodia Institute of Geophysics
Journal of Environmental Protection and Ecology | Year: 2011

In the last decades problems of anthropogenic change of a global and regional climate and adaptation of human activity to new climatic conditions have become one of the most paramount problems of modern civilization. The Black Sea region in this respect deserves the significant attention. The Black Sea plays an important role in formation of weather and regional climate. As World ocean and atmosphere, also the Black Sea and the atmosphere continuously interact among themselves and exchange mechanical and thermal energy and substances. Therefore, it is expedient to consider the Black Sea and the atmosphere as an uniform hydro-thermodynamic system to solve successfully the problems of marine and weather forecasts and possible anthropogenic changes of a regional climate. In this paper we present methodology for development of a limited-domain coupled regional modelling system 'the Black Sea-atmosphere' and some results of preliminary numerical experiments for the Black Sea region. The coupled regional model should become the basis for simulation and forecast of possible changes of regional climate for the Black Sea region taking into consideration interaction between the Black Sea and atmosphere. The model consists of separate blocks, each of them represents mathematical model, having independent significance and describing hydro-thermodynamic processes in separate objects of the natural environment (sea, atmosphere, active layer of the soil). The coupled model is based on the full systems of the ocean and atmospheric hydro-thermodynamic equations, one-dimensional equations of planetary boundary layer, on molecular heat and moisture transfer equations in the active layer of the soil and on the heat and moisture balance equations of the underground surface.

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