Natalia Zhukova

Discrimination between stochastic dynamics patterns of ambient noises (Case study for Oni seismic station)

Investigation of complex dynamics of ambient seismic noise remains as an important scientific research challenge. In this work we investigated dynamical features of the ambient noises at Oni seismic station, Georgia. We used stochastic model reconstruction method from measured data sets. Seismic records for different time periods around Oni seismic station have been analysed.It was shown that the dynamics of fluctuations of seismic noise vertical component undergoes essential changes for considered time period from 2005 to 2012. These changes are more noticeable for time periods of preparation and aftershock activity of strong M6.0 earthquake occurred in 2009 in the vicinity of Oni seismic station.

Scaling features of ambient noise at different levels of local seismic activity: A case study for the Oni seismic station

Investigation of dynamical features of ambient seismic noise is one of the important scientific and practical research challenges. We investigated scaling features of the ambient noises at the Oni seismic station, Georgia, using detrended fluctuation analysis method. Data from this seismic station, located in the epicentral zone of Oni M6.0, 2009, earthquake, were selected to include time periods with different levels of local seismic activity.It was shown that the investigated ambient noise is persistent long-range correlated at calm seismic conditions in the absence of earthquakes. Fluctuation features of the analyzed ambient noises were affected by local earthquakes, while remote seismic activity caused just slight quantitative changes. Processes related to the preparation of a strong local earthquake may cause quantifiable changes in fluctuation features of ambient noises. Fluctuation features of seismic noise for periods of increased local seismic activity cease to be long-range correlated and appear to become a complicated mixture of random and correlated behaviours.

The Analysis of Variability of Short Data Sets Based on Mahalanobis Distance Calculation and Surrogate Time Series Testing

In this work, we present convenient for short time series approach which is based on the multivariate Mahalanobis distance calculation, combined with the surrogate time series testing. In order to test the ability of this approach to differentiate changes which could occur in complex processes, we analyzed data sets of different origins. We used seismological, meteorological, physiological, and economic data sets. Exactly, we analyzed data sets of inter earthquake times (IET), inter earthquake distances (IED), and differences in consecutive magnitudes (DM) compiled from southern Californian earthquake catalogue, data sets of yearly number of warmer and colder days derived from maximal air temperature data bases in Tbilisi, Georgia, arterial systolic, and diastolic blood pressure time series of healthy persons, as well as components of Index of Economic Freedom (IEF) and exchange rate time series of three southern Caucasian countries. It was shown that used approach, even in the case of relatively short time series, may effectively be used to quantify dynamical changes occurred in different natural complex processes.

Influence of High Energy Electromagnetic Pulses on the Dynamics of the Seismic Process Around the Bishkek Test Area (Central Asia)

Investigation of dynamical features of the seismic process as well as the possible influence of different natural and man-made impacts on it remains one of the main interdisciplinary research challenges. The question of external influences (forcings) acquires new importance in the light of known facts on possible essential changes, which occur in the behavior of complex systems due to different relatively weak external impacts. Seismic processes in the complicated tectonic system are not an exclusion from this general rule. In the present research we continued the investigation of dynamical features of seismic activity in Central Asia around the Bishkek (Kyrgyzstan) test area, where strong electromagnetic (EM) soundings were performed in the 1980s. The unexpected result of these experiments was that they revealed the impact of strong electromagnetic discharges on the microseismic activity of investigated area. We used an earthquake catalogue of this area to investigate dynamical features of seismic activity in periods before, during, and after the mentioned man-made EM forcings. Different methods of modern time series analysis have been used, such as wavelet transformation, Hilbert Huang transformation, detrended fluctuation analysis, and recurrence quantification analysis. Namely, inter-event (waiting) time intervals, inter-earthquake distances and magnitude sequences, as well as time series of the number of daily occurring earthquakes have been analyzed. We concluded that man-made high-energy EM irradiation essentially affects dynamics of the seismic process in the investigated area in its temporal and spatial domains; namely, the extent of order in earthquake time and space distribution increase. At the same time, EM influence on the energetic distribution is not clear from the present analysis. It was also shown that the influence of EM impulses on dynamical features of seismicity differs in different areas of the examined territory around the test site. Clear changes have been indicated only in areas which, according to previous researches, have been characterized by anomalous increase of average rates of strain release and thus can be regarded as close to the critical state.