ОПЫТ КОМПЛЕКСИРОВАНИЯ ГЛОБАЛЬНЫХ ГЕОФИЗИЧЕСКИХ НАБЛЮДЕНИЙ

The technique of joint analysis of heterogeneous time series of geophysical monitoring systems for the purpose of detecting time intervals and specific periods of bursts of synchronous behavior is presented. The technique is based on the use of the Fourier‐aggregated signals and spectral measures of coherent behavior of multivariate time series, estimated in moving time windows. The article presents results of the analysis of data of underground electrical surveys at stations located in Kamchatka, Altai and Italy; the data were analysed together with torsion pendulum movements in Tula (Russia) and the time series of seismic noise parameters at the Japanese islands for the interval 2012–2015. The analysis identified a number of significant bursts of coherent behavior for these observations, some of which are presumably due to the strong mantle Okhotsk Sea earthquake of 24 May 2013. The coherent behavior of various geophysical fields before and after strong earthquakes is interpreted as a manifestation of the general pattern of increasing synchronization of fluctuations of complex systems at their approach to the rapid changes in their properties. Излагается методика совместного анализа разнородных временных рядов систем геофизического мониторинга с целью выделения временных интервалов и характерных периодов всплесков их синхронного поведения. Методика основана на использовании Фурье‐агрегированных сигналов и спектральных мер когерентного поведения многомерных временных рядов, оцениваемых в скользящих временных окнах. В качестве примера рассматриваются данные подземных электрических наблюдений на станциях, расположенных на Камчатке, Алтае и Италии, совместно с показаниями крутильных маятников в Туле и временными рядами изменения параметров сейсмического шума на Японских островах для интервала наблюдений 2012–2015 гг. В результате анализа выделен ряд значимых всплесков когерентного поведения полей в рассмотренном ряду наблюдений, часть из которых предположительно связана с сильнейшим мантийным Охотоморским землетрясением 24.05.2013 г. Когерентное поведение различных геофизических полей до и после сильных землетрясений интерпретируется как проявление общей закономерности увеличения синхронизации флуктуаций сложных систем при их приближении к резким изменениям своих свойств.

Cross-Correlation Earthquake Precursors in the Hydrogeochemical and Geoacoustic Signals for the Kamchatka Peninsula

We propose a new type of earthquake precursor based on the analysis of correlation dynamics between geophysical signals of different nature. The precursor is found using a two-parameter cross-correlation function introduced within the framework of flicker-noise spectroscopy, a general statistical physics approach to the analysis of time series. We consider an example of cross-correlation analysis for water salinity time series, an integral characteristic of the chemical composition of groundwater, and geoacoustic emissions recorded at the G-1 borehole on the Kamchatka peninsula in the time frame from 2001 to 2003, which is characterized by a sequence of three groups of significant seismic events. We found that cross-correlation precursors took place 27, 31, and 35 days ahead of the strongest earthquakes for each group of seismic events, respectively. At the same time, precursory anomalies in the signals themselves were observed only in the geoacoustic emissions for one group of earthquakes.Comment: 21 pages, 5 figures, 1 table; to be published in "Acta Geophysica". arXiv admin note: substantial text overlap with arXiv:1101.147

Precursory groundwater level changes in the period of activation of the weak intraplate seismic activity on the ne margin of the bohemian massif (central Europe) in 2005

We analyse continuous measurements of groundwater level in two deep wells VS-3 and V-28 at the experimental hydro-meteorological station situated on the NE margin of the Bohemian Massif, central Europe, characterized by the weak intraplate seismic activity. The aim of our study is to examine the relationships between changes in the groundwater level and earthquake occurrence. Based on the tidal and barometric response of the water level, we estimated selected elastic parameters of the observed aquifers: the shear modulus G, the Skempton ratio B, the drained matrix compressibility β and the undrained compressibility βu. Using these parameters and assuming the homogeneous poroelastic material, we derived the sensitivity of the wells to the crustal volume strain. During the observation period from November 1998 to December 2005 we detected in the VS-3 well two pre-seismic steps, related to August 10, 2005 (M = 2.4) and October 25, 2005 (M = 3.3) earthquakes. Amplitudes of the recorded precursory changes (+6 cm and +15 cm) are several times higher than the values predicted from the theoretical precursory crustal strain and the strain sensitivity of the well. Therefore, we presume that the observed pre-seismic water level steps can be attributed to heterogeneity of poroelastic material. We consequently propose the hypothesis of the origin of precursory events based on the presumption of a sensitive site, at which the well is situated

Analysis of multidimensional geophysical monitoring time series for earthquake prediction

A method is presented for detection of synchronous signals in multidimensional time series data. It is based on estimation of eigenvalues of spectral matrices and canonical coherences in moving time windows and extraction of an aggregated signal (a scalar signal, which accumulates in its own variations only those spectral components which are present simultaneously in each scalar time series). It is known that an increase in the collective behavior of the components of some systems and an enlarged spatial radius of fluctuations of their parameters could be regarded as an important precursor of an oncoming catastrophe, i.e. abrupt change of the system's parameter values. From that point of view, detection of synchronous signals in various geophysical parameters, measured at points of some network, covering a given area of the Earth's crust, is of interest for identifying precursors of strong earthquakes. Some examples are presented of the use of this technique in the processing of real geophysical time series