Abstract
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.
Highlights
One of the fundamental problems of geophysical monitoring is ’complexation’ of different observations and measurements
It is noteworthy interesting that the first burst of coherence corresponds to the right‐hand end of the time window 120–150 days from 12 December 2012 and has the characteristic period of about four days – it falls in the time interval before the mantle Okhotsk Sea earthquake of 24 May 2013
‐ Underground electrical measurements in the three different regions of the globe (Kamchatka, Altai, Italy) show a significant burst of joint coherence for oscilla‐ tions with periods of about 24 hours in the time frag‐ ment 12000–16000 hours from the beginning of 2012, which corresponds to the positions of the moving time window of the length of 28 days from mid‐April to the end of October 2013;
Summary
One of the fundamental problems of geophysical monitoring is ’complexation’ of different observations and measurements. The methods are based on the analysis of canonical coherences, mul‐ tidimensional spectral matrices and canonical correla‐ tion coefficients of the wavelet decomposition of sig‐ nals in moving time windows, with all available samp‐ les (the so‐called method of aggregated signals). The purpose of these algorithms is the detection of a very weak non‐stationary signals of common origin, having both harmonic oscillation behavior or sharply non‐ stationary, wavelet character, within multivariate time series monitoring to identify their specific periods (or time scales). An important result of this study is extracting the time interval of strong coherence before and after the powerful mantle earthquake (M=8.3) that occurred in the Okhotsk Sea on 24 May 2013
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