Abstract
The latest aspects of the physical properties of seismic electric signals (SES) that are used for earthquake prediction in Greece are described. The procedure currently followed for the selection of a site appropriate for the collection of SES and for the electric dipole configuration of such a station are reviewed. The process of constructing a map indicating the seismic areas for which such a station is sensitive is also described. A review of other electrical precursors observed in Greece is given, along with a summary of the newest theoretical models of the generation of SES. The compatibility of these models with the existing data on SES is discussed. Furthermore, a number of unsolved problems are listed, along with suggestions for future experimentation.
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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