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| Titel |
Extracting preseismic electromagnetic signatures in terms of symbolic dynamics |
| VerfasserIn |
K. Karamanos, A. Peratzakis, P. Kapiris, S. Nikolopoulos, J. Kopanas, K. Eftaxias |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 12, no. 6 ; Nr. 12, no. 6 (2005-09-20), S.835-848 |
| Datensatznummer |
250010891
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| Publikation (Nr.) |
 copernicus.org/npg-12-835-2005.pdf |
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| Zusammenfassung |
| When a heterogeneous material is strained, its evolution toward breaking is
characterized by the nucleation and the coalescence of micro-cracks before
the final break-up. Electromagnetic (EM) emission in a wide frequency
spectrum ranging from very low frequencies (VLF) to very high frequencies
(VHF) is produced by micro-cracks, which can be considered as the so-called
precursors of general fracture. Herein we consider earthquakes (EQs) as
large-scale fracture phenomena. We study the capability of nonlinear time
series analysis to extract features from pre-seismic electromagnetic (EM)
activity possibly indicating the nucleation of the impending EQ. In
particular, we want to quantify and to visualize temporal changes of the
complexity into consecutive time-windows of the time series. In this
direction the original continuous time EM data is projected to a linguistic
symbolic sequence and then we calculate the block entropies of the optimal
partition. This analysis reveals a significant reduction of complexity of the
underlying fracto-electromagnetic mechanism as the catastrophic events is
approaching. We verify this result in terms of correlation dimension
analysis. We point out that these findings are compatible with results from
an independent linear method which uses a wavelet based approach for the
estimation of fractal spectral characteristics. Field and laboratory
experiments associate the epoch of low complexity in the tail of the
precursory emission with the nucleation phase of the impending earthquake. |
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