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| Titel |
Unfolding the procedure of characterizing recorded ultra low frequency, kHZ and MHz electromagetic anomalies prior to the L'Aquila earthquake as pre-seismic ones – Part 1 |
| VerfasserIn |
K. Eftaxias, L. Athanasopoulou, G. Balasis, M. Kalimeri, S. Nikolopoulos, Y. Contoyiannis, J. Kopanas, G. Antonopoulos, C. Nomicos |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 9, no. 6 ; Nr. 9, no. 6 (2009-11-25), S.1953-1971 |
| Datensatznummer |
250007063
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| Publikation (Nr.) |
 copernicus.org/nhess-9-1953-2009.pdf |
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| Zusammenfassung |
| Ultra low frequency, kHz and MHz electromagnetic (EM) anomalies were recorded
prior to the L'Aquila catastrophic earthquake that occurred on 6 April 2009.
The main aims of this paper are threefold: (i) suggest a procedure for the
designation of detected EM anomalies as seismogenic ones. We do not expect to
be able to provide a succinct and solid definition of a pre-seismic
EM emission. Instead, we aim, through a multidisciplinary analysis, to
provide the elements of a definition. (ii) Link the detected MHz and kHz
EM anomalies with equivalent last stages of the earthquake preparation
process. (iii) Put forward physically meaningful arguments for quantifying
the time to global failure and the identification of distinguishing features
beyond which the evolution towards global failure becomes irreversible. We
emphasize that we try to specify not only whether a single EM anomaly is
pre-seismic in itself, but also whether a combination of kHz, MHz, and ULF
EM anomalies can be characterized as pre-seismic. The entire procedure
unfolds in two consecutive parts. Here in Part 1 we focus on the detected kHz
EM anomaly, which play a crucial role in our approach to these challenges. We
try to discriminate clearly this anomaly from background noise. For this
purpose, we analyze the data successively in terms of various concepts of
entropy and information theory including, Shannon n-block entropy,
conditional entropy, entropy of the source, Kolmogorov-Sinai entropy,
T-entropy, approximate entropy, fractal spectral analysis, R/S analysis and
detrended fluctuation analysis. We argue that this analysis reliably
distinguishes the candidate kHz EM precursor from the noise: the launch of
anomalies from the normal state is combined by a simultaneous appearance of a
significantly higher level of organization, and persistency. This finding
indicates that the process in which the anomalies are rooted is governed by a
positive feedback mechanism. This mechanism induces a non-equilibrium
process, i.e., a catastrophic event. This conclusion is supported by the fact
that the two crucial signatures included in the kHz EM precursor are also
hidden in other quite different, complex catastrophic events as predicted by
the theory of complex systems. However, our view is that such an analysis by
itself cannot establish a kHz EM anomaly as a precursor. It likely offers
necessary but not sufficient criteria in order to recognize an anomaly as
pre-seismic. In Part 2 we aim to provide sufficient criteria: the fracture
process is characterized by fundamental universally valid scaling
relationships which should be reflected in a real fracto-electromagnetic
activity. Moreover, we aim to answer the following two key questions: (i) How
can we link an individual EM precursor with a distinctive stage of the EQ
preparation process; and (ii) How can we identify precursory symptoms in EM
observations that indicate that the occurrence of the EQ is unavoidable. |
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