Abstract
Abstract. Ultra low frequency-ULF (1 Hz or lower), kHz and MHz electromagnetic (EM) anomalies were recorded prior to the L'Aquila catastrophic earthquake (EQ) that occurred on 6 April 2009. The detected anomalies followed this temporal scheme. (i) The MHz EM anomalies were detected on 26 March 2009 and 2 April 2009. The kHz EM anomalies were emerged on 4 April 2009. The ULF EM anomaly was appeared from 29 March 2009 up to 3 April 2009. The question effortlessly arises as to whether the observed anomalies before the L'Aquila EQ were seismogenic or not. The main goal of this work is to provide some insight into this issue. More precisely, the main aims of this contribution are threefold: How can we recognize an EM observation as pre-seismic one? We aim, through a multidisciplinary analysis to provide some elements of a definition. How can we link an individual EM anomaly with a distinctive stage of the EQ preparation process? The present analysis is consistent with the hypothesis that the kHz EM anomalies were associated with the fracture of asperities that were distributed along the L'Aquila fault sustaining the system, while the MHz EM anomalies could be triggered by fractures in the highly disordered system that surrounded the backbone of asperities of the activated fault. How can we identify precursory symptoms in an individual EM precursor that indicate that the occurrence of the EQ is unavoidable? We clearly state that the detection of a MHz EM precursor does not mean that the occurrence of EQ is unavoidable; the abrupt emergence of kHz EM emissions indicate the fracture of asperities. The observed ULF EM anomaly supports the hypothesis of a relationship between processes produced by increasing tectonic stresses in the Earth's crust and attendant EM interactions between the crust and ionosphere. We emphasize that we attempt to specify not only whether or not a single EM anomaly is pre-seismic in itself, but mainly whether a combination of emergent ULF, MHz and kHz EM anomalies could be characterized as pre-earthquake.
Highlights
A catastrophic EQ occurred on 6 April 2009 (01 h 32 m 41 s UTC) in central Italy (42.35◦ N–13.38◦ E) with magnitude MW=6.3
A major class of seismo-EM signals is rooted in anomalous propagation of EM signals over epicentral regions associated with the variation of Earth-ionosphere wave-guide due to a pre-seismic LAI-coupling
We argue that the detected MHz and kHz EM anomalies were emitted from within the focal zones
Summary
A catastrophic EQ occurred on 6 April 2009 (01 h 32 m 41 s UTC) in central Italy (42.35◦ N–13.38◦ E) with magnitude MW=6.3. Pre-seismic EM emissions have been internationally observed before large EQs (Hayakawa and Fujinawa, 1994; Hayakawa, 1999; Hayakawa et al, 1999; Smirnova et al, 2001; Hayakawa and Molchanov, 2002; Varotsos, 2005; Pulinets and Boyarchuk, 2005; Ida et al, 2005; Eftaxias et al, 2007a, Molchanov and Hayakawa, 2008) These seismo-EM signals may be conveniently classified into the following two major classes (Uyeda et al, 2009 and references therein):. On the large (geological) scale, intense MHz and kHz EM emissions precede EQs that: (i) occurred in land (or near coast-line), (ii) were strong (magnitude 6 or larger), (iii) were shallow (Eftaxias et al, 2002, 2004, 2006, 2007b; Kapiris et al, 2004a, b; Karamanos et al, 2006) Their lead time is ranged from a few days to a few hours. A seismic shift in thinking towards basic science will result a renaissance of strict definitions and systematic experiments in the field of EQ prediction (Cyranoski, 2004)
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