The underlying model for defect parameters in materials of geophysical interest and Seismic Electric Signals

Here, we investigate whether the bulk or the shear is the appropriate modulus for the defect parameters in different materials by focusing on those of geophysical interest. We show that the self-diffusion process and just also the bulk modulus should be related to defect parameters. It is this interrelation which accounts for the emission of electric signals before fracture, and is thus in accordance with the physical basis of the Seismic Electric Signal prior to earthquakes in Greece

Recent aspects on possible interrelation between precursory electric signals and anomalous bioeffects

A possible geophysical mechanism based on the conception of criticality and on new aspects of biological effects caused by electromagnetic fields is discussed as a stimulus to the unusual animal behavior prior to large earthquakes. This mechanism is related to transient electric signals of low frequency and intensity, which are emitted from the pre-focal area several days before the impending earthquake and fulfill all the conditions set by a recent bioeffect model

Diffusion in periclase by combination of analytical formulas and thermodynamic model

Analytical formulas for the temperature dependence of elastic constants of MgO combined with a thermodynamic model, which interconnects bulk properties to point defect parameters, can successfully reproduce the self diffusion coefficients of periclase at temperatures representative of the Earth's mantle conditions. <br><br> Although the calculated diffusion coefficients are estimated from a single measurement and cover a broad range of values (i.e. five orders of magnitude), an almost excellent agreement with the experimental ones is observed. The slight discrepancy at the highest temperature lies at error margins

Stability of a power law relation between characteristics of earthquakes and electric precursors

New data were used to test the credibility of a previously reported power law relation between the stress drop of earthquakes and the lead time of precursory SES. Here, we found that the critical exponent of this power law is very sensitive and remains stable around 0.33 only for appropriate sets of data. This value is in full agreement with the reported one in literature for critical phenomena. That means this power law is not an artifact, but probably implies that real physical dynamic processes evolving to criticality are present in the pre-focal area when the SES is emitted. An attempt to advance the underlying physics of the interconnection of the stress drop and the lead time of the precursory SES is still in progress

Temporal dependence of the selectivity property of SES stations in western Greece

The selectivity property of the SES stations, IOA, PIR and PAT in western Greece, based on reported precursory SES signals and associated large earthquakes (<i>M<sub>w</sub></i>≥5.4) that occurred from 1983 to the end of 2008, has been examined. Interesting temporal dependence of the sensitive ability of these stations has been unveiled. Physical mechanisms for the observed changes in selectivity might be related with tectonic and geodynamic events. For instance, selectivity for IOA exhibits a time dependence, for PAT probably is related to the activation of Wadati-Benioff zone while for PIR seems to be related to the specific tectonics of two confined areas such as the Cephalonia Transform Faulting zone in Ionian Sea and the southwestern part of the Hellenic Trench

Power law relationship between parameters of earthquakes and precursory electrical phenomena revisited II

The credibility of the power law relation, reported by Dologlou (2009) between the stress drop of an earthquake and the lead time of the preceded Seismic Electric Signal, SES, has been checked through additional new data from 9 June 2008 to 7 April 2010. Three earthquakes with <i>M</i><sub>w</sub>≥5.5 have been found in Greece during this period. A critical exponent α (e.g. 0.328) has been obtained which compares very well with the one reported (α=0.332) by Dologlou (2009). The stability of this exponent might imply that critical dynamic processes, of mechanical (earthquakes) and also of electromagnetic (SES) sense dominate the pre focal area when the SES signal of the impending earthquake is emitted

Electrical precursors of earthquakes in Aegean Sea during the last decade (1997?2007)

International audienceThe purpose of this study is to investigate some properties of the Seismic Electric Signals (SES) that preceded large earthquakes which occurred in the Aegean Sea (24?27)° E, (37?40)° N, during the last decade. Our main interest is focused on the important parameter of the lead time ?t, which is the time difference between the occurrence of the earthquake and the detection of the associated SES signal. Two groups of lead times, a short (i.e. ?t~ some weeks) and a long one (?t~ some months) have been observed. We examine whether this difference could be related to the regional tectonics. Furthermore the property of SES selectivity is discussed

Power law relationship between parameters of earthquakes and precursory electrical phenomena

A number of Seismic Electric signals data have been accumulated during the last two decades that also includes the signals observed before the magnitude 6 class earthquakes that occurred in Greece very recently i.e., the first two months of 2008. <br><br> Using all the available data we investigate whether a possible interconnection exists between the lead time of Seismic Electric Signals and the stress drop of subsequent earthquakes. We show that for "non thrust" earthquakes a power law relation emerges with an exponent value around 0.29, the possible physical meaning of which is discussed. This value is very close to the range of critical exponents that govern the fracture processes and is also comparable with the value of the slope, found much earlier by the VAN group, in the linear relation between the logarithm of the SES amplitude and the earthquake magnitude

Evolving towards a critical point: A possible electromagnetic way in which the critical regime is reached as the rupture approaches

International audienceIn analogy to the study of critical phase transitions in statistical physics, it has been argued recently that the fracture of heterogeneous materials could be viewed as a critical phenomenon, either at laboratory or at geophysical scales. If the picture of the development of the fracture is correct one may guess that the precursors may reveal the critical approach of the main-shock. When a heterogeneous material is stretched, its evolution towards breaking is characterized by the appearance of microcracks before the final break-up. Microcracks produce both acoustic and electromagnetic(EM) emission in the frequency range from VLF to VHF. The microcracks and the associated acoustic and EM activities constitute the so-called precursors of general fracture. These precursors are detectable not only at laboratory but also at geophysical scales. VLF and VHF acoustic and EM emissions have been reported resulting from volcanic and seismic activities in various geologically distinct regions of the world. In the present work we attempt to establish the hypothesis that the evolution of the Earth's crust towards the critical point takes place not only in a mechanical but also in an electromagnetic sense. In other words, we focus on the possible electromagnetic criticality, which is reached while the catastrophic rupture in the Earth's crust approaches. Our main tool is the monitoring of micro-fractures that occur before the final breakup, by recording their radio-electromagnetic emissions. We show that the spectral power law analysis of the electromagnetic precursors reveals distinguishing signatures of underlying critical dynamics, such as: (i) the emergence of memory effects; (ii) the decrease with time of the anti-persistence behaviour; (iii) the presence of persistence properties in the tail of the sequence of the precursors; and (iv) the acceleration of the precursory electro-magnetic energy release. Moreover, the statistical analysis of the amplitudes of the electromagnetic fluctuations reveals the breaking of the symmetry as the theory predicts. Finally, we try to answer the question: how universal the observed electromagnetic critical behaviour of the failing system is

Possible relationship between Seismic Electric Signals (SES) lead time and earthquake stress drop

Stress drop values for fourteen large earthquakes with MW ≥ 5.4 which occurred in Greece during the period 1983–2007 are available. All these earthquakes were preceded by Seismic Electric Signals (SES). An attempt has been made to investigate possible correlation between their stress drop values and the corresponding SES lead times. For the stress drop, we considered the Brune stress drop, ΔσB, estimated from far field body wave displacement source spectra and ΔσSB derived from the strong motion acceleration response spectra. The results show a relation may exist between Brune stress drop, ΔσB, and lead time which implies that earthquakes with higher stress drop values are preceded by SES with shorter lead time