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1

Additional evidence on some relationship between seismic electric signals and earthquake source parameters

Varotsos P., Sarlis N., Skordas E., Tanaka H., Lazaridou M.

Acta Geophysica Polonica

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2005

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Vol. 53, nr 3

293-298

EN

We provide recent experimental evidence which further supports the inter-relation between the earthquake source parameters and the selectivity properties of Seismic Electric Signals. The cases of two major earthquakes with magnitudes larger than 6.0, that occurred in Greece during 2004-2005, are presented.

2

SES activity recorded at Keratea station on April, 2003

Varotsos P., Sarlis N., Skordas E., Lazaridou M.

Acta Geophysica Polonica

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2004

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Vol. 52, nr 1

45-48

EN

Two notes on the seismic electric signals recorded at the Keratea station, Greece, are presented. Both these signals as well as the subsequent seismic activ-ity have been analysed in the natural time domain. They have been finally fol-lowed by a 4.7 earthquake on June 13, 2003 with an epicenter at 38.6N, 23.7E (i.e., around 65 km north of Athens).

3

Four notes on SES activity at the Ioannina Observatory, Greece

Varotsos P., Sarlis N., Skordas E., Lazaridou M.

Acta Geophysica Polonica

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2003

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Vol. 51, nr 2

147-153

EN

Four notes are presented on the seismic electric signals recorded at the Ioannina Observatory, Greece and their relation to the seismicity of the area. The motes were issued between November 2, 2002 and January 12, 2003.

4

Seismic electric signals and seismicity: on a tentative interrelation between their spectral

Varotsos P., Sarlis N., Skordas E.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 3

337-354

EN

We show that the spectral content of the seismic activity, in the area candidate to suffer an earthquake and which evolves consecutively in time with every new event, falls on the spectral content of the Seismic Electric Signals (SES) activity, just before the occurrence of the main shock. The key point is that both spectra have to be defined and calculated in a new time domain, termed as "natura1" time. Thus, since the spectrum of the SES is known well in advance, the continuous inspection of the spectrum of the evolving seismic activity may lead to an estimation of the time window of the impending main shock with an accuracy of around a few days. Both spectra exhibit a feature compatible with that obtained from the theory of dynamic phase transitions (critical phenomena).

5

Note on an important SES activity at Ioannina station (IOA)

Varotsos P., Sarlis N., Skordas E., Lazaridou M.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 3

355-359

6

Comments on the transmission of electric signals in dielectric media

Sarlis N., Varotsos P.

Acta Geophysica Polonica

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2001

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Vol. 49, nr 3

277-285

EN

Recent findings indicate that the maximum horizontal principal stress s1 has a significant component perpendicular to the fault. This, upon assuming that the direction of s1 coincides with the dipole moment of the emitting source, is combined with "overamplification" phenomenon discussed recently. The numerical results strengthen the model suggested for the explanation of the "selectivity effect" of the Seismic Electric Signals.

7

A note on the spatial extent of the Volos SES sensitive site

Varotsos P., Sarlis N., Skodras E.

Acta Geophysica Polonica

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2001

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Vol. 49, nr 4

425-435

EN

A very strong disturbance, with a duration of around two hours, was recorded at Volos SES sensitive area on March 17, 2001. It was clearly detected in a zone with spatial dimensions (a few tens km) x (several km); this zone, if the disturbance is actually a SES activity, might reveal the extent of the relevant SES sensitive site

8

Transmission of stress induced electric signals in dielectric media. Part III

Varotsos P., Sarlis N., Skodras E.

Acta Geophysica Polonica

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2000

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Vol. 48, nr 3

263-297

EN

The frequency dependence of the electric field produced by an electric current dipole lying inside or very close to a highly conductive cylinder (s), of infinite length and radius R, embedded in a significantly less conductive medium (s') is investigated. The study is extended to the case when the dipole is located inside or very close to a highly conductive layer (s), of infinite extent and width w, embedded in a significantly less conductive medium (s'). At large distances d from the source and for appreciably low frequencies, i.e., f<fc or f >f0, the electric field is attenuated with a skin depth significantly smaller than deltaout having as a lower limit the skin depth deltain for a full volume of conductivity s. The properties of the recordings, at remote distances, from a current dipole source emitting an exponentially decaying signal of unit initial amplitude and a relaxation time constant t is also studied. The source is located either inside a full volume of conductivity s' or inside a conductive half-space at a depth h (<< d). In the case of homogeneous medium s', a certain relaxation time t0 = žs'd(2)/4 exists due to the diffusion dynamics, leading to the following conclusions. If t << t0 the recordings have an enlarged duration of around t0 and an amplitude orders of magnitude smaller than that corresponding to the static case. If t > t0 the recordings have a duration almost equal to that of the emitted signal, and arrive after a time of around t0, and their amplitude approaches that of the static case. In the case of the current source located within a conductive half-space, the signal recorded at remote observation sites on the interface, arrives in two parts. The first part (which "diffuses" from the source to the interface and then propagates as a surface wave) has a duration significantly smaller than the second part ("solely diffusing" through the conductive medium). The study is extended to the case of a series of signals emitted at equal time-intervals. The application of the above to the earth explain the absence of co-fracture signals but do indicate, that the precursory Seismic Electric Signals reach detectable values at certain sites on the earth's surface.

9

Transmission of stress induced electric signals in dielectric media. Part II

Varotsos P., Sarlis N., Lazaridou M.

Acta Geophysica Polonica

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2000

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Vol. 48, nr 2

141-177

EN

In the previous paper the electric field Einside, inside a conductive path (and along its axis), having a conductivity s appreciably larger than that of the host medium, s', was studied in the static approximation, for the case of a current dipole source parallel to the path. Here, the same problem is studied but for a source perpendicular to the path. The following two types of paths we considered: (i) a cylindrical channel of radius R and infinite length, and (ii) a layer of width w and infinite extent. If D denotes the distance of the source from the path, and d the distance of the measuring site from the source, we find that the electric field Einside at remote sites (e.g., d/R or d/w of the order of 10(2)) varies as 1/D for the case of a source neighboring to the conductive cylinder, while it is almost independent of D (and w) for the case of a layer. In the case of the cylinder, the values of the ratio Einside/Ehost at (d/R)crit (see the previous paper); significantly exceed (e.g., by one order of magnitude for usual conductivity ratios between 200/1 and 4000/1, but for appreciably small values of D/R, e.g., D/R=2) the corresponding values when the dipole is parallel to the path. The general case, when the dipole source forms a certain angle with its neighboring highly conductive path terminating inside the host medium, is also investigated. The following four points emerge as far as the electric field Eoutside measured inside the more resistive medium but close to an edge is concerned. First, its direction is regulated from the angle between the emitting dipole and the direction of the (elongated) conductive path (as well as from the distance of the source). Second, its amplitude is usually larger than that of Ehost by a factor of around s/s', but there arc also some cases of over-amplification, i.e., the value of Eoutside/Ehost significantly exceeds the conductivity ratio s/s': such an over-amplification may even occur in cases of conductive paths that are not connected. Third, its amplitude versus the distance from the edge varies only slowly, i.e., [Eoutside] 1/r(t) where t is around (but smaller than) unity. Fourth, for a circularly polarized EM plane wave incident on the surf ace of a conductive half-space (containing a highly conductive path close to the interface), the direction of the electric field variations, measured on the surface but close to the end of the path, is generally different from the direction of Eoutside arising from a dipole source which forms a certain angle with its neighboring conductive path. Finally, the above points are applied to the case of the low frequency electric signals that are detected before earthquakes; this results in a natural explanation of the procedure that is followed to determine the parameters of an impending earthquake from the components of the precursory electric signal.

10

Statistical evaluation of eqrthquake prediction results. Comments on the success rate and alarm rate. II

Varotsos P., Sarlis N., Lazaridou M.

Acta Geophysica Polonica

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1998

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Vol. 46, nr 3

261-271

EN

Following the procedure of Varotos et al. (1996) for an earthquake prediction method, that issues predictions whenthe expected megnitude Mpred (with a tolerance ?M0 exeeds a certain threshold, i.e., Mpred>mp, we show that: (1) The method also naturally predicts a fraction of the earthquakes (EQ) with magnitudes (MEQ) smaller than the target, i.e. mp - DMŁMEQ