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

Varotsos P., Sarlis N., Skodras E.

Acta Geophysica Polonica

2001

Vol. 49, nr 4

425-435

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

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

Varotsos P., Sarlis N., Skodras E.

Acta Geophysica Polonica

2000

Vol. 48, nr 3

263-297

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.