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2 Acta Geophysica Polonica

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Preseismic Earth's electric field anomalies recorded at Lesvos station, northeastern Aegean

Hadjicontis V., Mavromatou C., Eftaxias K.

Acta Geophysica Polonica

2002

Vol. 50, nr 2

151-158

Significant electromagnetic preseismic activity has been recently recorded at the telemetric VAN station of Lesvos Island, northeast Aegean, Greece. This was followed, after a few weeks, by intense seismic activity with Ms 5.8, close to Psara island (38.5°N, 25.6°E). These field results are strongly correlated with laboratory experiments aiming at detection of electromagnetic signals before the fracture of rock samples.

Anomalous piezoelectric effect: analysis of experimental data and numerical simulation

Teisseyre K., Hadjicontis V., Mavromatou C.

Acta Geophysica Polonica

2001

Vol. 49, nr 4

449-462

Interpretation of laboratory experiments on anomalous piezoelectric effects found in samples of various non-piezoelectric rocks leads us to formulate the model of transient electric polarization and its relaxation. A change of the load results in polarization in the rock, the electric signal appears immediately at a given moment, and later we observe the signal relaxation as an exponential decrease in time. Assumption of double mechanism of relaxation or, for most cases, even triple mechanism: quick, slower and the slowest relaxation, is made to obtain a better agreement between simulation and the experiments. Other complications of the model seem to be useful in the search for adequate reconstruction of electric signal rise and decay. The following elements were assumed, and positively tested in many simulations: opposite components of polarization in case of serrate stimulus curve (load rate shaped like toothed curve), the large bay of the opposite polarization during release of the load (theoretically not expected in non-piezoelectric materials) and kind of the polarization saturation during the test with the repeating load history.