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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS009 Oral Presentation 2022
Recent results on seismic electric signals (SES)
Prof. Panayiotis Varotsos
Physics Department University of Athens IASPEI
Efthimios S Skordas, Nicholas V Sarlis
Seismic Electric Signals (SES) are low frequency ( 1Hz) electric signals that precede earthquakes. [P.
Varotsos and K. Alexopoulos, Tectonophysics 110, 73 (1984); ibid Tectonophysics 110, 99 (1984)] Since
the 80s, it has been suggested that they are emitted from the focal area when the stress reaches a
critical value. During the last several years, our knowledge on the SES has been advanced through
detailed experimental and theoretical studies, which among others include the following: First, for SES
activities preceding major earthquakes and for epicentral distances ~100 km, the electric field arrives 1
to 2 s before the time derivative of the horizontal magnetic field [P. Varotsos, N. Sarlis and E. Skordas,
Phys. Rev. Lett. 91, 148501 (2003)]. An explanation, should consider, beyond criticality, the fact that
the transmission through a weakly conductive medium like the Earth, of low frequency electromagnetic
fields, obeys diffusion type equations. Second, in the aforementioned case it is also observed that the
electric field components of SES exhibit markedly different time evolution. This difference, if properly
measured, is of profound importance since it can reveal the distance of the measuring site from the
epicenter of the impending earthquake [P. Varotsos, N. Sarlis and E. Skordas, Appl. Phys. Lett. 86,
194101 (2005)]. Third, the introduction of the new concept of natural time [P. Varotsos, N. Sarlis and E.
Skordas, Practica Athens Acad. 76, 294 (2001)] revealed new properties of the SES activities that were
hitherto unknown. For example, the study of the normalised power spectrum in the natural time domain
shows that all SES activities fall on a universal curve which coincides to that expected from the theory of
critical phenomena [P. Varotsos, N. Sarlis and E. Skordas, Phys. Rev. E 66, 011902 (2002)].
Furthermore, the SES activities exhibit infinitely ranged temporal correlations and hence memory which
is markedly stronger than that found from the analysis of electric signals emitted from man-made
sources [P. Varotsos, N. Sarlis and E. Skordas, Phys. Rev. E 67, 021109 (2003); ibid 68, 031106
(2003)].
Keywords: seismic electric signals, electric field transmission, magnetic field variations