Features of criticality in precursory seismic electric signals and earthquakes in Greece

Very recently the recordings of precursory seismic electric signals (SESsf) in the island of Kōzu-shima, Japan, have been reported, and their interrelation with subsequent earthquakes was shown to be beyond chance. Almost simultaneously, the recording of SES activity in northern Greece was also reported, which was followed by a magnitude 5.7 earthquake in northern Greece. These facts strengthen the aspects on the precursory nature of SESs and also enable the updating of a previously found power law relation between the earthquake stress drop and the lead time of SESs. They led to an exponent of 0.330, which falls in the range of critical exponents for fracture. The stability of this exponent, which results from a large amount of data during the last 30 yr, is remarkable and may thus confirm features of criticality in the pre-seismic region after the SES emission. The underlying physics are also discussed.