The critical behaviour of a power law between preseismic electric signals and earthquakes of different mechanism in Greece and Japan
The consistency of the critical exponent in the power law relation between the stress drop of the earthquake and the lead time of the precursory seismic electric signal is checked using new data from the recent Mw 4.9 earthquake of strike-slip mechanism that occurred on 12 November 2013 in northern Evia island, Greece and the megathrust Mw 9.0 Tohoku earthquake on 11 March 2011, in Japan. For the first case, the derived exponent is in excellent agreement with previous ones obtained from all non thrust events analysed by the author and matches the value of critical exponent for fracture. On the other hand, the megathrust Tohoku earthquake follows the behaviour of all thrust events studied by the author, and thus, the calculated exponent significantly deviates from this critical value. The different behaviour between non thrust and thrust-type events could be attributed to the fact that thrust mechanism earthquakes usually occur in collision or subduction zones which are characterised by high accumulation of strain. However, a larger number of thrust events are required in order to obtain reliable results and shed light in the above experimental findings.