Fluctuations of the entropy change under time reversal: Further investigations on identifying the occurrence time of an impending major earthquake

A procedure has been developed in a previous publication (Skordas E. S. et al., EPL, 128 (2019) 49001) for the identification of the occurrence time of the Tohoku earthquake of magnitude that occurred in Japan on 11 March 2011 based on natural time analysis of seismicity. Using the complexity measure that quantifies the fluctuations of the entropy change of seismicity under time reversal, we show here that, in the longer scales, the complexity measure of the entire Japanese region starts increasing from 22 December 2010 (the date at which is minimized) reaching a maximum close to the appearance of a Seismic Electric Signals activity (evidenced from the recording of anomalous magnetic field variations on the z-component) in the beginning of January 2011; then it gradually diminishes until just before the mega earthquake. On the other hand, around two days before its occurrence, the complexity measure in the candidate epicentral area exhibits an abrupt increase. This difference reveals, well in advance, that the M7.3 earthquake on 9 March 2011 was a foreshock.