On the seismic regime of the Japan region before the Tohoku mega-earthquake (Mw = 9)

The seismic regime taking place before the Tohoku mega-earthquake was studied using the catalog of the Japan Meteorological Agency (JMA). We show that the Tohoku earthquake was preceded by a 6–7-year period of regional reduction in the b -value and in the rate of main shocks. The space-time regions that involved precursory activation were nearly identical with the predictive phenomena that were previously detected by A.A. Lyubushin from an analysis of seismic noise based on data from the Japanese F-net. We discovered a previously unknown effect of correlation between the number of main shocks and the b -value. Both the ordinary foreshock activation and the longer weaker tendency, which consist in a precursory increase in the seismicity rate, were identified in the vicinities of M ≈ 7 Japanese earthquakes (similarly to the seismicity in the Generalized Vicinities of large earthquakes based on worldwide data).