  The Tohoku EQ (11th of March, 2011, M = 9.0) in Japan falsified the proposed
EQ magnitude range (M = 7.0 - 8.5) of the same seismogenic regional area that
had been determined by the compiled hazard maps, study of historical data, or
other probabilistic methods while a larger magnitude (M > 9.0) had been
proposed for all subduction zones. The observed discrepancy between the
proposed EQ magnitude range and the actual one of the Tohoku EQ is studied in
this work in terms of the cumulative seismic energy release of the study area
and by the use of the Lithospheric Seismic Energy Flow Model (LSEFM). The
results indicate that the Tohoku mega-earthquake magnitude could be predicted
quite accurately provided that a long past seismic history had been available
for use by the LSEFM procedure. Moreover, the presence, of the missing historic
1855 EQ (7.0 < M < 8.0) from seismic catalogs, was predicted backwards by the
LSEFM method and its existence was verified by the Ishibashi (2004) work on
Japanese historic seismicity. The recurrence time of the Tohoku EQ is estimated
as being at least as 100 years. It is proposed frequent monitoring of the
Japanese area seismic potential by compiling regularly in time the
corresponding seismic potential maps.
  Key words: Tohoku earthquake, earthquake magnitude, lithosphere, cumulative
seismic energy, mega-earthquakes, seismic potential maps.
