  Applying Detrended Fluctuation Analysis (DFA) to the geomagnetic data
recorded at three measuring stations in Japan, Rong et al. in 2012 reported
that anomalous magnetic field variations were identified well before the
occurrence of the disastrous Tohoku $M_w$9.0 earthquake that occurred on 11
March 2011 in Japan exhibiting increased "non-uniform" scaling behavior. Here,
we provide an explanation for the appearance of this increase of "non-uniform"
scaling on the following grounds: These magnetic field variations are the ones
that accompany the electric field variations termed Seismic Electric Signals
(SES) activity which have been repeatedly reported that precede major
earthquakes. DFA as well as multifractal DFA reveal that the latter electric
field variations exhibit scaling behavior as shown by analyzing SES activities
observed before major earthquakes in Greece. Hence, when these variations are
superimposed on a background of pseudosinusoidal trend, their long range
correlation properties -quantified by DFA- are affected resulting in an
increase of the "non-uniform" scaling behavior. The same is expected to hold
for the former magnetic field variations.
