  Xu et al. [J. Asian Earth Sci. {\bf 77}, 59-65 (2013)] It has just been
reported that approximately 2 months prior to the $M_w$9.0 Tohoku earthquake
that occurred in Japan on 11 March 2011 anomalous variations of the geomagnetic
field have been observed in the vertical component at a measuring station about
135 km from the epicenter for about 10 days (4 to 14 January 2011). Here, we
show that this observation is in striking agreement with independent recent
results obtained from natural time analysis of seismicity in Japan. In
particular, this analysis has revealed that an unprecedented minimum of the
order parameter fluctuations of seismicity was observed around 5 January 2011,
thus pointing to the initiation at that date of a strong precursory Seismic
Electric Signals activity accompanied by the anomalous geomagnetic field
variations. Starting from this date, natural time analysis of the subsequent
seismicity indicates that a strong mainshock was expected in a few days to one
week after 08:40 LT on 10 March 2011.
