On the anomalous changes of seismicity and geomagnetic field prior to the 2011 Mw 9.0 Tohoku earthquake

In Xu et al. (2013), it has just been reported that approximately 2 months prior to the Mw 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 (4-14 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 main shock was expected in a few days to one week after 08:40 LT on 10 March 2011.