The history of the big earthquakes and those aftershocks

I compiled the history of the big earthquakes and those aftershocks. As you can see below, the powerful aftershock occurred just two months later at the earliest. So we need to be very cautious about the aftershock this time around.

The name of earthquake                                                   Aftershock

Ansei-Tōkai earthquake on Dec 23, 1854                        Nov 7, 1855
  (M8.4)                                                                             (M7.0〜7.5)

Meiji-Sanriku earthquake on June 15, 1896                      Aug 31, 1896 
  (M8.2〜8.5)                                                                    (M7.2)

Great Kantō earthquake on Sep 1, 1923                           Jan 15, 1924
 (M7.9)                                                                               (M7.3)

Sumatra earthquake on Dec 26, 2004                               Mar 28, 2005
 (M9.1)                                                                               (M8.6)     

Great East Japan earthquake on Mar 11, 2011                             ?
(M9.0)