Electricity demand being low on the weekend, railways can keep trains 
running today.  JR East has announced limited suspension on only the 
Kururi Line in southern Chiba.  (I am not sure what rolling blackouts 
has to do with this line which is powered by diesel rather than 
electricity.)

JR East Ban'etsu Line will reopen today, allowing access to 
Aizu-Wakamatsu and Kouriyama via Niigata.  Tobu, which is already 
running trains toward Aizu-Wakamatsu via the Nikko area will increase runs.

JR East has announced that they plan to reopen the Joban Line to Katsuta 
by April 10.  Cars standing idle at Katsuta depot will be brought back 
to work and congestion will be relieved.

Details here:
http://www46.atwiki.jp/earthquakeinfo_en/pages/15.html