Tokyo area trains are running on a normal or near-normal basis.  Off 
peak frequency is about 80%  There are changes in service patterns 
during the daytime.

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The Joban Line is now open to Hitachi City and Takahagi.  Extreme 
rush-hour congestion caused by vehicle shortages is over at last.  Ltd. 
Express Hitachi is not running yet.  The Mito Line has also reopened.

JR Central Tokaido Line (west of Atami) and Gotemba Line are back to a 
near-normal schedule.  Like elsewhere, daytime services are curtailed.

The Tohoku Shinkansen opens between Morioka and Ichinoseki in the afternoon.

In the Sendai area the Tohoku Line opened between Fukushima and Iwanuma. 
  Now it is possible to get from Kouriyama to Sendai by local train.

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JR East has still not uploaded the latest timetable to their official 
Narita Express English language pages.  It looks like things will stay 
this way.  Use their Japanese timetable:
http://www.jreast.co.jp/railway/pdf/nex_timetable.pdf

Rail services in Tokyo area, updated April 7:
http://www46.atwiki.jp/earthquakeinfo_en/pages/40.html
(Narita Express departures at Tokyo, Shinjuku and Yokohama also in this 
page)