Medium-Sized Quake
From the reports I’ve seen, a 5.0 or 5.1 M quake hit southwest Ibaraki Prefecture (36.048N 139.932E) 5 minutes ago at 4:05 pm Japan time. That’s about 40 km perhaps north of Central Tokyo. It was felt as a Japanese “4” in northern Kanto, and as a “3” in Tokyo. Some parts of Tokyo felt it as a “4,” and frankly, it was pretty strong where I am. Maybe not a “4,” but very close to it.
No reports of great damage so far, or warnings of Tsunamis.
For reference: two good Japan quake reportage sites include Hinet and Tenki. They tend to have quake reports up within a few minutes of the quake. The Hinet site has copy-and-pastable map coordinates which you can then plug into Google Maps Japan to see where the epicenter was.