At 7:23 AM eastern US time Sunday, a strong magnitude 5.8 earthquake took place in the Pacific Ocean off the coast of southeastern Japan. The quake was widely felt in Tokyo, with citizens reporting the shaking lasted 15 seconds and was "very odd" with not only vertical shaking, but horizontal and even "circular" motion.
No Tsunami Buoys are in "Event Mode" so the belief is that no dangerous Tsunami waves were generated by the quake.
The video below shows the Japan Earthquake Early Warning System as it detected the quake. Thanks to this system, people in Japan had between five and fifteen seconds warning that an earthquake was happening.
No word of any injuries or deaths.
Japan is perhaps the single most seismically active place in the world, sitting atop the Pacific "Ring of Fire" and as such, they have literally thousands of earthquake monitoring units all over the country, which are tied together to give as much early warning as possible when a quake takes place.