The largest aftershock to hit Japan since the March 11 earthquake killed at least four people and injured 100 others on Thursday. It also caused a small amount of radioactive water to slosh out of spent fuel pools at the Onagawa Nuclear Power Plant, but higher levels of radioactivity were not detected outside the building. The Onagawa plant also lost power, but the emergency generators kicked in and power has since been restored. Meanwhile, Tokyo Electric Power continues to release radioactive water into the Pacific Ocean to make room for more contaminated water that has flooded the basement of the No. 2 reactor building. Once the water has been emptied from the facility, the utility will check to see whether the leak has been plugged before pumping in water from the basement, a key step in restoring cooling systems at the troubled reactor.