An earthquake with a preliminary magnitude of 5.1 struck off Japan's Fukushima Prefecture on Friday, the weather agency here said.According to the Japan Meteorological Agency (JMA), the temblor, which occurred at 3:19 p.m. local time, struck at a depth of 30 km.An earthquake with a preliminary magnitude of 5.1 struck off Japan's Fukushima Prefecture on Friday, the weather agency here said.According to the Japan Meteorological Agency (JMA), the temblor, which occurred at 3:19 p.m. local time, struck at a depth of 30 km.