An earthquake with a preliminary magnitude of 5.1 rocked areas northeast of Tokyo early Monday, the weather agency said, noting no tsunami warning was issued.The 12:50 a.m. quake, which occurred in northern Ibaraki Prefecture, measured lower 5 of the Japanese seismic scale of 7 in Hitachi and registered 4 in nearby Takahagi, the Japan Meteorological Agency said.There were no immediate reports of injuries in the prefecture, local police said.The quake had no major impact on the Tokai No. 2 nuclear power station in the prefecture, its operator said.Related coverage:READ FULL ARTICLE