「余震」発表取りやめ　東日本大震災後１０年で―気象庁

　気象庁は１日、東日本大震災を引き起こした東北地方太平洋沖地震（マグニチュード＝Ｍ９、最大震度７）の余震域で震度５弱以上の地震が起きた場合、「余震と考えられる」としてきた発表方法を取りやめた。１０年が経過して余震と明確に判断できなくなったほか、もともと日本海溝沿いでは長期的にＭ７～８級の地震が繰り返し起きているため。
　担当者は「防災上の観点では、余震であるかに関係なく、大きな地震や津波に備えてほしい」と説明している。
　余震域は南北６００キロ、東西３５０キロの長方形。青森県沖から千葉県にかけての沿岸部と日本海溝の東側までの沖合が含まれる。今年は２月１３日に福島県沖でＭ７．３、最大震度６強、３月２０日に宮城県沖でＭ６．９、最大震度５強の地震がそれぞれ発生した。科学的には巨大なＭ９地震の影響は１０年を超えて長く続くため、余震域内で発生する地震の統計は今後も公表する。（2021/04/01-10:31）

The Japan Meteorological Agency has stopped using the term "aftershocks" for strong earthquakes occurring in areas around the focus of the March 2011 9.0-magnitude quake that devastated the country's northeast.
   The agency had been referring to the possibility of an aftershock of the 2011 quake which measured up to 7, the highest level on the country's seismic intensity scale, when temblors measuring lower 5, the fifth-highest level, or higher occurred in areas designated as the 2011 quake aftershock zone.
   The decision to avoid describing such quakes as aftershocks came as it became difficult to make clear judgments as 10 years have passed since the massive jolt and also because quakes with a magnitude of 7 to 8 have repeatedly been occurring along the Japan Trench off the coast of eastern Japan.
   But the agency will continue to disclose data on earthquakes occurring in the aftershock zone because the impact of the 9.0-magnitude quake lasts over 10 years.
   "I want people to prepare for possible powerful earthquakes and tsunamis regardless of whether they are aftershocks or not," an agency official said.