The national weather agency plans to issue an initial tsunami warning without an estimate of how high the waves would be, in the event of a massive earthquake measuring magnitude 8 or higher, agency officials said.
The Japan Meteorological Agency's plan was on Wednesday reported to a government study group reviewing tsunami warnings in light of the devastating tidal waves that struck the nation's Pacific coast on March 11 following a magnitude 9.0 quake.
Under the new policy, an initial tsunami warning issued within three minutes of a temblor of magnitude 8 or stronger will bear such descriptions as 'A giant tsunami is feared,' instead of concrete estimates, to prompt swift evacuations.
The change is partly prompted by criticism after the March tsunami that the agency's initial warning, which projected tidal waves of between 3 and 6 meters along Iwate and Fukushima prefectures, undershot the height of the actual tsunami and apparently led to a delay in residents' evacuations to higher ground.
The agency had previously put an emphasis on giving precise forecasts in issuing weather and other kinds of warnings.