Japan’s Meteorological Agency lifted the main tsunami warnings issued after Monday’s magnitude-7.7 earthquake off Iwate Prefecture, but kept tsunami advisories in force and maintained a rare mega-quake alert for seven prefectures, public broadcaster NHK reported.
The agency said residents across 182 cities and towns from Hokkaido to Chiba should continue to prepare for a possible larger follow-on event along two deep-sea Pacific trenches. Officials said the probability of a “mega-quake” — a magnitude-8 or 9 event — remains elevated in the hours and days after a major offshore shock of this size.
The first tsunami waves have already reached Japan’s eastern coast, with a 40-centimetre wave recorded at Miyako port in Iwate, Ada Derana reported citing BBC. Tsunami wave forecasts of up to three metres along the Pacific coasts of Iwate and Hokkaido remain the working planning assumption.
The sequence caps a day of intense seismic and public-safety activity after the initial 7.7 quake and mega-quake alert triggered evacuation orders for nearly 172,000 residents across Hokkaido, Aomori, Iwate, Miyagi and Fukushima. The JMA upgraded the quake from 7.4 to 7.5 to 7.7 over the course of the afternoon — a common pattern on large Pacific-trench events, where initial magnitudes are revised upward as seismologists process the full waveform.
Officials continue to urge residents under advisories not to return to low-lying coastal areas, warning that second and third waves can be higher than the first. The Tohoku Shinkansen remained suspended between Tokyo and Shin-Aomori.
The quake struck off the same Iwate coast as the March 2011 Tōhoku earthquake, which killed more than 18,000 people and triggered the Fukushima Daiichi nuclear disaster.
Sources: NewsFirst, Ada Derana.
