Japan’s Rare Megaquake Warning Sparks Tsunami Fears After 7.5 Quake Jolts Northern Coast

Tokyo – Japan’s Meteorological Agency (JMA) has released an uncommon “megaquake advisory” for the Hokkaido-Sanriku coastal region, following a 7.5-magnitude earthquake that rattled the eastern shore of Aomori Prefecture, just south of Hokkaido. While the initial quake on Monday resulted in limited structural harm and left 34 individuals with minor injuries, the alert highlights an elevated possibility of a much more severe tremor in the vicinity.

JMA officials emphasized that this advisory does not constitute a precise prediction, with the odds of a magnitude 8 or greater event pegged at roughly 1 percent. As reported by the Associated Press, the measure aims to bolster public readiness amid echoes of the devastating 2011 disaster, which claimed nearly 20,000 lives. Authorities urged coastal dwellers across 182 municipalities—from Hokkaido to Chiba Prefecture—to stay alert, maintain emergency supplies on hand, and be poised for swift evacuations.

The advisory stems from intensified seismic activity along the Hokkaido-Sanriku coast, where the Pacific Plate subducts under the Japanese archipelago, forming the Japan Trench and Chishima Trench—zones notorious for spawning some of the nation’s most powerful historical quakes.

Drawing a stark comparison to 2011, experts referenced by the Associated Press noted that the magnitude 9.0 Tohoku earthquake, which unleashed the Fukushima nuclear crisis, followed a magnitude 7.3 foreshock just two days prior in the identical Japan Trench area. JMA officials highlighted this week’s sequence as eerily reminiscent, prompting the precautionary notice.

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In a worst-case projection for this zone, government assessments outline dire consequences: tsunamis surging up to 30 meters (about 98 feet), as many as 199,000 deaths, the collapse of 220,000 buildings, and economic damages exceeding 31 trillion yen (roughly $198 billion). With winter’s chill setting in, an additional 42,000 people could face hypothermia risks in the aftermath.

This alert marks a shift from last year’s broader “Nankai Trough” warning for southern Japan, which fueled widespread anxiety, including stockpiling and disrupted events. The current JMA directive is narrower, zeroing in on the Hokkaido-Sanriku corridor to encourage measured vigilance without undue alarm.