Japan Issues Megaquake Advisory After Magnitude 7.5 Quake — Tsunami Up To 98 Feet Warned

Japan issued a nationwide megaquake advisory after a magnitude 7.5 earthquake struck off the northern coast, near Aomori, leaving 34 people with mostly minor injuries and causing damage to roads and buildings. Authorities warned that a subsequent offshore megaquake could generate a tsunami up to 98 feet (about 30 meters) high in some areas and outlined a severe, worst-case scenario for human and economic losses.

What Happened

The Japan Meteorological Agency (JMA) said Monday’s quake originated off the eastern coast of Aomori Prefecture on Honshu, just south of Hokkaido. The tremor was widely felt; some residents described prolonged shaking and rushed outdoors with children and pets. Local officials reported mostly mild injuries but noted localized structural damage to roads and buildings.

"The tremor was something that we've never experienced. It lasted maybe for about 20 seconds," said Daiki Shimohata, a civil servant in Hashikami, recalling how he carried his 2-year-old daughter and 1-year-old son outside.

Why Officials Issued the Advisory

The advisory is not a prediction of an imminent, larger quake, the JMA emphasized; it estimates the short-term probability of a magnitude 8.0 or greater event at roughly 1%. Still, seismologists say the recent quake temporarily increased the risk in the Hokkaido–Sanriku region, where the Pacific Plate forms the Japan Trench and Chishima Trench — areas with a history of large earthquakes and tsunami generation.

Risk Estimates and Potential Impact

Government modeling for a hypothetical offshore Hokkaido–Sanriku megaquake projects a possible tsunami up to 98 feet, a worst-case death toll approaching 199,000 people, destruction of up to 220,000 houses and buildings, and economic losses up to 31 trillion yen (about $198 billion). Officials also warned tens of thousands could face hypothermia in winter if mass displacement occurs.

Geographic Scope

The advisory covers 182 municipalities stretching from Hokkaido down to Chiba Prefecture. It complements a separate Nankai Trough advisory issued last August for Japan’s southern Pacific coast after a magnitude 7.1 quake off Miyazaki.

Advice to Residents

Cabinet disaster-prevention official Tsukasa Morikubo said the advisory gives no specific time or location for a larger quake but urged calm preparedness. Officials recommend:

• Keep an emergency bag with several days' worth of supplies, water, medications, sturdy shoes and a flashlight.
• Wear helmets or carry hard-soled shoes when evacuating; consider sleeping in day clothes for a faster response.
• Secure heavy furniture to walls or floors and plan evacuation routes with family members.
• Register for local emergency alerts and check relief stockpiles and shelter equipment maintained by municipalities.

Historical Context

Officials cited the March 11, 2011 magnitude 9.0 quake and tsunami — which followed a magnitude 7.3 temblor two days earlier in the Japan Trench — as a reminder of how a sequence of events can escalate rapidly. That 2011 disaster killed nearly 20,000 people and caused the Fukushima Daiichi nuclear accident, and it remains a benchmark for the scale of devastation possible from large trench earthquakes.

Communication And Public Response

Authorities said lessons were learned after last year’s Nankai Trough advisory, which used technical jargon and prompted widespread confusion, panic buying and event cancellations. Officials now aim for clearer, more actionable messaging to avoid unnecessary alarm while ensuring people prepare effectively.

Bottom line: The current advisory is a call to preparedness, not an immediate prediction. Residents in affected areas should review evacuation plans, prepare emergency kits, and stay tuned to official channels for updates.