A magnitude 7.7 earthquake — revised upward from an initial estimate of 7.5 — struck 100 kilometers off Japan's Iwate Prefecture on Monday afternoon, shaking communities along the same Sanriku coastline where tsunamis killed tens of thousands in 1896, 1933, and 2011. The Japan Meteorological Agency issued tsunami warnings for waves up to three meters and ordered evacuations for nearly 172,000 people across five prefectures. Observed waves peaked at 80 centimeters at Kuji Port, well below the forecast level, and all tsunami warnings were lifted by Tuesday morning. At least 26 buildings were damaged in Aomori Prefecture and around 200 power outages were reported across the affected area.
With tsunami warnings cleared, Japan's attention has turned to an elevated aftershock risk. The JMA issued a rare 'Subsequent Earthquake Advisory' covering 182 municipalities from Hokkaido to Chiba Prefecture, valid through April 27 at 5 p.m. The agency placed the probability of a magnitude 8 or greater earthquake along the Japan Trench at roughly 1 percent — ten times the normal baseline rate. Prime Minister Sanae Takaichi urged residents to continue daily activities while maintaining immediate evacuation readiness, advising them to confirm shelter locations and keep emergency supplies accessible.
