Japanese authorities have issued a follow-up earthquake advisory after a large tremor struck off the Sanriku coast on the evening of 20 April, warning that the risk of a massive earthquake along the Chishima (Kuril) and Japan Trench has risen above normal levels. The Japan Meteorological Agency's alert covers 182 municipalities stretching from Hokkaido in the north to Chiba Prefecture near Tokyo, urging residents to review their disaster preparedness. The Sanriku and Chishima coastal zones are among Japan's most seismically active regions and have historically produced some of the world's most destructive tsunamis, making such advisories a serious public safety concern.