A megaquake advisory issued for the first time following a major earthquake off the eastern coast of Aomori Prefecture last week was lifted at midnight on Dec. 15. The government ended its call for special disaster preparedness under the “off the coast of Hokkaido and Sanriku subsequent earthquake advisory” after one week.
Subsequent Earthquake Advisory Lifted
Despite lifting the advisory, the government will continue to recommend preparedness measures, such as securing furniture to prevent it from tipping over, as the possibility of a sudden powerful earthquake still exists.
“We appreciate that people responded calmly to the advisory without any major confusion,” said Jiro Akama, state minister for disaster management and food safety, at a news conference on Dec. 16. “We plan to assess the extent to which the advisory contributed to disaster management and preparedness later.”
The Cabinet Office will survey local governments and businesses in the targeted regions to identify best practices and challenges related to the advisory.
The initial earthquake struck off the eastern coast of Aomori Prefecture at 11:15 p.m. on Dec. 8, registering a maximum seismic intensity of an upper 6 on the Japanese scale of 7 in Hachinohe, Aomori Prefecture. A tsunami of up to 70 centimeters was recorded in Kuji Port in Iwate Prefecture.
The subsequent earthquake advisory, covering 182 municipalities across seven prefectures from Hokkaido to Chiba, was issued at 2 a.m. on Dec. 9 due to concerns about a major earthquake occurring in succession. This marked the first time the advisory had been issued since its introduction in December 2022.
The government had urged people to continue social and economic activities while rechecking daily preparedness measures, including securing furniture and confirming evacuation sites and routes. It also called for “special preparedness,” such as sleeping in clothing that allows for immediate evacuation and keeping emergency supplies by the bedside.
According to the Japan Meteorological Agency, seismic activity that intensified on Dec. 8 is gradually declining, but the number of earthquakes is expected to remain higher than usual for the time being.
The advisory anticipated a magnitude 8 or higher earthquake. A worst-case scenario could involve a magnitude 9 earthquake along the Japan Trench or Chishima Trench, potentially triggering tsunami of up to 30 meters and causing as many as 200,000 deaths.
Globally, the likelihood of a major subsequent earthquake occurring within a week after a magnitude 7 earthquake is estimated at about one in 100. A magnitude 7-class quake occurred two days before the 2011 Great East Japan Earthquake.
On Dec. 12, while the advisory was in effect, an earthquake struck off the eastern coast of Aomori Prefecture, registering a maximum seismic intensity of 4 in 38 municipalities across Hokkaido, Aomori, Iwate, Miyagi and Akita prefectures. A tsunami advisory was briefly issued for parts of Hokkaido and Aomori Prefecture, as well as Iwate and Miyagi prefectures, but the quake was smaller than the magnitude 8-class event feared as a subsequent earthquake.
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