Japanese govt issues its first 'megaquake' warning after powerful tremor

By Shoko Oda

An earthquake off the coast of Japan’s southern island of Kyushu prompted the government to issue its first-ever warning for a megaquake from an undersea trough running southeast along the archipelago. 
 

Bullet trains were running at reduced speeds, national broadcaster NHK is permanently displaying cautionary graphics and a semiconductor factory temporarily halted production.

Defined as a major tremor occurring in 100- to 150-year cycles, a megaquake could surpass the damage from the March 2011 earthquake and tsunami that devastated the northeastern coast of the main island of Honshu. Thursday’s warning was for a major tremor originating from the Nankai trough, a trench where the Philippine sea plate subducts underneath the Eurasian continental plate. 

 

The precautionary warning system, implemented several years ago, kicks in when a magnitude-6.8 or larger earthquake strikes an area where the megathrusts are expected to occur, or when anomalous shifts in the plates are detected. Depending on the size of the earthquake at the time, the authorities can issue different levels of caution, and in some cases warn people to evacuate away from tsunami-prone areas for as long as a week.

The magnitude-7.1 earthquake that struck off the coast of Kyushu Thursday didn’t cause any major damage or tsunami. The island is home to semiconductor factories operated by Sony Group Corp. Taiwan Semiconductor Manufacturing Co. has opened one factory there, is about to open a second one later this year, and is considering a third as well.

NHK broke into Olympics coverage to cover the quake and the subsequent megaquake warning, and continued to issue bulletins on Friday. A 2019 analysis by a government panel estimated that more than 230,000 deaths could occur in the worst case scenario from a Nankai trough quake.

Big earthquakes have followed smaller tremors in the past. Foreshocks began two days prior to the 2011 9-magnitude earthquake, the most powerful recorded in Japan. Damage from the major tremor and resulting tsunami killed almost 20,000 and triggered a meltdown and radiation leakage from a nuclear facility in Fukushima.

Central Japan Railway Co. said its bullet trains are running slower between Tokyo and western Japan until the warning lifts. Japan’s regulatory body said it issued alerts to all nuclear power plants in the nation to take precaution.

Local governments and companies are responding after the Japan Meteorological Agency issued the advisory on Thursday. 

Chipmaker Rohm Co. temporarily suspended operations in Miyazaki prefecture in Kyushu and said safety checks are under way. 

Chubu Electric Power Co., a utility covering central Japan, said it has set up a network to strengthen communication between headquarters and branch offices, according to the spokesperson. The company’s Hamaoka Nuclear Power Plant, which has reactors that have been offline since 2011, is under an “earthquake standby” alert with 300 people at the site as of 7:30 p.m. Thursday, checking facilities handling hazardous materials and taking emergency safety measures.