The Japan Meteorological Agency (JMA) has issued its first advisory of a megaquake along the Nankai Trough, which is a 900-km undersea fault. It runs from Kyushu to Shizuoka. The Japanese government estimates suggest that there is 70-80 % earthquake probability near Nankai Trough.

In what comes as a shocking estimate, a 'megaquake' is feared to rock Japan, leading to a subsequent tsunami, resulting in almost 298,000 deaths and damage that can cost up to USD 1.8 trillion, the government report said, according to NHK World report.

The megaquake warning comes as Myanmar and Thailand grapple with a devastating earthquake of 7.7 magnitude. The Japanese government's estimate adds that the megaquake is likely to see 1.23 million people evacuating the impacted areas, which is approximately 10 percent of the country's population.

What is Nankai Trough?

Earlier in August 2024, the Japan Meteorological Agency (JMA) issued its first advisory of a megaquake along the Nankai Trough, which is a 900-km undersea fault that runs from Kyushu to Shizuoka.

Japan has taken up the issue with utmost seriousness, given the volatile tectonic activity where the Philippine Sea Plate undergoes a subduction beneath the Eurasian Plate. This happens to be the continental plate Japan sits on. Moreover, the tectonic activity is expected to be storing energy, giving rise to earthquakes up to magnitude 9.1.

Japanese govt estimates

The Japanese government estimates suggest that the Nankai Trough has a probability of 70-80 per cent of earthquakes in the upcoming three decades. According to historical estimates, megaquakes occur after a gap of every 100-200 years. The last Nankai Trough quake off Shikoku in 1946 recorded a preliminary magnitude of 8.0 and killed more than 1,300 people.

In 2013, a government disaster prevention team said a magnitude 9.1 Nankai Trough quake could generate a tsunami exceeding 10 meters within minutes, killing as many as 323,000 people, destroying more than 2 million buildings and causing economic damage of more than 220 trillion yen (USD 1.5 trillion) to large swaths of Japan's Pacific coast.

The accumulating tectonic strains could result in a megaquake roughly once in 100 to 150 years. Last year, Japan issued its first-ever megaquake advisory that there was a "relatively higher chance" of a quake as powerful as magnitude 9 in the trough, after a magnitude-7.1 quake occurred at the edge of the trough.

Myanmar, Thailand grappling with devastating earthquake

The warning in Japan comes as a 7.7 magnitude earthquake hit midday Friday, toppling thousands of buildings, collapsing bridges and buckling roads.

So far, 2,886 people have been reported dead in Myanmar and another 4,639 injured, according to state television MRTV, but local reports suggest much higher figures.

The earthquake also rocked neighboring Thailand, causing the collapse of a high-rise building under construction in Bangkok. One body was removed from the rubble early Wednesday, raising the death toll in Bangkok to 22 with 34 injured, primarily at the construction site.

Japan is one of the world's most earthquake-prone countries, and the government sees about an 80% chance of a magnitude 8 to 9 earthquake along the tremulous seabed zone- Nankai Trough. The trough is off Japan's southwest Pacific coast and runs for approximately 900 km (600 miles), where the Philippine Sea Plate is subducting under the Eurasian Plate. The accumulating tectonic strains could result in a megaquake roughly once in 100 to 200 years.

A magnitude 9 quake in 2011 that triggered a devastating tsunami and the triple reactor meltdowns at a nuclear power plant in northeast Japan killed more than 15,000 people.

Japan's economy could lose as much as $1.81 trillion in the event of a long-anticipated megaquake off its Pacific coast, which could trigger devastating tsunamis, the collapse of hundreds of buildings and potentially killing about 300,000 people.