To be a bit more precise, the Nankai ("South Sea") Trough is a tectonic subduction zone to the south of Japan, roughly the entire length from Izu to Kyushu:

https://en.wikipedia.org/wiki/Nankai_Trough

And Nankai megathrust earthquakes are those caused by plate movement there:

https://en.wikipedia.org/wiki/Nankai_megathrust_earthquakes

Statistically major earthquakes occur here every 90-200 years, and the last was in 1946.

I've heard there's been a lot of redevelopment in Nagoya, in preparation for a possible future earthquake from the Nankai Trough.

Exactly one month ago, there was almost consecutive daily earthquakes in Kantō region. Always a good reminder the whole country lies on seismically active fault lines.

[dead]