After a 7.1-magnitude earthquake shook southern Japan on August 8, the Japan Meteorological Association (JMA) issued its first-ever “megaquake advisory”.
The agency says the country should prepare for a possible “megaquake” one day that could kill hundreds of thousands of people.
The advisory concerns the Nankai Trough in the Pacific Ocean.
Megaquake
A megaquake is an earthquake with a magnitude larger than 8.
These so-called “megathrust quakes” usually come in pairs, with the second often rupturing in the subsequent two years — the most recent “twin” earthquakes took place in 1944 and 1946.
These quakes have been known to unleash dangerous tsunamis along Japan’s southern coast.
Nankai Trough
The Japan Meteorological Association (JMA) warning is the first issued under new rules drawn up after a 2011 earthquake, tsunami and nuclear disaster killed around 18,500 people.
The advisory concerns the Nankai Trough in the Pacific Ocean. The Nankai Trough is an underwater subduction zone (nearly 900 km long) where the Eurasian Plate collides with the Philippine Sea Plate, pushing the latter under the former and into the Earth’s mantle.
A subduction zone is a region where tectonic plates collide with each other, and the heavier one slides under another.
The 800 km undersea Nankai Trough runs from Shizuoka, west of Tokyo, to the southern tip of Kyushu Island.
It has been the site of destructive quakes of magnitude eight or nine every century or two.
