Japan issues its first-ever ‘megaquake advisory’: What does it mean?

Sub: Geo

Sec: Geomorphology

Japan’s First “Megaquake Advisory” Issued Following Earthquake

Event: A 7.1-magnitude earthquake struck southern Japan on Thursday, August 8, prompting the Japan Meteorological Agency to issue its first-ever “megaquake advisory.”
Advisory Details: The advisory highlighted an increased likelihood of strong shaking and large tsunamis, particularly along the Nankai Trough, a subduction zone along Japan’s southwest Pacific coast. However, it did not predict a specific major earthquake.

About the Nankai Trough:

It is a “subduction zone” between two tectonic plates in the Pacific Ocean, where massive earthquakes have hit in the past.
This 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.
Location: It 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.
These so-called “megathrust quakes”, which often occur in pairs, have been known to unleash dangerous tsunamis along Japan’s southern coast.
Historical Context: Known for causing megaquakes (magnitude >8), the trough experiences significant earthquakes every 100-150 years. The last twin earthquakes occurred in 1944 and 1946.

Source: IE