Japan issues its first-ever 'megaquake warning'; know all about 'big one'

A 7.1 earthquake in southern Japan led to a warning from the Meteorological Agency about possible major quakes. Prime Minister Kishida canceled his Central Asian trip for earthquake preparedness. Experts predict a 70-80% chance of a major quake in the Nankai Trough. Earthquakes with a magnitude greater than 8 are classified as megaquakes.