Japan just issued its first-ever megaquake advisory. What does it mean? [Video]

By Mari Yamaguchi The Associated Press

TOKYO (AP) — Japan, one of the most earthquake-prone nations on earth, issued its first-ever “megaquake advisory” last week after a powerful quake struck off the southeastern coast of the southern main island of Kyushu.

The magnitude 7.1 quake caused no deaths or severe damage but the advisory has led to widespread confusion and a lingering sense of worry — in a country well accustomed to regular quakes — about when the next big one will hit.