An 8.1 Mw earthquake and subsequent tsunami in Nankaidō, Japan, kills over 1,300 people and destroys over 38,000 homes.

The moment magnitude scale is a measure of an earthquake's magnitude based on its seismic moment. Mw was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Before Hanks and Kanamori (1979), Kanamori (1977) developed Mw scale for large earthquakes above 7.5. Thus Mw and M are not the…