The 2004 earthquake that occurred in the Indian Ocean near Sumatra, Indonesia triggered a series of tsunamis that killed over 200000 people in 14 countries.
The deadliest known quake in history shook China in 1556, taking about 830,000 lives.
Sometimes there are many small earthquakes before the big one. These small ones are called foreshocks. After the big earthquake, the mainshock, again there may be many small quakes. These are called aftershocks.
Most earthquakes happen along the edges of Earth's big plates.