This video excerpt from NOVA: "Deadliest Earthquakes" shows how Earth’s crust is made up of rocky slabs, called plates, and how those plates are constantly moving. As molten rock rises from Earth's interior and cools to form new crust, it forces older crust to grind against other plates or sink beneath them. Using ground movement data, scientists are able to calculate stress levels at these plate boundaries. This stress is released in a matter of seconds during an earthquake, sometimes generating as much energy as thousands of nuclear bombs.

This video is available in both English and Spanish audio, along with corresponding closed captions.