A massive earthquake hit Japan earlier today, registering 8.9 on the Richter scale and the largest ever recorded for Japan. The tsunami triggered by the quake brought a 10m high wall of water in northern Japan, and other countries are now waiting for it to hit their shores.

But what causes earthquakes and tsunamis and what can we do to protect ourselves from their destructive power?

The tsunami of December 26th 2004 has focused the world's attention on this terrifying consequence of an underwater earthquake. Michael McIntyre explores the underlying wave mathematics.