1. The plates rub against each other in opposite directions. This causes the most horrific earthquakes.

2. The plates pull away from each other, causing major earthquakes and volcanoes.

3. The plates slip under one another, causing violent earthquakes, landslides, and the formation of volcanoes.

4. The plates push towards each other, folding upwards to form mountains.

On average there are about 45 recorded earthquakes a day, few of which are strong enough to be newsworthy. The magnitude of earthquakes is measured on the Richter scale, named after Charles Richter. Of course, many earthquakes occur under the sea, sometimes causing huge tidal waves called Tsunamis. Earthquakes, as we know, can cause massive destruction and loss of life. Some famously devastating earthquakes include the 1923 quake at Tokyo in Japan that killed about 143 000 people and the 1755 quake that killed 60 000 in Lisbon, Portugal. An earthquake in China in 1556 killed approximately 830 000 people.

Earthquakes are also extremely expensive, because the infrastructure they destroy has to be replaced. This is why seismology is one of the better funded branches of geology - it is worth investing in ways of observing and predicting earthquakes and reducing the damage they cause. A 1906 earthquake in San Francisco cost $500 million.