A seismologist says, ‘There are huge “plates” on the surface of the Earth which press and move against one another. Because there is friction between these plates, they fail to move for many years...

A seismologist says, ‘There are huge “plates” on the surface of the Earth which press and move against one another. Because there is friction between these plates, they fail to move for many years until the pressure becomes huge and then they move suddenly, an event we experience as an earthquake. That is why San Francisco had a huge earthquake in 1906 and also why they expect another one at any time now.’