G07: I&S Forces of Nature: Earthquake

An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.

A top South African earthquake expert predicted a year ago that South Africa was ‘almost certain to be hit by a major earthquake. It’s not a matter of if, but when’. The Daily Express in April 2010 quoted Dr Chris Hartnady of the Umvoto Africa CSIR Satellite centre as saying that the coastal harbour cities of Durban and Cape Town are the areas most likely to be hit by an earthquake because of the rapid spread of the East African Rift fault-lines.

Have you ever assured someone that your friend is reliable by saying that he or she "has both feet on the ground"? The fact that such a phrase exists shows how much comfort we take in the idea that the ground beneath our feet is unmoving, unchanging and dependable. Indeed, much of our civilization, from our houses and buildings to our energy, food and water sources, depends on unmoving earth.

To experience the drama of plate tectonics -- the jostling of the giant plates that carry continents and oceans -- try this experiment: Sit in a comfortable chair, hold your hand out, and watch your fingernails grow. That's about the average speed of a tectonic plate. But wait around long enough, and even the tortoise crawl of plate tectonics will have dramatic and deadly consequences. Though plate tectonics is a global phenomenon and virtually invisible to us in our daily lives, it introduces enormous stresses in the crust where we live. From time to time, stressed-out crust releases the stress in sudden fits: earthquakes.