EarthquakesCBC News Online May 13, 2008An earthquake is one of the most destructive events in the natural world. More than three million people were killed in earthquakes in the 20th century alone. Although scientists are able to predict which regions are most likely to be hit, it is impossible to predict when a major quake will occur.

What is an earthquake?
The ground beneath our feet seems rock-solid, but our planet's surface is in fact a dynamic grid of slowly moving sections, known as tectonic plates. Normally, this motion is imperceptible to humans, showing itself only on geological time scales (North America and Europe, for example, are drifting apart at the rate of just five centimetres per year). The movement causes stress to build in the crust. If the stress rises beyond a critical threshold, a portion of the crust will give way, shifting suddenly and violently. This sudden motion usually occurs along a fault or fracture – a zone of weakness in the earth's crust. The result is what we call an earthquake.