Earthquakes
An earthquake is one of the most terrifying phenomena that nature can dish up. We generally think of the ground we stand on as "rock-solid" and completely stable. An earthquake can shatter that perception instantly, and often with extreme violence.
Up until relatively recently, scientists only had unsubstantiated guesses as to what actually caused earthquakes. Even today there is still a certain amount of mystery surrounding them, but scientists have a much clearer understanding.
There has been enormous progress in the past century: Scientists have identified the forces that cause earthquakes, and developed technology that can tell us an earthquake's magnitude and origin. The next hurdle is to find a way of predicting earthquakes, so they don't catch people by surprise.
In this article, we'll find out what causes earthquakes, and we'll also find out why they can have such a devastating effect on us.
Shaking Ground
An earthquake is a vibration that travels through the earth's crust. Technically, a large truck that rumbles down the street is causing a mini-earthquake, if you feel your house shaking as it goes by, but we tend to think of earthquakes as events that affect a fairly large area, such as an entire city. All kinds of things can cause earthquakes:
- volcanic eruptions
- meteor impacts
- underground explosions (an underground nuclear test, for example)
- collapsing structures (such as a collapsing mine)
But the majority of naturally-occurring earthquakes are caused by movements of the earth's plates, as we'll see in the next section.
We only hear about earthquakes in the news every once in a while, but they are actually an everyday occurrence on our planet. According to the United States Geological Survey, more than three million earthquakes occur every year. That's about 8,000 a day, or one every 11 seconds!
Earthquakes have caused a great deal of property damage over the years, and they have claimed many lives. In the last hundred years alone, there have been more than 1.5 million earthquake-related fatalities. Usually, it's not the shaking ground itself that claims lives -- it's the associated destruction of manmade structures and the instigation of other natural disasters, such as tsunamis, avalanches and landslides.