People who have lived through an earthquake describe it as one of the worst experiences of their lives. When one strikes, people are usually too shocked to move. The ground, which was a few moments before seemed so solid, suddenly beneath their feet like a trampoline. Pictures are shaken from the walls. If the earthquake is severe enough, the walls themselves may topple. Lives may be lost.
Measuring Earthquakes
The intensity of an earthquake is determined by a measure called the Richter scale. An earthquake measuring 4.0 is considered minor, causing little, if any, harm. One measuring 8.0 is more than 1,000 times as powerful; it can do immense damage. Another measure of the destructive power of an earthquake is the number of lives lost. One of the greatest natural disasters in history was the earthquake that struck China in 1556. The earthquake killed almost a million people.
What People Know About Earthquakes
Scientists who study the causes of earthquakes are called seismologists. They have learned a lot about these scary occurrences. We know that the earth’s crust or surface is made out of rock five or twenty miles thick. That crust is split into pieces. The separate pieces, or plates, fit break lines, which are known as “faults.” Heat from the earth’s inside puts pressure on these plates, causing them to move. Sometimes they rub against each other; at other times one plate may ride up over another (creating mountains!). These kinds of movements cause earthquakes.
Areas that lie along faults in the earth’s crust are especially vulnerable to earthquakes. But quakes can occur anywhere in the world. San Francisco lies on the San Andreas Fault, where the Pacific and North American plates meet. It has had two major earthquakes in the last century. The Pacific coast regions of Central and South America, where the Nazca and South American plates meet, have also suffered many earthquakes and will continue to do so.
Staying Safe
Unfortunately, we still do not know enough about earthquakes to be able to predict precisely when one will occur. We do, however, make sure that today’s buildings and bridges are strong enough to stand up to them. That is the reason why the 1989 San Francisco earthquake, which measured 6.9 on the Richter scale, took so few lives. But earthquakes are still to be feared. If you are caught in one, your first thought might be to flee to open space. Studies tell us, however, that if you are in a building, it is probably safer to stay inside. Look for shelter under a sturdy table or in a doorway.
