For many years, people all around the world have tried to predict or detect approaching earthquakes to prevent deaths and major disasters.
People have long looked for early indicators of impending earthquakes. For example, the ancient Chinese—and still some today—look for signs such as for instance, strange behaviors of animals or the sudden change in water levels. Methods like these, perhaps surprisingly, can be reliable at times. In 1975, for instance, the city of Haicheng was evacuated very quickly using these indicators; the warnings proved correct, ultimately saving hundreds of thousands of lives.
But, these methods can be unreliable because some offer no visible signs. For example, in 1976, 240,000 people died in the city of Tangshan because no warnings were given. Nowadays, more reliable indicators like the pattern of seismic waves in the ground are used to warn people of approaching earthquakes. Foreshocks, or mild tremors, are usually one indicator of major quakes. The trouble is experts don’t always know whether some of these tremors are isolated events or signs of a bigger quake.
Based on historical records, a major earthquake could happen anytime. It is also reasonable to predict that during the next 100 years, there will be several major earthquakes. Detection of minor tremors, however, can shorten the odds of a big quake causing huge death tolls.
Predicting earthquakes is difficult, but detecting them is much easier than it used to be. Sensors are now able to transmit warnings of an earthquake to a target destination at the speed of light, which is much faster than the shock waves. Shock waves travel at the speed of sound. After the San Francisco earthquake of 1989, aftershocks could have been devastating because of unstable debris in the area. But thanks to the sensors, warnings were sent from the focus of the quake 60 miles away and reached people 25 seconds in advance of the shock waves, thus giving them enough time to get away.
Scientists know that nothing can stop movement of the earth's crust, but it might be possible to stop major quakes by causing smaller ones. The longer there aren’t earthquakes on an active fault line, the larger a quake will be when it does happen; thus, causing minor quakes will keep larger ones from occurring. But this trick is unlikely to be used in more densely populated areas. When it has been tested, the minor earthquakes produced did not always happen in the places they were expected to happen.
Methods for detecting earthquakes have changed throughout the years. Scientists hope to one day develop ways to prevent more major quakes and save increased number of lives.
[Source: The Kingfisher Young People's Book of Planet Earth]