Why do earthquakes occur and how are they measured? Here are facts and Web sites that teachers and parents can use to educate themselves and kids about the Virginia-centered earthquake that rocked the East Coast of the United States today.
Here is some information on plate tectonics, the theory that continents, mountains, volcanoes and earthquakes are created when vast geological plates in the Earth’s outer layer move and collide.
In January 2010 a powerful earthquake struck Haiti; it measured 7.0 on the Richter scale, one way that scientists measure quakes, and left more than 200,000 people dead. A Chilean earthquake a month later rated as an 8.8 on the Richter scale. The earthquake in Japan last March that triggered a devastating tsunami was measured at 8.9.
What do those rankings really mean? To understand how earthquakes are rated, go to this Scholastic Web site. There you will learn about how the measuring scale for earthquakes works. Here are some comparisons, according to Scholastic:
9.0 — Causes complete devastation and large-scale loss of life.
8.0 — Very few buildings stay up. Bridges fall down. Underground pipes burst. Railroad rails bend. Large rocks move. Smaller objects are tossed into the air. Some objects are swallowed up by the earth.
7.0 — It is hard to keep your balance. The ground cracks. Roads shake. Weak buildings fall down. Other buildings are badly damaged.
6.0 — Pictures can fall off walls. Furniture moves. In some buildings, walls may crack.
5.0 — If you are in a car, it may rock. Glasses and dishes may rattle. Windows may break.
Are recent earthquakes connected, even if they aren’t on the same geographical plates? According to National Geographic, there is a theory that says it is possible. Read about it here.
Earthquakes sometimes trigger tsunamis, a word that comes from the Japanese word for harbor wave. They are not huge waves that ride on top of the surface of the ocean.
They are, rather, huge waves created by some undersea disturbance--an earthquake or volcanic eruption--that travel in all directions from the point of that disturbance. The principle is the same as the ripples you see if you throw a rock into water.
But these waves can travel in the open water as fast as 450 miles per hour. As they approach the shoreline, where the waters are much less deep, the ocean bottom pushes them up to a great height, sometimes as high as 100 feet.
It has long been said that the state at the highest risk of a tsunami is Hawaii. Hawaii is struck about once a year, with a particularly damaging one every seven years.
According to FEMA, Alaska is also at high risk, and the states of California, Oregon and Washington are hit with a damaging tsunami about every 18 years.