Shake, rattle, and roar!

Have you ever experienced an earthquake? It can be scary, with deep rumbling noises and a whole lot of shaking going on. Earthquakes can cause buildings, bridges, and other structures to collapse.

The San Francisco earthquake of 1906 lasted only a minute or less. But it ruptured gas pipes and electrical lines, igniting massive fires.

The quake was felt from Los Angeles in the south to Coos Bay, Oregon, in the north. The Richter scale, which measures earthquake severity, was not devised until 1935. But geologists estimate that the 1906 quake was a 7.8. (The strongest quake ever recorded was a 9.5 in Chile in 1960.)

What causes earthquakes? Scientists believe that Earth's crust (rocky outer shell) is made up of huge rigid plates (see inset map). These rocky plates move about 1/2 inch to 4 inches a year. When they collide, shift, or move apart, the pressure or release of pressure can cause an earthquake.

States with the most quakes: I he map of the United States shows which states had the highest percentage of major quakes from 1974 to 2003. The color key enables you to quickly spot those states. The map gives the exact percentage of quakes for the 15 states with a percentage of 0.1% or greater.

The worst quakes: The U.S. map also shows the location of the 20 strongest earthquakes in U.S. history. (No. 1 is the most intense. See the red numbers on the map.)

QUESTIONS

1. Which state had the greatest percentage of major U.S. earthquakes during the years 1974 to 2003?

2. Which state had the second-highest percentage of major earthquakes during the same years?

3. Which tectonic plate or plates border the U.S. West Coast?

4. What effect might that have on the number of earthquakes on the U.S. West Coast?

5. Where does the North American Plate meet the Eurasian Plate?

6. How might that affect the number of earthquakes striking the U.S. East Coast?

7. Which state had 7.3% of all major earthquakes that hit the U.S. from 1974 to 2003?

8. Where did the strongest earthquake in U.S. history strike?

9. Three intense earthquakes hit which town in the southern U.S.?

10. The largest number of intense earthquakes hit which state?

1. Alaska

2. California

3. Pacific and North American plates

4. Since the West Coast is located where two plates meet, earthquakes are more likely to happen there.

5. The plates meet in the middle of the Atlantic Ocean

6. Since the fault line is so far out in the ocean, there is less likelihood of earthquakes on the U.S. East Coast.

7. Hawaii

8. Prince William Sound, Alaska

9. New Madrid, Missouri 

10. Alaska