1. An earthquake is a sudden movement of the earth's crust caused by the release of stress accumulated along geologic faults or by volcanic activity.
2. The first scientifically studied earthquake occurred in Lisbon, Portugal in 1755. Lakes were raised all over Europe and 70,000 people were killed.
3. The largest recorded earthquake in the world was a magnitude 9.5 in Chile on May 22, 1960.
4. The largest recorded earthquake in the United States was a magnitude 9.2 that struck Prince William Sound, Alaska on Good Friday, March 28, 1964. It killed 200 people, destroyed much of Anchorage and created tsunamis along the west coast of the United States.
5. The most destructive quake that has occurred in the United States was the 1906 quake in San Francisco. It is possible that 2,500 people were killed in that quake.
6. The most active fault zone is the United States is the San Andreas Fault. This fault zone runs up the west coast, and is not one major fault but rather a zone that has many segments. Every year, southern California has about 10,000 earthquakes. Most of them are so small they can barely be felt, but several hundred reach a magnitude of 3.0. Only about 15 -20 reach a magnitude of 4.0.
7. Earthquakes occur in the central portion of the United States also. Some very powerful earthquakes have occurred along the New Madrid fault in the Mississippi Valley.
8. From 1975-1995 there were only four states that did not have any earthquakes. They were: Florida, Iowa, North Dakota, and Wisconsin.
9. The intensity of an earthquake is measured using a Richter scale and it is recorded in a seismometer.
10. During an earthquake, people should move away from buildings if they are outside and into a doorway or under a table if they are inside. Most people die from being caught in a building collapse or from being hit by falling debris during an earthquake. Sometimes earthquakes can break gas lines or dump flammable materials causing fires and explosions.