Facts about Earthquakes
- Earthquakes strike suddenly, violently, and without warning at any time of the year and at any time of the day or night.
- Smaller earthquakes often follow the main shock.
- An earthquake is caused by the breaking and shifting of rock beneath the Earth’s surface. Ground shaking from earthquakes can collapse buildings and bridges; disrupt gas, electric, and phone service; and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive ocean waves (tsunamis).
- Most earthquake-related injuries result from collapsing walls, flying glass, and falling objects.
- Several thousand shocks of varying sizes occur annually in the United States, and 70 to 75 damaging earthquakes occur throughout the world each year. All 50 states and all U.S. territories are vulnerable to earthquakes. Where earthquakes have occurred in the past, they will happen again.
- California experiences the most frequent damaging earthquakes; however, Alaska experiences the greatest number of large earthquakes—most located in uninhabited areas.
- Earthquakes occur most frequently west of the Rocky Mountains, although historically the most violent earthquakes have occurred in the central United States.
- The largest earthquakes felt in the United States were along the New Madrid Fault in Missouri, where a 3-month-long series of quakes from 1811 to 1812 included three quakes larger than a magnitude of 8 on the Richter Scale. These earthquakes were felt over the entire eastern United States (over 2 million square miles), with Missouri, Tennessee, Kentucky, Indiana, Illinois, Ohio, Alabama, Arkansas, and Mississippi experiencing the strongest ground shaking.
- The Richter Scale, developed by Charles F. Richter in 1935, is a logarithmic measurement of the amount of energy released by an earthquake. Earthquakes with a magnitude of at least 4.5 are strong enough to be recorded by sensitive seismographs all over the world.
- It is estimated that a major earthquake in a highly populated area of the United States could cause as much as $200 billion in losses.