Earthquakes happen when the parts of the Earth's crust called plates rub, scrape or bump against each other. About half a million earthquakes happen each day, but they are small or too far below the surface for people to feel them. Powerful earthquakes can be felt thousands of miles away and can cause landslides, floods and tsunamis, or tidal waves.
Earthquakes are rated based on their magnitude, which is the amount of energy they release. As of 2014, the largest earthquake in recorded history happened in Chile in May 1960. It had a magnitude of 9.5. The deadliest earthquake happened in China in 1556 and killed 830,000 people. The largest earthquake in the United States happened in Alaska in March 1964 and had a magnitude of 9.2. Alaska has the most earthquakes in North America, an average of 24,000 annually. Southern California has 10,000 earthquakes a year, most of which are never felt. Florida and South Dakota have the fewest earthquakes.
Earthquakes usually happen about 50 miles below the surface of the Earth. Some happen as far as 400 miles below the surface. The plates can move anywhere between 0.3 to 5.9 inches a year.
Earthquakes cannot be predicted, but one can take precautions and be prepared when it happens.