What is an "earthquake"?

What is an "earthquake"?

Tom Jordan (Director, Southern California Earthquake Center (SCEC)) gives expert video advice on: What is the probability of a severe earthquake striking a major city?; Where do earthquakes most often occur?; What are the most common earthquake myths? and more...

An earthquake is any shaking of the ground - usually intense shaking of the ground - caused by either natural sources or by humans. The most common types of earthquakes are those caused by ruptures of geologic faults or earthquakes associated with volcanic activity.