What is an earthquake "fault"?

What is an earthquake "fault"?

Tom Jordan (Director, Southern California Earthquake Center (SCEC)) gives expert video advice on: What is a geologic fault?; What is the "Richter Scale" of an earthquake?; What is the "Moment Magnitude Scale" of an earthquake? and more...

An earthquake fault is a zone within the earth's crust where the rocks have been weakened by previous earthquakes, and where we expect earthquake slip to occur.