What is a fault line

A fault line is a large crack in between two tectonic plates. In an earthquake being on a fault line can be rather dangerous because a huge crack could open up underneath you. Fault lines are also areas often affected by earthquakes.

One of the largest fault lines in the world is the San Andrea's fault line which runs roughly 1300 km through California America. The coordinates of America are 48.1667° N, 100.1667° W.  The more the tectonic plates move and collied the more fault lines are created. Here is a picture of a fault line for you.