How do we know a fault exists?

Sometimes earthquakes leave surface evidence, such as surface ruptures or fault scarps (cliffs made by earthquakes).

Sometimes a large earthquake has broken the fault since instrumental recordings began in 1932.

Sometimes the fault produces small earthquakes that can be recorded with the denser seismographic network established in the 1970s.

What are the chances an earthquake could hit your favorite locations? Make a One-Step Earthquake Forecast here.
To see locations of current major earthquakes, go the Hazards Viewer and click on one of the Earth globes on the right hand side.
Risk Alert