It detects a quake that has already started
Sensors close to an earthquake pick up its first waves and quickly estimate the stronger shaking that may follow. A warning can outrun those slower waves and reach people farther away first. If you are close to the epicenter, you may get little warning—or none at all.
Do not spend the warning checking your phone
Those few seconds are for one thing: protecting yourself. Move away from windows, do not run outside, and cover your head and neck. The same alert can automatically slow trains, open doors or pause sensitive equipment.
- Drop to your hands and knees
- Cover under sturdy furniture if you can
- Hold On until the shaking stops
After the shaking
Magnitude is only one clue. How a quake feels also depends on its depth, your distance, the soil beneath you and the building around you. Check the USGS shaking map and local reports for the fuller picture.