Editing P wave (section)

===As an earthquake warning===

Advance earthquake warning is possible by detecting the nondestructive primary waves that travel more quickly through the Earth's crust than do the destructive [[S wave|secondary]] and [[Rayleigh wave]]s.

The amount of warning depends on the delay between the arrival of the P wave and other destructive waves, generally on the order of seconds up to about 60 to 90 seconds for deep, distant, large quakes such as the [[2011 Tohoku earthquake and tsunami|2011 Tohoku earthquake]]. The effectiveness of a warning depends on accurate detection of the P waves and rejection of [[ground vibrations]] caused by local activity (such as trucks or construction). [[Earthquake early warning]] systems can be automated to allow for immediate safety actions, such as issuing alerts, stopping elevators at the nearest floors, and switching off utilities.