How long does an earthquake last?

Road damage near Dee stream with failure of embankment fill. Inangahua earthquake, May 1968.

Road damage near Dee stream with failure of embankment fill. Inangahua earthquake, May 1968.

This depends on the size of the earthquake and the observer's distance from it, because earthquake waves spread out as they travel whilst becoming weaker.

A magnitude 6 earthquake several hundred kilometres away can be often be felt for 30–40 seconds. The actual duration of slip on the earthquake fault is usually quite brief — just a few seconds for a magnitude 6 for example. This is because the fault rupture spreads very quickly, so the whole process of faulting is over very quickly.

During the very largest earthquakes, fault rupture can continue for up to 5 minutes as the rupture spreads over a length of say 1000km. For these earthquakes very high levels of aftershocks mean that continuous ground shaking can be felt for some hours.