An earthquake is the shaking of the surface o the earth. it could cause great dangerous and damage to all the living and non-living things on Earth. it would not last very long, usually it will last 30 second to a minute or even just a couple second, but for the very large Earthquakes it will last 5 minutes or even longer.
Earthquakes are formed when the surface of the earth is moving. (Crustal change)
Here is some really significant example from past: in 2008-5-12 14:28 earthquake occurred China WenChuan, for magnitude of 8.0for around 2 minutes plus really strong aftershock, causes 69227 people died and 17923 people missing and 845200000000.00 RMB(169040000000.00 dollars) ; in 1976-7-28 earthquake occurred China Tangshan for magnitude of 7.8 for 23 second, causes 242769 people died 708851 people hurt and almost 4000 kid became an orphan and 3000000000.00 RMB(600000000.00) after 30 years in 2012 the earthquake visit that city again and the scientist say it's because of the earthquake in 30 years before. 1920-12-16 earthquake occurred HaiYuan, China for magnitude 8.5 for 12 minutes, and really strong aftershocks of three years, causes 288200 people died and 300000 people hurt
from this example up there we could see that earthquakes can cause really powerful damages to the Earth and the living and non-living things on the Earth.
learn more in this website:https://www.en.wikipedia.org/wiki/Earthquake