The shifting of tectonic plates often causes shuddering and shaking of the Earth's crust, particularly in areas near active fault lines like those in California. Japan, which rests on the notorious "Ring of Fire" fault line, experiences more than 2,000 tremors every single year.
Earthquakes may be so mild that only sophisticated instruments detect them. Or they can be so powerful that they violently shake the ground, causing everything from soil to cement to ripple like waves on a pond, tearing huge gashes in what was a seemingly solid surface only moments earlier.
Yet earthquakes alone aren't typically what kill people — instead, collapsing buildings crush, trap and suffocate you. When this happens in heavily populated areas, tens of thousands of people may die.
In January 2010, a magnitude 7.0 quake struck Haiti, a poor country with many ramshackle buildings. After the dust had settled, more than 200,000 people were dead. Some estimates topped 300,000, making it one of the deadliest earthquakes in history.
Even if you live an in area where construction is meant to withstand earthquakes, you probably don't want to be around when one hits. Our best building materials can only take so much abuse before they crumble under the might of a tectonic shift.