What are earthquakes and why do they happen in certain parts of the world?

The Earth’s crust is broken up into several pieces called tectonic plates, which fit together like a jigsaw puzzle.

This formation is “mostly stable, but along the edges they are moving,” Columbia University geophysicist Michael Steckler said.

"Earthquakes typically start at the end of a long cycle of building up stress along a fault," says San Diego State University professor Matthew Weingarten.

Earthquakes typically occur along edges of tectonic plates. But their impacts may be felt in a broader region.

Earthquakes that occur in the ocean don’t always attract attention, but those that occur close to where people live can cause deaths and injuries, most often from collapsed buildings.

What should you do if you’re in a building when earthquake shaking begins?

In regions of the world with known active fault lines, including California and Japan, building codes are often designed to withstand earthquakes. But that’s not true everywhere.

In many countries, including the United States, if you’re inside when an earthquake occurs, it’s advisable to drop to the ground, cover your head — for example, by crawling under a desk or other sturdy structure — and hold onto that structure, he said. Try to avoid areas near glass windows and don’t use building elevators.

If you’re outside, try to remain in an area away from buildings or trees that could fall.

Depending on the location, there may be secondary hazards triggered by earthquakes, such as landslides, fires or tsunamis.

AP video by Javier Arciga

AP produced by Javier Arciga