Earthquakes: What causes them, and why they're so destructive

You've seen the destruction that can be caused by an earthquake, and you may have even lived through one. You also know they can be deadly. But where does the mountain-moving force of an earthquake come from?

While you may think you're standing on solid ground, the earth beneath you isn't really stable at all. The earth's crust is made up of about 12 major techtonic plates that fit together like a big jigsaw puzzle. These huge slabs of land float on superheated magma, and constantly shift, bump and grind against one another.

It's there, along the seams, where earthquakes tend to happen.

When friction between the two plates is violent enough, seismic shockwaves ripple through the ground-- rattling everything that stands on it. The stronger and shallower the quake, the more violent the destruction.

The most violent type of earthquake is born in a subduction zone, where one techtonic plate is shoved beneath another. While one plate is forced downward into the mantle, the other jets upward-- often violently. This is the type of quake that rocked Nepal in May 2015.

When subduction happens under the ocean, it can create, giant, unstoppable waves called tsunamis-- like the ones that killed thousands in Japan and Indonesia.

On average, earthquakes kill about 10,000 people each year. Sometimes, numbers are far higher. The quake that hit Haiti in 2010 killed more than 300,000 people by some counts, making it one of the deadliest earthquakes on record.

It is estimated that there are 500,000 detectable earthquakes in the world each year. Of those, 100,000 of them are strong enough to be felt, and 100 cause damage. That's about .1 percent.

The magnitude of an earthquake is measured using the Richter Scale, which runs from zero to 10, with 10 being the strongest. Every whole number increase on the scale means 10 times more ground motion change.

In recorded history, the world has never experienced an earthquake that was a 10 on the Richter Scale, but scientists predict an average of one earthquake with a magnitude of 8 or higher every year.

The fact is, the earth's crust is restless and always on the move. You can't see earthquakes coming, but you can prepare for them.

Engineers are now designing stronger buildings, resilient enough to survive a direct hit. Scientists are crunching data to project the power of future quakes, and anticipate when and where they could strike next.

Right now, we can only estimate the probability an earthquake will occur. But perhaps one day, we will learn to predict them-- minimizing their destruction and saving countless lives. 

More: NationalGeographic.com

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