May 5 – Whole Lot A Shakin’ Goin’ On

Today’s Factismal: There were nearly 4,000 earthquakes today.

There was just a Mw 7.5 earthquake off of Papua New Guinea today. And there was a Mw 7.8 temblor in Nepal last week. And they aren’t alone; over the past week, there were nearly 30,000 earthquakes. But don’t worry. There were that many earthquakes the week before, too. And there will be that many next week as well. The fact is that every day there are 4,000 earthquakes and every year there are nearly one and a half million earthquakes across the globe.

One year of earthquakes across the world. (Image courtesy the USGS)

One year of earthquakes across the world. (Image courtesy the USGS)

These earthquakes happen because the Earth is very slowly cooling down. Radioactive decay in the mantle (the thick solid section between the liquid outer core and the crust) and solidification of the outer core create heat inside the Earth. That heat, plus a little “fossil heat” from the Earth’s formation, creates convection in the mantle. And the motion of the mantle drives motion of the Earth’s crust, breaking it into large rigid sections called plates. As the plates collide to form mountain ranges or scrape alongside in transform zones, they release energy as earthquakes.

The different layers of the Earth. Only the outer core is molten; everything else s solid!

The different layers of the Earth. Only the outer core is molten; everything else is solid!

And what a lot of energy they release! A magnitude 2.5 earthquake will give off enough energy to power a home for 14 hours, and there are nearly 1,300,000 earthquakes that large every year. Even better, the energy goes up much faster than the magnitude. A magnitude 4 earthquake gives off enough energy to power a home for 1.6 years. Fortunately, the number of earthquakes also decreases faster than the magnitude; there are only about 13,000 magnitude 4 earthquakes every year.

There are a lot more small earthquakes, but the big ones release a lot more energy!

There are a lot more small earthquakes, but the big ones release a lot more energy!

And that relationship between energy and magnitude is why we can’t prevent a large earthquake by triggering a lot of small ones. It takes about 33 magnitude 7 earthquakes to release the same energy as one magnitude 8. So let’s suppose that you live in a place where you get a magnitude 8 about once every hundred years. You’d need to have a magnitude 7 every three years to release the strain. Or you could do it with a magnitude 6 every month. Or a magnitude 5 every day. Or a magnitude 4 every 45 minutes. Or a magnitude 3 every minute. Obviously, this is not a good idea.

What is a good idea is keeping up with the most recent earthquakes using either the Rapid Earthquake Viewer or the USGS Earthquake Monitor. And please contribute to science by telling the USGS if you felt the earth move!
http://earthquake.usgs.gov/earthquakes/dyfi/

One thought on “May 5 – Whole Lot A Shakin’ Goin’ On

  1. Pingback: September 8 – How Thai The Moon | Little facts about science

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s