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How Animals Sense Earthquakes

They pick up on one of the waves we humans don’t feel

Ceres the red-ruffed lemur at the National Zoo

At the National Zoo in Washington D.C., Kyle the orangutan and Kojo the gorilla stopped eating and climbed to the top of a tree just ten seconds before the shaking began.

At the same time, the 64 flamingos started racing around and then huddled together.

And the red-ruffed lemurs sounded the alarm a full 15 minutes before the quake hit.

What do other animals pick up on that we humans can’t?

Most cases of animals picking up on a quake in advance aren’t days in advance, but usually seconds or minutes, and we now have a most likely explanation of what’s happening.

An earthquake sends out two waves, known as the P wave and the S wave.

According to the U.S. Geological Survey, an earthquake releases energy in the form of seismic waves. The fastest wave, and therefore the first to arrive at a given location, is called the P wave or compressional wave because it alternately compresses and expands material in the same direction it is traveling. The S wave is slower than the P wave and arrives next, shaking the ground up and down and back and forth.

The P wave, which is smaller and travels faster, is not felt by most humans. The S wave is the one we humans feel, and it’s the one that does the damage. But many non-human animals also feel the P wave, and that’s what they’re reacting to “before” the quake actually happens.

Seismologists have developed warning systems that also pick up on the P wave, and that’s how they can give advance warning seconds before the shaking begins. Some advance warning systems can detect P waves up to 90 seconds before the shaking.

That wouldn’t explain what the red-ruffed lemurs were reacting to a full 15 minutes before the shaking began yesterday – or indeed the earliest known case from Ancient Greece in 373 BCE, when rats, weasels, snakes and centipedes were seen leaving their homes several days before a quake hit the land. But it does explain most of the animal behavior that we hear about after most earthquakes.

Some of the more famous examples include:

* The elephants and monkeys who were seen moving to higher ground just before the Japan quake earlier this year.

* The reports of zebras banging their heads against zoo doors at a Chinese zoo just before the huge quake there in 2008. (Elephants started swinging their trunks, and peacocks all began screeching together five minutes ahead of the S wave and the shaking.)

* And animals, both wild and domestic, who seen literally heading for the hills in the islands of Southeast Asia just before the deadly tsunami struck there in December 2004. There were even reports of elephants in Thailand carrying tourists to safety before the coastlands were flooded.

Tsunamis are a different phenomenon. After all, a tsunami that’s set in motion by a quake in the ocean can take hours to hit the land, and is not accompanied by either an S or a P wave. What’s going on in that case must be something else altogether.

One possibility is that certain animals sense the earthquake itself, even if it’s thousands of miles away. We know that elephants pass the knowledge they’ve learned from generation to generation. A matriarch who has experienced a quake or tsunami may well have taught her young to head for higher ground whenever they feel the ground rumble. (And elephants have a particular ability to pick up low-frequency rumblings through their feet. Other animals, too, may have learned that when the elephants head for the hills, it’s a good idea to follow them.

There’s a lot we don’t know about what other animals do know.

One thing, though, that was easy to see yesterday was that those animals at the National Zoo were very frightened but unable to do what all their instincts were screaming at them to do: Get to safety – fast!