If you’ve ever experienced one, you know that an earthquake is kind of a big deal. Scientists are still trying to figure out how to predict them, and there’s buttloads of data to be gleaned from each occurrence that go toward this lifesaving goal.

Your students aren’t seismologists (yet), but with this easy peasy experiment, you can help them understand some of the important info that an earthquake can provide. Here, the smelly little nerds will learn about the difference in travel times of P waves and S waves during an earthquake, and how this info can be used to calculate your distance from the quake’s epicenter.

**Simulating A Hallquake**

For this Demo Science science demo, you’ll need three pieces of paper, a writing utensil, measuring tape, and a long, empty hallway.

Ask your students for names of cities; it doesn’t matter which cities, really, so just pick three. (If any of them suggest Valdivia, Chile, they get an A+ and can go home for the rest of the day.) Write one city on each piece of paper, then hang your “signs” in the hallway at different distances from your classroom door.

Make sure your fellow teachers know what you’re up to and their doors closed so your shenanigans won’t disrupt their classes. Then, take your class out into the hallway and ask for three volunteers. Designate one student as the earthquake epicenter, another as the P wave, and the third as the S wave. Have all three kids stand beside each other by the classroom door. Tell P Wave Kid to run, and S Wave Kid to walk, down the hall past the city signs at your prompt. Then, call “Earthquake!” and set them on their way.

Have P Wave Kid stop when he/she reaches the first city, and S Wave Kid stop when P Wave Kid does. Then, have the rest of your students measure P’s and S’s distance from Epicenter Kid. Bring ‘em all back and repeat the whole process, this time with P Wave stopping at city #2. Repeat again with P Wave stopping at the third city.

What do the students’ measurements show? Why is there a difference in how far the P and S waves made it?

**It’s A Sciencequake!**

P waves and S waves travel at different speeds because they contain different amounts of energy. Additionally, P waves can travel through both solid and liquid materials fairly easily, while S waves can only travel through solid materials. Knowledge of these properties allow us to calculate the travel times and distances of the P and S waves. This info, in turn, is crucial for seismologists when trying to determine a quake’s epicenter.

**Photo credit: Raymond Hitchcock via Foter.com / CC BY-SA**