Feelin’ those Seismic Waves: Where was that quake?

Today we learned a lot about wave energy, and how it is related to earthquakes! The earth is made of layers; the top rigid layer, the lithosphere, is made of big sheets of rock called tectonic plates that float on top of the semi-solid asthenosphere in constant motion. Sometimes the plates get stuck on each other as they try to move past. This causes a buildup of elastic energy to be stored inside the rock. Eventually, the energy becomes too much to withstand and the plates move – this is an earthquake!

During an earthquake, the stored elastic energy is converted into kinetic energy in the form of waves. The waves propagate radially away from the focus and epicenter of an earthquake in all directions, which is why earthquakes can be felt in places far away from the epicenter. The fastest waves are called P-waves, or primary waves. These waves cause the first shakes we feel during an earthquake. S-waves, or secondary waves, propagate more slowly and arrive second. This concept is similar to when we count the time difference between lightning and thunder: we know the storm is close when the time between the lightning we see and the thunder we hear is close together.
In the case of earthquakes, the difference in arrival times can be used to triangulate the location of an earthquake’s epicenter. 

The class used seismograph data from 3 different cities (Denver, Chicago, and Houston) to calculate the arrival time interval of P- and S-waves, and then used this data to triangulate the location of the earthquake’s epicenter!