On April 1, 2014, there was no fooling about the magnitude 8.2 earthquake that occurred offshore of Chile. Several locations across the globe felt the ground shake and were placed under tsunami warnings. And then, there was a M7.6 aftershock. Did you feel these earthquakes? Or a better question… did Tyler Arboretum feel these earthquakes?
Let me back up and give a quick “Earthquake 101” tutorial. An earthquake is a sudden release of energy within the Earth’s crust that can cause destruction and may trigger tsunami formation. That energy travels throughout the Earth and across the globe, and it is released through two types of energy waves – P waves (or Primary waves) and S waves (Secondary waves). The P waves are the first to arrive at a location, and think of their movement as stretching a Slinky across the floor, and when you push forward on the Slinky, it compresses and expands the spring, and then when the energy dissipates, it returns to its normal state. Think of rocks compressing and expanding as the P waves move through the Earth (yes, rocks do that!). The S waves are the second ones to arrive. They take longer because they travel through the Earth as if they were a section of stretched rope that was flicked up and down on one end. The up-and-down wave form moves forward (ultimately), but gets there by doing an up-and-down motion along the length of the rope. If you want to learn more about earthquakes, check out these great general earthquake resources on the Pennsylvania Earth Science Teachers Association (PAESTA) website, and the US Geological Survey has a helpful image showing the differences between P waves and S waves.
OK, now that you are set on the basics of earthquake the motion and the energy waves that travel through the Earth, I have to introduce a couple of additional terms. Seismology is the scientific study of earthquake, a seismometer is the instrument that records these P and S waves, and a seismogram is the record we can see of when those energy waves arrive at a station and how intense they were (the Greek term for earthquake is seismos). There are numerous seismometers across the globe, constantly measuring any ground movement from the energy release. In fact, one of these seismometers is located right across the street from Tyler Arboretum at Penn State Brandywine! It is buried in the ground in a secret location on campus, but the image to the left shows the small silver device we have (before it was buried) that is mighty in what it can record!
Below is the seismogram (the digital data recording) that our seismometer puts out. Each horizontal line represents two hours of time. The first record below is a snapshot from the April 1st earthquake offshore from Chile and the second one is from the M7.6 aftershock. Can you see the energy “kick” from the P wave, the light blue right before the 0:00 time on the right in the first image? And then on the next line, there is a larger, dark blue “kick” from the arrival of the S wave. This data helps scientists do a little bit of math to then be able to go back and determine the location of the epicenter of the earthquake at the surface (the actual location, at depth, is called the focus of an earthquake).
Pretty impressive! So even though you and I did not feel any ground shaking, those energy waves from Chile certainly made it all the way here to Media!
Now who can forget the 2011 Virginia Earthquake that occurred on August 23, 2011, at 1:51 pm EDT? Yes, many of us did feel the Earth shake, and the Penn State Brandywine seismometer recorded those energy waves as well, in the image below (the X axis is distance in degrees latitude away from the epicenter, the Y axis represents how long it took the signal to arrive to these recording stations after the original energy release). Looking for more resources on the Virginia earthquake? Check out the PAESTA website as well.
So, let’s revisit the original question… has Tyler Arboretum ever experienced an earthquake? You bet! We have in the past, and we certainly aren’t done feeling the Earth move under our feet….