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Seismic Wave Types

By Edited Nov 13, 2013 0 0

What does an earthquake feel like?

Earthquakes are intimidating forces of nature that are very hard to predict. If I were sitting at my desk and an earthquake hit me there would be quite a few different shakings I would feel. Different seismic wave types are responsible for these different ground shakings. When an earthquake occurs, there are two different seismic wave types that I would feel. The first waves that would hit me are called P waves. These P waves, or body waves, travel through the Earth’s body, not on the surface. They are able to travel through solids, liquids, and gasses. P waves change the volume of the solid, liquid, or gas through a series of contractions and expansions. It’s very possible that I won’t even feel the P waves if the earthquake isn’t large enough because they occur beneath the Earth’s surface. Overall, the first seismic wave type that would hit would be P waves, or body waves, which I may or may not feel depending on the magnitude of the earthquake.

The next seismic wave type that would hit me would be S waves. The time between the P waves and S waves can vary, but for the sake of argument let’s say there’s a two-minute gap. S waves, or surface waves, travel along the surface of the Earth and are responsible for most of the damages caused by earthquakes. These surface waves can be subdivided into two different types of waves, Rayleigh waves and Love waves. Depending on the earthquake, you could feel one type or both types of waves. Love waves are faster than Rayleigh waves and move in a snakelike fashion, so if I was at my desk it would feel like the earth is shaking. Rayleigh waves would come next and are similar to ocean waves, thus they would create rolling sensations or swaying in a tall building (Love waves can produce swaying as well). Overall, that’s what I would experience if I were sitting at my desk.  

If my friend were to be further away from the epicenter than me, or where the earthquake struck, then his experience would be a little different. As the seismic waves types move away from the focus in a spherical fashion, they lose steam the further they go. So although I could’ve been knocked to the ground by the quake, he could’ve felt a less violent sensation and would not be knocked to the ground. Also, because the P and S waves travel at different speeds, there would be a greater interval between when the P and S waves struck, possibly around three minutes. (Note that seismic instruments, such as a seismograph, can measure this S-P interval.) In conclusion, my friend would feel a weaker shaking as well as a longer gap between the P and S waves.  

A little side note, in 2003 I experienced the San Simeon earthquake that had a magnitude of 6.5. I was in a movie theater when the quake struck. We were watching the preview for Cold Mountain during a scene when there was a large explosion and that’s when it hit. At first I was like, “Whoa!! When did the Fremont install such a great sound system?” And then the shaking continued. My friends and I all looked down the row to see if someone was shaking our seats. Finally, someone in the audience yelled, “Earthquake!” The light bulb clicked on and we all scrambled outside. Looking back on it, I realize that I never felt the P waves. Also, the shaking was similar to one of those foot massage seats at a fair where you put in fifty cents and it massages you by vibrating. Therefore, I can deduce that those waves were Love waves. Fortunately or unfortunately, I did not feel or see any Rayleigh waves occur. Anyways, that’s my personal experience with an earthquake, feel free to comment and share your own experience.

The information geologists have gathered about the two different seismic wave types allow us to have earthquake preparedness. Obviously, earthquake insurance can be purchased from insurances companies, but the best way to prepare for an earthquake is to know what to do when one occurs as well as having a safety plan. If you’re inside when an earthquake hits, it’s best to crawl under a sturdy table and grab onto one of its legs. If you are inside and close to a door, it’s best for you to run outside as far away from anything tall. This will provide you with safety from anything falling. Also, if you’re outside that’s usually a good sign. As mentioned, just try and stay away from any tall objects. Predicting earthquakes is merely a dream now, so it’s necessary to pack some food, water, and basic supplies to survive if a large earthquake strikes. Overall, the P and S seismic wave types radiate out from an earthquake and can cause tremendous amounts of damage. This can be avoided by having basic safety plans and earthquake preparedness. 



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