Earthquake Waves

Earthquake Waves

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Earthquake Waves Or, Why are they saying all those nasty things about Rahleigh? Following the "Primer" is an activity to show the difference between P and S-Waves and how Earthquakeologists use them to determine the epicenter...

Earthquake wave Primer : Earthquakes travel in four different ways, or waves types. They are: 1.

P-Wave: These are called 'P' for Primary Wave. They are the ones that travel fastest and thereby are usually "felt" first. They are basically sound waves that travel thru the earth from the epicenter of an earthquake. Physics types know this as a longitudinal wave. It "shakes" things in the same direction it travels. For example, if a P-Wave is traveling West to East, all the things in the way, like people and buildings, will oscillate or move back and forth in the West-East direction. Similar to a long straight line of bumber cars! The one in the rear hits the first one and it hits the one in front of it and so on and so on. After each collision, the car bounces back to its original position only to be hit and bumped forward again. Some properties? a. FAST! They can travel up to 20 times the speed of sound in air! b. Usually noticed like, "I heard the earthquake coming!" This is because it IS, indeed, a sound wave. Most often it isn't noticed tho. c. Very little, if any, damage.

2.

S-Wave: These Secondary Waves are much slower and much more destructive than P-Waves. They are transverse waves. This means they make the earth vibrate perpendicularly to the direction of the wave travel. Not getting it? Think of a rope loosely held by two people. One person starts moving his/her/its hand up and down rapidly. Notice the "wave" in the rope goes from person 'A' to person 'B' while the rope itself simply vibrates up and down - perpendicular to the direction between the two people. This wave causes damage due to its configuration. It causes buildings to be thrust upward from the ground then the ground drops out from under it as the wave travels by.

3.

Rayleigh Wave: This is a combination P and S-Wave. It's analogous to an ocean wave. It's both longitudinal AND transverse. It's hard to envision, but look at the diagram below. The surface, while being told to vibrate forward and backward in the direction of the wave is also told to vibrate up and down perpendicular to the direction of the wave. Got it? The result is the surface moving in a vertical circular path - back and forth AND up and down. The Rayleigh wave is particularly damaging because it tells structures to move in two directions at once.

4.

Love Wave: Not a scary sounding wave, right? Damaging, yes! This one is sorta a Rayleigh Wave on its side. It tells the surface to move forward and backward AND left and right at the same time, sorta like a surface circle. Also, very damaging.

The Activity : Have class in the hallway. Have two earthquake waves volunteers - the P-Wave has to run or AT LEAST walk FASTand the S-Wave walks slowly. Set three or four kids up at random recorded distances down the hallway to represent towns or states or countries, your choice. Now, the P and S volunteers start at the epicenter around a corner of the hallway out of sight from the recorders. At a sound, or the drop of a ball or some other symbolic signal, the P-Wave RUNS around the corner and

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Earthquake Waves

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down the hall while the S-Wave walks. It's important that they each keep a constant speed on their respective journeys. As each reaches the "city" person, time is recorded by a stopwatch person.

Analysis : Now, back in the classroom, data is shared. I like the kids to construct a full data chart with distances between cities, times of each P and S-Wave, and can calculate the location of epicenter. Using simple V = d/t, velocity = distance divided by time, they should be able to deduce from the arrival times at the 3 or 4 cities of each wave where they started.

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