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Recording earthquake waves.

Monday & Tuesday we used model seismographs to learn how different types of earthquake waves are recorded. We tested how the seismograph would react when we shook the desk from different directions, and at different distances from the seismograph. We also tested reaction to the amount of force applied when shaking the desk.

Wednesday we learned how to read a real seismogram using a copy of the 1964 Alaska earthquake seismogram recorded in Bellingham, WA. Students analyzed the recording, located the arrival time of the first P-wave, and identified aftershocks.

Friday the class learned how to use data from three seismograph stations to locate the epicenter of an earthquake.


Earthquake waves radiate outward in all directions from the earthquake source.

Vibrations from an earthquake can be recorded with a seismograph; a seismogram is the recording made by a seismograph.

The epicenter of an earthquake is the point on the earth’s surface directly above the focus, or point of origin, of the earthquake.

Scientists can use data from seismograms recorded at several locations to pinpoint the epicenter of the earthquake.


1. What happened when we changed the direction of our pounding?
Answer: When we tested parallel (P-waves) and vertical (Surface waves), the seismograph made poor recordings. Our seismograph only recorded the perpendicular S-waves, because that is what it is designed to do. So, scientists use three different seismographs in order to record all three waves, one machine each for P-, S-, and Surface waves.

2. What happened when we changed the distance of pounding from the seismograph?
Answer: the closer to an earthquake epicenter, the stronger the seismic waves will be. In other words, the waves have more amplitude when closer to the source.

3. What happened when we changed the force of our pounding?
Answer: The stronger the force of the earthquake, the stronger the seismic waves will be. In other words, the waves have more amplitude when they are created by stronger earthquakes.

4. Why do seismologists need data from three seismograph stations in order to locate the epicenter of an earthquake?
Answer: Scientist use the difference between the P- and S-wave arrival times to calculate how far away an earthquake is from a seismograph station. This can then be plotted on a map, by drawing a circle with a radius equal to the distance to the epicenter around the seismograph station. This is then repeated for the other two stations and the point where the three circles intersect is the location of the earthquake epicenter.




Epicenter: The point on the surface of the earth directly above the focus of an earthquake

Focus: The location where the rupture of an earthquake begins and energy is released.

P-Wave: A primary (compressional) earthquake wave that travels through the body of the earth; first to reach seismograph stations during an earthquake

S-Wave: A secondary earthquake wave; travels slower than a P-wave and is the second wave to reach seismograph stations during an earthquake. It travels through the earth in a series of crests and troughs.

Surface Wave: An earthquake wave that travels on or near the surface of the earth

Seismograph: An instrument that detects, records, and measures the vibrations produced by an earthquake Seismologist: A scientist that studies earthquakes

Seismogram: The record made by a seismograph; the paper on which earthquakes are recorded

: The study of earthquakes

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