Activity
- Human Waves (PDF)
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Introduction
An earthquake generates a series of waves that penetrate the Earth and may travel either through the earth's interior (body waves) or near Earth's surface (surface waves). Each wave has a characteristic speed and style of motion (See graphic below). There are four basic types of seismic waves; two preliminary body waves (P & S) that travel through the Earth and two slower surface waves (Love and Rayleigh) that travel along the surface of the Earth. [More about seismic waves below.]
Building Response to Seismic Waves
Animation to characterize behavior of three seismic waves. The seismogram shows the arrival times of the three generalized waves. This highly simplified cartoon is intended to portray:
1) Timing of the seismic waves (P fastest)
2) The time (x-axis on the seismogram) it takes for the seismic waves to travel
from an earthquake about 80° away)
3) Different ways the seismic waves strike a building
(P = bump; S = shear; surface = rolling wobble).
This image just shows a single body-wave path through the Earth to avoid cluttering the image. Waves travel in all directions from an earthquake.
Direct Link to Seismic Building (Medium 1mb)
Direct Link to Seismic Building (Large 2mb)
Which motion might cause the most damage? (Answer: surface waves.)
La animacion se está disponible en Ingles y Español, sin embargo el texto en la pagina completa esta en Ingles.
Para informacion en español respecto a hondas sismicas ir a: One-Pager #5, “Explorando la Tierra Usando Sismología“
Direct Link to Real Trees-En Espanol (Medium 1mb)
Direct Link to Real Trees-En Espanol (Large 2mb)
More About Seismic Waves
The different types of energy waves shake the ground in different ways and also travel through the earth at different velocities. P waves travel most directly and are fastest. Here we look at single paths for each wave, but recognize that the seismic waves travel away from the earthquake or explosion in all directions at once. Plus, combinations, reflections, and diffractions produce many other types of seismic waves, but they can be left to the seismologists. For many classroom applications simply addressing P and S waves is enough, but it is also good to know about the destructive and convoluted surface waves. The figure below left and the PowerPoint presentation in the Resources link below show how the P & S waves travel.
House Shake Motion
A: P waves, or compressional waves, are seismic body waves that shake the ground back and forth in the direction that the wave is moving. P waves travel fastest and are generally felt first. They usually cause very little damage. [Figure from REV: http://rev.seis.sc.edu/definition.html]
B: S, or secondary waves or shear waves, are seismic body waves that shake the ground back and forth perpendicular to the direction the wave is moving.
C: Surface waves (not shown in the house images) roll the ground in a back-and-forth, up- and-down motion.
Resources
- A complete PowerPoint presentation that uses Seismic wave animations
- Why do seismic paths curve? Why don’t they just go straight? (PDF)
- “Exploring the Earth using Seismology“ (la versión en Castellano (Español)
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Animations By Jenda Johnson
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