Because of the elastic properties of Earth materials (rocks) and the presence of the Earth's surface, four main types of seismic waves propagate within the Earth. Compressional (P) and Shear (S) waves propagate through the Earth’s interior and are known as body waves. Love and Rayleigh waves propagate primarily at and near the Earth's surface and are called surface waves. Wave propagation and particle motion characteristics for the P, S, Rayleigh and Love waves can be demonstrated using a single slinky.
By attaching 5 slinkys to a wood block 5 people can hold the ends of the 5 slinkys (stretched out in different directions to about 3-4 m each) while one person holds the wood block. The person holding the block and can generate P or S waves (or even a combination of both) by hitting the wood block with a closed fist or causing the block to move quickly up and then down or left and then right. The purpose of this demonstration is to show that the waves propagate in all directions in the Earth from the source (not just in the direction of a single slinky).
Students will be able to:
Seismic shadow zones have taught us much about the inside of the earth. This shows how P waves travel through solids and liquids, but S waves are stopped by the liquid outer core.
The wave properties of light are used as an analogy to help us understand seismic-wave behavior.
The shadow zone is the area of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves. The different phases show how the initial P wave changes when encountering boundaries in the Earth.
The shadow zone results from S waves being stopped entirely by the liquid core. Three different S-wave phases show how the initial S wave is stopped (damped), or how it changes when encountering boundaries in the Earth.
Seismic waves travel at different speeds through different materials. In this 2-layer model two wave fronts leave an impact at the same time but the lower layer is faster.
Seismic waves travel a curving path through the earth due to changes in composition, pressure, and temperature within the layers of the Earth.
Animation shows the race between the direct seismic wave vs. the deeper, longer-path critically refracted seismic wave. Graph records the arrival times.
In this model of increasing velocity with depth, the critically refracted seismic rays speed up with depth as they pass 5 different velocity boundaries.
A video demonstration of how a slinky can be a good model for illustrating P & S seismic waves movement.
Video lecture on wave propagation and speeds of three fundamental kinds of seismic waves.
Working in both small groups and as a whole class, students investigate the classic Earth science analogy: "Seismic waves radiate outward from an earthquake's epicenter like ripples on water". A discrepant image connects the unfamiliar concept of the spreading out of seismic waves to the more familiar scenario of ripples on water radiating outwards in all directions after a droplet falls onto a pool.
Earthquakes create seismic waves that travel through the Earth. By analyzing these seismic waves, seismologists can explore the Earth's deep interior. This fact sheet uses data from the 1994 magnitude 6.9 earthquake near Northridge, California to illustrate both this process and Earth's interior structure.
This poster combines a visualization of ground motion resulting from the February 21, 2008 M 6.0 earthquake that occurred near Wells, NV, with the image of a faucet to illustrate a classic Earth science functional analogy: "Seismic waves radiate outward from an earthquake's epicenter like ripples on water".
Seismic waves from earthquakes ricochet throughout Earth's interior and are recorded at geophysical observatories around the world. The paths of some of those seismic waves and the ground motion that they caused are used by seismologists to illuminate Earth's deep interior.
An interactive website, where one can investigate the classic Earth science analogy; "Seismic waves radiate outward from an earthquake's epicenter like ripples on water".
jAmaSeis is a free, java-based program that allows users to obtain and display seismic data in real-time from either a local instrument or from remote stations.
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