Larry Braile, Purdue University braile@purdue.edu
, web.ics.purdue.edu/~braile
Sheryl Braile, Happy Hollow School
West Lafayette, IN
CSTA Conference, October 2009
Palm Springs, CA
This PowerPoint file: http://web.ics.purdue.edu/~braile/new/SeismicWaves.ppt

 Slinky – P, S, Rayleigh, Love waves;
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
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Reflection and transmission; energy carried by waves; elastic rebound/plate motions and the slinky; 5-slinky model – waves in all directions, travel times to different distances.
Human wave demo – P and S waves in solids and liquids.
Seismic wave animations – P, S, Rayleigh, Love waves; wave motion; wave propagation activity.
Seismograms – Viewing seismograms on your computer (AmaSeis software).
Seismic Waves software – Wave propagation through the Earth.

 Fundamental concept (worth spending time on)
 Different approaches for different settings or size of group
 Different learning styles
 Reinforce with more than one approach
 Demonstrations, animations and hands-on activities
 Use one or more approach for authentic assessment

Measuring Elasticity of a Spring
Standard
Spring
Mass
Length
of
Spring
Added
Mass
(g)
0
100
200
300
400
Spring
Extension
(cm)*
(adding masses)
0.0
3.7
7.7
11.4
15.3
Spring
Extension
(cm)*
(removing masses)
0.3
3.6
7.5
11.4
15.1
Wood
* Difference in length of spring before and after adding mass.

4
2
0
0
10
8
6
Elasticity of a Spring
16
14
12
Adding mass:
Removing mass:
1. Deformation (stretching) is proportional to applied force (mass).
2. Spring returns to its original shape
(length) when force is removed.
50 100 150 200 250 300 350 400
Added Mass (grams)

Slinky and human wave demo and wave tank and elasticity experiments: http://web.ics.purdue.edu/~braile/edumod/slinky/slinky.htm
http://web.ics.purdue.edu/~braile/edumod/slinky/slinky.doc
http://web.ics.purdue.edu/~braile/edumod/slinky/slinky.pdf

Characteristics of Seismic Waves
Table 2: Seismic Waves
Particle Motion Typical Velocity Type (and names)
P,Compressional
, Primary,
Longitudinal
S, Shear,
Secondary,
Transverse
Alternating compressions
(“pushes”) and dilations
(“pulls”) which are directed in the same direction as the wave is propagating (along the raypath); and therefore, perpendicular to the wavefront
Alternating transverse motions (perpendicular to the direction of propagation, and the raypath); commonly polarized such that particle motion is in vertical or horizontal planes
V
P
~ 5 – 7 km/s in typical Earth’s crust;
>~ 8 km/s in
Earth’s mantle and core; 1.5 km/s in water; 0.3 km/s in air
V
S
~ 3 – 4 km/s in typical Earth’s crust;
>~ 4.5 km/s in
Earth’s mantle; ~ 2.5-3.0 km/s in (solid) inner core
Other Characteristics
P motion travels fastest in materials, so the P-wave is the first-arriving energy on a seismogram. Generally smaller and higher frequency than the S and Surface-waves. P waves in a liquid or gas are pressure waves, including sound waves.
S-waves do not travel through fluids, so do not exist in Earth’s outer core
(inferred to be primarily liquid iron) or in air or water or molten rock
(magma). S waves travel slower than P waves in a solid and, therefore, arrive after the P wave.

Characteristics of Seismic Waves
L, Love,
Surface waves,
Long waves
Transverse horizontal motion, perpendicular to the direction of propagation and generally parallel to the
Earth’s surface
V
L
~ 2.0 - 4.5 km/s in the Earth depending on frequency of the propagating wave
Love waves exist because of the
Earth’s surface. They are largest at the surface and decrease in amplitude with depth. Love waves are dispersive, that is, the wave velocity is dependent on frequency, with low frequencies normally propagating at higher velocity. Depth of penetration of the
Love waves is also dependent on frequency, with lower frequencies penetrating to greater depth.
R, Rayleigh,
Surface waves,
Long waves,
Ground roll
Motion is both in the direction of propagation and perpendicular (in a vertical plane), and “phased” so that the motion is generally elliptical – either prograde or retrograde
V
R
~ 2.0 - 4.5 km/s in the Earth depending on frequency of the propagating wave
Rayleigh waves are also dispersive and the amplitudes generally decrease with depth in the
Earth. Appearance and particle motion are similar to water waves.

A simple wave tank experiment
– a ping pong ball is dropped onto the surface of the water; small floats aid viewing of the waves; distance marks on the bottom of the container allow calculation of wave velocity.

(also, see the 4-page slinky write-up at: http://web.ics.purdue.edu/~braile/edumod/slinky/slinky4.doc
)
 P and S waves
 Love and Rayleigh waves
 Wave reflection and transmission
 Elastic rebound
 Waves carry energy
 The five slinky model (waves in all directions and different travel times to different locations
– the way that earthquakes are located)

Seismic waves carry energy.
Observe the shaking of the model building when P and S waves are propagated along the slinky.

The 5-slinky model for demonstrating that seismic waves propagate in all directions and the variation of travel time with distance.

The human wave demonstration illustrating P and S wave propagation in solids and liquids.

Animation courtesy of Dr. Dan Russell, Kettering University http://www.kettering.edu/~drussell/demos.html
(Developed by L. Braile) http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm

Animation courtesy of Dr. Dan Russell,
Kettering University http://www.kettering.edu/~drussell/demos.html

Direction of propagation
Animation courtesy of Dr. Dan Russell,
Kettering University http://www.kettering.edu/~drussell/demos.html

Deformation propagates. Particle motion consists of alternating compression and dilation. Particle motion is parallel to the direction of propagation (longitudinal). Material returns to its original shape after wave passes.

Deformation propagates. Particle motion consists of alternating transverse motion. Particle motion is perpendicular to the direction of propagation (transverse). Transverse particle motion shown here is vertical but can be in any direction. However, Earth’s layers tend to cause mostly vertical (SV; in the vertical plane) or horizontal (SH) shear motions. Material returns to its original shape after wave passes.

Deformation propagates. Particle motion consists of elliptical motions
(generally retrograde elliptical) in the vertical plane and parallel to the direction of propagation. Amplitude decreases with depth. Material returns to its original shape after wave passes.

Deformation propagates. Particle motion consists of alternating transverse motions. Particle motion is horizontal and perpendicular to the direction of propagation (transverse). To aid in seeing that the particle motion is purely horizontal, focus on the Y axis (red line) as the wave propagates through it. Amplitude decreases with depth. Material returns to its original shape after wave passes.

You can download the animations separately to run more efficiently:
( http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm
).
A complete PowerPoint presentation on the Seismic wave animations is also available at: http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.ppt
Demonstrate the AmaSeis software for displaying and analyzing seismograms; software available at: http://bingweb.binghamton.edu/~ajones/
A tutorial on AmaSeis and links to seismograms that can be downloaded and viewed in AmaSeis available at: http://web.ics.purdue.edu/~braile/edumod/as1lessons/UsingAmaSeis/UsingAmaSeis.htm
The IRIS Seismographs in Schools program: http://www.iris.edu/hq/sis

24-Hour Screen Display
Extracted Seismogram
The AS-1 Seismometer
(developed by Alan Jones,
SUNY Binghamton, NY)

Teaching Modules and Tutorials: http://web.ics.purdue.edu/~braile/edumod/as1lessons/as1lessons.htm

From Alan Jones, SUNY, Binghamton http://bingweb.binghamton.edu/~ajones/
Cross Section
Through Earth
Stations for
Seismograms
Earthquake
* Wavefront
Ray Path
Seismograph
Ray Path is perpendicular to wavefront