Making Waves: Seismic Waves
Activities and Demonstrations
Larry Braile, Purdue University
braile@purdue.edu,
web.ics.purdue.edu/~braile
Sheryl Braile, Happy Hollow School
West Lafayette, IN
sjbraile@gmail.com
CSTA Conference,
October 2011
Pasadena, CA
This PowerPoint file: http://web.ics.purdue.edu/~braile/new/SeismicWaves.ppt
Seismic Waves
Slinky – P, S, Rayleigh, Love waves;
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.
Why use several approaches for teaching
about seismic waves?
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
Elasticity – a property of materials that results
In wave propagation and earthquakes
Measuring Elasticity of a Spring
Added Spring Spring
Mass Extension Extension
(g) (cm)* (cm)*
Standard (adding (removing
masses) masses)
Spring
Length
0 0.0 0.3
PVC Pipe
of
Spring
100 3.7 3.6
200 7.7 7.5
Mass
300 11.4 11.4
400 15.3 15.1
Wood
* Difference in length of spring before and after adding mass.
Elasticity of a Spring
Stretching (length - original length, cm) 16
14 Adding mass:
Removing mass:
12
10
8
6
1. Deformation (stretching) is
4 proportional to applied force (mass).
2. Spring returns to its original shape
2 (length) when force is removed.
0
0 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
Type (and Particle Motion Typical Velocity Other Characteristics
names)
P,Compressional Alternating VP ~ 5 – 7 km/s in P motion travels fastest in materials,
, Primary, compressions typical Earth’s so the P-wave is the first-arriving
Longitudinal (“pushes”) and dilations crust; energy on a seismogram. Generally
(“pulls”) which are >~ 8 km/s in smaller and higher frequency than
directed in the same Earth’s mantle and the S and Surface-waves. P waves in
direction as the wave is core; 1.5 km/s in a liquid or gas are pressure waves,
propagating (along the water; 0.3 km/s in including sound waves.
raypath); and therefore, air
perpendicular to the
wavefront
S, Shear, Alternating transverse VS ~ 3 – 4 km/s in S-waves do not travel through fluids,
Secondary, motions (perpendicular typical Earth’s so do not exist in Earth’s outer core
Transverse to the direction of crust; (inferred to be primarily liquid iron)
propagation, and the >~ 4.5 km/s in or in air or water or molten rock
raypath); commonly Earth’s (magma). S waves travel slower
polarized such that mantle; ~ 2.5-3.0 than P waves in a solid and,
particle motion is in km/s in (solid) therefore, arrive after the P wave.
vertical or horizontal inner core
planes
Characteristics of Seismic Waves
L, Love, Transverse horizontal VL ~ 2.0 - 4.5 km/s Love waves exist because of the
Surface waves, motion, perpendicular to in the Earth Earth’s surface. They are largest at
Long waves the direction of depending on the surface and decrease in
propagation and frequency of the amplitude with depth. Love waves
generally parallel to the propagating wave are dispersive, that is, the wave
Earth’s surface 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, Motion is both in the VR ~ 2.0 - 4.5 km/s Rayleigh waves are also dispersive
Surface waves, direction of propagation in the Earth and the amplitudes generally
Long waves, and perpendicular (in a depending on decrease with depth in the
Ground roll vertical plane), frequency of the Earth. Appearance and particle
and “phased” so that the propagating wave motion are similar to water waves.
motion is generally
elliptical – either
prograde or retrograde
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.
Seismic waves and the slinky
(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.
Wave animations
Seismic Wave
animations
(L. Braile)
http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm
The “people wave” (Dan Russell):
Animation courtesy of Dr. Dan Russell, Kettering Univ.
http://www.kettering.edu/~drussell/demos.html
Dan Russell animations – Rayleigh
wave Direction of propagation
Animation courtesy of Dr. Dan Russell,
Kettering University
http://www.kettering.edu/~drussell/demos.html
Compressional Wave (P-Wave) Animation
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.
Shear Wave (S-Wave) Animation
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.
Rayleigh Wave (R-Wave) Animation
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.
Love Wave (L-Wave) Animation
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
IRIS Seismographs in Schools program: http://www.iris.edu/hq/sis
IRIS Wave Visualizations:
http://www.iris.edu/hq/programs/education_and_outreach/visualizations
USGS/SCEC SAF EQ Simulations:
http://earthquake.usgs.gov/regional/nca/simulations/shakeout/
IRIS AmaSeis
Software
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
The Seismic Waves
program
From Alan Jones, SUNY, Binghamton
http://bingweb.binghamton.edu/~ajones/
Earthquake
Cross Section
Through Earth
* Wavefront
Ray Path
Stations for
Seismograms Seismograph
Ray Path is perpendicular
to wavefront
Earthquake Time T1
Cross Section
Through Earth
* Wavefront
Ray Path
Stations for
Seismograms Seismograph
Ray Path is perpendicular
to wavefront
Earthquake Time T2
Cross Section
Through Earth
* Wavefront
Stations for Ray Path
Seismograms Seismograph
Ray Path is perpendicular
to wavefront
Earth’s
interior
structure and
seismic
raypaths that
are used to
determine the
Earth
structure.
http://www.iris.edu/hq/
files/programs/educati
on_and_outreach/less
ons_and_resources/i
mages/ExplorEarthPo
ster.jpg