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 2015
Sacramento, CA
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.
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Why use several approaches for teaching
about seismic waves?
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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
Mass
(g)
Spring
Extension
(cm)*
(adding
masses)
Spring
Extension
(cm)*
(removing
masses)
0
0.0
0.3
100
3.7
3.6
200
7.7
7.5
300
11.4
11.4
400
15.3
15.1
Standard
Spring
PVC Pipe
Length
of
Spring
Mass
Wood
* Difference in length of spring before and after adding mass.
Stretching (length - original length, cm)
Elasticity of a Spring
16
14
Adding mass:
Removing mass:
12
10
8
6
1. Deformation (stretching) is
proportional to applied force (mass).
2. Spring returns to its original shape
(length) when force is removed.
4
2
0
0
50
100
150
200
250
Added Mass (grams)
300
350
400
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
names)
Particle Motion
Typical Velocity
Other Characteristics
P,Compressional
, Primary,
Longitudinal
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
VP ~ 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
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, Shear,
Secondary,
Transverse
Alternating transverse
motions (perpendicular
to the direction of
propagation, and the
raypath); commonly
polarized such that
particle motion is in
vertical or horizontal
planes
VS ~ 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
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
VL ~ 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
VR ~ 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
wave energy. Distance marks
on the bottom of the container
allow calculation of wave
velocity. A stopwatch can be
used to time the wave travel
time to each distance –
calculate wave velocity.
Repeat measurements can
improve accuracy and allow
estimation of measurement
error. Slow motion video can
also be used to improve time
measurements. You can also
video with phone or camera.
Seismic waves and the slinky
(also, see the 4-page slinky write-up at:
http://web.ics.purdue.edu/~braile/edumod/slinky/slinky4.doc)
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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
Rayleigh wave propagation
Seismic Wave animations (L. Braile)
http://web.ics.purdue.edu/~braile/edu
mod/waves/WaveDemo.htm
Courtesy of Dr. Dan Russell, Penn State University
The “people wave” (Dan Russell):
Courtesy of Dan Russell, Penn St. Univ. http://www.acs.psu.edu/drussell/
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/
Quake Catcher Network – MEMS accelerometers: http://qcn.stanford.edu/
IRIS AmaSeis
Software
24-Hour Screen Display
Extracted Seismogram
The AS-1 Seismometer
(developed by Alan Jones,
SUNY Binghamton, NY)
Teaching Modules and Tutorials for educational seismographs:
http://web.ics.purdue.edu/~braile/edumod/as1lessons/as1lessons.htm
(in module 13, you can download real seismic data from past years and use
with the AmaSeis program on your computer even if you do not have a
seismograph)
IRIS educational seismographs web page:
http://www.iris.edu/hq/sis/resources/seismometers
The AS-1 is a portable effective classroom tool for teaching about earthquakes
and the instruments that record them. The AS-1 has been loaned to many
teachers through the Seismographs in Schools program. The AS-1 electronics
have recently been redesigned and production is currently underway!
EQ-1 Seismograph:
http://wardsci.com/product.asp_Q_pn_E_IG0018602_A_Vertical+School+Seis
mometer
TC-1 Slinky Seismograph: http://cgiss.boisestate.edu/bsu-network/
http://cgiss.boisestate.edu/construction-of-the-tc1/
http://tc1seismometer.wordpress.com/
Stream View- The helicorder screen now has the flexibility to display up to three
streams of data simultaneously. These can include a local educational seismometer,
a remote educational seismometer over the jAmaseis network (in true real-time), or
research-quality seismometers stored at the IRIS Data Management Center (in near
real-time). IRIS Seismographs in Schools information: http://www.iris.edu/hq/sis.
http://www.iris.edu/hq/programs/education_and_outreach/software/jamaseis
The Seismic Waves
program
From Alan Jones, SUNY, Binghamton
http://bingweb.binghamton.edu/~ajones/
Earthquake
Cross Section
Through Earth
Stations for
Seismograms
*
Wavefront
Ray Path
Seismograph
Ray Path is perpendicular
to wavefront
Earthquake
Cross Section
Through Earth
*
Time T1
Wavefront
Ray Path
Stations for
Seismograms
Seismograph
Ray Path is perpendicular
to wavefront
Earthquake
Cross Section
Through Earth
Stations for
Seismograms
*
Time T2
Wavefront
Ray Path
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