Making Waves: Seismic Waves Activities and Demonstrations

Larry Braile, Purdue Universitybraile@purdue.edu, web.ics.purdue.edu/~braile

Sheryl Braile, Happy Hollow SchoolWest Lafayette, INCSTA Conference, October 2009Palm Springs, 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

Wood

PVC

Pip

e

Mass

SpringLength of Spring

Standard

Measuring Elasticity of a SpringAdded 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

* Difference in length of spring before and after adding mass.

Elasticity – a property of materials that resultsIn wave propagation and earthquakes

0 50 100 150 200 250 300 350 4000

2

4

6

8

10

12

14

16

Added Mass (grams)

Stre

tchi

ng (l

engt

h - o

rigin

al le

ngth

, cm

)Elasticity of a Spring

Adding mass:

Removing mass:

1. Deformation (stretching) isproportional to applied force (mass).

2. Spring returns to its original shape(length) when force is removed.

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

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.

Characteristics of Seismic 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.

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 seismicwaves 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

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

Seismic Wave animations(Developed by L. Braile)

http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm

Dan Russell animations – The people wave

Animation courtesy of Dr. Dan Russell, Kettering University

http://www.kettering.edu/~drussell/demos.html

Dan Russell animations – Rayleigh wave

Animation courtesy of Dr. Dan Russell, Kettering University

http://www.kettering.edu/~drussell/demos.html

Direction of propagation

Compressional Wave (P-Wave) Animation

Deformation propagates. Particle motion consists of alternatingcompression 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

The IRIS Seismographs in Schools program:http://www.iris.edu/hq/sis

24-Hour Screen Display

Extracted Seismogram

(developed by Alan Jones, SUNY Binghamton, NY)

IRIS AmaSeisSoftware

The AS-1 Seismometer

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

*Earthquake

Wavefront

Ray Path

Ray Path is perpendicular to wavefront

Seismograph

Cross SectionThrough Earth

Stations forSeismograms

The Seismic Waves program

From Alan Jones, SUNY, Binghamtonhttp://bingweb.binghamton.edu/~ajones/