159171571 Seismic Waves

7/21/2019 159171571 Seismic Waves

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Making Waves: Seismic WavesActivities and Demonstrations

This PowerPoint file: http://web.ics.purdue.edu/~braile/new/SeismicWaves.ppt

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Seismic Waves Slinky – P, S, Rayleigh, Love waves;

Reflection and transmission; energy carried by

waves; elastic rebound/plate motions and theslinky; 5-slinky model – waves in all directions,travel times to different distances.

Human wave demo – P and S waves in solids andliquids.

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 propagationthrough the Earth.

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Why use several approaches for teachingabout seismic waves?

Fundamental concept (worth spending time

\=[-9i85o

n)

Different approaches for different settings or size ofgroup

Different learning styles

Reinforce with more than one approach

Demonstrations, animations and hands-on activities

Use one or more approach for authenticassessment

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Standard

Measuring Elasticity of a Spring

Added

Mass(g)

Spring

Extension(cm)*

(adding

masses)

Spring

Extension(cm)*

(removing

masses)

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

Wood

P V C P i p e

Mass

Length

of

Spring 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.

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10

12

14

16

r i g i n a l l e n g t h , c m )

Elasticity of a Spring

Adding mass:

Removing mass:

0 50 100 150 200 250 300 350 4000

2

4

6

8

Added Mass (grams)

S t r e t c h i n

g ( l e n g t h -

1. Deformation (stretching) is

proportional to applied force (mass).

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

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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

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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

VP ~ 5 – 7 km/s in

typical Earth’scrust;

>~ 8 km/s in

Earth’s mantle and

core; 1.5 km/s in

P motion travels fastest in materials,

so the P-wave is the first-arrivingenergy on a seismogram. Generally

smaller and higher frequency than

the S and Surface-waves. P waves in

a liquid or gas are pressure waves,

Characteristics of Seismic Waves

propagating (along t e

raypath); and therefore,

perpendicular to the

wavefront

water; 0.3 km/s in

air

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 horizontalplanes

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.

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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 de endent on

Characteristics of Seismic Waves

frequency, with lower frequenciespenetrating to greater depth.

R, Rayleigh,

Surface waves,

Long waves,Ground roll

Motion is both in the

direction of propagation

and perpendicular (in avertical 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 onfrequency of the

propagating wave

Rayleigh waves are also dispersive

and the amplitudes generally

decrease with depth in theEarth. Appearance and particle

motion are similar to water waves.

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A simple wavetank experiment

– a ping pong

ball is droppedonto the surfaceof the water;

viewing of thewaves; distance

marks on the

bottom of thecontainer allowcalculation of

wave velocity.

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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, S, Love and Rayleigh waves

Wave reflection and transmission

Elastic rebound

Waves carry energy

The five slinky model

Seismic waves carryenergy. Observe theshaking of the model

building when P and Swaves are propagated

along the slinky.

The 5-slinky model for demonstrating that seismicwaves propagate in all directions and the variation

of travel times to different locations – theway that earthquakes are located).

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The human wave demonstration illustrating P and S

wave propagation in solids and liquids.

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Additional PPTs (resonance model, slinky and model building,

iPhone accelerometers):http://web.ics.purdue.edu/~braile/new/Resonance.ppt

Resonance impulse video: http://web.ics.purdue.edu/~braile/new/DSCN0215.avi

Resonance frequencies: http://web.ics.purdue.edu/~braile/new/DSCN0112.avi

Shaking of model building: http://web.ics.purdue.edu/~braile/new/DSCN0220.avi

(Place videos in same folder as the PPT)

http://web.ics.purdue.edu/~braile/new/Accelerometer.ppt

Resonance frequencies: http://web.ics.purdue.edu/~braile/new/DSCN0112.avi

iPhone accelerometer: http://web.ics.purdue.edu/~braile/new/DSCN2846.avi

iPhone accelerometer 2: http://web.ics.purdue.edu/~braile/new/DSCN2844.avi



(Place videos in same folder as the PPT)

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Wave animations

Direction of propagation

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

The “people wave” (Dan Russell):

ttp: we . cs.pur ue.e u ~ ra eedumod/waves/WaveDemo.htm

Rayleigh wave

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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 itsori inal sha e after wave asses.

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Shear Wave (S-Wave) Animation

Deformation propagates. Particle motion consists of alternatingtransverse motion. Particle motion is perpendicular to the direction ofpropagation (transverse). Transverse particle motion shown here isvertical but can be in any direction. However, Earth’s layers tend to

cause mostly vertical (SV; in the vertical plane) or horizontal (SH) shearmotions. Material returns to its original shape after wave passes.

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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. Materialreturns to its original shape after wave passes.

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ove Wave (-Wave) Animation

Deformation propagates. Particle motion consists of alternatingtransverse motions. Particle motion is horizontal and perpendicular tothe direction of propagation (transverse). To aid in seeing that theparticle motion is purely horizontal, focus on the Y axis (red line) as the

wave propagates through it. Amplitude decreases with depth. Materialreturns to its original shape after wave passes.

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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 isalso 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 andv ewe n ma e s ava a e 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 (highly recommended) :

http://www.iris.edu/hq/programs/education_and_outreach/visualizations

USGS/SCEC SAF EQ Simulations:http://earthquake.usgs.gov/regional/nca/simulations/shakeout/

USGS EQ Simulations (Brad Aagaard): http://profile.usgs.gov/baagaard(highly recommended)

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The Quake Catcher Networkhttp://qcn.stanford.edu/

MEMS AccelerometerTime

Screen shot of 3-component

accelerometerrecords

(accelerograms oracceleration

seismograms)

Z (vertical)

Y (horizontal)

X (horizontal) A c c e l e r a

t i o n ( m / s 2

)

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24-Hour Screen Display

Extracted Seismogram

IRIS AmaSeis

Software

(developed by Alan Jones,

SUNY Binghamton, NY)

The AS-1 Seismometer

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

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The Seismic Wavesprogram

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

*Earthquake

Wavefront

Ray Path

Ray Path is perpendicular

to wavefront

Seismograph

Cross Section

Through Earth

Stations forSeismograms

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*

Earthquake

Wavefront

Ray Path

Ray Path is perpendicularto wavefront

Seismograph

Cross SectionThrough Earth


Time T1

*Earthquake

Wavefront

Ray Path

Ray Path is perpendicularto wavefront

Seismograph

Cross Section

Through Earth


Time T2

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Earth’sinteriorstructure and

seismicraypaths thatare used to

determine theEarthstructure.

http://www.iris.edu/hq/ files/programs/education_and_outreach/lessons_and_resources/images/ExplorEarthPo

ster.jpg

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159171571 Seismic Waves