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Understanding Earthquakes
By: Brooke Delucci,
Courtney Stamps,
Maria Johnson,
Jordan Anglin
What are Seismic Waves
 Seismic waves are the waves of energy caused by the
sudden breaking of rock within the earth or an
explosion. They are the energy that travels through
the earth and is recorded on seismographs.
(Japan Earthquake)->
Seismic Waves
 Not all waves are created equal!
 You need to be able to see the specific “faces” that each
wave can have, based on three important characteristics:
frequency, wavelength, and amplitude.
 Frequency is a measurement of how many cycles can
happen in a certain amount of time… cycles per second.
 Wavelength is defined as the distance from a particular
height on the wave to the next spot on the wave where it
is at the same height and going in the same direction.
 Amplitude is a measure of how big the wave is.
Defining Waves
Amplitude (energy of the wave)
Wavelengths (length of the waves)
Defining Waves
Transverse Waves
 Transverse waves are the
waves that have the classical
wave shape everyone thinks of
when they imagine a wave.
 Particles of the medium move
perpendicular to the direction the
transverse wave itself is moving.
Different Seismic Waves
 The are many different seismic
waves, but all of basically of four
types:
1.
Compressional or P (for primary)
2.
Transverse or S (for secondary)
3.
Love
4.
Rayleigh
 Body waves travel through the interior of
the Earth. They create ray paths refracted by
the varying density and modulus (stiffness)
of the Earth's interior. The density and
modulus, in turn, vary according to
temperature, composition, and phase.
 Surface waves are analogous to water
waves and travel along the Earth's surface.
They travel slower than body waves.
Because of their low frequency, long
duration, and large amplitude, they can be
the most destructive type of seismic wave.
They are called surface waves because they
diminish as they get further from the
surface.
Compressional Waves (P waves)
• P waves are also known as compressional waves, because of
the pushing and pulling they do. Subjected to a P wave,
particles move in the same direction that the wave is moving
in, which is the direction that the energy is traveling in, and is
sometimes called the ‘direction of wave propagation’.
• This is the fastest kind of seismic wave, and, consequently,
the first to 'arrive' at a seismic station.
• Usually people can only feel the bump and rattle of these
waves.
• http://www.geo.mtu.edu/UPSeis/images/Pwave_animation.gif
Transverse Waves (S waves)
 This is the second wave you feel in an earthquake.
 An S wave is slower than a P wave.
 S waves move rock particles up and down, or side-toside--perpendicular to the direction that the wave is
traveling in (the direction of wave propagation).
 Transverse waves are always characterized by
particle motion being perpendicular to wave motion.
 http://www.geo.mtu.edu/UPSeis/images/Swave_animation.gif
Love Waves
 The first kind of surface wave is called a Love wave,
named after A.E.H. Love, a British mathematician who
worked out the mathematical model for this kind of
wave in 1911.
 It's the fastest surface wave and moves the ground
from side-to-side. Confined to the surface of the
crust, Love waves produce entirely horizontal motion.
 http://www.geo.mtu.edu/UPSeis/images/Love_animat
ion.gif
Rayleigh Waves
 Rayleigh wave, named for John William Strutt, Lord
Rayleigh, who mathematically predicted the existence of
this kind of wave in 1885.
 A Rayleigh wave rolls along the ground just like a wave
rolls across a lake or an ocean. Because it rolls, it moves
the ground up and down, and side-to-side in the same
direction that the wave is moving.
 Rayleigh waves are the slowest of all the seismic wave
types.
 As a Rayleigh wave passes, a particle moves in an elliptical
trajectory that is counterclockwise.
http://www.geo.mtu.edu/UPSeis/images/Rayleigh_animation.gif
When the earth quakes…
• Every earthquake sends
out an array of seismic
waves in all directions.
• Recordings of seismic
waves from earthquakes
gave us the first clues
about the earth’s
composition. When
traveling through the
earth, seismic waves
frequently pass through
materials that alter the
speed of the waves.
Earths Structure:
Crust
• Two different types of crust: thin oceanic crust that underlies the ocean basins and
thicker continental crust that underlies the continents.
• Each type is made up of different types of rock causing the waves to travel in
various paths and speeds depending on the material they are passing through.
• Oceanic crust is composed mostly of basalt which is a sedimentary rock allowing
waves to travel easily resulting more destruction on the surface.
• Continental crust is mostly granite, a igneous rock type, which is of a much lower
density allowing it to “float” on the deeper layer of higher density material called
the mantle
• From about 10 to 200 km is the lithosphere region of the crust which is formed of
lithosphere plates that are floating on the mantle.
Discontinuity Boundary
• There is a distinct difference
between the outer shell of the
earth and the denser mantle, the
surface between the two is
known as the Mohorvicic
Discontinuity or Moho.
• The Moho was detected by a
sharp increase downward in the
speed of waves at a certain depth.
• The observations were made
during a 1909 earthquake.
• This is considered to be the lower
boundary of the crust.
The Mantle
 Within the mantle there is a steady increase
of temperature as depth increases known as
the geothermal gradient. This gradient is
responsible for the different rock behaviors
which form the boundaries between the
upper mantel and the lower mantle.
 The materials in the mantle are aluminum,
silicon, iron, magnesium, and oxygen. These
rocks and minerals are all of the denser
materials called peridotite.
 Upper Mantle: Comprised of a temperature
cool enough to causing rocks to be brittle
enough to break under stress and produce
earthquakes. As the rocks break energy is
produced causing waves to distribute in all
directions.
Mantle Continued
 Lower Mantle: Has a much higher heat level causing the rocks to
be soft and flow when subject to stress instead of breaking.
Although soft, the rock here is not yet molten causing it to be
plastic like.
 This part of the earth is also referred to as the asthenosphere
which is partially molten material that flows but is not a liquid.
The Core
 The core is earth's source of internal heat
because it contains radioactive materials
which release heat as they break down
into more stable substances.
 S waves inability to travel through the
core suggests that at least the outer core
is a liquid. The temperatures here are
adequate to melt the iron-nickel alloy
making up the Earth’s core .
 The inner core is a solid even though its
temperature is higher than the outer
core. Tremendous pressure produced by
the weight of the overlying rocks forces
the atoms to be so tightly packed that a
liquid state cannot occur.
 At 660 km Mesosphere begins where the
pressure become so great that the
material can no longer flow.
How waves react in the earth
 When seismic waves hit a
surface (boundary)
between very different
materials they may
bounce off this surface
causing reflections,
refractions, and scattering
of the wave paths.
Reflection
 A seismic reflection occurs when a wave impinges on a change in rock
type (which usually is accompanied by a change in seismic wave
speed). Part of the energy carried by the incident wave is transmitted
through the material and part is reflected back into the medium that
contained the incident wave.
 In seismology, reflections are used to prospect for petroleum and
investigate Earth's internal structure.
 The amplitude of the reflection depends strongly on the angle that
the incidence wave makes with the boundary and the contrast in
material properties across the boundary
Refraction
 Refraction: When seismic waves pass through different
types of materials their speed is altered and consequently
their path through the materials may be bent causing
refraction. Refraction may occur at a distinct boundary like
reflection, but it also occurs when the material changes
slowly.
 All paths through the earth tend to bend upward. This is a
result of refraction because materials deeper in the earth
conduct seismic waves faster than materials above.
 When a seismic wave hits any interface, there can be
reflection, refraction, scattering, or it can stop completely.
Scattering
 Scattering is a general physical process
where waves are forced to deviate from a
straight trajectory because of a nonuniform medium that it must pass through.
 Reflections that undergo scattering are
often called diffused reflections because
the waves disperse in all directions.
Epicenter
 The epicenter of an earthquake is the point on the Earth's surface directly
above the underground area where the rock breaks which is called the
focus of the earthquake.
 The intensity of ground shaking depends on distance from the epicenter
and on the type of bedrock underlying the area.
 In general, loose unconsolidated sediment is subject to more intense
shaking than solid bedrock
 When an Earthquake occurs, seismic waves are emitted from the focus
(=hypocenter) there are several paths that it can take through the earth
before emerging again at the surface.
Plate Tectonics
 All plates are moving in different directions at
different speeds.
 2 to 10 centimeters per year about the speed that
fingernails grow.
 The place where two plates meet is called a plate
boundary.
 The name of the boundary depends on the way they
move in relation to each other.
3 Types of Movement
 Convergent Boundaries: crashing
 Divergent Boundaries: pulling apart
 Transform Boundaries: sideswiping
Cause of earthquakes, volcanoes, oceanic trenches,
mountain range formation, and many other geologic
phenomenon.
Convergent Boundaries
 Two plates moving
toward each other. A
very slow “collision.”
 Sometimes the plate
sinks under another
causing a subduction
zone.
 The subducting plate breaks into smaller pieces that
become locked in place before suddenly moving to
generate large earthquakes.
 The South American Plate is being lifted up creating
the Andes mountains.
Types of Convergence
-Trenches, volcanic arc, and mountains
-Island volcanic arcs and trenches
-Mountain ranges
Divergent Boundaries
 Two plates are moving apart.
 New crust is created by magma pushing up from the mantle.
 The pulling apart causes a rift in the plates and can cause
volcanoes to form mostly underwater.
 Mid-Atlantic Ridge in Iceland.
Transform Boundaries
 The zone between two plates sliding horizontally past each
other.
 They are sometimes marked by linear valleys were rock has
been ground up by sliding.
 Most are found on the ocean floor.
 The most famous land one is the San
Andreas Fault zone in
California.
San Andreas Fault
 1,300 km long
 Cuts through 2/3 of
California.
 The west slice is slowly
moving north.
 The sliding causes
several earthquakes.
What is Fracking?
 The process of drilling down
and creating tiny explosions
to shatter and crack hard
shale rocks to release the
gas inside.
 Water, sand and chemicals
are injected into the rock at
high pressure which allows
the gas to flow out to the
head of the well.
Why is Fracking Such a Big Deal?
 Most of the water used for
fracking is collected from a
well and processed.
However, there are some
concerns that chemicals can
escape sometimes and find
their way into our drinking
water.
 The other big concern with
fracking is that it causes
small Earth tremors.
Does Fracking Cause Earthquakes?
 http://www.youtube.com/watch?v=3GPWZfNHeNM
Where is the New Madrid Fault?
 The New Madrid Fault system
extends 120 miles southward
from the area of Charleston,
Missouri, and Cairo, Illinois,
through New Madrid and
Caruthersville, following
Interstate 55 to Blytheville and
on down to Marked Tree,
Arkansas. It crosses five state
lines and cuts across the
Mississippi River in three
places and the Ohio River in
two places.
Major Concerns with the New Madrid
Fault
 Many are concerned that
with recent earthquakes
around the world that they
have caused the New
Madrid plates to shift.
 2nd highest risk area in the
United States for an
earthquake.
 3% chance of another major
earthquake in the area in
the year 2040.
Earthquakes In Arkansas
 December 16, 1811 – 7.7
magnitude earthquake in
northeast Arkansas with a
7.0 magnitude aftershock
earthquake that followed.
 January 5, 1843 – 6.3
magnitude earthquake in
northeast Arkansas.
 April 30, 2003 – 4.0
magnitude earthquake in
Blytheville.
 February 10, 2005 – 4.1
magnitude earthquake in
northeast Arkansas.
 May 1, 2005 – 4.2
magnitude earthquake in
northeast Arkansas.
 February 28, 2011 – 4.7
magnitude earthquake in
central Arkansas.
Last Earthquake In Arkansas
 There are small earthquakes
in Arkansas almost every
day.
 Many are attributing them
to fracking.
 The last one recorded was
on June 15, 2012 at 1:23 pm.
 It was a 2.2 magnitude
earthquake so more than
likely they are not felt.
What To Do In An Earthquake
 Get in a doorway.
 If you can’t get in a
doorway get under a desk
or a large piece of
furniture.
 Don’t go down a stairway
because the stairs may
collapse.
 http://www.youtube.com/
watch?v=I2eqRYxOef0
References
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http://www.bbc.co.uk/news/uk-14432401
http://8020vision.com/2011/04/17/congress-releases-report-on-toxic-chemicals-used-in-fracking/
http://www.treehugger.com/culture/burning-tap-water-and-more-gasland-exposes-the-natural-gas-industry.html
http://www.youtube.com/watch?v=3GPWZfNHeNM
http://earthquake.usgs.gov/earthquakes/states/arkansas/hazards.php
http://earthquake.usgs.gov/earthquakes/states/historical_state.php
http://earthquake.usgs.gov/earthquakes/eqarchives/last_event/states/states_arkansas.php
http://www.youtube.com/watch?v=I2eqRYxOef0
http://room1halcombeschool2012.blogspot.com/2012/02/earthquake-practice.html
http://activerain.com/blogsview/2562810/the-california-shakeout-2011-biggest-earthquake-drill-in-history
http://www.scchealth.org/docs/ems/docs/prepare/newmadrid.html
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http://boingboing.net/2011/03/14/geologist-explains-s.html
http://en.wikipedia.org/wiki/Seismic_wave
http://www.geo.mtu.edu/UPSeis/waves.html
http://www.geo.mtu.edu/UPSeis/images/P-wave_animation.gif
http://www.physicsclassroom.com/class/waves/u10l1c.cfm
http://www.geo.mtu.edu/UPSeis/images/Love_animation.gif
http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html
http://www.studyphysics.ca/newnotes/20/unit03_mechanicalwaves/chp141516_waves/lesson43.htm
References
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http://pubs.usgs.gov/gip/dynamic/understanding.html
http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml
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Krauskopf, Konrad. (2010). The Physical Universe. New York:The Mcgraw Hill Companies p. 551-560,
573-581.
http://faculty.weber.edu/bdattilo/shknbk/notes/insdearth.htm
http://www.visionlearning.com/library/module_viewer.php?mid=69
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