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Earthquakes and The Earth’s Interior
GLY 2010 - Summer 2013 - Lecture 14
1
Earthquake
• A sudden motion or trembling in the
Earth caused by the abrupt release of
slowly accumulated strain
• Strain is a change in the shape or
volume of a body as a result of stress
2
Seattle Earthquake, 2/28/01
• Movie of Microsoft
laboratory during
the earthquake
• Bill Gates was
giving a
presentation when
the quake occurred
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Focus, aka Hypocenter
• The initial rupture point of an
earthquake, where strain energy is
first converted to elastic wave energy
• The point within the Earth which is
the center of an earthquake
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Epicenter
• The point on the Earth's surface
that is directly above the focus of
an earthquake
5
Seismograph
• An instrument that detects,
magnifies, and records vibrations of
the Earth, especially earthquakes
• The resulting record is a seismogram
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Principle of the
Modern Seismograph
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Seismograph Animation
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Example
Seismogram
• Seismogram showing an earthquake - the
three different traces represent vibrations
in different directions
• First peaks are P waves, the second peaks
the S waves
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Microearthquake Seismogram
• Magnitude 1.8 quake, Japan
• N = North South
Orientation
• E = East-West Orientation
• Z = Vertical orientation
• This earthquake had only P
and S waves – surface
waves did not develop
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Moderate Earthquake Seismogram
• Magnitude 5.1 quake,
Norwegian Sea
• Note well-developed
surface waves (Love
and Rayleigh) which
have much greater
amplitude than the P
and S waves
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Richter Scale
• Numerical scale of earthquake
magnitude
• Devised in 1935 by the
seismologist C.F. Richter
• Defined local magnitude as
the logarithm, to the base 10,
of the amplitude in microns of
the largest trace deflection
that would be observed on a
standard torsion seismograph
at a distance of 100 km from
the epicenter
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Richter Scale Continued
• Measures the vibrational amplitude of
the earth in response to seismic waves
• Does NOT measure the energy release
13
Mercalli Scale
• Arbitrary scale of earthquake intensity,
ranging from I (detectable only
instrumentally) to XII (causing almost
total destruction)
• Based on human perception of the
earthquake, and damage observed after
the earthquake is over
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Number of Earthquakes/Year
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Isoseismal Map,
Loma Prieta
Earthquake,
1989
• A different view
• This earthquake
stopped the
World Series of
1989 for several
days
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Isoseismal Map of Prince
William Sound Earthquake, 1964
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Prince William Sound
Earthquake Damage
18
Anchorage
Building
• J.C. Penney building
• Very little damage to adjacent building, with
steel-frame construction
19
Energy Released by Earthquakes
• A great earthquake releases the
equivalent of 1 billion tons of TNT or
more, over a period of 1-2 minutes
• Most intense energy release per unit
time of any natural event, except
meteorite impact
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Catastrophic
Event
Energy
Releases
21
Areal Distribution of Earthquakes
22
Current US
Seismicity
• Current as of
7/9/13 at
14:25 EDT
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Seismicity of the United States, 1990 - 2000
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Seismicity of Alaska, 1990 - 2000
• Many earthquakes are associated with the Aleutian
Island Volcanic Arc, located above a subduction
zone
25
Seismicity of Hawaii, 1990 - 2000
• Most earthquakes on the the big island of Hawaii, associated
with Hot Spot volcanism
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Seismic Hazard – 2008 Map
• Peak Acceleration as a percent of g, with 2%
probability of exceedence in 50 years
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Western
Hemisphere
Seismic Risk
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Global Seismic Hazard
• Peak Acceleration as a percent of g, with 2% probability of
exceedence in 50 years
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Depth of Focus
• Earthquakes are classified by the depths of
their foci below the surface, as follows:
 Shallow 0-70 kilometers
 Intermediate 70-300 kilometers
 Deep 300-700+ kilometers
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Indonesia Earthquake
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Cause of Indonesian Earthquake
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Worldwide Recent Earthquakes
Tuesday, July 9, 2013 about 14:30 EDT
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Afghanistan Seismicity
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Earthquake Damage
• Earthquakes can cause damage in a number
of ways

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

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
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Building Collapse
Tsunami waves
Seiche waves
Landslides
Liquefaction
Fire
Disease
35
Building Collapse
• Izmit, Turkey
Earthquake, August 17,
1999
• Magnitude 7.4
• Click video to play
(with sound)
36
Collapse Studies
• Video from the Pacific
Earthquake Research
Center
• Shake Table
Demonstration of
Column Collapse
• From KRON, Channel
4, San Francisco, CA
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Tsunami
• Gravitational sea wave produced by any
large-scale, short-duration disturbance of
the ocean floor
• Disturbances caused principally by a
shallow submarine earthquake, but also
by submarine earth movement,
subsidence, or volcanic eruption
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Tsunami Animation
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Indonesian Tsunami
• Animation of tsunami movement across
Indian Ocean
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Tsunami Velocity
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Phuket, Thailand Video
• Home video of tsunami hitting
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Tsunami Damage
Steinbrugge Collection, Earthquake Engineering
Research Center, University of California, Berkeley
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Tsunami Harbor Damage
• Photo: Joseph Penzien, Steinbrugge Collection 44
Sri Lanka - Before
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Sri Lanka - After
46
Tohoku Earthquake, 3-11-11
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Seiche
• Free or standing-wave oscillation of the
surface of water in an enclosed or semienclosed basin (as a lake, bay, or harbor)
48
Landslides
• Earthquakes may trigger mass movement
of rock and sediment on unstable slopes
• Damage is most likely to occur after fire
removes vegetation, or clear-cutting of
forests
49
Quake Triggered Landslide Damage
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Landslide Damage, Continued
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House Destroyed by Landslide
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Public Policy
• Rebuilding allowed if no immediate threat
of injury or death
• Liability waiver mandatory
53
Liquefaction
• Liquefaction is a physical process that takes
place during some earthquakes that may
lead to ground failure
• As a consequence of liquefaction, soft,
young, water-saturated, well sorted, fine
grain sands and silts behave as viscous
fluids rather than solids
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Liquefaction Animation
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Liquefaction Failure
• Steinbrugge Collection
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Liquefaction Failure
• Steinbrugge Collection
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Fire
• Fire often does more damage than the earthquake
itself
 Underground pipelines and tanks rupture
 Above ground tanks may rupture or tip over, spilling
contents
 Water lines break
 Streets are blocked by debris
 Downed electrical lines may spark, setting off fires
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Fire
• Photo: Arnold Genthe, Steinbrugge Collection
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San Francisco, 1906
After the fire
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Managua, Nicaragua
• Photo: Karl V. Steinbrugge
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Tilted Gasoline Tank
• Steinbrugge Collection
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Disease
• Earthquakes can cut underground sewer and
water lines
• No drinking water
• Only available water is contaminated
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Broken Sewer Pipe, Chile
• Photo: Karl V. Steinbrugge
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Seismic Wave Types
• There are several types of seismic waves
• P(rimary) waves are the fastest
• S(econdary or shear) waves are the next
fastest
• L (surface) waves are the slowest
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P Wave Diagram
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S Wave Diagram
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P and S Wave Animation
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Surface Waves
• Travel only along the surface, not
through an object
• Generated by P and S waves interacting
with the surface
• Slowest type of seismic waves
• Cause the most damage to structures, and
generally cause the most deaths
69
Rayleigh Waves
Rayleigh waves are one type of surface waves
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Rayleigh Waves
• First described by Lord Rayleigh in 1885
• Rayleigh waves are created by rock particles moving
forward, up, backward, and down in elliptical orbits
oriented in a vertical plane that includes the direction
of propagation
• This produces a distinct rolling motion of the surface
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Love Waves
• Love waves are the other type of surface
wave
72
Love Wave Damage
• Love waves were named after A.E.H. Love, who first
described them in 1912
• The rock moves from side to side in a horizontal
plane at right angles to the direction of travel
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Seismic Wave Animation
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Reflection and Refraction
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Wave Reflection and Refraction
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Haitian Earthquake
• On January 12, 2010 a magnitude 7.0
earthquake struck with epicenter near Léogâne,
about 25 kilometers west of Port-au-Prince,
Haiti
• An estimated three million people were
affected by the quake
• Haitian Government reports estimated 230,000
people had died, 300,000 had been injured and
1,000,000 made homeless.
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Haiti Earthquake
Location
• Quake
location was in the vicinity of
the northern boundary where the
Caribbean tectonic plate shifts
eastwards by about 20 millimeters per
year in relation to the North American
plate.
• The location and focal mechanism suggest that the January
2010 quake was caused by a rupture of the EnriquilloPlaintain Garden fault, which had been locked for 250 years,
gathering stress
• The rupture was roughly 65 kilometers long with mean slip
of 1.8 meters
• Preliminary analysis of the slip distribution found amplitudes
of up to about 4 meters using ground motion records from all
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over the world
2010 Chile Earthquake
• The 2010 Chilean earthquake occurred off the coast of the
Maule Region of Chile on February 27, 2010
• The earthquake triggered a tsunami which devastated several
coastal towns in south-central Chile and damaged the port at
Talcahuano
• Tsunami warnings were issued in 53 countries, causing minor
damage in the San Diego area of California and in the Tohoku region of Japan, where damage to the fisheries business
was estimated at US $66.7M
• Seismologists estimate that the earthquake was so powerful
that it may have shortened the length of the day by 1.26
microseconds
• Precise GPS measurement indicated the telluric movement
moved the entire city of Concepción 3.04 metres to the west.
• The latest death toll as of May 15, 2010 is 521 victims 79
Chile Earthquake
Location
• The earthquake took place along
the boundary between the Nazca
and South American tectonic
plates, at a location where they
converge at a rate of 80
millimeters a year.
• This earthquake was
characterized by a thrust-faulting
focal mechanism, caused by the
subduction of the Nazca plate
beneath the South American.
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Chile Earthquake Effects
• Chile has been at a convergent plate boundary that
generates megathrust earthquakes since the Paleozoic
(500 million years ago)
• The segment of the fault zone which ruptured in this
earthquake was estimated to be over 700 km long
with a displacement of almost 10 meters
• GPSstudies indicate that the earthquake shifted
Santiago 28 cm to the west-southwest and moved
Concepción at least at least 3 meters to the west
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