What are Earthquakes?
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The shaking or trembling caused by the sudden release of energy after the shifting of tectonic
plates
Usually associated with faulting or breaking of rocks
Continuing adjustment of position results in aftershocks. These are sometimes as
big as the initial quake
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What is the Elastic Rebound Theory?
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Explains how energy is
stored in rocks
– Rocks bend until the
strength of the rock
is exceeded
– Rupture occurs and
the rocks quickly
rebound to an
undeformed shape
– Energy is released in
waves that radiate
outward from the
fault
The Focus and Epicenter of an Earthquake
• The point within
Earth where
faulting begins is
the focus
• The point directly
above the focus
on the surface is
the epicenter
Seismographs
record earthquake
events
Where Do Earthquakes Occur and How Often?
~80% of all earthquakes occur in the circum-Pacific belt
– most of these result from convergent margin activity
– ~15% occur in the Mediterranean-Asiatic belt
– remaining 5% occur in the interiors of plates and on
spreading ridge centers
– 150,000 quakes strong enough to be felt are recorded yearly
The Economics and Societal Impacts of EQs
• Buildings collapsehomelessness
• Fire from gas pipe bursts
• Tsunamis follow in coastal
areas
• Ground failure-slides
• Poor countries take longer
to rebuild and other
tragedies result (Haiti:
cholera, rapes)
Damage in Oakland, CA, 1989
What are Seismic Waves?
• Response of solid/liquid rock
material to the arrival of energy
fronts released by rupture
• Two types:
– Body waves
• P and S-primary and secondary
– Surface waves
• R and L
Body Waves: P and S waves
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Body waves
– P or primary waves
• fastest waves
• travel through solids,
liquids, or gases
• compressional wave,
material movement is
in the same direction
as wave movement
– S or secondary waves
• slower than P waves
• travel through solids
only
• shear waves - move
material
perpendicular to
wave movement
Surface Waves: R and L waves
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Surface Waves
– Travel just below or along the ground’s surface
– Slower than body waves; rolling and side-to-side
movement
– Especially damaging to buildings
How is an Earthquake’s Epicenter Located?
Seismic wave behavior
– P waves arrive first, then S waves, then L and R
– Average speeds for all these waves is known and put on a
chart
– After an earthquake, the difference in arrival times at a
seismograph station can be used to calculate the distance
from the seismograph to the epicenter.
How is an Earthquake’s Epicenter Located?
• Time-distance graph
showing the average
travel times for P- and
S-waves.
• The farther away a
seismograph is from
the focus of an
earthquake, the longer
the interval between
the arrivals of the Pand S- waves
How is an Earthquake’s
Epicenter Located?
• Three seismograph
stations are needed to
locate the epicenter of an
earthquake
• A circle where the radius
equals the distance to the
epicenter is drawn
• The intersection of the
circles locates the
epicenter
• TRIANGULATION!
An Earthquake’s “Focus”
• The focus of an earthquake is the point
beneath Earth's surface where rock breaks
under stress and causes the earthquake
How are the Size and Strength of an Earthquake Measured?
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Modified Mercalli Intensity Map
– subjective measure of the kind of damage
done and people’s reactions to it
– isoseismal lines identify areas of equal
intensity
– 1994 Northridge, CA earthquake,
magnitude 6.7
How are the Size and Strength of an Earthquake Measured?
• Magnitude up to 18
– Richter scale
measures total
amount of energy
released by an
earthquake;
independent of
intensity
– Each increase is
equivalent to ten
times the previous
whole number; e.g.
an 8 is ten times
worse than a 7 and
100 times worse
than a 6.
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THE MERCALLI SCALE- based on observing effects from 1-12 not on a seismometer
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I. Instrumental Not felt by many people unless in favourable conditions.
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II. Feeble Felt only by a few people at best, especially on the upper floors of buildings. Delicately suspended objects
may swing.
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III. Slight Felt quite noticeably by people indoors, especially on the upper floors of buildings. Many do not
recognize it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a truck.
Duration estimated.
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IV. Moderate Felt indoors by many people, outdoors by few people during the day. At night, some awakened.
Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing
motor cars rock noticeably. Dishes and windows rattle alarmingly.
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V. Rather Strong Felt outside by most, may not be felt by some outside in non-favourable conditions. Dishes and
windows may break and large bells will ring. Vibrations like large train passing close to house.
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VI. Strong Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken;
books fall off shelves; some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight.
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VII. Very Strong Difficult to stand; furniture broken; damage negligible in building of good design and
construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly
designed structures; some chimneys broken. Noticed by people driving motor cars.
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VIII. Destructive Damage slight in specially designed structures; considerable in ordinary substantial buildings with
partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments,
walls. Heavy furniture moved
.IX. Ruinous General panic; damage considerable in specially designed structures, well designed frame structures
thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.
X. Disastrous Some well built wooden structures destroyed; most masonry and frame structures destroyed with
foundation. Rails bent.
XI. Very Disastrous Few, if any masonry structures remain standing. Bridges destroyed. Rails bent greatly.
XII. Catastrophic Total damage - Everything is destroyed. Total destruction. Lines of sight and level distorted.
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What are the Destructive Effects of Earthquakes?
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Ground Shaking
– amplitude, duration, and damage increases in poorly
consolidated rocks
Can Earthquakes be Predicted?
Earthquake Precursors
– changes in elevation or tilting of land surface, fluctuations in
groundwater levels, magnetic field, electrical resistance of the
ground. Animal behaviour
– seismic gaps
Can Earthquakes be Predicted?
Earthquake Prediction Programs
– include laboratory and field studies of rocks before, during,
and after earthquakes
– monitor activity along major faults
– produce risk assessments
EARTHQUAKES?
IN NOVA SCOTIA?????
Can Earthquakes be Controlled?
• Graph showing the
relationship between the
amount of waste injected
into wells per month and
the average number of
Denver earthquakes per
month
• Some have suggested
that pumping fluids into
seismic gaps will cause
small earthquakes while
preventing large ones
• Largest Earthquakes in the World Since
1900
• "12 of the Most Destructive Earthquakes“
• Mid-Plate Earthquakes: World of Earth
Science
• YouTube - San Francisco Earthquake of 1906
YouTube - 1989 San Francisco (Loma Prieta) Earthquake World Series footage
NBC News on 1989 San Francisco Earthquake - Oct., 1989! YouTube
• YouTube - SEP 19 1985 WORST EARTHQUAKE
MEXICO CITY
• YouTube - MEGA QUAKE KOBE 1995
• YouTube - Earthquake Destruction
• YouTube - Port-au-Prince Before and After
• Pat Robertson - Haiti's Pact w/ Devil Created Earthquake YouTube
• http://www.theglobeandmail.com/news/world/projectjacmel/haiti-one-year-later/haitis-babyboom/article1864286/
• YouTube - 2010 Earthquake (Magnitude 8.8) and Tsunami
hit Chile affecting the capital Santiago
• Japan Tsunami: Nuclear crisis worsens - YouTube
• The result of an earthquake is often a Tsunami. Tsunami is
Japanese for “Harbour Wave”
• The 2004 Indian Ocean earthquake was an undersea megathrust
earthquake that occurred at 00:58:53 on December 26, 2004, with an
epicentre off the west coast of Sumatra, Indonesia. The quake itself is
known by the scientific community as the Sumatra-Andaman
earthquake. The resulting tsunami itself is given various names,
including the 2004 Indian Ocean tsunami, Asian Tsunami,
Indonesian Tsunami, Boxing Day Tsunami, and, simply, The
Tsunami.
• The earthquake was caused by subduction and triggered a series of
devastating tsunamis along the coasts of most landmasses bordering
the Indian Ocean, killing nearly 230,000 people in fourteen countries,
and inundating coastal communities with waves up to 15 meters
(50 feet) high[5]. It was one of the deadliest natural disasters in
recorded history. Indonesia was the hardest hit, followed by Sri Lanka,
India, and Thailand.
• With a magnitude of between 9.1 and 9.3, it is the second largest
earthquake ever recorded on a seismograph. This earthquake had the
longest duration of faulting ever observed, between 8.3 and 10
minutes. It caused the entire planet to vibrate as much as 1 cm
(0.4 inches)and triggered other earthquakes as far away as Alaska.
• The plight of the many affected people and countries prompted a
widespread humanitarian response. In all, the worldwide community
donated more than $7 billion (2004 U.S. dollars) in humanitarian aid
• http://geology.com/articles/tsunamigeology.shtml
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Tsunami - Caught On Camera - P1 - YouTube
YouTube - 2004 Boxing Day Tsunami
YouTube - Strange fishes after Tsunami
YouTube - 2004 Boxing Day Tsunami
YouTube - Tsunami Footage - Penang Beach
[HD] Hereafter (2010) - Realistic Tsunami Scene
– YouTube
• Petra Nemcova: Surviving the Tsunami – YouTube