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EARTHQUAKES
1988 Armenian Earthquake – Spitak Communications Building
USGS
EARTHQUAKES
Occur in all plate boundaries
Diverging
Converging
Continent/ocean (Subduction)
Ocean/ocean (Subduction)
Continent/continent (Collision)
Transform
PLATE BOUNDARIES
WORLD WIDE DISTRIBUTION OF EARTHQUAKES
Earthquakes Terms
 Focus – point
within the earth
where initial slip
is generated
 Epicenter – point
on the earth’s
surface directly
above the focus
 Seismic waves move outward
from focus
SEISMIC WAVES
P-WAVE (Primary)
 Fastest seismic
 Travels through liquids and solids inside
the Earth
 Compresses and expands in the direction
of wave movement.
Tasa
S-WAVE (Secondary)
 2nd fastest
 Travels through solids inside the earth
 Moves with a shearing motion
perpendicular to wave travel
TASA
SURFACE WAVES
 Slowest wave
 Travels on the earth’s surface
 Moves with an elliptical motion or shearing
 Potentially most destructive
TASA
Earthquake Waves
MEASURING EARTHQUAKES
TASA
Seismograph
SEISMIC WAVE – TRAVEL TIME
Amount of time
between P and S
waves are
directly related to
distance to the
epicenter
Tarbuck &Lutgens
LOCATING AN EARTHQUAKE
3 Seismic Stations Required
Press & Siever
MEASURING EARTHQUAKES
INTENSITY (EFFECTS)
 Modified Mercalli Intensity Scale
Measures damage produced by
an earthquake
 Useful for:
 historic quakes
 earthquake engineering
 pin-pointing damaged localities
Guiseppe Mercalli
1850-1914
What affects intensity?
 Amount of energy released in the
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earthquake
Distance from the epicenter
Type of bedrock
Population density
Building construction
1989 Loma Prieta Earthquake
USGS
MEASURING EARTHQUAKES
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MAGNITUDE (Wave Amplitude)
Richter Scale – based on largest amplitude of a
seismic wave from seismograph during an
earthquake
An increase by 1 in
magnitude equals 10x
increase in amplitude
Measure of the amount
of energy released
Energy released increases
32 x’s for each unit
Charles Richter
1900-1985
Earthquake Energy Equivalents
Education and Outreach IRIS Consortium: www.iris.edu
MEASURING EARTHQUAKES
MOMENT MAGNITUDE
 More accurate than Richter Scale
 Estimates total amount of energy released
 Takes into account several factors
 Displacement along fault
 Area of ruptured surface
 Strength of underlying rock
 More precisely measures large
earthquakes, similar magnitudes
as Richter for smaller quakes
 Can be verified by field studies of
fault displacement measurements
EARTHQUAKE HAZARDS
 Ground shaking
 Liquefaction
 Fire
 Subsidence &
uplift
 Landslides &
avalanches
 Tsunamis
Mexico City Earthquake, September 19, 1985
USGS
Earthquake Hazard
GROUNDSHAKING
 Strain accumulation
 One side of the fault is moving in
opposition to
the other side
of the fault
 Result: ground
cracks and
structures collapse
Mexico City Earthquake, 1985
Oklahoma University
Ground Shaking and Cracking
San
Francisco
Earthquake
1906
G.K. Gilbert
1992 - Landers, CA - 7.5 M Earthquake
Kobe, Japan
 January
17, 1995
 6.9M
Press & Siever
Kobe, Japan
 Expressway fell
on it’s side
 6308 killed
Press & Siever
Tohoku, Japan
March 11,2011
Magnitude 9.0
 401 aftershocks
 4 foreshocks
 18,000+ killed
Ground Shaking
Material Amplification
 Surface waves are relatively small in solid
crystalline bedrock
 Surface waves amplify (increase) in poorly
consolidated sediments
Prentice Hall
Mexico City Earthquake, 1985
City built on
lake
sediments
that
amplified
seismic
waves
1985 Mexico City Earthquake - M 8.1
Earthquake Hazard
LIQUEFACTION
 Sand grains saturated with water shake
 Sand grains are detached
 Sand is unable to support overlying weight
of buildings
Niigata, Japan
1964
Karl V. Steinbrugge
LIQUEFACTION
Marina District in San Francisco
Loma Prieta Earthquake – 1989 M 7.1
Nimitz Freeway
1989 Loma Prieta Earthquake – M 7.1
Dennis Laduzinski
Earthquake Hazard
FIRE
San Franscico, 1906
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Kobe, Japan 1995
Causes:
Gas mains break
Gas stoves, water heaters, etc. in homes
Inadequate water supply
Firefighters can’t reach fire
Blasting sometimes used to create a fire
break
Fire
San Francisco Earthquake 1906
 April 18, 1906
 5:15 am
 Shaking lasted
about 1 minute
 700-3000 killed
 8.3M estimated
 $400 million in
damages
(Image © Archive Photos)
Earthquake Hazard
SUBSIDENCE & UPLIFT
Alaska Earthquake 1964
Prince William
Sound
Fault Scarp
of 16 feet
USGS
Earthquake Hazard
LANDSLIDES & AVALANCHES
 Unstable material shaken loose
 Rock, sediment or ice
 Steep slopes
2002 Alaska Earthquake
Yungay, Peru
8M
earthquake
 20,000
killed in
Yungay
 50,000
more killed
elsewhere
Overlandy.com about 2003
Earthquake Hazard
TSUNAMIS
Seismic Sea Wave
Causes:
 Submarine landslide
 Fault displacement
 Volcanic eruption
TASA
Tsunami
Tsunamis
in the
Pacific
Hilo, Hawaii
April 1, 1946 – 159 Deaths
NOAA
Indian Ocean
Tsunami
NOAA
Natl. Inst. of Advanced Industrial
Science & Technology
Indian Ocean Tsunami
Dec. 26, 2004
Patong Beach, Phuket
Banda Aceh, Sumatra
Reuters
Banda Aceh, 2004 Tsunami
Japan, 2011 Tsunami
video2
video1
video2
HAZARD ASSESSMENT
 Develop understanding of the earthquake
source
 Determine earthquake potential
 Predict effects of
earthquakes
 Apply research
results
Coalinga, CA 1983 Earthquake
USGS
Shaking Hazard Map
World Seismic Hazard
Press & Siever
San Andreas
Fault
south of
San
Francisco
R.E. Wallace, USGS
EARTHQUAKE
PREDICTION (when)
verses
EARTHQUAKE
FORCASTING (where)
Earthquake Studies
 Tilt of rocks
 Swarms of micro
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earthquakes
Groundwater changes
Radio Waves
Creep verses locked faults
Foreshocks/Aftershocks
Animal behavior
and more . . .
Parkfield, CA - SAFOD
San Andreas Fault
Observatory at Depth
USGS
Parkfield, CA
Earthquake Capitol of the World
6M earthquakes - 21 year average
1881
1901
1922
1934
1966
1992 (4.5 M)
1994 (5 M)
2004!
Earthquake Probability
San Andreas Fault
Chinese Predict Haicheng
Earthquake February 1975
Prediction based on:
 Foreshocks
 Many large foreshocks before main event
 Animal Behavior
 Snakes came out of hibernation
 Rats scurried around
 Large farm animals behaved
differently near epicenter
Collapsed Factory
China Virtual Earthquake Museum
Chinese fail to predict Tangshan
Earthquake July 28, 1976
 2nd most devastating earthquake in history
(worst was also in China 1556, 830,000 died)
 8.2 M
 750,000 died
 No foreshock events
ChinaStock