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Earth Shattering
Quakes
Earth Science
Earthquake
 The vibration of Earth produced by
the rapid release of energy within
the lithosphere.
Elastic Rebound Hypothesis
  Earthquakes are produced when the
strength of a rock is exceeded, it breaks,
and then causes a sudden release of
stored energy called seismic waves.
Imperial Fault, CA
Elastic Rebound
Focus
  The point within the Earth where an
earthquake starts.
 Located along a fault beneath the surface
Epicenter
  The location on the surface directly
above the focus.
Faults
  Fractures in the Earth’s crust where
movement has occurred.
Normal Faults
  When the hanging wall block moves
lower than the footwall block
Area
under
fault
plane
Area above
fault plane
Normal Faults
Where is the footwall?
Reverse Faults
  When the hanging wall block moves
higher than the footwall block
 fault plane is between 30-90°
Reverse Faults
Thrust Faults
  When the hanging wall block moves
higher than the footwall block
 fault plane is <30°
Thrust Faults
Strike-Slip Faults
  When the movement is horizontal
and parallel to the fault
Strike-Slip San Andreas Fault
  1300 km fault in CA
  Displacement occurs
along 100-200 km long
segments
  Each fault segment
behaves differently
 Some segments slowly slip
(fault creep)
 Some segments regularly slip
in small earthquakes
 Some segments stay locked
for 100’s of years and
produce large earthquakes
San Andreas Fault
1906
San Francisco
8.3 earthquake
1989
Loma Prieta
7.1 earthquake
Seismic Waves
  Earthquakes produce body waves and
surface waves
 Body waves travel through Earth’s interior
 Surface waves travel on the Earth’s surface
P Waves
  Body waves that push (compress) and
pull (expand) rock in the direction
the waves travel.
P Waves
S Waves
  Body waves that shake particles at
right angles to the direction the
waves travel.
S Waves
Surface Waves
  When body waves reach the surface.
  Move slower than body waves
  Move side-to-side and up-and-down
  Larger than body waves & therefore more destructive
Surface Waves
Raleigh Waves
Surface Waves
Love Waves
Seismograms
  A record of ground motion produced
by a seismograph
Richter Scale (old school)
  Measurement based on the height of
the largest seismic wave (P, S, or
surface wave) recorded on a
seismogram.
 A tenfold increase in wave height equals
and increase of 1 on the Richter Scale
 For example, a M5.0 earthquake is 10
times greater than a M4.0 earthquake
Richter Scale (old school)
Moment Magnitude
(new school)
  Measurement based on the amount of
displacement that occurs along a fault.
  The seismogram
  The amount of movement along the fault
  The area of surface break
  The strength of the broken rock
Moment Magnitude
(new school)
Moment
Effects Near Epicenter
Number
Magnitude
per Year
< 2.0
Not felt
>600,000
2.0-2.9
Potentially perceptible
>300,000
3.0-3.9
Rarely felt
>100,000
4.0-4.9
Can be strongly felt
13,500
5.0-5.9
Can be damaging shocks
1,400
6.0-6.9
Destructive in built-up areas
110
7.0-7.9
Serious damage
12
≥ 8.0
Destroys communities
0-1
Modified Mercalli Scale
  Measurement based upon earthquake
INTENSITY in terms of the effects
at different locations
Modified Mercalli Scale
•  I. Not felt except by a very few under especially favorable conditions.
• 
II. Felt only by a few persons at rest, especially on upper floors of buildings.
•  III. Felt quite noticeably by persons indoors, especially on upper floors
of buildings. Many people do not recognize it as an earthquake.
• 
IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make
cracking sound.
• 
V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned.
•  VI. Felt by all, many frightened. Some heavy furniture moved; a few
instances of fallen plaster. Damage slight.
• 
VII. Damage negligible in buildings 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.
• 
VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse.
Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls.
•  IX. Damage considerable in specially designed structures. Damage great in
substantial buildings, with partial collapse. Buildings shifted off foundations.
• 
X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed. Rails bent.
• 
XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.
•  XII. Damage total. Objects thrown into the air.
Modified Mercalli Scale
Earthquake Triangulation
1. 
Examine seismograms from
3 different stations
2.  Measure the time between P
& S waves for each
seismogram
3.  Use a travel-time graph to
determine the distance of
each station from the
epicenter
Earthquake Triangulation
4. Draw circles on a globe
to show the possible
epicenters (the circle
radius is the distance
of each station to the
epicenter)
5. The point of
intersection between
the 3 stations is the
epicenter
Causes of Earthquake Damage
  Seismic shaking
Causes of Earthquake Damage
  Seismic shaking
  Liquefaction
Causes of Earthquake Damage
  Seismic shaking
  Liquefaction
  Landslides & Mudflows
Causes of Earthquake Damage
  Seismic shaking
  Liquefaction
  Landslides & Mudflows
  Tsunamis