Earthquakes
A. Strain – The deformation of
Causes for Crustal
materials
in response to stress.
movement:
B.
Stress – The total force acting on
crustal rocks per unit of area.
B. Elastic (temporary breaking or
bending)
C. Plastic (permanently breaking
or bending of the surface)
•
Tensional Stress- pulls outward
(extensional stress)
•
Compressional Stress- pushes
inward
•
Shearing- pulls in two opposite
directions
Folds–(elastic) There are 2 types of
bends that can occurs in Earth’s crust.
Anticline folds
up like a
capital “A”
Syncline
“sinks”
Faults (plastic deformation) – breaks in the
Earth’s crust along which Earth’s crust moves.
Faults produce 2 sides
(walls):
Foot wall –
The side of
the fault
which is
thicker at
the bottom
(you can
“walk” up it)
Hanging wall
– The side of
the fault
which is
thicker at the
top (you can
“hang” from
it)
Normal Fault
Normal Fault – Tension pulls rock apart,
forcing the footwall up and the hanging wall
down.
Normal
Fault
Animation
Normal Fault
Stress =
Tension
Normal Fault Examples
Left: Fault scarp near Hebgen Lake,
Montana, after the magnitude 7.1
earthquake of August 18, 1959, shows a
displacement of 5.5 to 6.0 m.
Right: This section of the normal fault
scarp was produced by the earthquake of
October 28, 1983, at Borah Peak, Idaho.
Left: Dixie Valley-Fairview Peaks, Nevada
earthquake
December 16, 1954
Reverse Fault
Reverse Fault – Compression causes the
hanging wall to move up and the
footwall to move down.
Reverse
Fault
Animatio
n
Reverse Fault
Stress =
Compression
Reverse Fault Example –
Collision Zones
Bam, Iran 2003
Below: Before and after pictures of the 2,000 yr.
old citadel in the city of Bam, the largest mudbrick structure in the world.
Map showing
the AlpineHimalayan Belt.
Earthquakes in Iran and
neighboring regions (e.g.,
Turkey and Afghanistan)
are closely connected to
their position within the
active Alpine-Himalayan
belt near the convergence
of the Arabian and
Eurasian plate.
The Mw 6.5 Bam
Earthquake
destroyed nearly
80% of the adobe
buildings killing
more than 26,000
people.
Thrust Faults - Reverse Faults
•
Reverse faults result from
compressional stresses along
convergent boundaries.
•
The hanging wall block has moved
up relative to the footwall block.
•
A Thrust Fault is a special case of a
reverse fault where the dip of the
fault is less than 15o
•
It is a reverse fault at a very low
angle.
•
There are two types of converging
plate boundaries.
1.Subduction boundaries
2.Collision boundaries
Strike-slip Fault
Strike-Slip Fault – Shearing forces two parts of
Earth’s crust past each other with NO vertical
movement.
Strike-Slip
Animation
Strike-Slip
Fault
Stress =
Shearing
Strike-Slip Faults - Transform Faults
•
Strike-slip faults result from shear stresses acting on the
lithosphere along transform boundaries.
•
Horizontal motion can be right lateral or left lateral.
•
Earthquakes along these boundaries tend to be shallow focus with
depths usually less than about 100 km. Richter magnitudes can be
large.
Earthquakes Defined
Earthquakes are vibrations of the earth caused by the
rupture and sudden movement of rocks that have been
strained (deformed) beyond their elastic limit. The
forces that cause deformation and the build-up of
strain energy in the rock are referred to as stresses.
Earthquakes occur along faults.
•
Faults are fractures in the lithosphere where regions
of rock move past each other (displaced).
•
The focus is the point on the fault where rupture
occurs and the location from which seismic waves are
released.
•
•
The epicenter is the point on the earth’s surface
directly above the focus.
When the fault ruptures, waves of energy called
seismic waves spread out in all directions.
Inside Earthquakes Video
Footage for California Earthquake in
1989
Part of Documentary showing
footage from 2011 Earthquake in
Japan
Earthquake
Seismic Waves
Body waves travel through the interior (body) of the earth
as they leave the focus. They include P-waves and Swaves.
•
Primary (P) -Travel twice as fast as S-Waves, are compressional
Movement: rocks are squeezed and pushed in the same direction as
the wave moves.
-Move similar to a slinky that is stretched and then released.
•
Secondary (S)-Travel half as fast as P-Waves, rolling Movement:
rocks shifted up and down perpendicular to the direction of the wave.
-Move similar to a rope that is being shaken up and down.
Surface waves travel parallel to the earth’s surface. They
are the slowest and most damaging because they cause the
most ground movement. They include Love and Rayleigh
Waves.
Love Waves - complex, horizontal
motion
•
When combined, these waves move the ground up and
down and side to side simultaneously.
•
-They cause the most damage because the create the most
ground movement and take the longest time to pass an
Rayleigh Waves - Rolling or elliptical
area.
motion.
Interior seismic waves – These
waves travel through the inner layers of
Earth.
-Travel half as fast as PWaves.
Primary
Waves
-Rolling Movement: rocks
shifted up and down
perpendicular to the
direction of the wave.
-Move similar to a rope
that is being shaken up
and down.
Secondary
Waves
COMPARE P WAVES AND S WAVES
How do we measure earthquakes?
Richter Scale
-Created by Charles Richter in 1934.
-This scale measures earthquakes
based on the largest seismic wave
recorded during a quake.
-The scale is from 0-10. Every whole
number up on the scale represents
an increase in energy of ten times
more.
Mercalli Scale
-The original scale used to
measure quakes. Created
in 1902 by Giuseppe
Mercalli.
-Considered less
accurate, because it uses
eyewitness observations
of damage to estimate the
intensity of the quake.
MERCALLI
SCALE
Moment Magnitude Scale
-Introduced in 1979.
**This is the most accurate scale
used today**
-Measures earthquake strength based on the amount of energy released by calculating
size of the fault, amount of movement, and type of rock (stiffness).
-The moment magnitude scale is preferred over the Richter scale by seismologists
because it is more accurate.
-When hearing about an earthquake on the news, this is typically the final, most
accurate magnitude given.
Richter Scale
Moment
Magnitude
New Madrid, MO,
1812
8.7
8.1
San Francisco, CA
1906
8.3
7.7
Prince William, AK
1964
8.4
9.2
Northridge, CA,1994
6.4
6.7
Earthquake
Earthquake Depth
Shallow
earthquakes
cause the
most damage.
Intermediate
earthquakes
cause
moderate
damage
Deep
earthquakes
cause the
least damage.
Liquefaction
Liquefaction is a quicksand like condition that occurs in watersaturated soil and rock. The shaking of earthquake waves causes the soil
or rock to turn into a weak, fluid-like mass. Structures built on areas that
liquefy may fall over or sink.
The figure below shows how liquefaction can
occur. Shaking of water-saturated soils causes
the particles to settle, driving the water out
from between the particles and forcing it
upward, thus liquefying the areas above.
Above: Buildings in Niigata, Japan, fell over
when the sediments below them liquefied
during the 1964 earthquake
Landslides
Vibration of water saturated sediment can force water into
pore spaces between sediment grains reducing friction and
permitting the mass to slide down slope.
Turnnagin Heights,Alaska,1964- This landslide
occurred during the massive recording breaking
earthquake
This massive landslide near Oso, Washington, in March, 2014, killed 43 people and was
one of the most deadly in U.S. history. This occurred to heavy rains over saturated the
soil the gravity pulled the mountain downward on top of this small town.
Largest Earthquake in US History
Alaska, 1964
Alaska - March 27, 1964
-This is the most powerful
U.S. earthquake in recorded
history.
-It registered as a 9.2 on the
Richter scale.
-The rumbling lasted nearly
5 minutes.
-Ground fissures, collapsing
buildings, and tsunami
killed over 130 people
-The Pacific Ocean Tsunami
Center was created shortly
after this earthquake and
has predicted several
tsunamis, saving lives.
San Francisco,
California – 1906
San Francisco, California – 1906 (7.7 on
Richter)
-Significant earthquake in that it was one of
the first instances where scientists were
able to record information on seismic waves.
-Caused approximately $400,000,000 of
damage (at the time)
-Several eye-witness accounts refer to the
movement of the roads to be similar to the
undulation of waves in the ocean.
-Fires raged on for days, and S.F. had to be
rebuilt.
Full Documentary on
Earthquakes
Indian Ocean – December
26, 2004
9.2/9.3 magnitude earthquake, making it one of
the most powerful ever recorded on Earth.
-The infamous tsunami that ensued killed over
200,000 to 250 people in more than 11 countries,
most bodies were never found..
-Released an amount of energy 1502 times more
powerful than the Hiroshima atomic bomb.
The Los Angeles Times reported: “Miles beneath
the waters of the Indian Ocean, a massive piece
of the Earth’s crust had heaved, buckled and
shifted. Along a fracture zone hundreds of miles
long, it moved, releasing pent-up energy
equivalent to the power of more than 1,000
atomic bombs. The waters above reared up and
crashed down, creating a wave that was now
racing across the ocean at 500 mph…The records
of history and evidence encoded in coral reefs
show that tsunamis have hit the Indian Ocean
seldom but with great force.”
The Full PBS Documentary
on the 2004 Tsunami
Chile –
May 22, 1960
The most powerful earthquake
ever officially recorded at a
magnitude of 9.5.
-The damage is estimated to be
at over 3 billion dollars, and
nearly 6,000 killed.
-Once the red slab that is “stuck”
finally gives way, this is when the
earthquake occurs. The recoil of
the plate causes the energy to be
released.
Haiti-2010
Over
a quarter
of a million people were killed in
7.0
on
1/12/10
this very shallow but rather low magnitude
earthquake. Many of these deaths occurred
because; it occurred in the countries capital, most
of the community was poor living in poorly built
structures, it occurred in the middle of the night
while most were sleeping in their homes and their
government literally abandoned them leaving
more to die from treatable diseases and starvation.
•
7.1 magnitude earthqauke
•
52 aftershocks
•
over 250,000 dead
•
1,800,000 homeless.
•
Quake was created by a blind thrust fault
with a very shallow quake and poor
constructed homes lead to high deaths.
Cause of the earthquake. Haiti lies right on the
boundary of the Caribbean and North American
plates. There was slippage along a conservative
plate boundary that runs through Haiti. On 12
January 2010, a magnitude 7 earthquake hit
Haiti at 16:53 local time.
CNN Report on Haitian Earthquake
Chile (2/27/10)
8.8 (MM)
•
shook central Chile creating a
tsunami.
•
Lasted 3 minutes and was ranked as
8th largest in the world
•
killed 802 people
BBC Reports on
Earthquake in Chile
2010
Japan- 3/11/11
8.9 shallow quake created a 23-30 foot
tsunami which spread over 1500 miles,
around 11,000 dead at this time but numbers
will increase, nuclear crisis still impacts the
soils and water/ocean of Japan.
Japan is located on the eastern edge of the
Eurasian Plate. The Pacific Plate, which is an
oceanic plate, subducts (sinks under) the
Eurasian Plate, which is a continental plate,
to the east of Japan.
The process of subduction is not smooth.
Friction causes the Pacific Plate to stick.
Pressure builds and is released as an
earthquake.
News Report and Footage
from the Japanese Tsunami
of 2011
The Guardian MagazineJapanese Tsunami
Largest
Quakes
in
History
1. May 22, 1960, Chile (9.5) The world's most powerful earthquake left 4,485 people dead
and injured and 2 million homeless and killed a further 170 people as the tsunami hit
the coasts of Japan and the Philippines.
2. March 27, 1964, a magnitude 9.2 hit Prince Island Sound, Alaska. The earthquake
caused landslides in Anchorage and raised parts of outlying islands by as much as 11
meters. The 67meter high tsunami killed another 128 people.
3. December 26, 2004, a magnitude 9.1 hit Sumatra, Indonesia. (The Tsunami of the
Impossible) The deadliest tsunami ever spread to 14 countries killing 230,000 thousand
people.
4. November 4, 1952 a magnitude 9.0 hit Kamchatka, Russia, known as the USSR. A
volcanic peninsula was the epicenter but the tsunami hit Hawaii. No deaths occurred
but it was 3000 miles from the epicenter.
Images from top ten worst earthquakes in history
Tsunami
Tsunami Formation animation
Tsunami-
A tsunami is a series of great sea waves
caused by an underwater earthquake,
landslide, or volcanic eruption. More
rarely, a tsunami can be generated by a
giant meteor impact with the ocean.
•
The first wave in a tsunami is not
necessarily the most destructive.
Tsunamis are not tidal waves that curl
but rather a WALL of water that
rapidly floods inward towards the land
with tremendous speed and height.
•
The powerful shock wave of energy
travels rapidly through the ocean as
fast as a commercial jet but goes
UNFELT in the ocean by fisherman.
•
Once a tsunami reaches shallow water
near the coast first, the ocean water
disappears along the beach and recedes
outwards towards the deep ocean.
•
Then, it is slowed down, the series ofIndependently made series
waves catch-up to each other and
of live video from 2004
builds UPWARD.
Tsunami
•
The top of the wave moves faster than
the bottom, causing the sea to rise
CNN
dramatically.
Footage and story
on the 2004 Tsunami