Download Strike-Slip Fault

Stresses, Faults,
Folds, and
Earthquakes
Types of Stresses on Layers of Rocks:
Types of Folds
Anticline- an upward fold in the rock
Syncline- a downward fold in the rock
Syncline “sinks”
Anticline folds up
like a capital “A”
Syncline
Anticline
Syncline
Anticline
4 Types of Faults
Fault- A break in the Earth’s surface where
movement occurs.
Hanging Wall and Footwall
Hanging Wall (HW)- The piece of rock that is wider at the top,
where your head would be located in the elevator.
Footwall (FW)- The piece of rock that is wider at the bottom,
where your feet would be located in the elevator.
***You can “walk” up the footwall
Normal and Strike-Slip Faults
• Normal Fault- Tension
pulls rock apart and the
HW moves down and
the FW moves upward.
NORMAL FAULTS
• Strike-Slip FaultShearing pushes and
pulls two rocks layers
past each other without
any upward or
downward motion.
STRIKE-SLIP FAULTS
Reverse and Thrust Faults
• Reverse FaultCompression forces
the HW upward and
the FW downward.
• Thrust Faultcompression creates
a reverse fault in
which the HW slides
at a very low angle
over the FW.
COMPRESSION FAULTS
Strike-slip Fault
Stress= Shearing
Reverse Fault
Stress = Compression
Normal Fault
Stress = Tension
PRACTICE
IDENTIFYING
FAULTS
Reverse, Normal, or Strike-Slip Fault?
Normal Fault
Tension
Hanging Wall Sinks Down
Reverse, Normal, or Strike-Slip Fault?
Strike-Slip Fault
Shearing
Horizontal Movement of Layers
Reverse, Normal, or Strike-Slip Fault?
Reverse
Compression
Hanging wall is pushed up
JAPAN QUAKE’S FAULT LINE
The earthquake occurred
along this convergent plate
boundary where subduction
happens (convergent
boundary).
What type of stress/fault is
occuring here?
Elastic Rebound
Tsunami Formation
Earthquakes
EARTHQUAKES
Focus and Epicenter
Fault- A break in the
earth’s crust where
movement occurs.
Focus- the origin of an
earthquake
underground.
Epicenter- the point on
the earth’s surface
directly above the focus
of an earthquake.
Earthquake Waves
•
•
Primary Wave- waves that move through
Earth by causing particles in rocks to move
back and forth in the same direction.
(compressionial waves)
– Primary wave move twice a fast
as secondary.
– Primary waves can travel through
liquid or plastic materials as well as
solids- but the speed changes as it
travels through solids.
Secondary Waves- wave that move
through the earth by causing particles in
rocks to move a right angles to the
direction of the wave. ( up and down
motion)
– Secondary waves can travel through
plastic or solid materials but NOT
liquid.
COMPARE P WAVES AND S WAVES
Interior of the Earth and Seismic Waves
• P Waves can travel
through both solids
and liquids
• S waves can travel
through solids but
not liquids.
• Based on the speed,
direction and angles
of the waves, we
can determine the
consistency of the
interior of the Earth!
• Shadow zone- areas
on Earth (opposite
to origin of quake)
where no P or S
waves are felt.
Shadow Zones
Surface Earthquake Waves
Surface waves usually follow the P
and S wave, traveling along the
land surface like water waves.
There are several types of surface
waves; the two most important are
Raleigh waves (R) and Love waves
(L) , named for the scientists who
first identified them.
A. Raleigh Waves-The R waves
move continuously forward, although
the individual particles move vertically
in an elliptical path
B. Love Waves- The L waves also
travel forward, but the individual
particles move back and forth
horizontally.
How do we measure earthquakes?
**The original (less used today) scales**
Richter Scale
-Created by Charles Richter in 1934.
-This scale measures earthquakes based
on the largest seismic wave recorded
during a quake.
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.
-The scale is from 0-10. Every whole
number up on the scale represents an
increase in energy of ten times more.
MERCALLI SCALE
Moment Magnitude Scale
**This is the most used scale today**
-Introduced in 1979 in order to be more accurate than the Richter and Mercalli Scales,
because its based on physical features of the quake instead of recordings using
instruments.
-Measures earthquake strength based on the amount of energy released. This amount
is calculated by analyzing the physics of the earthquake.
-The moment magnitude scale is preferred over the Richter scale by seismologists
because it is more accurate.
-In simple terms, this scale multiplies the area of the fault surface and the distance the
Earth moves along the fault to calculate the magnitude.
Earthquake
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
Famous Earthquakes
1) Anchorage, 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 an
ensuing tsunami killed over 130 people.
2) San Francisco, California – 1906
-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.
Famous Earthquakes
3) 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 people.
-Released an amount of energy 1502 times more
powerful than the Hiroshima atomic bomb.
4) 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.
TSUNAMI
A series of waves that
occurs when the ocean is
disturbed by earthquakes,
underwater explosions or
impacts.
12/26/04- Southeast Asia
experienced a large scale
earthquake along the Ring
of Fire that created a series
of tsunamis that killed
225,000 people and
displaced over 1.2 million
people! The tsunami
slammed into the coasts of
several nations within two
hours after the quake.
tsunami animation