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Standard 8-3.8
EARTHQUAKES
Assessing Prior Knowledge
and Relativity
• What have you heard about
earthquakes lately?
• Why should we study earthquakes?
Falcon Focus
• 8-1.1 The standard metric unit of
length used in a science lab is…
• a. Celsius
• b. Gram
• c. Liter
• d. Meter
Essential Question
• WHAT CAUSES
EARTHQUAKES AND
WHERE DO THEY
HAPPEN?
INTRODUCTION
• http://video.nationalgeographic.com/video/p
layer/environment/environment-naturaldisasters/earthquakes/earthquake-101.html
The earthquake that caused the most
destruction in history occurred in the Shansi
province of China on January 23,1556. An
estimated 830,000 people were killed.
The second most destructive earthquake also
occurred in China--in July, 1976--and killed
255,000 people.
The definition of an earthquake is…
vibrations that cause the breaking of
rocks.
These vibrations move in all directions
through the earth. They begin at a point
along a fault.
Earthquakes
• Forces___ and __Stresses__ (8-3.7–
tension, compression, and shearing) along
faults can build up as blocks of rock are
pushed (compression or shearing) or pulled
apart (tension). If the __pressure___ or
stress becomes too great, the rock breaks at a
weak point along the fault and
___energy_____ is released
Earthquakes
• ____Earthquakes_____ are vibrations produced
when rocks break along a ___fault_____. The
term earthquake describes the sudden slip on a
fault and includes the ground shaking and
radiating _____seismic waves___ that is caused
by the slip. ___Volcanic Activity____, or other
geologic processes, may cause stress changes in
the earth that can also result in an earthquake.
The earth’s crust is constantly
experiencing pressure from forces
within and around it. This pressure
builds up over time, and eventually
causes the crust to break. This
becomes a fault.
Let’s experience it…
Faults are divided into three main groups:
Normal fault - when two plates are moving apart
and one side of the fracture moves below the
other; (caused by tension forces!)
Reverse fault - when two plates collide and one
side of the fracture moves on top of another;
(caused by compression forces!!)
Strike-slip - when two plates slide past each
other. (caused by shear forces!)
Three Types of Faults
Strike-Slip
Reverse
Normal
An earthquake begins along a fault (a
crack in the earth’s surface) at a point
called the focus.
Directly above the focus is a point on
the earth’s surface called the epicenter.
Epicenter
Focus
Seismologists have stations all over the world
that continuously collect information about
earthquakes. This kind of information can help
scientists figure out where larger, more
destructive earthquakes may strike by mapping
out the location of smaller ‘quakes. They also
get a greater understanding of the changes the
earth’s crust makes as the earthquakes occur.
How do they do this???
When the fault ruptures with a sudden movement
energy is released that has built up over the
years. This energy is released in the form of
vibrations called 'seismic waves'… earthquakes!
It is actually when these seismic waves reach the
surface of the earth that most of the destruction
occurs, which we associate with earthquakes.
Parts of the Earthquake
• The energy spreads outward in all directions as
vibrations called ____seismic waves_____.
• The _focus____ of the earthquake is the point in
the crust, or mantle, where energy is released.
• The _epicenter___ is the point on Earth’s surface
directly above the focus; energy that reaches the
surface is greatest at this point.
Focus –
point inside the Earth where an
earthquake begins
Epicenter – point on Earth’s surface above focus
Focus, Epicenter, and Fault
WHAT CAUSES EARTHQUAKES?
• Used to describe both sudden slip on a fault,
and the resulting ground shaking and radiated
seismic energy caused by the slip
• Caused by volcanic or magmatic activity,
• Caused by other sudden stress changes in
the earth.
What causes earthquakes?
• Tectonic plates move past each other causing
stress. Stress causes the rock to deform
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
What Causes an Earthquake?
Cause of Earthquakes
 Aftershocks and Foreshocks
• An aftershock is a small earthquake that
follows the main earthquake.
• A foreshock is a small earthquake that often
precedes a major earthquake.
Earthquakes can also cause landslides, sudden
eruptions as in the case of a hot lava flow from a
volcano or giant waves called tsunamis. Sometimes new
land mass are also formed. Such earthquakes are
attributed with the creation of the greatest undersea
mountain range and the longest land mountain range.
Landslides & Tsunamis
• http://video.nationalgeographic.com/video/1
01-videos/landslides
• http://video.nationalgeographic.com/video/1
01-videos/tsunami-101
…And that was
just a 7.2 on
the Richter
scale!
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Focus, Epicenter, and Fault
Earthquake Hazard Potential Map
Parkfield, CA
“Earthquake Capital of the World”
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
– more than 150,000 quakes strong enough to be felt are
recorded each year
Review!!!
• http://www.iknowthat.com/mhscience/Earth
quakes/Fixed.htm
• http://www.iknowthat.com/mhscience/Earth
quakes/earthquake_movie.html
Focus and Epicenter of Earthquake
HOMEWORK
• .
FALCON FOCUS
•
A.
B.
C.
D.
THE POINT ON EARTH’S SURFACE
WHERE THE GREATEST ENERGY
FROM THE EARTHQUAKE IS
RELEASED IS ___________.
THE EPICENTER
THE FOCUS
THE ASTHENOSPHERE
THE FAULT
FALCON FOCUS
•
A.
B.
C.
D.
THE POINT ON EARTH’S SURFACE
WHERE THE GREATEST ENERGY
FROM THE EARTHQUAKE IS
RELEASED IS ___________.
THE EPICENTER
THE FOCUS
THE ASTHENOSPHERE
THE FAULT
ESSENTIAL QUESTION
• HOW WOULD YOU COMPARE AND
CONSTRAST THE THREEE TYPES OF
SEISMIC WAVES?
INTRODUCTION
• IN A POP AND LOCK DANCE MOVE,
STUDENTS WILL DEMONSTRATE THE
3 TYPES OF SEISMIC WAVES
SEISMIC WAVES
• _SEISMIC WAVES___ are waves
generated by an earthquake that travel
through the Earth. These waves can cause
the ground to move forward, backward,
up, down, and even to ripple. Seismic
Waves are generated at the __SAME___
time but move in different ways, and at
different speeds.
Seismic
Waves in
the Earth
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
3 TYPES OF SEISMIC WAVES
• PRIMARY (P) WAVES
• SECONDARY (S) WAVES
• SURFACE WAVES
CONSIDERED AS BODY WAVES
Seismic Waves
8.2 Measuring Earthquakes
Earthquake Waves
 Body Waves
• Identified as P waves or S waves
• P waves
- Are push-pull waves that push (compress) and
pull (expand) in the direction that the waves
travel
- Travel through solids, liquids, and gases
- Have the greatest velocity of all
earthquake waves
PRIMARY (P) WAVE
• Move out from the earthquake focus, the
point where the energy is released
• Travel the fastest of the three waves
• Move through solid and liquid layers of
Earth (it also can move in gas)
• Push and pull rock creating a back-andforth motion in the direction the wave is
moving (longitudinal wave)
Primary Waves (P Waves)
• A type of seismic wave that compresses
and expands the ground
• The first wave to arrive at an
earthquake
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
8.2 Measuring Earthquakes
Earthquake Waves
 Body Waves
• S waves
- Seismic waves that travel along Earth’s outer
layer
- Shake particles at right angles to the direction
that they travel
- Travel only through solids
- Slower velocity than P waves
 A seismogram shows all three types of
seismic waves—surface waves, P
waves, and S waves.
Secondary Waves (S Waves)
•
•
•
•
Move out from the earthquake focus
Move slower than primary waves
Can only move through solid rock
Move at right angles to primary waves
causing rocks to move up and down and
side to side (transverse wave)
Secondary Waves (S Waves)
• A type of seismic wave that moves the
ground up and down or side to side
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Body Waves: P and S waves
•
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
Comparing Seismic Waves
SURFACE WAVES
• Form when P and S waves reach the surface
• Can cause the ground to shake making rock sway
from side to side and roll like an ocean wave
• These waves cause the most destruction
• They move back and forth and in a rolling motion
along the surface
• They release all of the energy of the earthquake
Surface Waves: R and L waves
•
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
Surface Waves
• Move along the Earth’s surface
• Produces motion in the upper crust
– Motion can be up and down
– Motion can be around
– Motion can be back and forth
• Travel more slowly than S and P waves
• More destructive
Seismic Waves Paths Through the Earth
Earth’s Interior Showing
P and S Wave Paths
• Scientists use the principle that the speed and
direction of a seismic wave depends on the
material it travels through. Because of the
behavior of these different waves, scientists have
indirect evidence for the solid inner core and
liquid outer core of Earth; because earthquake
waves travel faster through the mantle than
through the crust, scientists know that the mantle
is denser than the crust.
Earthquake Waves & Earth’s Interior
ACTIVITY
• CREATE S, P, AND SURFACE WAVES
USING A STRING AND A SLINKY
Primary or
“P” Wave
Secondary
or “S”
Wave
Measuring Earthquakes
• The movement of materials in the __outer_
core (which is a liquid) of the Earth is
inferred to be the cause of Earth’s
_magnetic field___. A compass needle
will align with the lines of force of Earth’s
magnetic field. __Iron__ and _Nickel__
are metals that easily magnetize, and are
inferred to be the metals in Earth’s core.
Measuring Earthquakes
• The energy spreads outward in all directions as
vibrations called ___Seismic Waves____. Seismic
waves can be measured and recorded by a
____seismograph_______.
• __Seismographs______ are instruments or a
device that detects and records seismic or
earthquake waves. It measures the vertical ground
motion and the horizontal ground motions (N-S/EW). It also traces wave shapes onto paper and
translates waves into an electronic signal.
Measuring Earthquakes
• The vibration record, called a seismogram, looks
like jagged lines on paper. Seismograms are
traces of amplified, electronically recorded ground
motion made by seismographs.
• Measuring the time between the arrival of the P
and S waves determines the distance between the
recording seismograph and the earthquake
epicenter.
Measuring Earthquakes
Earthquake Waves
 Seismographs are instruments that
record earthquake waves.
 Seismograms are traces of amplified,
electronically recorded ground motion
made by seismographs.
Seismograph
Types of Seismographs
Seismogram Printout
Seismic wave behavior
– P waves arrive first, then S waves, then L and R
How
is an speeds
Earthquake’s
Located?
– Average
for all theseEpicenter
waves is known
– 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.
Determining the location of an earthquake
First, distance to earthquake is determined.
1. Seismographs record seismic waves
2. From seismograph record called the seismogram, measure time delay
between P & S wave arrival
3. Use travel time curve to determine distance to earthquake as function
of P-S time delay
Now we know distance waves traveled, but we don't know the direction from
which they came.
We must repeat the activity for each of at least three (3) stations to
triangulate a point (epicenter of quake).
Plot a circle around seismograph location; radius of circle is the distance to the
quake.
Quake occurred somewhere along that circle.
Do the same thing for at least 3 seismograph stations; circles intersect at
epicenter. Thus, point is triangulated and epicenter is located.
Locating an Earthquake
How is an Earthquake’s Epicenter
Located?
Time-distance graph
showing the average
travel times for P- and Swaves. The farther away a
seismograph is from the
focus of an earthquake,
the longer the interval
between the arrivals of
the P- and S- waves
Time-Travel Curve
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
Locating an Earthquake Epicenter
• Triangulate means to use three positions to
determine an exact location.
What is Triangulation?
• Triangulation identifies the epicenter of an
earthquake. The location of an earthquake’s
epicenter is found by plotting circles on a map
from the records of three seismograph stations and
finding the point where the three circles intersect.
Triangulation is the process of determining the
location of a point by measuring angles to it from
known points at either end of a fixed baseline,
rather than measuring distances to the point
directly.
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Triangulation
of 3 stations
to locate
earthquake
epicenter
How do scientists calculate how far a location is
from the epicenter of an earthquake?
• Scientists calculate the difference
between arrival times of the P waves and
S waves
• The further away an earthquake is, the
greater the time between the arrival of
the P waves and the S waves
Earthquakes are measured using the Richter
Scale. The strongest earthquake ever
measured was a 9.5 on the Richter Scale. This
is a measurement of the amount of energy
released from the earthquake.
8.2 Measuring Earthquakes
Measuring Earthquakes
 Historically, scientists have used two
different types of measurements to
describe the size of an earthquake
—intensity and magnitude.
 Richter Scale
• Based on the amplitude of the largest seismic
wave
• The _Richter Scale expresses the magnitude of
an Earthquake and measures the energy released.
The scale goes from 1 to 10 .
How are the Size and Strength of an Earthquake
Measured?
•
Magnitude
– Richter scale
measures total amount
of energy released by
an earthquake;
independent of
intensity
– Amplitude of the
largest wave produced
by an event is
corrected for distance
and assigned a value
on an open-ended
logarithmic scale
Determining the magnitude of an earthquake
Magnitude -- measure of energy released during earthquake.
There are several different ways to measure magnitude.
Most common magnitude measure is Richter Scale, named for
the renowned seismologist, Charles Richter.
Richter Magnitude
• Measure amplitude of largest S wave on seismograph record.
• Take into account distance between seismograph &
epicenter.
Intensity
• Intensity refers to the amount of damage done in an
earthquake
How are the Size and Strength of an Earthquake
Measured?
•
•
Intensity
– subjective measure
of the kind of
damage done and
people’s reactions
to it
Modified Mercalli Intensity Map
– 1994 Northridge, CA earthquake,
magnitude 6.7
How are Earthquakes Measured? Richter
Scale
9.5
9.2
9.2
9.1
9.0
8.8
8.7
8.6
8.5
8.5
8.5
Chile, May 22, 1960
Indian Ocean (Sumatra tsunami) Dec 26,2004
Prince William Sound, Alaska, March 28, 1964
Andreanof Islands, Aleutian Islands, Pacific,
March 9, 1957
Kamchatka, Russia, November 4, 1952
Off the Coast of Ecuador, January 31, 1906
Rat Islands, Aleutian Islands, Pacific,
February 4, 1965
India-China Border, August 15, 1950
Kamchatka, Russia, February 3, 1923
Banda Sea, Indonesia, February 1, 1938
Kuril Islands, Pacific, October 13, 1963
Earthquake Waves (Review)
• Primary Wave (P-Wave) First set of waves
– Move side to side
– FASTEST wave
• Secondary Wave (S-Wave) Second set of
waves
– Move up and down
– Travel slow
• Surface Wave
– Move up and down & side to side
– MOST DANGEROUS
– SLOWEST Wave
Closure
• Create a Venn Diagram contrasting and
comparing the 2 types of seismic waves.
Homework
• Study for Quiz
• Place the following words in your glossary.
• Primary wave, Secondary wave, Surfaces
wave, Longitudinal wave, Transverse wave,
Richter Scale, Seismograph, Seismogram,
Magnitude, and Intensity.
FALCON FOCUS
•
A.
B.
C.
D.
S WAVES CANNOT TRAVEL THROUGH LIQUIDS
AND P WAVES SLOW DOWN IN LESS RIGID
MATERIALS. IN EARTH’S OUTER CORE, S
WAVES CANNOT BE DETECTED AND P WAVES
SLOW DOWN. THESE SUGGEST THAT ____.
THE OUTER CORE MAY BE LIQUID
THE OUTER CORE MAY BE SOLID
THERE ARE NO EARTHQUAKES IN THE OUTER
CORE
THE OUTER CORE IS THE THICKEST LAYER OF
THE EARTH
ESSENTIAL QUESTION
• IN YOUR OWN WORDS, EXPLAIN
HOW SEISMIC WAVES MOVE FROM
THE FOCUS OF AN EARTHQUAKE?