7. 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.
8. 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.
9. 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
10. 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.
11. 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…
12. 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!)
14. 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.
16. 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???
17. 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.
18. 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.
19. Focus – point inside the Earth where an
earthquake begins
Epicenter – point on Earth’s surface above focus
21. 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.
22. What causes earthquakes?
• Tectonic plates move past each other causing
stress. Stress causes the rock to deform
24. Cause of Earthquakes
What Causes an Earthquake?
• An aftershock is a small earthquake that
follows the main earthquake.
• A foreshock is a small earthquake that often
precedes a major earthquake.
Aftershocks and Foreshocks
25. 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.
39. 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
43. FALCON FOCUS
• THE POINT ON EARTH’S SURFACE
WHERE THE GREATEST ENERGY
FROM THE EARTHQUAKE IS
RELEASED IS ___________.
A. THE EPICENTER
B. THE FOCUS
C. THE ASTHENOSPHERE
D. THE FAULT
44. FALCON FOCUS
• THE POINT ON EARTH’S SURFACE
WHERE THE GREATEST ENERGY
FROM THE EARTHQUAKE IS
RELEASED IS ___________.
A. THE EPICENTER
B. THE FOCUS
C. THE ASTHENOSPHERE
D. THE FAULT
46. INTRODUCTION
• IN A POP AND LOCK DANCE MOVE,
STUDENTS WILL DEMONSTRATE THE
3 TYPES OF SEISMIC WAVES
47. 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.
51. Earthquake Waves
8.2 Measuring Earthquakes
Body Waves
• P waves
• Identified as P waves or S waves
- Have the greatest velocity of all
earthquake waves
- Are push-pull waves that push (compress) and
pull (expand) in the direction that the waves
travel
- Travel through solids, liquids, and gases
52. 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-and-
forth motion in the direction the wave is
moving (longitudinal wave)
53. 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
54. Earthquake Waves
8.2 Measuring Earthquakes
Body Waves
• S waves
- Seismic waves that travel along Earth’s outer
layer
- Slower velocity than P waves
- Shake particles at right angles to the direction
that they travel
- Travel only through solids
A seismogram shows all three types of
seismic waves—surface waves, P
waves, and S waves.
55. 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)
56. 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
57. 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
60. 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
61. 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
62. 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
66. • 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.
70. 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.
71. 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/E-
W). It also traces wave shapes onto paper and
translates waves into an electronic signal.
72. 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.
73. Earthquake Waves
Measuring Earthquakes
Seismographs are instruments that
record earthquake waves.
Seismograms are traces of amplified,
electronically recorded ground motion
made by seismographs.
78. How is an Earthquake’s Epicenter Located?
Seismic wave behavior
– P waves arrive first, then S waves, then L and R
– Average speeds for all these 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.
79. 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.
81. How is an Earthquake’s Epicenter
Located?
Time-distance graph
showing the average
travel times for P- and S-
waves. 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
83. 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
84. Locating an Earthquake Epicenter
• Triangulate means to use three positions to
determine an exact location.
85. 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.
90. 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
91. 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.
92. Measuring Earthquakes
8.2 Measuring Earthquakes
Historically, scientists have used two
different types of measurements to
describe the size of an earthquake
—intensity and magnitude.
Richter Scale
• The _Richter Scale expresses the magnitude of
an Earthquake and measures the energy released.
The scale goes from 1 to 10 .
• Based on the amplitude of the largest seismic
wave
93. 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
94. 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
95. How are the Size and Strength of an Earthquake
Measured?
• Modified Mercalli Intensity Map
– 1994 Northridge, CA earthquake,
magnitude 6.7
• Intensity
– subjective measure
of the kind of
damage done and
people’s reactions
to it
97. 9.5 Chile, May 22, 1960
9.2 Indian Ocean (Sumatra tsunami) Dec 26,2004
9.2 Prince William Sound, Alaska, March 28, 1964
9.1 Andreanof Islands, Aleutian Islands, Pacific,
March 9, 1957
9.0 Kamchatka, Russia, November 4, 1952
8.8 Off the Coast of Ecuador, January 31, 1906
8.7 Rat Islands, Aleutian Islands, Pacific,
February 4, 1965
8.6 India-China Border, August 15, 1950
8.5 Kamchatka, Russia, February 3, 1923
8.5 Banda Sea, Indonesia, February 1, 1938
8.5 Kuril Islands, Pacific, October 13, 1963
98. 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
99. Closure
• Create a Venn Diagram contrasting and
comparing the 2 types of seismic waves.
100. 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.
101. FALCON FOCUS
• 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 ____.
A. THE OUTER CORE MAY BE LIQUID
B. THE OUTER CORE MAY BE SOLID
C. THERE ARE NO EARTHQUAKES IN THE OUTER
CORE
D. THE OUTER CORE IS THE THICKEST LAYER OF
THE EARTH
102. ESSENTIAL QUESTION
• IN YOUR OWN WORDS, EXPLAIN
HOW SEISMIC WAVES MOVE FROM
THE FOCUS OF AN EARTHQUAKE?
