Title: EARTHQUAKES
1EARTHQUAKES
2Global Earthquake Locations
3What are Earthquakes?
- The shaking or trembling caused by the sudden
release of energy - Usually associated with faulting or breaking of
rocks - Continuing adjustment of position results in
aftershocks - Shaking of earth due to movement of rocks along a
fault.
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5- Rocks under stress accumulate strain energy over
time. - When stress exceeds strength of rocks, rock
breaks. - Strain energy is released as seismic waves. The
longer that energy is stored up and is maintained
without release, the more likely that a strong
earthquake will occur.
6The animation below of a subduction zone, where
an oceanic plate is converging with a continental
plate, attempts in cartoon fashion to show the
deformation of the continental plate that
precedes each earthquake.
7- What is FAULT?
- A break or crack in rock along which movement of
the earths crust occurs. - Can be visible on the crust or can be far
underground. - Can be only a meter long or they can extend for
hundreds of kilometers.
8FAULT
9Earthquakes can happen along any type of plate
boundary. They also occur along faults which are
large cracks in the earths crust. Most faults
are associated with large plate boundaries where
violent earthquakes usually occur.
10- Movement of rock along a fault can release a
tremendous amount of energy This movement can
release three main forces on adjoining areas of
the crust - Tension results when a system of forces pulls
or stretches an object from opposite sides. - Compression results when a system of forces
pushes an object from opposite sides. - Shearing - results when a system of forces is
applied to an object in different directions.
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13What is the Elastic Rebound Theory?
All rocks have an elastic limit. If the forces
acting on these rocks exceed this limit, or
overcome the friction between blocks, the crust
snaps and an earthquake occurs.
14What is the Elastic Rebound Theory?
- Explains how energy is stored in rocks
- Rocks bend until the strength of the rock is
exceeded - Rupture occurs and the rocks quickly rebound to
an undeformed shape - Energy is released in waves that radiate outward
from the fault
15KINDS OF FAULT
- Normal Fault
- one block can move down and the other can move
up, or vice versa. - occurs where forces tend to pull section of the
earths crust apart. - tends to follow the gravitational pull on the
fault blocks involved.
16- The fault plane on the normal fault is generally
very steep. In a normal fault the two involved
blocks are (by gravity) pulling away from one
another causing one of the fault blocks to slip
upward and the other downward with respect to the
fault plane (it is hard to determine whether both
or just one block has moved.).
17- The exposed upward block forms a cliff-like
feature known as a FAULT SCARP. A scarp may range
from a few to hundreds of meters in height and
their length may continue for 300 or more
kilometers (around 200 miles). - FAULT SCARP landforms that form cliffs and
ridges along the fault. (book definition)
18Normal Fault
19KINDS OF FAULT
- 2. Thrust Fault
- one block moves over another block
- occurs where forces tend to push sections of the
crust together. - When thrust faults are exposed on the surface
overburnden material lies over the main block.
They are normally associated with areas of folded
surfaces and or mountaineous regions. The dip
angles of thrust faults are normally not as steep
as a normal fault.
20Thrust Fault
21KINDS OF FAULT
- 3. Strike-slip Fault (Transcurrent Fault)
- the movement of the blocks is horizontal
- known as the San Andreas fault of California.
This fault marks the margin line between the
Pacific and North American Plates. - On the surface, scarps form as hills crossing the
fault zone are torn apart by movement over time.
22- Actually anything crossing this fault zone is
either slowly torn apart, or offset. - Rivers crossing the fault line are called offset
streams and are classic signatures of fault
activity along the San Andreas. - These faults can be very long, the San Andreas is
nearly 600 miles long.
23Strike-slip Fault
24Three Types of Faults
Strike-Slip
Thrust
Normal
25EARTHQUAKE AND PLATE TECTONICS
The lines on the map indicate plate boundaries.
26The Focus and Epicenter of an Earthquake
- The point within Earth where faulting begins is
the FOCUS, or hypocenter - The point directly above the focus on the surface
is the EPICENTER
27Three Types of Focus
- Shallow-focus
- earthquake originates between the earths surface
and a depth of 70 kilometers below the surface. - earthquakes in this class are detected at all
three types of plate boundaries-trenches, ridges
and fault boundaries. - most earthquakes have shallow focus.
28Three Types of Focus
- 2. Intermediate-focus
- earthquake originates between 70 and 300
kilometers beneath the surface. - 3. Deep-focus
- earthquake originates 300 to 700 kilometers below
the surface. - Both occurs at trench boundaries, where one plate
moves under another.
29Detecting Earthquakes
- An earthquakes energy moves from the focus as
Seismic Waves. (Sizmik) - These waves travel to all directions.
- An earthquake generates 3 kinds of seismic waves.
- These waves are
- P-waves (Primary)
- S-waves (Secondary)
- L-waves (Surface)
30Waves
- In the illustration below, P-waves have the
movement like that of Slinky. While S-waves have
the movement of a snake or a rope. L-waves has
movements of an ocean wave.
31P or Primary Wave
- The fastest seismic wave
- Can travel through any material on earth- solid
or liquid - P-waves compress and expand particles that lie on
their path
32S or Secondary Wave
- It moves at half the speed of P-waves
- Can travel only through solids
- Movement within the earth resembles to wavelike
motion that results when one shakes a stretched
rope from side to side.
33L or Surface Wave
- The slowest wave
- Moves along the earths surface
- Causes most damage among all waves
- Resembles thw motion of ocean waves.
34Using Seismographs to Find the Epicenter
- Seismograph- A sensitive instrument that measures
and records seismic waves.
35How does it work?
- A seismograph has a heavy weight suspended from a
support that is attached to bedrock. During an
earthquake, inertia keeps the weight and the pen
attached to it still. When a seismic wave passes,
the support, base and revolving paper drum shake.
Thus, the pen marks zigzag lines on a paper drum,
recording the movements of the earth. The
recorded lines are the...
36Seismogram
- A recording or the recorded lines of a
seismograph. - In the figure below, there are 3 distinct groups
of zigzag lines that correspond to the different
kinds of seismic waves.
37The Epicenter and the Seismogram
- Scientists analyze the time difference between
the arrival of the P and S waves. - By doing so, they can calculate the distance to
the earthquakes epicenter.
38How do they do it?
- Note Please refer to the pictue at the past
slide. - Readings from 3 seismograph stations are needed
to locate the epicenter of the earthquake. Assume
that a scientist calculates the distance from
Station A to the epicenter to be 1000 km. The
distance is determined on the difference of
arrival time of the 2 waves. The scientist knows
the distance of A to the epicenter. The scientist
draws a circle on a map which has a radius the
equivalent of 100 km. Meanwhile,Stations B and C
determines the distance to be at 500 and 400 km,
respectively. Again, they draw circles. The
meeting point of the circles is the epicenter.
39Seismic Waves and The Earths Interior
- The seismic waves that result from an earthquake
spread throughout the earth. - Geologists study the speed and the paths of
seismic waves to learn about the earths
interior. - Our knowledge of the earths layers relied on the
changes in speed and direction of seismic waves.
40Seismic Waves and The Earths Interior
- Early in the century, geologists discovered that
large areas on the side of the earth away from
the earthquake focus do not receive waves. Look
at the image below.
41P-Waves and the Earths Interior
- In the case of P-waves, they can pass through the
mantle, the liquid outer core, and the solid
inner core. Notice the small shadow zone at the
image. It has been stated that P-waves can pass
through all particles.
42S-Waves and the Earths Interior
- While at the S-waves, a large shadow zone is
formed. Again, it has been staterd that S-waves
can only pass through solids. - This discovery has enabled scientists to conclude
that the outer core is liquid.
43Types of Earthquake
- 1. Tectonic type- earthquake that result from the
upward and downward movements of the crustal
plates due to pressure. - 2. Volcanic type- earthquakes produced by the
pressure generated by magma rising through faults
towards the earths surface.
44Intensity
- Intensity- measure of an earthquakes effect or
damage in a place. - Modified Mercalli Scale named after Guiseppe
Mercalli is used as a basis for the intensity of
an earthquake.
45Modified Mercalli Scale Intensity Scale-
Description
- Intensity Scale- Description
- I-Not felt
- II-Felt by persons at rest
- III- Felt indoors
- IV- hanging objects swing
- V- felt outdoors
- VI- felt by all
46Modified Mercalli Scale Intensity Scale-
Description
- VII- difficult to stand
- VIII- steering of cars affected
- IX- general panic
- X-most masonry and frame structures destroyed
with their foundations - XI- rails bent gently
- XII- damage nearly total
47Magnitude Richter Scale
- Magnitude- measures the energy released during
quake by measuring the amplitude of the largest
wave recorded on the seismogram - Richter Scale- named after Charles Richter used
as basis for the magnitude. The scale is
logarithmic, one point increases in the scale
means tenfold increases
48Richter ScaleMagnitude Scale- Description
- 1- only detectable when an ultrasensitive
seismometer - 2- hardly susceptible shocks
- 3- very feeble shocks
- 4- feeble shocks
- 5- earthquakes with moderate strength
49Ritcher ScaleMagnitude Scale- Description
- 6- strong earthquakes
- 7-major earthquakes
- 8- great earthquakes
- 9-never occurred
50How are the Size and Strength of an Earthquake
Measured?
- Intensity
- subjective measure of the kind of damage done and
peoples reactions to it - isoseismal lines identify areas of equal intensity
- Modified Mercalli Intensity Map
- 1994 Northridge, CA earthquake, magnitude 6.7
51- Measuring Earthquakes
-
- The power (magnitude) of an earthquake is
measured on the Richter scale, using an
instrument called a seismometer. -
- The Richter scale is numbered 0-10 with 10 being
the most powerful. The Richter scale is
logarithmic an earthquake measuring 7 is 10
times more powerful than one measuring 6 and 100
times more powerful than one measuring 5. Up
until 2 on the Richter Scale only instruments
will detect the earthquake. Earthquakes above 6
cause serious damage and sometimes many deaths -
- The Mercalli scale measures the damage caused by
an earthquake. The Mercalli scale goes from I to
XII e.g. VI. Everyone feels movement. People
have trouble walking. Objects fall from shelves.
Pictures fall off walls. Furniture moves. Plaster
in walls might crack. Trees and bushes shake.
Damage is slight in poorly built buildings. No
structural damage.
52How 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
53Effects Of Earthquakes The Richter Scale
- After an earthquake, its description usually
includes a number from 1 to 9 in the Richter
Scale. - This number indicates the magnitude or the total
amount of energy released.
54Charles F. Richter The Inventor
- He was a geologist stationed at the California
Institute Of Technology. - Before he invented it, earthquakes were measured
at a much less scientific scale. Personal
observations were made, and scientists had to use
this to base their conclusions. - This method greatly reduced the guesswork in
determining the magnitude of an earthquake.
55What do earthquakes do to the Earth?
- Earthquakes do a lot of effects on the earth.
These include - Structural damage
- Benito Juarez Hospital, Mexico City. (taken in
1985)
56What do earthquakes do to the Earth?
- Tsunami, a Japanese word meaning harbor wave.
These are really different from the actual harbor
waves, but can do a significant amount of damage.
57What Controls the Level of Shaking?
- Magnitude
- More energy released
- Distance
- Shaking decays with distance
- Local soils
- amplify the shaking
58Is there such a thing as Earthquake Weather???
No!
59Earthquake Effects - Ground Shaking
Northridge, CA 1994
60Earthquake Effects -Ground Shaking
Northridge, CA 1994
61Earthquake Effects - Ground Shaking
Loma Prieta, CA 1989
KGO-TV News ABC-7
62Earthquake Effects - Ground Shaking
Kobe, Japan 1995
63Earthquake Effects - Ground Shaking
Kobe, Japan 1995
64Earthquake Effects - Surface Faulting
Landers, CA 1992
65Earthquake Effects - Liquefaction
Source National Geophysical Data Center
Niigata, Japan 1964
66Earthquake Effects - Landslides
Source National Geophysical Data Center
Turnagain Heights, Alaska,1964 (upper left
inset) Santa Cruz Mtns, California , 1989
67Earthquake Effects - Fires
Loma Prieta, CA 1989
KGO-TV News ABC-7
68Earthquake Effects - Tsunamis
1957 Aleutian Tsunami
Photograph Credit Henry Helbush. Source
National Geophysical Data Center
69Earthquake Preparedness Before- develop a
disaster plan secure your home store flammable
pack survival kit lightly and conduct
earthquake drills.
70Earthquake Preparedness
During- cover your head look for a safe place
to hide temporarily stay in an open area go to
a higher ground for tsunami alert and move away
from steep elevations.
71Earthquake Preparedness
After- exit building calmly see if you have
injuries and do not enter a building in attempt
to save someone.
72QUIZ
- 1. Which activities are earthquakes usually
associated with? - 2. What is a fault?
- 3-5. Name the 3 movements of rock.
- 6. What causes these movements? (2 words.)
- 7. Which theory explains the cause why
earthquakes occur?
73QUIZ
- 8-10. Name all types of faults.
- 11. There are 3 types of focuses, the Shallow,
_______, and the Deep. - 12. What is the slowest wave?
- 13. Name the instrument that detects earthquakes
and its recordings. - 14. At least how many circles are needed to
locate the epicenter?
74QUIZ
- 15. Which wave can penetrate the cores?
- 16. Which wave cannot penetrate the outer core?
- 17. Who invented a scale used to describe an
earthquake? - 18-19. Which main effects were described here?
- 20. Name at least an engineering technique given.
75Thank you for viewing and have a good day!
76References
- www.google.com
- Integrated Science book
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78 QUIZ
- Fill in the blanks
- Earthquake is the the shaking or trembling caused
by the sudden release of ________. - The point within Earth where faulting begins is
the FOCUS, or ___________. - Shaking of earth due to movement of rocks along a
_________.
79 QUIZ
- 4. Can be visible on the ________ or can be far
underground. - 5. ________ is where an oceanic plate is
converging with a continental plate. - 6. San Andreas fault is what kind of fault?
- 7. _______ results when a system of forces pushes
an object from opposite sides.
80 QUIZ
- 9. If the forces acting on these rocks exceed
this limit, or overcome the ________ between
blocks, the crust snaps and an earthquake occurs.
- 10. One block can move down and the other can
move up, or vice versa is a _______ fault. - 11. The point directly above the focus on the
surface is the _________.
81 QUIZ
- 12. ______ focus earthquake originates between
the earths surface and a depth of 70 kilometers
below the surface. - 13. _________ results when a system of forces is
applied to an object in different directions. - 14. The exposed upward block forms a cliff-like
feature known as a ______.
82 QUIZ
- 15. In ______ focus , the earthquake originates
between 70 and 300 kilometers beneath the surface.
83 answers
- Fill in the blanks
- Energy
- Hypocenter
- Fault
- Crust
- Subduction zone
- Strike-slip
- Compression
84 Answers
- Fill in the blanks
- 9. Friction
- 10. Normal
- 11. Epicenter
- 12. Shallow
- 13. Shearing
- 14. Fault scarp
- 15. Intermediate