Title: Earthquakes
1Chapter 21
2Section 1
3History of earthquakes
- First recorded earthquake was in China in 1177
B.C. - Greek mythology stated that they were caused by
Posseidon, God of the Sea who had the power of
earth shaker - a tsunami often followed, so it was an
appropriate power for a sea god - The 1811-1812 earthquakes in New Madrid, Missouri
were so widespread that they were felt in Boston,
Massachusetts.
4- Seismology
- Where do they happen?
- Study of earthquakes
- Occur near tectonic plate boundaries
- Tectonic platelarge pieces of Earths crust that
move on top of the softer rock beneath it - Movement causes plates to rub against each other
- Faultoccurs where there is a break in the
Earths crust along the area where the plates are
rubbing against each other
5- Earthquakes can happen because those blocks of
crust move suddenly along the faults - Regions where a large number of these earthquakes
occur are called earthquake zones
6World map of tectonic plates
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9- Tectonic plates push against each other and build
up potential energy - Potential energy energy an object has because of
its position and shape created by stress - When stored energy is released, it becomes
kinetic energy (the energy of motion) - An earthquake is kinetic energy traveling through
the Earth
10- Rocks can be deformed by the stress at a plate
boundary - Similar to a rubber band stretchingonce it
breaks, the pieces return to their original shape - This is called elastic rebounddeformed rock
returns to its original shape - This causes a huge amount of energy to be
released and the ground shakes
11- Are all earthquakes the same?
- Earthquakes vary depending on where they
originate - Some earthquakes occur along faults in the middle
of tectonic plates - 3 types of boundaries that can create
earthquakes - Transformmake strike-slip fault
- Convergentreverse fault
- Divergentnormal fault
12- Transform
- Convergent
- Divergent
- Causes moderate to shallow earthquakes
- Crust slides horizontally
- Form strike-slip faults
- Strong, deep earthquakes
- Crust slides vertically
- Create reverse faults
- Weak, shallow earthquakes
- Crust is pulled away from each other slide
vertically - Creates normal faults
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14Hanging wall
Foot wall
Strike slipthe plates slip past each other
Reversethe hanging wall moves upward relative to
the foot wall
Foot wall
Hanging wall
Normalthe hanging wall moves down relative to
the foot wall
15Strike slip example
16Reverse fault example
17Dixie Valley-Fairview Peaks, Nevada earthquake
December 16, 1954
Normal fault example
18San Andreas Fault
All photos courtesy of USGS
19Bigger faults make bigger earthquakes
20- Kinetic energy is released in the form of seismic
waves - Seismic waves waves of energy that travel
through the Earth, away from an earthquake in all
directions - 2 types of waves
- Surface wavestravel only on Earths surface
- Body wavestravel through Earths interior
include p waves and s waves - Each type travels thru Earths layers at
different speeds due to the intensity of the wave
and the material they go thur (ex. Rock, soil,
liquid)
21- P for primary
- S for secondary
- P waves travel through solids, liquids and gases
- Fastest seismic waves
- Called primary waves because they are the first
to be detected - Move rock particles back and forth by squeezing
and stretching the rock - S waves are second fastest
- Stretches rock back and forth
- Also called secondary waves and shear waves
- Cannot travel thru gas or liquid b/c they cannot
spring back to their original shape
22- Move the ground surface up and down as the wave
travels - Does not affect the rock deep below the surface
- Can feel like a roller coaster ride
- Travel more slowly than body waves
- Most destructive type of wave
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24Section 2
25- Seismologists use instruments called seismographs
to locate earthquakes - Seismographinstruments that record seismic waves
and are located near or on the surface of the
Earth - When the waves move the seismograph, it creates a
seismograma tracing of ground movement
26Seismograph
27- Seismograms are used to find an earthquakes
epicenter - epicenterthe point on the Earths surface
directly above the earthquakes starting point - Focusthe point inside the Earth where the
earthquake began
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29- Seismologist find the epicenter using the S-P
time method - They collect seismograms from different locations
put them on a graph - They can see the distance each location is from
the beginning of the earthquake - This helps them locate the epicenter
30- To find the distance from one location to the
epicenter - Record time between p wave and s wave
- Measure amplitude
- Plot them on the graph
- That will give you the distance to the epicenter
- If you have many of these, you can plot them on a
map and find the epicenter
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32- Measuring strength
- Richter scale
- Earthquake energy
- Seismograms can be used to find earthquake
strength - Measures earthquake strength
- Developed by Charles Richter in 1930s
- As the magnitude increases, the amount of energy
released increases - Each time magnitude increases, the amount of
energy released is 31.7 times greater - A m 4.0 is 31.7 times stronger than a m 3.0!
33Richter Scale
34Section 3
35- Earthquake-hazard levela measure of how likely
an area is to experience an earthquake - This is determined by past and present seismic
activity - Different areas of the country and the world have
varied hazard levels
36 The red zones are
the ones where seismic activity is most likely to
occur, and the white zones show areas where
seismic activity is least likely (but still
possible).
37- Forecasting
- Strength and frequency
- Seismologists use patterns to help predict
seismic activity - The strength of an earthquake is related to it
frequency (how often the occur) - There are many more weak earthquakes than there
are stronger earthquakes - The number strength of the earthquakes are
recorded and this helps predict future
earthquakes
38- States that areas along active faults that have
had few earthquakes are the places where strong
earthquakes will happen in the future - Those areas with few earthquakes are called
seismic gapsthere is a gap in seismic activity
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40- Buildings are often damaged or destroyed due to
the force of an earthquake
41Earthquake Effects - Ground Shaking
42Result of ground shaking
43Surface fault
Landslide resulting from earthquake
44- Are you prepared?
- Before shaking
- During shaking
- After shaking stops
- Preparation for earthquakes helps to save lives
and property - Have an earthquake-safety plan for you and your
family - Be prepared with medical and food supplies
- Get under table or desk and protect your head
- Stay away from power lines and buildings
- Move away from any dangers
- Be prepared for aftershocks
45What Controls the Level of Shaking?
- Shaking decays with distance
-aftershocks can continue for days, weeks or even
years!