Earthquakes

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Earthquakes

• I. Causes of Earthquakes

A. Why do earthquakes take place?
1. Rocks act the same way rubber bands work.
2. Applying stress to a rock will cause it to
bend or stretch.
3. Stress causes the rock to deform.
4. When the rock cant handle the stress it
eventually breaks.
5. The area in which a rock breaks is called a
fault.
6. When the break occurs energy is released.
7. The energy causes the rock to vibrate causing
an earthquake.
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B. There are three factors that cause breakage in
rock.
Force that squeezes rock layers together.
1. Compression -
2. Tension -
Force that stretches rock layers apart.
Force that causes the rock layers to slide by
each other.
3. Shear -
C. Each one of these forces will cause a
different fault.
Compression forces cause this type of fault
1. Reverse Faults-
2. Normal Fault-
Tension Forces cause this type of fault.
3. Strike-Slip Faults -
Caused by shear forces.
A.) Rocks move sideways past each other.
B.) San Andreas Fault in California is this type.
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II. Earthquake Energy
A. When rock breaks, energy is released as a
seismic wave.
Energy wave that moves outward, in every
direction, form the center of the earthquake.
1. Seismic Wave -
2. Epicenter - is the point on the earths
surface directly above the earthquake center.

• III. Types of Seismic Waves

A. There are three types of seismic waves.
Energy waves that
1. Primary Waves (P waves) -
move through the ground in a back and forth
motion.
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Examples of P waves
A.) Pushing down on your car and then letting go.

B.) A slinky.
P waves are the fastest moving earthquake
waves. (6km/s).
2. Secondary Waves (S Waves) - Move through the
ground in an up and down motion.
Examples
A.) teeter- totter, or seesaw.
S waves move half as fast as P waves. (3 km/s)
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Seismic Waves Cont.
3. Surface Waves (L Waves) -
Energy waves that
travel along the surface of the earth like waves
do in the ocean. (Rolling motion)
L waves move the slowest. (1 km/s)
Cause the most damage during an earthquake.

• IV. Using Seismic Wave

A. Scientists use the different speeds of seismic
waves to find the epicenter of an earthquake.
1. Seismograph Stations -
Place where the epicenter
Of an earthquake is measured.
2. When an earthquake occurs P waves will reach
the seismograph station before the S waves.
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Using seismic waves cont.
3. The further the epicenter, the higher the
interval between the P wave and the S wave
arrival time.
4. When seismic wave information is obtained by
at least three stations, the epicenter of an
earthquake can be found.
5. P waves travel 6 km/s and S waves travel 3
km/s.
6. When the waves arrive at the station we can
calculate the distance to the epicenter.
7. Scientists at each station draw a circle on a
map.
8. The radius of each circle is the distance away
the earthquake epicenter was.
9. The place where all three circles cross is the
epicenter.
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V. Earthquake Strength
A. A seismograph is used to measure the strength
of an earthquake.
1. The amount of energy released is the
earthquakes magnitude.
2. Magnitude is measured using the Richter Scale.

3. A 1 magnitude earthquake is the weakest and a
10 magnitude is the strongest.
4. There has never been a reading over 9.0
5. An earthquake that is 1 magnitude higher than
another releases 32 times more energy.
A.) How much more energy is released from an 8
mag. earthquake than a 6 mag. earthquake?
32 squared 1024 times more energy released.
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VI. Tsunamis
A. What is a tsunami?
1. Tsunami - An earthquake generated ocean wave.

B. How do they form?
1. An earthquake or landslide releases energy.

2. If under the ocean the energy will push
against the water, generating a powerful wave.

3. These waves can be from 30 to hundreds of feet
high.
4. Most occur in the Pacific Ocean.
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VII. Earthquake Safety
A. Preparing for an earthquake
1. Study the region you live in.
2. If there is an earthquake record in that area,
other earthquakes can happen.
B. Complete yourself.
C. Buildings and Highways
1. Buildings and highway over passes are being
reinforced with alternating layers of steel and
rubber.
2. Highways are built with concrete reinforced
with steel.
3. Some building foundations are built on rollers
that can slide on steel beams a few millimeters
to ease stress.