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Earthquake Notes
1. Focus and Epicenter
a. The focus is the point at which rock begins to move or break. This is where the earthquake starts
and is usually many kilometers below the surface.
b. The point on Earth’s surface directly above the focus is the epicenter of the earthquake.
https://www.youtube.com/watch?v=hkvkcN9rVHs
What is an earthquake 1:52
2. Seismic Waves
a. The energy released in an earthquake travels in
waves.
b. Body Waves- Waves that travel from the focus
of an earthquake through Earth.
i. Primary Wave- faster, compression,
and travels through all of Earth's layers
(solid and liquid).
ii. Secondary Wave- slower, shear, and
only travels through solids.
c. Surface waves- waves that travel along Earth’s
surface. These waves travel out from the
epicenter and are slower than body waves.
Surface waves may cause a lot of damage.
i. Love wave- particles of material move
from side to side
ii. Rayleigh wave- particles of material
move in elliptical patterns.
https://www.youtube.com/watch?v=gl4FvHKzAlU&list=PLGz_MIXgneZQfIh6DycRCmOHb1oyk_SUP
S waves and P waves 0:10
3. Recording Earthquakes
a. A seismograph detects and records waves that are produced by earthquakes that may have
started hundreds, even thousands, of kilometers away.
b. The record sheet is called a seismogram. This helps to determine the location of the earthquake.
A seismogram can also be used to determine the strength or intensity of an earthquake.
c. Geologists know the speed at which the different types of waves travel through various earth
materials. Based on the difference in the arrival times of the first P wave and the first S wave,
seismologists determine the distance between the epicenter and a seismometer.
d. To locate the earthquake epicenter, seismologists must have data from at least three
seismometers. Draw 3 circles on a map at the appropriate distances from 3 seismometers. The
point where all circles meet is the epicenter.
4. Measuring Earthquakes
a. The magnitude is a measure of the
amount of energy released in an
earthquake.
b. Charles Richter developed one widely
used scale of earthquake magnitude in
1935. This is called the Richter
scale.
c. The Modified Mercalli scale
measures earthquakes based on the
amount of damage caused.
5. Earthquake Hazards
a. In an earthquake, ground shaking and foundation failure may cause buildings to collapse and
fires to ignite.
b. A large earthquake may be followed by a series of smaller ones, called aftershocks, originating
close to the focus of the large earthquake. Aftershocks can cause damage to buildings and other
structures.
c. Liquefaction occurs when loose soil temporarily takes on the properties of a liquid.
d. A Tsunami is huge wave that can be caused by underwater earthquakes and landslides. It can
travel quickly across large expanses of water.
https://www.youtube.com/watch?v=P3KOkbTHiQg Liquefaction 1:33
https://www.youtube.com/watch?v=OjZNTvVJLiw Aftershock 2 hours after initial quake 0:51
https://www.youtube.com/watch?v=3t-ICrxXuBY earthquake swimming pool 1:23
https://www.youtube.com/watch?v=khZbqXxa4Y4 SF Quake Indoor footage 0:46
https://www.youtube.com/watch?v=ceym2c18OQM Japan Tsunami 5:45
6. Earthquake Mitigation
a. In areas that are prone to earthquakes, engineers have attempted to construct buildings that are
earthquake resistant. The hope is to decrease the cost of damage and loss of life.