Download chapter 6 earthquakes

CHAPTER 7
EARTHQUAKES
7.1 Notes
What are earthquakes?
• earthquakes - movements or shaking of the
ground when rock (plates) move suddenly
and release energy.
• aftershock – a release in energy after an
earthquake
Where do most earthquakes happen?
On plate boundaries (page 232)
What causes earthquakes?
• Movement of the tectonic plates
• When the plates break at a fault located at a
boundary
How do we know there are different
layers of the Earth?
• Because of seismic waves from earthquakes
• Seismic waves travel through solids faster than
liquids
• Seismic waves change direction when they change
the material they are going through (from a solid
to a liquid)
• elastic rebound – the sudden return of deformed
rock to its normal undeformed shape. (i.e. rubber
band)
7.1 Notes
•
seismic waves – waves of energy that travel
through and on the Earth
•
2 types of seismic body waves:
1. P-waves (primary waves) – the fastest seismic waves that
travel through solids, liquids, and gases
•
(the P-waves move like a slinky)
2. S-waves (secondary waves) – the second fastest seismic
waves that travel through solids
•
•
(the S-waves move like a snake)
1 type of seismic surface waves :
1. L-waves (land & last waves) – the slowest and most
destructive seismic waves that travel only on the surface/land
•
(the L-waves move in big slow circles)
7.2 Notes
Earthquake Measurements
• epicenter – the point on the
Earth’s surface directly above
the earthquake’s starting point
• focus – the point inside the
Earth where an earthquake
begins
7.2 Notes
• seismograph – an instrument at or near the
surface of the Earth that record seismic
waves (machine)
• seismogram – is a tracing of earthquake
motion created by a seismograph (paper)
How do you find an epicenter?
1. You need to find the S-P time difference
and that is the distance from the
seismograph to the epicenter.
•
P-wave time minus the S-wave time
2. Draw a circle around the seismograph
location.
3. Do this three times because you need three
seismograph stations to find an epicenter.
4. Where all three circles intersect is where
the epicenter is located.
To find an
epicenter you
need three
seismograph
stations. Where
are three radiui
interest is where
the epicenter is
located.
7.2 Notes
• The Richter scale measures the magnitude.
• magnitude – the strength of an earthquake
• The Mercalli scale measures the intensity.
• intensity – the amount of damage caused by an
earthquake
How do we measure an earthquake’s
intensity – the amount of damage caused
by an earthquake?
1. Magnitude – how strong it is (measured
by the Richter scale)
2. Population – the more people are around
when it happens the more dangerous it is
3. How much money it costs to repair the
damages – the more money it costs the
more damage was done
4. Location – Where did it happen?
How does the magnitude compare to the
other factors that measure the intensity?
Year
Earthquake Magnitude
Location
1970
San
Fernando
6.6
1990
Northridge
6.7
2005
San
Simeon
6.5
Location
setting
Los
Angeles
Area
Los
Angeles
Area
Small
town
Cost to
rebuild
Number of
deaths
$510
million
65
$40
billion
57
$250
million
2
7.3
• tsunami – a giant ocean wave that forms
after a volcanic eruption, an earthquake in
the ocean, a landslide, or a big asteroid
hitting the ocean.
• What is the major problem with a tsunami?
• Coastal flooding. Homes are destroyed due to
the water damage.