Earth Science 11
Name _______________________
Earthquakes
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There are more than a ____________ earthquakes each year
Several hundred move Earth’s surface significant distances
About ____ cause severe changes
Earthquake:
o Shaking of Earth’s crust caused by a __________________
o Result of the motions of ___________ plates
Can cause:
o Building collapse
o Explosions and fires from broken gas mains and electric wires
o Diseases from contaminated water supplies
o Food shortages due to supply routes becoming unusable
o Floods due to tsunamis
Causes of Earthquakes
Causes:
 __________ of a volcano
 __________ of a cavern
 __________ of a meteor
 __________ that builds up between two lithospheric plates
Elastic-rebound theory:
 Normally, the friction between plates prevents movement
 The ___________ cause the plates to change shape
 Eventually, the _________ becomes great enough to overcome the ___________________, and the
plates suddenly move (Earthquake)
Depth
 Focus:
o The ________ on the fault plane at which the ________ movement occurs
o The ________ of the ____________ released by the earthquake
o Can be up to 700 km deep
 Epicenter:
o The _______ on Earth’s __________ directly above the focus
Waves
 P-waves: A.k.a. compression waves, _________ waves
o Body wave – travel through the body of Earth
o Motion: back-and-forth
o Squeezes and stretches the rock material
o Able to travel though any material – ________________________________________________
o Velocity: about twice as fast as S-waves
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S-waves: A.k.a. shear waves, ___________ waves
o Body wave
o Motion: side-to-side
o Causes particles to move at right angles to the direction the wave is travelling
o Able to travel through __________ only
L-wave: __________ wave
o Motion: like ripples on a pond
o Travel slower than P-waves or S-waves
Seismograph
 Seismograph: ________________ that detects and ____________ earthquake waves
o Record horizontal/vertical motions
 Seismogram: The ___________ that records earthquake activity
o The first major zig-zag on the seismogram is the arrival of the P-wave (moves the fastest)
o The larger the zig-zag, the bigger the earthquake
Magnitude
 Seismograms can be used to determine the strength (magnitude) of the energy produced by the
earthquake
 Richter scale:
o Developed by Charles F. Richter in the 1940’s
o ______________ the amount of ___________ released by the earthquake
o Each _______________ number represents an earthquake ____ times stronger than the next
_________ number
o Ex. A magnitude 6 is 32 times stronger than a magnitude 5, and 1024 times stronger than
magnitude 4
 Seismic moment:
o Harder to measure than the Richter magnitude
o More accurate indicator of the total energy involved
o Ex. The 1906 San Francisco earthquake and 1964 Alaskan earthquake both had Richter
magnitude 8.3. However, the San Francisco earthquake had a seismic moment of 7.9; the
Alaskan earthquake 9.2. The Alaskan quake was stronger than the San Francisco quake.