Download Quaking, Shaking, Earth - East Hanover Township School District

1 What is an earthquake?
• Simply put:
• An earthquake is the shaking of the earth.
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2 - What causes an earthquake?
• Earthquakes are the Earth's natural
means of releasing stress.
• Due to the constant motion of the
Earth’ plates, this put stress on the
edges of the plates.
• To relieve this stress, the rocks tend
to bend, compress, or stretch.
An aerial view of the San Andreas fault in the Carrizo
Plain, Central California. Picture from www.usgs.gov
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3 - Locatin' the Shakin'
• Focus: the place on the Earth’s crust where the pressure was
released. Underground.
• Epicenter: the spot on the Earth’s surface directly above the focus.
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5 Normal Fault
•Rock above the fault
surface moves
downward in relation
to rock below the fault
surface.
•Sierra Nevada fault
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6 Reverse Fault
• Reverse faults result from
compression forces that
squeeze rock.
• If rock breaks from forces
pushing from opposite
directions, rock above a
reverse fault surface is forced
up and over the rock below
the fault surface.
• Cascadia
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7 Strike-slip Fault
• At a strike-slip fault, rocks on
either side of the fault are
moving past each other
without much upward or
downward movement.
• The San Andreas Fault is the
boundary between two of
Earth’s plates that are moving
sideways past each other.
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8 How does energy created by an earthquake
move through the Earth?
•Seismic waves are energy
waves that travel outward from
the source of the earthquake.
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10 P Waves
• Primary waves (P-waves)
cause particles in rocks to
move back and forth in the
same direction that the wave
is traveling.
• P-Waves are the fastest
waves and are felt first,
usually as a bang or a thump.
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11 S Waves
• Secondary waves (S-waves)
move through Earth by
causing particles in rocks to
move at right angles to the
direction of wave travel.
• These waves are slower than
P-Waves and more
destructive.
• AKA Transverse waves
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12 L Waves
• Surface waves (L-Waves) or land
waves move rock particles in a
backward, rolling motion and
a side-to-side, swaying
motion.
• Surface Waves reach the earth's
surface after P and S waves.
• Very destructive
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13 - How are seismic waves measured?
• Seismic waves from earthquakes
are measured with an instrument
known as a seismograph.
• Seismographs register the waves
and record the time that each
arrived.
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14 - Measuring Earthquake Magnitude
•Magnitude is a
measure of the
energy that is
released during an
earthquake.
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15 - Richter Scale
• The Richter magnitude scale is
used to describe the strength of
an earthquake and is based on
the height of the lines on the
seismogram.
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