1 What is an earthquake? •Simply put: • An earthquake is the shaking of the earth. Free powerpoint template: www.brainybetty.com 1
Jan 03, 2016
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.
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An aerial view of the San Andreas fault in the Carrizo Plain, Central California. Picture from www.usgs.gov
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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