Earthquakes

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Earthquakes

• An Earthquake is any vibrating, shaking or rapid
  motion of the Earths crust.
• Most Earthquakes occur at zones of weakness or a
  break in bedrock known as a fault.

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Folding
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Thrust
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• When the stress built up in the rock is greater
  than what the rock can resist, the crust shifts.
• A sudden release of energy radiates in all
  directions as vibrations.

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Cute Baby Moment
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• The focus is the place underground where the
  actual break occurs.
• The epicenter is the surface directly above the
  focus.

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Epicenter
focus
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• After the earthquake waves move away from the
  epicenter.
• When the waves reach a location the earth seems
  to shake.
• The further a location is from the epicenter the
  weaker the waves are when they reach that
  location.

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San Andreas Fault Video(45MIN)
https//www.youtube.com/watch?vb5f09mh-gIM
San Andreas Fault Video (4.5 min)
https//www.youtube.com/watch?v_YLjIvJXhpg
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There are two kinds of waves
P S
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P (primary waves)- travel through liquids and
solids. P waves move faster than S waves. P waves
cause particles to move in the direction of the
wave.
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S (secondary waves)- travel only through
solids. S waves are slower than P waves. S waves
cause particles to move at right angles to the
direction of the wave.
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L (Land) Waves are caused when P Waves and S
Waves Combine to cause a circular motion of the
rock particles. L waves cause the most
destruction during an Earthquake
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Land Waves
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• The characteristics waves have in different
  conditions allows geologists to infer properties
  of the Earths interior.
• https//www.youtube.com/watch?vyOGoKCK17a4

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Measuring Earthquakes

• There are two different ways to measure
  earthquakes.
• Magnitude scales- based on seismometer readings.
• Intensity scales- based on reports of damage.

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• Magnitude Scales
• Seismometer- an instrument designed to detect and
  measure seismic waves. A pen is attached to a
  heavy mass on a spring. When the ground shakes,
  the mass remains stationary and the paper moves
  under it.

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11 210 3100 41000 510000 5100000 71000000 8
10000000 9100000000 7 is 100X greater than a 5
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• Seismograph- a seismometer that makes a recording
  of seismic waves.
• Each magnitude is 10 times greater than the
  previous number.
• A magnitude 5 earthquake is 10 times stronger
  than a magnitude 4 earthquake. A magnitude 6 is
  100 times stronger than a magnitude 4.

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• Intensity scale-
• The Mercalli scale is based on the damage to
  structures and accounts of witnesses.
• 1-2 - may not be felt
• 5-6 - some dishes and windows break
• 7-8 - hard to stand, collapse of some structures.
• 10-11 - Visible waves on ground, total
  destruction.

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Since we know how fast P-waves and S-waves
travel, we can use this information to calculate
the distance to an epicenter
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Damage from Earthquakes

• Shaking- buildings may be damaged or collapse.
• Movement of crust- damages roads and railroads.
• Tsunamis- earthquakes in oceans cause large waves
  which may swamp coastal areas thousands of miles
  away.

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Human Dangers

• Fires- broken gas pipes often ignite.
• Broken water mains make it hard to fight fires.
• Landslides often occur in soft ground.
• Areas of high risk have stricter building codes
  to help keep structures from falling apart during
  quakes.

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• Locations of Earthquakes and Volcanoes
• Most all earthquakes and volcanoes occur in a
  belts of crustal activity.
• The largest belt surrounds the Pacific ocean
  which is an old ocean plate and is subducting all
  around its borders. It is called the Ring of
  Fire.

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Damage from Volcanoes

• Ash- may cover large areas, very difficult to
  deal with. Machines may not work, clogs air
  filters.
• Lava- smaller areas covered but nearly
  unstoppable.
• Toxic gasses- hot, fast-moving gasses may
  suffocate people.

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