EARTHQUAKES

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EARTHQUAKES
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What is an Earthquake?

• Shaking and vibration at the surface of the earth
  caused by the underground movement along a FAULT
  plane.
• Results from a sudden release of energy in the
  Earth's crust that creates SEISMIC WAVES.
• Tectonic plate interaction is the primary cause.

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1960 Valdivia Chile Earthquake

• Largest Earthquake ever recorded
• Moment Magnitude of 9.5!!!

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This Building Was Washed in by Tsunami Wave

• Generated a massive tsunami
• 2000 killed over 550M in damage

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Ocean-Continental Convergence Nazca Plate
subducting beneath S. American Plate
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122 Killed in Onagawa, Japan
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61 Killed Hilo, Hawaii
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S. AMERICAN PLATE
NAZCA PLATE
EPICENTER
TRENCH
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EPICENTER

• The location on Earths surface that lies
  directly above the forces of an earthquake (The
  Focus).

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FOCUS

• The zone within Earth where movement along a
  fault produces an earthquake.

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What is a FAULT?

• A FAULT is a fracture or zone of fractures
  between two blocks of rock.
• Faults allow the blocks to move relative to each
  other.
• Slow movement creep
• Rapid Movement earthquake
• Faults may range in length from a few millimeters
  to thousands of kilometers.

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3 Classifications of Faults

• 1. Normal Faults Rock above the fault plane has
  moved DOWN relative to the rock below.
  (Divergence)
• Normal Fault Flash Animation
• 2. Reverse (Thrust) Faults Rock above the fault
  plane moves UP relative to the rock below.
  (Convergence)
• Thrust Fault Flash Animation
• 3. Strike-Slip Faults A fault along which the
  movement is horizontal. (Transform)
• Strike-slip Fault Flash Animation

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Stress Deformation
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Sumatra Mega-thrust (Reverse) Fault
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Tsunami 2004, Dec. 26th

• http//www.news.cornell.edu/releases/Jan05/tsunami
  Vid640.html

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SUMATRA TSUNAMI 2004
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Sumatra Tsunami 2004
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So.

• How do Seismologists measure the strength of an
• EARTHQUAKE?

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Giuseppe Mercalli 1902 Qualitative Data
Charles Richter 1936 Quantitative Data
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Modified Mercalli Scale (Qualitative)
Mercalli Intensity(at epicenter) Witness Observations
I Felt by very few people barely noticeable.
II Felt by a few people, especially on upper floors.
III Noticeable indoors, especially on upper floors, but may not be recognized as an earthquake.
IV Felt by many indoors, few outdoors. May feel like heavy truck passing by.
V Felt by almost everyone, some people awakened. Small objects moved. Trees and poles may shake.
VI Felt by everyone. Difficult to stand. Some heavy furniture moved, some plaster falls. Chimneys may be slightly damaged.
VII Slight to moderate damage in well built, ordinary structures. Considerable damage to poorly built structures. Some walls may fall.
VIII Little damage in specially built structures. Considerable damage to ordinary buildings, severe damage to poorly built structures. Some walls collapse.
IX Considerable damage to specially built structures, buildings shifted off foundations. Ground cracked noticeably. Wholesale destruction. Landslides.
X Most masonry and frame structures and their foundations destroyed. Ground badly cracked. Landslides. Wholesale destruction.
XI Total damage. Few, if any, structures standing. Bridges destroyed. Wide cracks in ground. Waves seen on ground.
XII Total damage. Waves seen on ground. Objects thrown up into air.
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Richter Scale is Logarithmic Each magnitude is
10x stronger than the previous.
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MOMENT MAGNITUDE

• Invented in 1977 by Hiroo Kanamori
• Moment is a measure of earthquake size that takes
  into account how much the fault slips and over
  how much area.
• Identical to Richter for EQs 7 and smaller.
• More precise for measuring larger EQs.

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INTENSITY vs. MAGNITUDE

• The MAGNITUDE of an EQ is how much energy is
  released during the event.
• INTENSITY describes the perceptible moving,
  shaking and damage experienced during the event.
• Two EQs can have same magnitude, but very
  different intensity depending upon such variables
  as location relative to the epicenter, type of
  bedrock and soil in the region, as well as the
  type of fault where the EQ occurred.

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How are Earthquakes Recorded?

• A seismogram is a record written by a seismograph
  in response to ground motions produced by an
  earthquake, explosion, or other ground-motion
  sources

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How do Seismologists use this Data?
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Seismic Waves

• 1) Surface Waves Waves that travel along
• Earths outer layer.
• 2) Body Waves Travel through Earths
  Interior.2 Kinds
• P- Waves
• S-Waves
• Identified by how they travel through the
  materials within the Earth

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Surface Waves

• Love Waves
• The first kind of surface wave is called a Love
  wave, named after A.E.H. Love, a British
  mathematician who worked out the mathematical
  model for this kind of wave in 1911. It's the
  fastest surface wave and moves the ground from
  side-to-side.

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Surface Waves

• Rayleigh Waves
• The other kind of surface wave is the Rayleigh
  wave, named for John William Strutt, Lord
  Rayleigh, who mathematically predicted the
  existence of this kind of wave in 1885. A
  Rayleigh wave rolls along the ground just like a
  wave rolls across a lake or an ocean. Because it
  rolls, it moves the ground up and down, and
  side-to-side in the same direction that the wave
  is moving. Most of the shaking felt from an
  earthquake is due to the Rayleigh wave, which can
  be much larger than the other waves.

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P-Waves (Compression)
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S-Waves (Shear)
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Seismic Waves
P-Waves S-Waves
Primary Waves Secondary Waves
Faster Slower
Compression Push Wave Shear Waves
Direction of Particle Movement (Push/Pull) Direction of Particle Movement (Side to Side)
Moves through liquids and solids Stop when they reach a liquid medium
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P Wave Shadow Zone
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S Wave Shadow Zone
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ESRT Time/Travel Graph P and S Waves
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Sample Regents Problem
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ESRT Time/Travel GraphS - P Lag Time (3 min.)
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Calculate Distance from Seismic Station to
Epicenter of EQ Using ESRT
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Lets try it another way
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ESRT Time/Travel GraphP and S Waves
7 min
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Heres Another One8/07 test
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Take difference between P arrival and S arrival
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And..
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Lets Be Virtual Seismologists!

• Virtual Earthquake - An Introduction