Earthquakes

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Earthquakes
Chapter 22.5
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Real- Time Earthquake Data

• http//earthquake.usgs.gov/

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EQs
EQ Movement of Es lithosphere that occurs when
rocks in the lithosphere suddenly shift,
releasing stored energy. EQs occur b/c stress
forces of have exceeded the strength of
rock. Stress builds when rocks along 2 sides of a
fault snag and lock (friction) as stress
builds so does POTENTIAL ENERGY IN
ROCKS When rocks are strained beyond limit
they break move. (Potential ? Kinetic Energy in
form of seismic waves)
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Stress Strain on Rocks
Stress Force that squeezes rocks together,
pulls them apart, pushes in diff.
directions. Stress causes strain or deformation
(change in shape or volume) of rock
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Low Temp. Pressure Near Crust
High Temps. Pressure
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Folds
Anticline up facing fold Syncline down ward
facing fold
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Faults
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Types of Faults

• 1. Dip SlipMotion up or down fault surface
• Reverse or Thrust Hanging wall moves UP.
• b. Normal Hanging wall moves DOWN

http//www.windows.ucar.edu/tour/link/earth/geolo
gy/fault.html
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Types of Faults

• 2. Strike slip
• Sliding Horizontal Movement
• 3. Oblique slipdip-slip strike slip combined

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Plate Boundary Convergent
Interpretation of Tectonic History
Divergent
Transform
Normal
Thrust/Reverse
Strike-Slip
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EQ Vibrations

• EQ vibrations begin at a point called a FOCUS.
• Vibrations travel from focus through the earths
  crust as waves.
• Surface directly above the focus is called the
  epicenter.
• These waves can be detected and measured on
  earths surface with a SEISMOGRAPH.

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SEISMOGRAPHS
Instrument that measures records EQ waves.
Strength of EQ waves is referred to as MAGNITUDE.
Wave Motion http//sunshine.chpc.utah.edu/labs/s
eismic/index.htm?ASPIRE_Session964f1ed30b7e49ceb8
1bd77f444d9230
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3 Types of Seismic Waves

• 1. Primary Waves (P waves)
• 2. Secondary Waves (S waves)
• Surface Waves
• Each wave originates from the FOCUS of the
  earthquake.
• Each wave travels in a different way, at
  different speeds, and causes different amounts of
  destruction.

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Seismic Waves vibrations produced by energy
released during EQ

• P Waves Primary Wave
• Arrives 1st Travels FASTER
• Longitudinal / Travel in direction of wave
  motion.
• Compress Expand like accordion (like sound
  waves)
• Move through Solids Liquids

• Virtual EQs http//www.sciencecourseware.org/Virt
  ualEarthquake/VQuakeExecute.html
• Seismic Waves http//www.geo.mtu.edu/UPSeis/wav
  es.html

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Seismic Waves

• S Waves Secondary
• Transverse Material vibrates perpendicular (rt
  angles) to wave motion
• What you FEEL in an EQ
• Rock moves up down or side to side
• Arrive after P
• Move only through SOLIDS

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Seismic Waves Surface Waves

• Surface Waves develop when vibrations reach
  surface
• Slower than P waves
• Most destructive Different types of motion
• More P S wave animations http//www-rohan.sdsu
  .edu/rmellors/lab8/l8maineq.htm
• Video clip http//news.bbc.co.uk/1/hi/sci/tech/4
  126809.stm

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Rating Earthquakes

• Earthquakes are rated in terms of MAGNITUDE or
  INTENSITY by different scales.
• Moment Magnitude Scale
• Richter Scale
• Mercalli Scale

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Moment Magnitude Scale

• Uses a seismogram
• Rates on scale from 1- 10
• Looks at Eqs in terms of ENERGY
• Each releases 31 times more ENERGY than the
  before it.
• Example
• A 6 releases 31 times more energy than a 5,
  and a 5 releases 31 times more energy than a 4.
  The energy difference between a 4 and a 6 EQ on
  the richter scale is 31 X 31 961

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How much more energy does a 7.5 release compared
to a 4.5?

• Show your work here.

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Richter Scale

• Uses a seismogram
• Rates on scale from 1- 10
• Looks at Eqs in terms of the SIZE OF THE WAVES
• 1 3 Small earthquake waves very little
  shaking
• 4 6 Moderate earthquakes noticeable shaking
  and some damage
• 7 - 10 BIG Earthquakes Very destructive

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Measuring EQs Mercali Intensity Scale

• Measures observed effects of Earthquake on a 1
  12 scale
• Degree of shaking and damage
• Not an actual measure of seismic waves
• Link
• http//www.abag.ca.gov/bayarea/eqmaps/doc/mmi.html
  

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Mercali Intensity Scale

• Measures observed RESULTS of Earthquake on a 1
  12 scale
• Degree of shaking and DAMAGE to structures
• Dont need a seismogram
• Link
• http//www.abag.ca.gov/bayarea/eqmaps/doc/mmi.html
  

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EFFECTS OF EQs

• Deaths Injuries but mostly from collapsing
  structures
• Damage to buildings structures (collapse)
• Underground water and gas pipes break floods
  fires
• Landslides
• Tsunamis

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Seismic Waves are used to Study Earths Interior
P and S waves are bent and their velocities are
affected as they move through material of varying
density
Link http//sunshine.chpc.utah.edu/labs/seismic/
index.htm?ASPIRE_Session964f1ed30b7e49ceb81bd77f4
44d9230
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A

• What type of fold is shown here? (Anticline or
  Syncline)
• 2. Would these folds be created in a DUCTILE
  (high temp. pressure, deeper in crust) or
  BRITTLE (low temp pressure, at surface)
  environment?

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• 3. These folds in Newfoundland New Jersey would
  have be produced
• When Pangaea assembled 240 Ma.
• When Pangaea broke apart 100 Ma
• During the ice age as glacial ice sheets
  retreated 10 Ka
• They are currently being produced by New Jerseys
  current tectonic activity.
• 4. Support your answer to 2 with a reason.

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B

• Is this a dip-slip or strike slip fault? If
  dip-slip say what type of dip-slip (Thrust or
  Normal).
• Is this fold produced by compressional
  extensional or shearing forces?
• What type of plate boundary would you expect to
  find these faults? (Convergent Divergent
  Transform)

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G
H

• 8. Which fault would be produced by shearing
  forces?
• 9. Would fault H be made in an ancient rift
  valley or a mountain building zone? Support your
  answer with a reason.

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10. A. What type of fault can you see in this
picture ? B. Could this location be an
ancient subduction zone? Why or why not?
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11. A. What type of fault can you see in this
picture ? B. What type of plate boundary
produces these faults?
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12. A. What type of fault can you see in this
picture ? B. Could this location be an
ancient convergent plate boundary? Why or why
not?
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13. A. What type of fault can you see in this
picture ? B. What type of forces produced this
fault? (There are 2 forces)
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Latest Quakes

• http//earthquake.usgs.gov/eqcenter/recenteqsww/Qu
  akes/quakes_all.php
• Top Ten Lists
• http//earthquake.usgs.gov/eqcenter/top10.php

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Links

• Virtual Earthquakes
• http//www.sciencecourseware.org/VirtualEarthquake
  /VQuakeExecute.html
• Wave Types http//www.geo.mtu.edu/UPSeis/waves.htm
  l
• Triangulation Hearing EQs
• http//www.seismo.unr.edu/ftp/pub/louie/class/100/
  seismic-waves.html
• More virtual seismograms
• http//www-rohan.sdsu.edu/rmellors/lab8/l8maineq.
  htm
• Earthquakes outline subducting slab Interactive
  Web Lab
• http//openlearn.open.ac.uk/mod/resource/view.php?
  id172185

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