Chapter 11- Earthquakes by glu87355

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									     Chapter 11-
    Earthquakes
       Continuation of plate
tectonics- convection in the
  asthenosphere is still the
     driving force of moving
          lithospheric plates.
Where do earthquakes occur?

     At plate boundaries where pressure builds
      up and eventually breaks rock

      – Usually not in the middle of plates

     Faults occur where boundaries meet and
      rocks “pass their elastic limit”

      – Earthquakes often occur near these fault lines
      – Three types of faults
Types of faults

   1. Normal faults
    – Caused by TENSIONAL forces
    – Forces PULL OR STRETCH rocks
    – Rocks above fault line move downward
2.   Reverse-
     - caused by COMPRESSIONAL forces
     - rocks are PUSHED toward each other
     - rocks above fault line move upward
3.   Strike-slip fault
     - Caused by SHEAR forces
     - Rocks move PAST EACH OTHER
     with little up or down motion.
Oral Pop Quiz (24points)

    Be able to NAME, SHOW and
     DESCRIBE how the rocks move at
     the fault line
    Be able to tell which type of forces
     (compressional, tensional or shear)
     cause each type of fault.
Locating earthquakes using
seismic waves
   An earthquake creates seismic waves that
    travel away from the epicenter of an
    earthquake.
    – Epicenter is the place on the Earth’s surface
      directly above where the earthquake occurred.
   Primary waves (P-waves) move away
    from the earthquake’s epicenter at a
    certain rate
   Secondary waves (S-waves) move away
    from the epicenter at a different, slower
    rate.
   Surface waves (no cool abbreviation)
    move at the slowest rate.
   Point where plate movement occurs
    and energy is originated is called the
    focus (can be miles below the
    surface).
   Point on Earth’s surface above the
    focus is called the epicenter
Seismic waves

    All types of seismic waves (s,p and
     surface) are detected by
     seismographs and recorded on
     seismograms.
To be shown during class discussion:

* Recent earthquakes

* Seismograph video clips:
   Three types of seismic waves:

   P waves travel fastest
    – Move particles back and forth in the same
      direction
    – Cause little destruction
   S-waves travel slower, cause more damage
    – Move particles back and forth at a ninety
      degree angle to wave motion
   Surface waves travel slowest, cause the
    most damage
    – Move particles side-to-side and in a
      swaying motion
    Calculating distance from the
    location of an earthquake
   The difference in arrival time
    between p-waves and s-waves can
    be timed to determine how far away
    from the seismograph station the
    earthquake occurred.
   With at least three stations reporting,
    we can pinpoint the earthquake’s
    location using TRIANGULATION
    (see next slide or page 312 for
    example).
 Plate Boundaries
Divergent: very little earthquake activity
Volcanic activity can vary

Convergent: earthquake activity is
 strong and often very deep.
Also, great amount of volcanic activity at
 subduction zones.

Transform: Earthquakes are frequent
  and often shallow.
Little to no volcanic activity.
Other Info:
   Seismic waves are recorded on paper
    called seismograms.
   The energy from earthquakes
    sometimes causes tsunamis- giant
    seismic ocean waves.
   The Richter Scale is used to measure
    the intensity of earthquakes
    – Largest recorded 9.3 2004 Indian Ocean
    – Each number jumps x32 in intensity.
   “Hot spots” are places on Earth that
    possess volcanic and earthquake
    activity but are NOT near plate
    boundaries.
            Lab Report

   How do seismologists locate the
    epicenter of earthquakes?

   Similarly, how did we find the epicenter
    of an earthquake in class?
Extra Credit Earthquake
Report

    By Permission Only
    Location, date and time
    Pictures
    Damage (cost), deaths, injuries
    Magnitude
    Difference in P/S waves in Punxsy
    Search USGS Top Ten for list of
     earthquakes. Also a list on p. 318.
    Other research
    Plates involved
Chapter 11 Test Questions


    Explain how Primary and Secondary
     waves are used to pinpoint the
     location of an earthquake’s epicenter

    Calculate the difference in
     earthquake magnitude using the
     Richter Scale
Homework:

   Page 330 Questions 1-9.
    – Write out answers



   Answer these questions.

    – THIS IS YOUR CHANCE!!!

								
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