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EARTHQUAKES

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Title: EARTHQUAKES Author: Teacher Last modified by: teacher Created Date: 3/22/2004 8:54:41 PM Document presentation format: On-screen Show (4:3) Company – PowerPoint PPT presentation

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Title: EARTHQUAKES


1
EARTHQUAKES
  • Section 21.2

2
What is an earthquake?
  • WHAT IS AN EARTHQUAKE?
  • An earthquake is a movement of Earths crust
    caused by a release of energy  
  • WHAT CAUSES AN EARTHQUAKE?
  • Eruption of a volcano
  • Collapse of a cavern or building
  • Major cause stress between two plates

3
Where do EQs occur in the world?
4
They occur along Plate Boundaries
5
Where do EQs occur in the U.S.?
6
What Causes Earthquakes?
  • Friction builds up between two plates
  • The stress causes the plates to deform or
    stretch
  • Eventually, the stress becomes great enough that
    it overcomes friction and the plates move
  • The plates snap back into their original shape
    and begin building up friction again

7
Damage from a 1906 EQ
8
What is the Focus of an EQ?
  • Point on the fault (or plates) where movement
    first occurs
  • Where an earthquake starts
  • 3 types
  • Shallow (0-70km)
  • Intermediate (71-300km)
  • Deep (301km and higher)

9
Epicenter
  • Point on the Earths surface directly above the
    focus
  • What is reported as the location of an earthquake

10
Earthquake waves
  • P-waves primary waves travel through solids,
    liquids, and gases back and forth motion
  • P waves are ______________ waves.

11
Earthquake waves
  • S-waves secondary waves travel through solids
    only side to side motion (snake)
  • S waves are ___________ waves

12
Earthquake waves
  • L-waves surface waves
  • Combination of up and down and back and forth
    motion
  • Cause the most damage due to their rolling action
    and long wavelengths

13
EARTHQUAKE!
14
EQ wave Diagram
15
Locating an earthquake
  • Seismograph an instrument that detects and
    records earthquake waves
  • P-waves always arrive first, then S-waves, then
    L-waves

16
Determining distance to the epicenter
  • P and S Waves Graph pg.767 Under Graphing
    Skills
  • As distance increases, the travel time for
    seismic waves increases also.

17
Locating an Epicenter
  • To locate the exact location of an epicenter, you
    must have points from three separate seismograph
    locations around the world

18
Earthquake Magnitude
  • Richter Scale
  • Developed by Charles Richter in the 1940s
  • Measures the amount of energy released by the
    earthquake itself
  • Scale from 1-10 (weakest - strongest)
  • Each number is 32 times stronger than the next
    lower number (Ex 6 is 32 times stronger than
    a 5 and 1024 times stronger than a 4)

19
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20
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21
Earthquake Prediction
  • We cannot predict earthquakes other than giving
    periods of time in which we think they will
    occur.
  • Earthquakes are most common along sliding plate
    boundaries, but they can occur in other places.
  • http//earthquake.usgs.gov/learn/kids/
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