Earthquake Waves

1
Earthquake Waves
Chapter 6-2
2
Focus and epicenter
Actual location of fault Up to 700 km below
surface
3
Focus and epicenter
Surface location directly above the focus
Actual location of fault Up to 700 km below
surface
4
P-waves

• Primary waves
• Compression waves
• Travel in a horizontal direction
• First to arrive at a distant location

5
S-waves

• Secondary waves
• - vibrate at right angles
• to p-wave
• - particles move back
• and forth but wave
• moves forward
• - second to arrive at
• distant location

6
Surface Waves

• Surface waves
• - travel parallel to
• Earths surface
• - have greatest height
• - move like an ocean
• wave
• - last to arrive at
• distant location

- are responsible for damage
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Locating Epicenter

• Time lag between P-wave and S-wave indicate how
  far the earthquake is from a seismograph station.

Lag Time
8
Locating Epicenter

• The lag time tells us how far we are from an
  earthquake but not from which direction

Epicenter can be any where on radius of the circle
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Locating Epicenter

• At least ____ seismograph stations are needed to
  pinpoint the epicenter of an earthquake

Infinite number of possible epicenters
10
Locating Epicenter

• At least ____ seismograph stations are needed to
  pinpoint the epicenter of an earthquake

Possible epicenter
Possible epicenter
Two seismograph stations narrow possible
epicenters down to two
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Locating Epicenter

• At least three seismograph stations are needed to
  pinpoint the epicenter of an earthquake

epicenter
Three epicenters narrows possible locations down
to one
12
DEMO
13
Measuring Earthquakes

• Mercalli Scale
• - rates earthquake
• according to level of
• damage at a given
• location
• - 12 steps to scale
• - same earthquake can
• have different rating at
• different locations

14
Measuring Earthquakes

• Richter Scale
• - rates earthquakes
• magnitude based
• on size of seismic
• waves
• - works well with
• small, nearby
• quakes
• - waves are
• measured by a
• seismograph

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Measuring Earthquakes

• Moment Magnitude Scale
• - estimates the total
• energy released by an
• earthquake
• - can rate all earthquakes
• - scientists look at type
• and strength of waves,
• amount of movement,
• and strength of rocks
• that broke

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Video

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