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Inside Earth: Chapter 2 Earthquakes

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Title: Inside Earth: Chapter 2 Earthquakes


1
Inside Earth Chapter 2- Earthquakes
  • Section 2 Measuring Earthquakes

2
Guide For Reading
  • What are the different kinds of seismic waves?
  • How does the energy of an earthquake travel
    through Earth?
  • What are the scales used to measure the strength
    of an Earthquake?

3
There are about ______ earthquakes per day,
worldwide.
  • 8,000

4
Most earthquakes begin below the earths surface
in the _______ within ______ kilometers from
Earths surface.
  • Lithosphere
  • 100

5
Focus
  • The point beneath Earths surface where rock
    breaks under stress and causes an earthquake

6
Epicenter
  • The point on Earths surface directly above an
    earthquakes focus

7
Seismic Waves
8
Seismic Waves
  • A vibration that travels through Earth carrying
    the energy released during an earthquake

9
Figure 11 At what point do seismic waves first
reach the surface?
  • The epicenter

10
What determines how much the ground shakes during
an earthquake?
  • How close a location is to the epicenter
  • The types of rock and soil surrounding the
    epicenter determines how much the ground shakes

11
Guide For Reading What are the different kinds
of seismic waves?
  • There are three types of seismic waves
  • Primary Waves (P waves)
  • Secondary Waves (S waves)
  • Surface Waves
  • An earthquake sends out two types of waves P
    waves and S waves
  • When the waves reach Earths surface at the
    epicenter, surface waves develop.

12
Primary Waves
13
Primary Waves (P Waves)
  • A type of seismic wave that compresses and
    expands the ground
  • The first wave to arrive at an earthquake

14
Describe how P waves move?
  • P waves compress and expand like an accordion
  • When P waves arrive they vibrate the particles of
    the crust forward and back along the path of the
    wave

15
Secondary Waves
16
Secondary Waves (S Waves)
  • A type of seismic wave that moves the ground up
    and down or side to side

17
How are P waves different from S Waves?
  • P waves compress and expand the ground
  • These waves cause buildings to contract and
    expand
  • P waves travel through solids and liquids
  • S waves vibrate from side to side
  • These waves vibrate from side to side and thrust
    the ground up and down, or back and forth
  • S waves can not move through liquids

18
Surface Waves
19
Surface Waves
  • A type of seismic wave that forms when P waves
    and S waves reach Earths surface

20
Why do you think surface waves produce more
severe ground movements than P waves and S waves?
  • Surface waves consist of loose soil, sand,
    gravel, mud, small rocks, not solid rock
  • These more loose substances are more likely shift
    and slide

21
Guide For Reading How does the energy of an
earthquake travel through Earth?
  • Seismic waves carry the energy of an earthquake
    from the focus, through Earths interior, to the
    epicenter, and across the surface

22
Detecting Seismic Waves
23
Seismograph
  • A device that records ground movements caused by
    seismic waves as they move through Earth

24
Describe how a mechanical seismograph records
ground movement.
  • A heavy weight attaches to a frame by spring or
    wire
  • A pen connected to the weight rests its point on
    a rotating drum
  • During an earthquake the seismic waves cause the
    drum to shake while the pen stays in place
  • The pen records lines on the paper around the drum

25
Measuring Earthquakes
26
There are at least ______ different measures for
rating earthquakes.
  • 20

27
Magnitude
  • The measurement of an earthquakes strength based
    on seismic waves and movement along faults

28
The Mercalli Scale
29
Mercalli Scale
  • A scale that rates earthquakes according to their
    intensity and how much damage they cause
  • Developed in the early twentieth century

30
An earthquakes ______ is the strength of ground
movement in a given place.
  • Intensity

31
The Mecalli scale has ______ steps and describes
how an earthquake affects ______, ______, and the
______.
  • 12
  • People
  • Buildings
  • Land surface

32
Figure 14 How would you rate the damage to the
Foligno city hall on the Mercalli scale?
  • The damage would probably rate VII - VIII

33
The Richter Scale
34
Richter Scale
  • A scale that rates seismic waves as measured by a
    particular type of mechanical seismograph

35
How does the Richter scale measure an earthquake?
  • The Richter scale measures seismic waves using a
    seismograph
  • Over time, mechanical seismographs were replaced
    by electronic seismographs

36
What is a strength of the Richter scale when
measuring earthquakes? What is a weakness?
  • Strength Provides accurate measurements for
    small, nearby earthquakes
  • Weakness Does not measure larger and more
    distant earthquakes well

37
How are the Mercalli scale and the Richter scale
similar? How are they different?
  • Both measure the strength of an earthquake
  • The Mercalli scale measures the strength in terms
    of extent people notice the earthquake and the
    amount of damage caused
  • The Richter scale measures the size of seismic
    waves

38
The Moment Magnitude Scale
39
Moment Magnitude Scale
  • A scale that rates earthquakes by estimating the
    total energy released by an earthquake

40
Why is the moment magnitude scale used today by
geologists to measure earthquakes?
  • The moment magnitude scale determines the total
    energy released by an earthquake
  • This scale uses a electronic seismograph that can
    measure earthquakes that are big or small, and
    near or far
  • Geologist examine movement along the fault and
    the strength of broken rock
  • These two measurements give a more accurate
    measurement of an earthquake

41
On which scale would an earthquakes strength
vary from one place to another? Explain.
  • The Mercalli scale because the amount of shaking
    that people would feel and the damage to objects
    would be greater in a place closer to the
    earthquakes epicenter

42
Checkpoint (Page 68)What are three scales for
measuring earthquakes? Explain what each one
measures.
  • Mercalli Scale
  • Measures earthquakes on how much damage they
    cause
  • Richter Scale
  • Measures seismic waves using a seismograph
  • Measures small and nearby earthquakes
  • Moment Magnitude Scale
  • Looks at the total energy released
  • Measures large and distant earthquakes
  • Helps scientists predict how much fault movement
    their was

43
Locating the Epicenter
44
How do scientists calculate how far a location is
from the epicenter of an earthquake?
  • Scientists calculate the difference between
    arrival times of the P waves and S waves
  • The further away an earthquake is, the greater
    the time between the arrival of the P waves and
    the S waves

45
Figure 17 Use the map scale to determine the
distances from Savannah and Houston to the
epicenter. Which one is closer?
  • Houston
  • 800 Km
  • Savannah
  • 900 km
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