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Types of Seismic Waves

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Types of Seismic Waves Seismic waves carry energy from an earthquake away from the focus, through Earth s interior, and across the surface. – PowerPoint PPT presentation

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Title: Types of Seismic Waves


1
Types of Seismic Waves
  • Seismic waves carry energy from an earthquake
    away from the focus, through Earths interior,
    and across the surface.

2
.
-
  • Focus Point beneath the earths surface where
    the earth moves
  • Epicenter The point on the surface directly
    above the focus. It is where the strength of the
    earthquake is strongest.

3
Types of Seismic Waves
  • P waves are seismic waves that compress and
    expand the ground like an accordion.
  • S waves are seismic waves that vibrate from side
    to side as well as up and down.

4
Types of Seismic Waves
-
  • Surface waves move more slowly than P waves and S
    waves, but they produce the most severe ground
    movements.

5
Seismic Waves Activity
- Earthquakes and Seismic Waves
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6
Types of Stress
- Forces in Earths Crust
  • The stress force called tension pulls on the
    crust, stretching rock so that it becomes thinner
    in the middle.

7
Types of Stress
- Forces in Earths Crust
  • The stress force called compression squeezes rock
    until it folds or breaks.

8
Types of Stress
- Forces in Earths Crust
  • Stress that pushes a mass of rock in two opposite
    directions is called shearing.

9
Kinds of Faults
- Forces in Earths Crust
  • Tension in Earths crust pulls rock apart,
    causing normal faults.

10
Kinds of Faults
- Forces in Earths Crust
  • A reverse fault has the same structure as a
    normal fault, but the blocks move in the opposite
    direction.

11
Kinds of Faults
- Forces in Earths Crust
  • In a strike-slip fault, the rocks on either side
    of the fault slip past each other sideways, with
    little up and down motion.

12
Changing Earths Surface
- Forces in Earths Crust
  • Over millions of years, the forces of plate
    movement can change a flat plain into landforms
    such as anticlines and synclines, folded
    mountains, fault-block mountains, and plateaus.

13
Changing Earths Surface
- Forces in Earths Crust
  • Over millions of years, the forces of plate
    movement can change a flat plain into landforms
    such as anticlines and synclines, folded
    mountains, fault-block mountains, and plateaus.

14
Building Vocabulary
- Forces in Earths Crust
  • A definition states the meaning of a word or
    phrase. As you read, write a definition of each
    Key Term in your own words.

Key Terms
Examples
stress
Stress is a force that acts on rock to change its
shape or volume.
The block of rock that lies above a normal fault
is called the hanging wall.
tension
The stress force called tension pulls on the
crust, stretching rock so that it becomes thinner
in the middle.
The rock that lies below is called the footwall.
In a strike-slip fault, the rocks on either side
of the fault slip past each other sideways, with
little up or down motion.
compression
The stress force called compression squeezes rock
until it folds or breaks.
A fold in rock that bends upward into an arch is
an anticline.
shearing
Stress that pushes a mass of rock in two opposite
directions is called shearing.
A fold in rock that bends downward to form a
valley is a syncline.
normal fault
Tension in Earths crust pulls rock apart,
causing normal faults.
A plateau is a large area of flat land elevated
high above sea level.
reverse fault
A reverse fault has the same structure as a
normal fault, but the blocks move in the opposite
direction.
15
Measuring Earthquakes
- Earthquakes and Seismic Waves
  • The Mercalli scale was developed to rate
    earthquakes according to the amount of damage at
    a given place.

16
Richter Scale
  • The Richter Scale for measures the 'size' or
    'strength' of an earthquake. This scale is
    quantitative and based on the amount of energy
    released by an earthquake.
  • The energy of a quake is a function of both the
    amplitude and the duration of a single wave.
  • The seismogram below shows waves with a wide
    range of amplitude and duration.
  • This would be magnitude 8 quake!

17
- Earthquakes and Seismic Waves
18
Seismic Wave Speeds
- Earthquakes and Seismic Waves
  • Seismographs at five observation stations
    recorded the arrival times of the P and S waves
    produced by an earthquake. These data are shown
    in the graph.

19
Seismic Wave Speeds
- Earthquakes and Seismic Waves
  • Reading Graphs
  • What variable is shown on the x-axis of the
    graph? The y-axis?
  • X-axisdistance from the epicenter
    y-axisarrival time.

20
Seismic Wave Speeds
- Earthquakes and Seismic Waves
  • Reading Graphs
  • How long did it take the S waves to travel 2,000
    km?
  • 7 minutes

21
Seismic Wave Speeds
- Earthquakes and Seismic Waves
  • Estimating
  • How long did it take the P waves to travel 2,000
    km?
  • 4 minutes

22
Seismic Wave Speeds
- Earthquakes and Seismic Waves
  • Calculating
  • What is the difference in the arrival times of
    the P waves and the S waves at 2,000 km? At 4,000
    km?
  • 2,000 3.5 minutes
  • 4,000 4.5 minutes

23
Locating the Epicenter
- Earthquakes and Seismic Waves
  • Geologists use seismic waves to locate an
    earthquakes epicenter.

24
The Modern Seismograph
- Monitoring Earthquakes
  • Seismic waves cause the seismographs drum to
    vibrate. But the suspended weight with the pen
    attached moves very little. Therefore, the pen
    stays in place and records the drums vibrations.

25
Instruments That Monitor Faults
- Monitoring Earthquakes
  • In trying to predict earthquakes, geologists have
    developed instruments to measure changes in
    elevation, tilting of the land surface, and
    ground movements along faults.

26
Using Seismographic Data
- Monitoring Earthquakes
  • The map shows the probability of a strong
    earthquake along the San Andreas fault. A high
    percent probability means that a quake is more
    likely to occur.

27
Earthquake Risk
- Earthquake Safety
  • Geologists can determine earthquake risk by
    locating where faults are active and where past
    earthquakes have occurred.

28
How Earthquakes Cause Damage
- Earthquake Safety
  • A tsunami spreads out from an earthquake's
    epicenter and speeds across the ocean.

29
Designing Safer Buildings
- Earthquake Safety
  • To reduce earthquake damage, new buildings must
    be made stronger and more flexible.

30
Asking Questions
- Earthquake Safety
  • Before you read, preview the red headings and ask
    a what, how, or where question for each heading.
    As you read, write answers to your questions.

Question
Answer
Where is the quake risk highest?
Earthquake risk is the highest along faults and
where past earthquakes have occurred.
31
Volcanoes and Plate Boundaries
- Volcanoes and Plate Tectonics
  • Volcanic belts form along the boundaries of
    Earths plates.

32
Volcanoes and Plate Boundaries
- Volcanoes and Plate Tectonics
  • Volcanoes often form where two oceanic plates
    collide or where an oceanic plate collides with a
    continental plate. In both situations, an oceanic
    plate sinks through a trench. Rock above the
    plate melts to form magma, which then erupts to
    the surface as lava.

33
Hot Spot Volcanoes
- Volcanoes and Plate Tectonics
  • A volcano forms above a hot spot when magma
    erupts through the crust and reaches the surface.

34
Properties of Magma
- Volcanoes and Plate Tectonics
  • Magmas viscosity depends on its physical and
    chemical properties.
  • Magma is made of elements and of compounds, among
    them silica.
  • Viscosity depends on silica content and
    temperature.

35
Magma Composition
- Properties of Magma
  • Magma varies in composition and is classified
    according to the amount of silica it contains.
    The graphs show the average composition of the
    two types of magma.

36
Magma Composition
- Properties of Magma
  • Reading Graphs
  • Study both graphs. What materials make up both
    types of magma?
  • Silica, other oxides, and other solids.

37
Magma Composition
- Properties of Magma
  • Reading Graphs
  • Which type of magma has more silica? About how
    much silica does this type of magma contain?
  • Rhyolite-forming magma about 70 percent.

38
Magma Composition
- Properties of Magma
  • Estimating
  • A third type of magma has a silica content that
    is halfway between that of the other two types.
    About how much silica does this type of magma
    contain?
  • About 60 percent

39
Magma Composition
- Properties of Magma
  • Predicting
  • What type of magma would have a higher viscosity?
    Explain.
  • Rhyolite-forming magma would have higher
    viscosity because it is higher in silica.

40
Magma Reaches Earths Surface
- Volcanic Eruptions
  • When a volcano erupts, the force of the expanding
    gases pushes magma from the magma chamber through
    the pipe until it flows or explodes out of the
    vent.

41
Composite Volcano Eruption Activity
- Volcanic Eruptions
  • Click the Active Art button to open a browser
    window and access Active Art about composite
    volcano eruption.

42
Kinds of Volcanic Eruptions
- Volcanic Eruptions
  • Within the last 150 years, major volcanic
    eruptions have greatly affected the land and
    people around them.

43
Landforms From Lava and Ash
- Volcanic Landforms
  • Volcanic eruptions create landforms made of lava,
    ash, and other materials. These landforms include
    composite volcanoes, shield volcanoes, cinder
    cone volcanoes, and lava plateaus.

44
Landforms From Lava and Ash
- Volcanic Landforms
  • A caldera forms when an volcanos magma chamber
    empties and the roof of the chamber collapses.
    The result is a large, bowl-shaped caldera.

45
Landforms From Magma
- Volcanic Landforms
  • Features formed by magma include volcanic necks,
    dikes, and sills, as well as batholiths and dome
    mountains.

46
Batholiths
- Volcanic Landforms
  • A batholith is a mass of rock formed when a large
    body of magma cools inside the crust. Several
    large batholiths form the core of mountain ranges
    in western North America. Half Dome in Yosemite
    National Park, California, is part of the Sierra
    Nevada batholith.

47
Outlining
- Volcanic Landforms
Volcanic Landforms
  • As you read, make an outline about volcanic
    landforms that you can use for review. Use the
    red headings for the main topics and the blue
    headings for the subtopics.
  • Landforms From Lava and Ash
  • Shield Volcanoes
  • Cinder Cone Volcanoes
  • Composite Volcanoes
  • Lava Plateaus
  • Calderas
  • Soils From Lava and Ash
  • Landforms From Magma
  • Volcanic Necks, Dikes and Sills
  • Dikes and Sills
  • Batholiths
  • Dome Mountains
  • Geothermal Activity
  • Hot Springs
  • Geysers
  • Geothermic Energy
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