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Earthquakes: What are they and what causes them to happen?

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The Richter Magnitude Scale How Do Scientists Know Where an Earthquake Has Happened? The location below the Earth s surface where the earthquake starts is called ... – PowerPoint PPT presentation

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Title: Earthquakes: What are they and what causes them to happen?


1
Earthquakes What are they and what causes them
to happen?
Shake, Rattle, and Roll!
  • Mrs. Hornsbys Fifth Grade Class

2
Table of Contents
  • Georgia Performance Standards
  • What is an Earthquake?
  • What are Earths layers?
  • What are Plate Tectonics?
  • What Happens When Plates Move?
  • Types of Plate Boundaries
  • The Theory of Continental Drift
  • What is a Fault?
  • What Happens when an Earthquake Starts?
  • How are Earthquakes Measured?
  • The Richter Magnitude Scale
  • How Long Does an Earthquake Last?
  • How Many Earthquakes Happen Each Year?
  • Where Do Earthquakes Occur Most Often in the
    United States?
  • The 25 Largest Earthquakes in the United States
  • Famous Earthquakes Around the World
  • Photos of Earthquake Damage
  • What Have You Learned?
  • References

3
Georgia Performance Standards
  • S5Cs4 Students will use ideas of system, model,
    change, and scale in exploring scientific and
    technological matters.
  • S5E1 Students will identify surface features of
    the Earth caused by constructive and destructive
    processes.
  • S5P1 Students will verify that an object is the
    sum of its parts.
  • M5D1 Students will analyze graphs.
  • M5N5 Students will understand the meaning of
    percentage

4
What is an Earthquake?
  • An earthquake is a shaking of the ground caused
    by a sudden release of energy in the Earths
    crust. More than a million of them occur each
    year! However, most are too small to be felt or
    to cause damage. Click the picture below to watch
    a video about earthquakes.

5
What are Earths Layers?
  • The Earths crust is the outer layer and is made
    of rock. It is very thin compared to the other
    layers.
  • The mantle is the very hot layer of rock beneath
    the crust. No one has ever been to the mantle,
    but rock from the mantle sometimes reaches the
    Earths surface through volcanoes.
  • The outer core is made of liquid, or molten iron.
  • The inner core is made of solid iron. Even though
    the core is the hottest layer, great pressure at
    the center of the Earth keeps the inner core
    solid.

Inner Core
Outer core
Mantle
Crust
6
What are Plate Tectonics?
  • Earths surface is made up of many plates that
    float on the soft rock of the mantle. As the
    mantle moves, the plates also move.
  • Plates move only a few centimeters each year.
  • When one plate moves, it affects the other
    plates.
  • As plates move around, they cause great changes
    in the Earths surface, such as mountains,
    valleys, volcanoes, and earthquakes!

7
What Happens When Plates Move?
8
Types of Boundaries
Wegeners Theory of Continental Drift
9
What is a Fault?
  • Many earthquakes occur along faults in the
    Earths crust. A fault is a place where pieces of
    the plates move.
  • A normal fault is where tension weakens the
    crust until the rock fractures, and one rock
    moves downward from another. This occurs when two
    plates are pulling apart, as in a divergent
    boundary.
  • A strike-slip fault is where two blocks of rock
    are moving past each other horizontally, as in a
    transform boundary. The famous San Andreas Fault
    is a strike-slip fault.
  • A Reverse fault is where a fault block is forced
    upward, usually during a collision with another
    block, as in a convergent boundary.

10
What Happens When an Earthquake Starts?
  • The sudden release of energy from an earthquake
    sends out several different shaking movements, or
    seismic waves.
  • Surface waves are ripples of energy that spread
    outward when rocks slip past each other along a
    fault, just like throwing a stone into a calm
    pond.
  • Body waves are seismic waves that travel through
    material rather than over its surface. There are
    two types of body waves P-waves and S-waves.
  • The P-wave is also known as the sound wave. It
    travels through the interior of the Earth rather
    than over the surface as a series of squeezes and
    stretches. P-waves reach everywhere around the
    Earth after about 20 minutes.
  • The S-wave, or shear wave, produces a shaking
    motion, like if you tied a rope to a poll and
    shook the other end side to side. S-waves can
    only travel in solid material.

11
How are Earthquakes Measured?
  • Earthquakes are measured by instruments called
    seismographs. It has a base that sets firmly in
    the ground, and a heavy weight that hangs free.
    When an earthquake causes the ground to shake,
    the base of the seismograph shakes too, but the
    heavy weight does not. The spring that it is
    hanging from absorbs all the movement. The
    seismograph records the difference in position
    between the shaking part and the motionless part.
  • The recording is called a seismogram. It is used
    to determine how large the earthquake was. A
    short wiggly line that wiggles very little means
    a small earthquake. A long wiggly line that
    wiggles a lot means a large earthquake.

12
The Richter Magnitude Scale
Description Richter Magnitudes Earthquake Effects
Micro Less than 2.0 Microearthquakes, not felt.
Very Minor 2.0-2.9 Usually not felt, but recorded.
Minor 3.0-3.9 Often felt, but rarely causes damage.
Light 4.0-4.9 Noticeable shaking of indoor items, rattling noises. Significant damage unlikely.
Moderate 5.0-5.9 Can cause major damage to poorly constructed buildings over small regions. Slight damage to well-designed buildings.
Strong 6.0-6.9 Can be destructive in areas up to about 100 miles across in populated areas.
Major 7.0-7.9 Can cause serious damage over larger areas.
Great 8.0-8.9 Can cause serious damage in areas several hundred miles across.
Rare Great 9.0 or greater Devastating in areas several thousand miles across.
13
How Do Scientists Know Where an Earthquake Has
Happened?
  • The location below the Earths surface where the
    earthquake starts is called the hypocenter.
  • The location directly above the hypocenter on the
    Earths surface is called the epicenter.
  • It take three seismographs to locate an
    earthquake. Scientists draw a circle on a map
    around the three seismographs where the radius of
    each is the distance from the station to the
    earthquake, the intersection of those three
    circles is the epicenter.

14
How Long Does an Earthquake Last?
  • Sometimes an earthquake has foreshocks. These are
    smaller earthquakes that happen in the same place
    as the larger earthquake.
  • The largest, main earthquake is called the
    mainshock.
  • Mainshocks always have aftershocks that follow.
    These are smaller earthquakes that occur
    afterwards in the same place as the mainshock.
    Depending on the size of the mainshock,
    aftershocks can continue for weeks, months, or
    even years after the mainshock!

15
Famous Earthquakes Around the World
  • San Francisco, California April 18, 1906
  • (Magnitude About 8)
  • Tokyo, Japan September 1, 1923
  • (Magnitude about 8.25)
  • Chile May 22, 1960
  • (Magnitude About 9)
  • Anchorage, Alaska March 27, 1964
  • (Magnitude About 8.5)

16
How Many Earthquakes Happen Each Year?
17
Where do Earthquakes Occur Most Often in the
United States?
18
Top 25 Earthquakes in the United States
(Percentage)
19
Earthquake Damage
20
What Have You Learned?
Click Here To review the Brain Pop video and
take the quiz!
Click Here To test your knowledge about
earthquake vocabulary!
21
References
  • http//earthquake.usgs.gov/learning/kids.php
  • http//www.exploratorium.com/faultline/
  • http//teacher.scholastic.com/activities/wwatch/ea
    rthquakes/
  • http//www.fema.gov/kids/quake.htm
  • http//www.ditto.com/default.aspx
  • Earthquake Statistics
  • The Largest Earthquakes in the United States
  • http//www.brainpop.com
  • Mountains, Volcanoes, and Earthquakes Harcourt
    Earth Science Grade 5, p. C14.
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