THE DYNAMIC EARTH - PowerPoint PPT Presentation

1 / 25
About This Presentation
Title:

THE DYNAMIC EARTH

Description:

http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continent s.shtml ... The Richter Scale which measures magnitude or strength using a seismograph ... – PowerPoint PPT presentation

Number of Views:113
Avg rating:3.0/5.0
Slides: 26
Provided by: Mar8432
Category:

less

Transcript and Presenter's Notes

Title: THE DYNAMIC EARTH


1
THE DYNAMIC EARTH
  • A Study of Plate Tectonics
  • And
  • Earthquakes

2
What is Plate Tectonics?
  • It is the current theory explaining the motions
    of Earths crust
  • It is a combination of two earlier ideas
  • Continental drift and
  • Sea floor spreading
  • http//www.enchantedlearning.com/subjects/astronom
    y/planets/earth/Continents.shtml

3
What is Continental Drift?
  • In 1912 Alfred Wegener proposed the idea that the
    continents were broken fragments originated from
    a single giant landmass called Pangaea
  • Evidence
  • The puzzle like fit of the continents as viewed
    on maps
  • The same rocks and fossils found on two
    continents that are now separated by oceans
  • Glacier evidence in locations that are now warm
  • Wegener did not have the scientific capability to
    fully prove his ideas but it wasnt long after
    his death that scientific evidence arose to
    support his proposals.

4
What is sea-floor spreading?
  • It is the process in which new ocean crust is
    created.
  • Mid ocean ridges are the location of new ocean
    crust
  • Ocean crust is older, thinner, denser, and basalt
    (mafic)
  • Continental crust is older, thicker, less dense,
    and granite (felsic)
  • Patterns of Magnetism
  • Records of the magnetism of the ocean floor
    reveal a pattern which shows the changes in
    polarity.
  • Polarity is the direction of the magnetic field
    of Earth
  • It has reversed several times
  • Rocks with s minerals will line up in the
    direction of the magnetic poles

5
Plate Tectonics
  • The Earth is made up of tectonic plates (breaks
    in earths crust) surrounded by boundaries.
    http//vulcan.wr.usgs.gov/Graphics/framework2.html
  • These boundaries are zones of crustal activity
    where most earthquakes and volcanoes occur.
  • The motion of the plates varies by the boundaries
    surrounding them
  • Divergent boundaries where plates are moving
    apart from one another such as at mid ocean
    ridges
  • Convergent boundaries where plates are
    colliding or diving under one another such as at
    trenches
  • Transform boundaries where plates are sliding
    past one another such as at faults

6
Divergent Boundaries
  • Where plates are moving apart
  • New crust is created
  • Mid ocean ridges or rifts
  • Forming under water chain of mountains
  • May be sites of small, shallow earthquakes

7
Convergent Boundaries
  • Where plates are diving under (subduction) or
    colliding with one another
  • Crust is being destroyed
  • Sites of volcanoes and earthquakes
  • Form different landforms depending on type of
    convergence
  • Ocean-ocean
  • Ocean-continent
  • Continent-continent

8
Ocean-Ocean Convergent Boundary
  • Where two ocean plates meet and one dives
    (subducts) under the other
  • Creates a chain of volcanic islands (island arcs)
  • Example - Japan

9
Ocean-Continent Convergent Boundary
  • Where an ocean plate dives (subducts) under a
    continental plate.
  • Creates a chain of coastal volcanic mountains
  • Examples the Cascades in the US
  • or the Andes in South America

10
Continent-Continent Convergent Boundary
  • Where two continental plates collide with one
    another
  • Creates high mountains
  • Example the Himalayas

11
What about the Hawaiian Islands
  • The Hawaiian Islands are volcanic islands yet
    they are not or near a plate boundary
  • They are in the middle of the Pacific Plate
  • They are located over a HOT SPOT

12
Transform Boundaries
  • Where plates are sliding past one another
  • Crust is not created or destroyed
  • Sites of many major earthquakes
  • Examples San Andreas Fault in California

13
What Drives the Tectonic Plates?
  • Convection current in the Mantle cause the plates
    on Earth to move.
  • Convection currents result from the changes in
    temperature and density of the magma
  • Hot magma rises in the mantle at a divergent
    boundary where it oozes out or
  • It slides under the crust pulling the plates
    apart
  • At a convergent boundary the cooler magma begins
    to sink and pulls the crust downward (subduction).

14
Activity at Plate Boundaries
  • Plate boundaries are areas of movement of Earths
    crust
  • When the Earths crust moves major events occur
  • Earthquakes, volcanoes, tsunamis, mountain
    building

15
What are Earthquakes?
  • An earthquake is a sudden movement of Earths
    crust that releases energy
  • Earthquakes generally occur at faults
  • Regions where there are breaks in Earths crust
    and plates slide past one another
  • http//www.crustal.ucsb.edu/ics/understanding/
  • http//earthquake.usgs.gov/recenteqs/

16
What Happens During an Earthquake?
  • When the earth moves a sudden release of stored
    energy occurs
  • Focus location of earthquake inside the crust
  • Epicenter location of earthquake on earths
    surface directly above the focus
  • The energy travels in the form of waves
    throughout the earth

17
Types of Earthquake Waves
  • There are two major types of earthquake waves
  • P-Waves primary waves
  • Travel fastest
  • Travel through solid and liquid
  • Known as compression waves
  • They move back and forth
  • S-Waves secondary waves
  • Travel slower
  • Travel through solids ONLY
  • Known as shear waves
  • They move side to side

18
Surface Waves
  • Another type of earthquake wave is a surface wave
    (L-Waves)
  • These waves are the slowest but they are the most
    destructive.
  • They shake the surface of the earth up and down.

19
What are the Characteristics of Earths Interior?
  • From the ESRT, you can gather all the information
    needed to describe the layers of the Earth
  • Temperature
  • Pressure
  • Density
  • Depth
  • The boundaries (interfaces) of each of the layers
    can also be determined.
  • In general you will find that as the depth in the
    Earth increases so does the
  • Temperature
  • Pressure
  • And density
  • Graphically,
  • it is a direct relationship.

20
What Do Earthquake Waves Tell us About the
Interior of the Earth?
  • Earthquakes and the study of the waves that
    travel through the earth help us draw conclusions
    (inferences) about the interior of the Earth.
  • The waves change direction and speed as they
    travel through the Earth
  • The speed increases as the density increases
  • From this we know that there are different layers
  • S-Waves do not travel through liquids
  • Directly opposite the location of the epicenter
    the stations receive p-waves only
  • From this it is concluded that the outer core of
    the earth is liquid

21
The Shadow Zone
  • The shadow zone is a belt that extends around the
    Earth
  • No p or s waves around at locations in the shadow
    zone
  • Its location is dependent on the location of the
    epicenter.

22
How are Earthquakes Measured?
  • There are two scales that record earthquake
    activity
  • The Mercalli Scale which measures the observable
    damage (intensity) from the earthquake
  • Scale is I to XII
  • The Richter Scale which measures magnitude or
    strength using a seismograph
  • Scale is 1 to 10 with each unit increasing 10X
  • Example an earthquake of magnitude 7 is 100 times
    stronger than a magnitude 5 (10x10)

23
How Do You Find the Epicenter of an Earthquake?
  • Find the arrival time of the p-wave and s-wave.
  • Subtract p s to get the difference
  • Use the difference and the time travel in the
    ESRT to find the distance to the epicenter
  • Do this for three seismograms
  • Draw a circle around each point, where all three
    intersect is the epicenter.
  • http//www.geo.mtu.edu/UPSeis/locating.html

24
How Do You Find the Origin of an Earthquake?
  • The origin is the actual time that the earthquake
    occurred.
  • For any seismic station the origin time will be
    the same
  • Origin time is equal to the p-arrival time the
    p travel time.

25
References
  • Textbook
  • Chapters 7, 8, and 9
Write a Comment
User Comments (0)
About PowerShow.com