Title: THE DYNAMIC EARTH
1THE DYNAMIC EARTH
- A Study of Plate Tectonics
- And
- Earthquakes
2What 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
3What 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.
4What 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
5Plate 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
6Divergent 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
7Convergent 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
8Ocean-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
9Ocean-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
10Continent-Continent Convergent Boundary
- Where two continental plates collide with one
another - Creates high mountains
- Example the Himalayas
11What 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
12Transform 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
13What 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).
14Activity 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
15What 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/
16What 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
17Types 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
18Surface 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.
19What 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.
20What 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
21The 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.
22How 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)
23How 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
24How 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.
25References
- Textbook
- Chapters 7, 8, and 9