Transcript EARTHQUAKES & VOLCANOES

OUR DYNAMIC EARTH
In what way or ways is our
Earth a dynamic planet?
PS5
UNIT OBJECTIVES
YWBAT:
 Define that time is an important component of every
geological process, and demonstrate understanding
of the scope of the time line of geologic
development.
 Identify natural processes that help change the
Earth.
 Identify the internal structure of the planet Earth.
 Describe constructive and destructive forces that
shape the land.
Structure of the Earth
• The Earth is an oblate spheroid. It is composed of a
number of different layers as determined by deep drilling
and seismic evidence (Figure 10h-1). These layers are:
• The core which is approximately 7000 kilometers in
diameter (3500 kilometers in radius) and is located at the
Earth's center.
• The mantle which surrounds the core and has a
thickness of 2900 kilometers.
• The crust floats on top of the mantle. It is composed of
basalt rich oceanic crust and granitic rich continental
crust.
• pp. 108 - 117 in the text
•
THEORY OF PLATE TECTONICS
• Theory development (pp 118-129 in text)
– 1600’s – maps began to get into the hands of
common people; Francis Bacon (1620) noted the
similarity of the shape of the continents on either
side of the Southern Atlantic; Francois Placet
(1666) suggested that prior to the Great Flood the
land was undivided by oceans and that the
Atlantic formed when Atlantis sank.
– 1912 – Alfred Wegener presented the Continental
Drift Theory which stated that the continents were
once joined together (Pangaea); over time they
drifted apart.
THEORY OF PLATE TECTONICS
(CONT.)
• In the 1960’s, new evidence caused
scientists to reconsider Wegener’s theory who, what and why?
So, How Does This Happen?
• The Earth releases its internal heat by convecting, or
boiling much like a pot of pudding on the stove. Hot
asthenospheric mantle rises to the surface and spreads
laterally, transporting oceans and continents as on a
slow conveyor belt. The speed of this motion is a few
centimeters per year, about as fast as your fingernails
grow. The new lithosphere, created at the ocean
spreading centers, cools as it ages and eventually
becomes dense enough to sink back into the mantle.
The subducted crust releases water to form volcanic
island chains above, and after a few hundred million
years will be heated and recycled back to the spreading
centers.
Complete WS “ What’s Happening During Convection?”.
Types of Plate Tectonic Boundaries
• There are three main
plate tectonic
environments: transform,
convergent, and
divergent. Plate
boundaries in different
localities are subject to
different inter-plate
stresses, producing these
three types of
earthquakes. Each type
has its own special
hazards.
• At transforms (strike-slip faults), earthquakes are
shallow, running as deep as 25 km; mechanisms
indicate strike-slip motion. Transforms tend to
have earthquakes smaller than magnitude 8.5.
• The San Andreas fault in California is a nearby
example of a transform, separating the Pacific
from the North American plate. At transforms the
plates mostly slide past each other laterally.
• At convergent boundaries (reverse faults),
earthquakes are found in several settings
ranging from the very near surface to
several hundred kilometers depth, since
the coldness of the subducting plate
permits brittle failure down to as much as
700 km. Convergent boundaries host
Earth's largest quakes, with some events
on subduction zones in Alaska and Chile
having exceeded magnitude 9.
• At spreading ridges, or similar divergent
boundaries (normal faults), earthquakes
are shallow, aligned strictly along the axis
of spreading, and show an extensional
mechanism. Earthquakes in divergent
environments tend to be smaller than
magnitude 8.
Earthquake occurrence in
different plate tectonic settings:
• This map of Earth's solid
surface shows many of
the features caused by
plate tectonics. The
oceanic ridges are the
asthenospheric spreading
centers, creating new
oceanic crust. Subduction
zones appear as deep
oceanic trenches. Most of
the continental mountain
belts occur where plates
are pressing against one
another. The white
squares locate examples
given here of the different
tectonic and earthquake
environments.
What Is Seismology?
Seismology is the study of earthquakes and seismic waves that move
through and around the earth. A seismologist is a scientist who
studies earthquakes and seismic waves.
What Are Seismic Waves?
• Seismic waves are the waves of energy caused by the sudden
breaking of rock within the earth or an explosion. They are the
energy that travels through the earth and is recorded on
seismographs.
• Types of Seismic Waves
• There are several different kinds of seismic waves, and they all
move in different ways. The two main types of waves are body
waves and surface waves. Body waves can travel through the
earth's inner layers, but surface waves can only move along the
surface of the planet like ripples on water. Earthquakes radiate
seismic energy as both body and surface waves.
P WAVES
•
The first kind of body wave is the P wave or primary wave. This is the
fastest kind of seismic wave. The P wave can move through solid rock and
fluids, like water or the liquid layers of the earth. It pushes and pulls the rock
it moves through just like sound waves push and pull the air. Have you ever
heard a big clap of thunder and heard the windows rattle at the same time?
The windows rattle because the sound waves were pushing and pulling on
the window glass much like P waves push and pull on rock. Sometimes
animals can hear the P waves of an earthquake. Usually we only feel the
bump and rattle of these waves.
The arrow shows the direction that the wave is moving.
S Waves
The second type of body wave is the S wave or secondary wave,
which is the second wave you feel in an earthquake. An S wave is
slower than a P wave and can only move through solid rock. This
wave moves rock up and down, or side-to-side.
The arrow shows the direction that the wave is moving.
SURFACE WAVES
• Surface waves move the ground up and down in circles
and do not affect the rock deep below the surface.
• They travel more slowly and are more destructive. Most
Earthquake damage comes from surface waves.
EARTHQUAKE MEASUREMENT
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seismographs – instruments that record seismic waves,
creates a seismogram
epicenter – point on Earth’s surface directly above the
Earthquake’s origin
focus – actual point of origin inside the Earth
S-P time – method used to find the epicenter of a quake
Mercalli Scale – rates earthquakes by their intensity; not
an exact measurement
Richter scale – used to measure quake intensities;
named after Charles Richter who developed it in the
1930s
Complete WS AND read pages 154-159 in text.
SUMMARY NOTES
 The solid Earth is layered with a lithosphere (crust); hot, CONVECTING mantle; and
a dense, metallic core.
 The outward transfer of Earth’s internal heat drives CONVECTION in the mantle that
propels the plates comprising Earth’s surface across the face of the globe.
 Lithospheric plates on the scales of continents and oceans constantly move at rates
of centimeters per year in response to movements in the mantle. Major geological
events, such as earthquakes, volcanic eruptions, and mountain building, result from
these plate movements.(CONTINENTAL DRIFT, PLATE TECTONICS, SEA FLOOR
SPREADING, FAULTS, BOUNDARIES)
 Landforms are the result of a combination of constructive and destructive forces.
Constructive forces include crustal deformation, volcanic eruption, and deposition of
sediment, while destructive forces include weathering and erosion.
 The Earth processes that we see today are assumed to be similar to those that
occurred in the past (Uniformitarianism)
Earthquakes Getting Ready for
the Big One
INTERNET RESOURCES
http://www.usgs.gov
http://quake.wr.usgs.gov
http://jei.umd.edu/agi/agi.html
http://www.geosociety.org
http://www.uic.edu/orgs/paleo/homepage.h
tml
WORKS CITED
• www.seismo.unr.edu/ftp/pub/louie/
class/100/plate-tectonics.html
• www.physicalgeography.net/fundamentals/10h.h
tml
• www.stemnet.nf.ca/CITE/earthquakes_measure
ment.htm
• www.geo.mtu.edu/UPSeis/waves.html
http://school.discovery.com/lessonplans/program
s/earthquakes-gettingready/
• http://volcano.und.nodak.edu/
• http://vulcan.wr.usgs.gov/
• http://www.geo.mtu.edu/volcanoes/