Transcript Surface Waves

And
Defining Earthquakes
• Shaking and trembling of the
earth’s crust.
• The waves travel in all
directions
• More than 1,000,000 occur a
year or one every 30 seconds
• Faulting is the most common
cause
• Earthquakes continue until all
the energy is used up
• TSUNAMIS- earthquake on
the ocean floor: causing waves
to become greater than 20
meters high
Three Types of Faults
Strike-Slip
Thrust
Normal
What is the Elastic Rebound Theory?
•
Explains how energy is
stored in rocks
– Rocks bend until the
strength of the rock
is exceeded
– Rupture occurs and
the rocks quickly
rebound to an
undeformed shape
– Energy is released in
waves that radiate
outward from the
fault
What causes earthquakes?
• Tectonic plates move past each other causing stress.
Stress causes the rock to deform
– Plastic deformation – does not cause earthquakes
– Elastic deformation – rock stretches then reaches a
breaking point, releasing energy.
Elastic Rebound – deformed rock
goes back to its original shape
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Focus – point inside the Earth where an
earthquake begins
Epicenter – point on Earth’s surface above
focus
Seismic Waves
• FOCUS- underground
point of origin
• EPICENTERaboveground of origin;
most violent shaking
occurs at the epicenter
• The three main types of
seismic waves are: P
waves, S waves, and L
waves
P Waves
• Primary waves
• Arrive first at the
epicenter
• Can travel
through solids,
liquids, and gases
• They are pushpull waves
S Waves
• Secondary waves
• Can travel through
solids, but NOT
through liquids and
gases
• Move in up-down
motion
Comparing Seismic Waves
R and L Waves
•
•
•
•
Surface waves
Slowest moving seismic waves
Travel on top of Earth’s surface
Cause most of damage to Earth, because
they bend and twist the surface
Surface Waves: R and L waves
•
Surface Waves
– Travel just below or along the ground’s surface
– Slower than body waves; rolling and side-to-side
movement
– Especially damaging to buildings
Surface Waves
• Move along the Earth’s surface
• Produces motion in the upper crust
– Motion can be up and down
– Motion can be around
– Motion can be back and forth
• Travel more slowly than S and P waves
• More destructive
How is an Earthquake’s Epicenter Located?
Seismic wave behavior
– P waves arrive first, then S waves, then L and R
– Average speeds for all these waves is known
– After an earthquake, the difference in arrival times at a
seismograph station can be used to calculate the distance
from the seismograph to the epicenter.
John Milne- 1893
• Seismograph-measures and
detects seismic waves
• Seismogram- Paper record
of waves
• Seismologist- scientist who
study earthquakes
• Richter Scale- a scale that
allows scientists to determine
earthquake strength based
on many readings
• 1-10 levels at which an
earthquake is measured on
amount of damage caused;
Above a 6 is very destructive
Typical
Seismogram
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
How are Earthquakes Measured?
Richter Scale
How are the Size and Strength of an Earthquake Measured?
•
Magnitude
– Richter scale
measures total amount
of energy released by
an earthquake;
independent of
intensity
– Amplitude of the
largest wave produced
by an event is
corrected for distance
and assigned a value
on an open-ended
logarithmic scale
How are Earthquakes Measured?
Mercalli Intensity Scale
Click Link for Interactive Demo
http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf
Earthquake Waves & Earth’s Interior
Tsunamis
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Formation of a tsunami
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Tsunami Warning System
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
VOLCANOES
• Volcano- place on Earth’s surface
that allows magma and other material
to erupt
• Magma- found beneath the Earth’s
surface, it is liquid rock
• Lava- magma that reaches the
Earth’s surface
Volcanic Fragments
• Volcanic Dust- less
that 0.25 mm in
diameter (flour)
• Volcanic Ash- more
than 0.25 less than 5
mm (rice)
• Volcanic Bombsfew cm to several
meters.
• Cinders- volcanic
bombs the size of golf
balls
Types of Volcanoes
• Cinder Cones- made of mostly of
cinders; formed from explosive
eruptions
• Shield- Made of quiet lava flows
• Composite- made up of alternating
layers of rock particles; explosive
eruptions, then quite lava flows
Volcanic Terminology
• Crater- funnel shaped • Dormant- sleeping
pit, or depression at
volcano
top of volcano
• Extinct- not known to
• Caldera- when a
have erupted in
crater becomes too
modern history
large, it collapses:
• Active- Erupts fairly
also can form when
regularly
the top of a volcano
collapses or explodes
Ring of Fire
Zones
• There are 3 zones:
• Ring of Fire- Extends nearly all the way
around the edge of the Pacific Ocean
• Mediterranean Sea- Italy, Greece,
Turkey
• Iceland and Atlantic Ocean- Mid
Atlantic Ridge
EXTRA! EXTRA!
• Mount St. Helens is a volcano
is Washington State
• San Andreas Fault in
California
• New Madrid Fault is where we
live