Download Earthquakes and Plate Boundaries

Earthquakes
Presented By
L.V. Sandaru Denuwan Somachandra
Locknath Saha
Srigunesan Sriragavarajan
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What are Earthquakes?
• Earthquakes are the vibrations in the ground that
result from movement along breaks in Earth’s
lithosphere
• These breaks are called faults
• The forces that move tectonic plates also push
and pull on rocks along the fault and if these
become big enough the blocks of rock on either
side of the fault can move horizontally or vertically
• The greater the force the larger and more
disastrous the earthquake
Where do Earthquakes Occur?
Earthquakes and Plate Boundaries
• Earthquakes result from the build up and release
of stress along active plate boundaries
• Some earthquakes occur more than 100km below
Earth’s surface
• The deepest earthquakes occur at convergent
plate boundaries
– Here the denser oceanic plate subducts into the
mantle
– These earthquakes release tremendous amounts of
energy
Earthquakes and Plate Boundaries
• Shallow earthquakes occur along divergent
plate boundaries, like mid-ocean ridges
• Shallow earthquakes also occur along
transform boundaries
• Along continental convergent boundaries,
earthquakes of varying depths occur
Rock Deformation
• When a force such as pressure is applied to
rock along plate boundaries, the rock can
change shape. This is called rock deformation.
• Eventually rocks can be deformed so much
that they break and move.
• This is a lot like bending a stick until it breaks
Faults
• When stress builds in places like a plate
boundary, rock can form faults.
• A fault is a break in Earth’s lithosphere where
one block of rock moves toward, away from,
or past another
• When rocks move in any direction along a
fault, an earthquake occurs
• The direction depends on the force applied
Types of Faults
Reverse Fault
• Forces push two blocks of
rock together.
• The rock above the fault
moves up relative to the
block of rock below the fault
• Occurs
at
convergent
boundaries
Normal Fault
• Forces pull two blocks of
rock apart.
• The rock above the fault
moves down relative to the
rock below the fault
• Occurs at divergent plate
boundaries
Strike-Slip
• Two blocks of rock slide
horizontally past each other
in opposite directions
• Occurs at transform plate
boundaries
Earthquake Focus and Epicenter
• When rock moves along a fault, they release energy that
travels as vibrations on and in Earth called seismic waves
• These waves originate where rocks first move along the
fault, at a location inside Earth called the focus
– An earthquakes focus can occur anywhere between Earth’s
surface and depths of greater than 600km
• Earthquakes are often referred to by their epicenter
– The epicenter is the location on Earth’s surface directly above the
earthquake’s focus
Seismic Waves
• During an earthquake, a rapid release
of energy along a fault produces
seismic waves
• Seismic waves travel outward in all
directions through rock
– Similar to a stone being dropped in
water, seismic waves move outward in
circles
– Seismic waves transfer energy through
the ground and produce the motion
that you feel during an earthquake
– The energy released is stronger near the
epicenter and decrease in energy and
intensity as you move outward
Types of Seismic Waves
Primary Waves (P-Waves)
• Causes rock particles to vibrate in the same
direction that waves travel
• Fastest seismic wave
• First to be detected and recorded
• Travels through solids and liquids
Secondary Waves (S-Waves)
• Causes rock particles to vibrate perpendicular to the
direction that waves travel
• Slower than P-waves, but faster than surface waves
• Detected and recorded after P-waves
• Only travels through solids
Surface Waves
• Cause rock particles to move in a rolling or
elliptical motion in the same direction that waves
travel
• Slowest seismic wave
• Generally causes the most damage
Mapping Earth’s Interior
• Scientists that study earthquakes are called
seismologists
• They use the properties of seismic waves to
map Earth’s interior
• P-waves and S-waves change speed and
direction depending on the material they
travel through
Inner and Outer Core
• Through extensive earthquake studies,
seismologists have discovered that S-waves
cannot travel through the outer core
• This discovery proved that Earth’s outer core
is liquid unlike the solid inner core
• By analyzing speed of P-waves traveling
through the core, seismologists also
discovered that the inner and outer cores are
composed of mostly iron and nickel
The Mantle
• Seismologists also have used seismic waves to
model convection currents in the mantle
• The speeds of seismic waves depend on the
temperature, pressure, and chemistry of the rocks
that the seismic waves travel through.
• Seismic waves tend to slow down as they travel
through hot material
– For example, seismic waves are slower in areas of the
mantle beneath mid-ocean ridges or near hotspots
– Seismic waves are faster in cool areas of the mantle
near subduction zones