Types of Faults and seismic waves

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Types of Faults and seismic waves
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What is a fault?

• A fault is a break in the rocks that make up the
  Earths crust, along which rocks on either side
  have moved past each other.
• The direction of movement along the fault plane
  determines the fault type.

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GEOLOGICAL CONCEPTSTYPES OF FAULTFootwall/Hangin
g wall from Mining geology
Miners put their lamps on the hanging wall and
walk on the foot wall.
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Three major Faults
Normal
Reverse
Strike-slip
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Normal Fault
The hanging wall moves down relative to the foot
wall. This fault type is caused by tensional
stress.
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Normal Fault
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Normal Fault
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Normal Fault
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Reverse Fault
The hanging wall moves up relative to the foot
wall. This fault is caused by Compressional
stress.
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Reverse Fault
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Reverse Fault
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Reverse Fault
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Strike-Slip Fault
The fault exists between two pieces of crust
and the Movement occurs horizontally where the
sides slide past each other.
This fault type is caused by shear stress.
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Strike-Slip Fault
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Strike Slip Fault
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Strike-Slip Fault
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Fault Movement Earthquakes

• An earthquake is caused by a sudden slip on a
  fault. The tectonic plates are always slowly
  moving, but they get stuck at their edges due to
  friction. When the stress on the edge overcomes
  the friction, there is an earthquake that
  releases energy in waves that travel through the
  earth's crust and cause the shaking that we feel.
  

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Focus- where the slip happens below
ground Epicenter-where the shaking is first felt
above ground directly above the focus.
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• Slippage along fault initiates seismic waves in
  all directions radiating from the focus.
• Seismic waves are vibrations that travel through
  the Earth carrying the energy released during
  earthquakes

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• There are two categories of seismic waves
• Body Waves Can travel through Earths inner
  layers (core, mantle, crust)-
• Primary and Secondary waves
• Surface Waves Can only travel through the
  surface layers (crust)
• Love and Rayleigh

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Primary Waves

• P waves- are the first waves to arrive at a
  seismograph station.
• -fastest form of wave, sometimes called
  compression waves.
• Can move through both liquids and solids.
• These waves cause rock particles to move back
  and forth in the same direction as the wave is
  traveling (push-pull).

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Secondary Waves

• S-Waves- arrive after the primary waves at the
  seismograph station.
• -Can travel through solids only.
• -Cause particles to move back and forth at right
  angles to the line of wave movement

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SEISMOLGYEARTHQUAKE LOCATIONTravel time versus
distance plots
Can construct distance versus travel time for
earthquakes knowing properties of earths
interior Note that with increasing distance the
arrival times for the various waves
separates. The 3 min 45 sec difference between
the arrival time of the P and S waves corresponds
to a distance of 2000 km.
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SEISMOLOGYLOCATING EARTHQUAKESTriangulation
-Need three different seismic stations to locate
an earthquake. -Measure the P-S arrival times and
convert these to distance. -Triangulate using
radius given by P-S travel times. -Triangulation
for position of an earthquake near New Madrid
using stations in Columbus, St Louis and Memphis
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Surface Waves

• Rayleigh wave-surface wave causing the ground to
  shake in an elliptical motion
• Because of its motion, it moves the ground up and
  down, and side-to-side in the same direction that
  the wave is moving
• Most of EQ shaking is due to this type of wave

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• Love wave- produce entirely horizontal motion
• Moves the ground side-to-side
• Named after A.E.H. Love a British mathematician

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http//web.ics.purdue.edu/braile/edumod/waves/Wav
eDemo.htmParticle_Motion
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Measuring Earthquakes

• Magnitude- the amount of energy released during
  an EQ
• Richter Scale- based on the largest seismic waves
  generated by the EQ on a factor of 10.
• Moment Magnitude Scale- considers the size of the
  fault rupture, the amount of movement, and rocks
  stiffness

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Modified Mercalli Scale

• Measures the intensity of the EQ using a rating
  system of the damage
• Scientists compile information from various
  observers within different zip codes to get a
  better understanding of the devastation caused by
  an EQ to determine its intensity.