1001 Severe Weather: Thunderstorms, Tornadoes

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10/01 Severe Weather Thunderstorms, Tornadoes
Lightning/Hazards 10/03 Midterm 10/05 Video 3
Extreme Weather Storms of the Century and Deadly
Skies (Assignment 1 due) (Assignment 3 hand
out)10/08 Thanks Giving No class 10/10
Severe Weather Hurricanes, Typhoons
Cyclones10/12 Groundwater Hazard
Revised course schedule
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Earthquakes

• What are Earthquakes?
• An earthquake is a sudden vibration or trembling
  in the Earth.
• More than 150,000 tremors strong enough to be
  felt by humans occur each year worldwide.
• Earthquake motion is caused by the quick release
  of stored energy in the rocks beneath the Earths
  surface.

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• Earthquakes occur when energy stored in
  elastically strained rocks is suddenly released.
• Sends waves of energy, called seismic waves,
  throughout the Earth.
• This release of energy causes intense ground
  shaking in the area near the source of the
  earthquake.
• This sudden release may cause one huge mass of
  rock to slide past another mass of rock into a
  different relative position. The break between
  these two rock masses is called a fault.
• EQs are definitely a geologic hazard for those
  living in earthquake prone areas.

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Origin of Earthquakes

• Most earthquakes occur where the crust undergoes
  deformation due to plate tectonic forces
  discussed in previous lecture.
• Usually earthquakes where rock breaks to produce
  faults.
• It is crucial in order to understand earthquakes
  to explore different pressures acting upon rocks
  and the resultant faults.

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Uniform stress from all directions
Differential stress stress is not equal from all
directions
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For any inclined fault plane we define the block
above the fault as the hanging wall block and the
block below the fault as the footwall block.
Normal Faults - are faults that result from
horizontal tensional stresses
Reverse Faults - are faults that result from
horizontal compressional stresses
A Thrust Fault is a special case of a reverse
fault where the dip of the fault is less than
15o. Thrust faults can have considerable
displacement, measuring hundreds of kilometers,
and can result in older strata overlying younger
strata.
Source adapted from www.tulane.edu
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• Strike Slip Faults - are faults where the
  relative motion on the fault has taken place
  along a horizontal direction. Such faults result
  from shear or transform stresses acting in the
  crust. Strike slip faults can be of two
  varieties, depending on the sense of
  displacement.
• left-lateral strike-slip fault.
• right-lateral strike-slip fault.

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Elastic rebound theory Earthquake cycle
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Earthquakes
Motion is transmitted from the point of sudden
energy release, the earthquake focus.
Movement of body waves away from the focus of the
earthquake. The epicenter is the location on the
surface directly above the earthquake's focus.
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Seismic waves
www.amnh.org/.../1999/hagenauer.html
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Seismometer
Seismogram
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How Seismographs Work
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Travel time curves
Step 1 Measure
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5300
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Richter Magnitude
Nomograph chart Uses the distance from the
earthquake (P S time in seconds) and the S-wave
amplitude (in mm) to determine the earthquake
magnitude)
ML log10A(mm) (Distance correction factor)
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Earthquake size and characteristics
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Isoseismal map
http//www.seismo.unr.edu/ftp/pub/louie/class/100/
mercalli.html
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Moment Magnitude Scale
Seismologists have more recently developed a
standard magnitude scale that is completely
independent of the type of instrument. It is
called the moment magnitude.

• Takes into account the nature of material that
  faulted (rigidity of rocks).
• The size of area that ruptured.
• And the amount of slippage.

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Shakemap
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http//www.seismo.nrcan.gc.ca/recent/index_e.php
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Earthquake frequency
Source Byrne Christopherson, 2006)
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Summary

• Different fault systems
• Elastic rebound theory strain and stress
• Seismic waves 4 types
• Locating epicenter using seismograms
• Different earthquake scales and maps, such as
  Richter, Mercalli, Moment magnitude and shaking
  maps
• Earthquake frequencies

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• Canadian Earthquake Hazards Program
• http//earthquakescanada.nrcan.gc.ca/hazard/index_
  e.php
• Other Institutions
• Geological Survey of CanadaEarthquakes
  CanadaPacific Geoscience CentreSouthern Ontario
  Seismic NetworkLithoprobe Seismic Processing
  Facility (LSPF)