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Geology

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Geology & Earth Science Earthquake Power Point Notes Body Waves P waves : Primary : Pressure : arrive at a given seismograph station first, can be transmitted through ... – PowerPoint PPT presentation

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Title: Geology


1
Geology Earth Science
  • Earthquake
  • Power Point Notes

2
Background
  • For centuries, people explained earthquakes with
    superstition and folk lore
  • Native Americans thought that the Earth was
    carried on the back of a mighty turtle a quake
    occurred when the beast took a step

3
Earthquake Definition
  • We now recognize earthquakes as the sudden
    movement of a crustal part of the earth (or
    lands surface), generally along a fracture,
    caused by the rapid release of slowly accumulated
    strain in crustal rocks

4
Origin of Earthquakes
  • The violent motion experienced during an
    earthquake can have one of several causes
  • plate tectonics (no duh!)
  • faulting
  • volcanic explosions
  • pressure changes
  • lubrication

5
Plate Tectonic Boundaries
  • Since we will cover this in the next chapter, for
    now we will cover the major types of plate
    boundaries
  • divergent
  • convergent
  • transform

6
Divergent Plate Boundaries
  • Divergent plate boundaries occur when plates are
    moving apart magma wells up towards the surface
    from depth to fill in the void left by the
    separation

7
Convergent Plate Boundaries
  • Convergent Plate Boundaries are characterized by
    plates moving toward one another and colliding
  • the processes of subduction and obduction occur
    at this type of boundary

8
Subduction and Obduction
  • As two plates meet, density differences will
    determine which plate is more likely to be shoved
    underneath the other the process of this plate
    diving under the other bully plate is called
    subduction

9
Subduction and Obduction
  • Sometimes as the plate is going underneath the
    over-riding plate, pieces of the downward
    traveling plate are scraped off onto the top of
    the bully plate this process is called obduction

10
Transform Plate Boundary
  • Transform plate boundaries occur when two plates
    are sliding past one another causing shallow
    earthquakes
  • The rate of sliding is determined by friction
    (when enough pressure builds up to overcome
    friction, movement occurs)

11
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12
Fault Vs Joint
  • A fault is a crack in a rock body along which
    movement occurs
  • A joint is a crack in a rock body along which no
    movement occurs

13
Faulting
  • Faulting occurs along all plate boundaries and
    many other places worldwide
  • Each side of the rock body slips and moves
    relative to the other rock body
  • Movement can be in any direction according to the
    stress applied
  • If this movement is sudden, its a quake

14
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15
Types of Faults
  • Normal hanging wall moves down relative to the
    foot wall
  • Caused by tensional forces (a pulling apart)
  • The first declination of the wave at the
    seismograph station goes down
  • Illustrate a normal fault

16
Types of Faults
  • Reverse hanging wall moves up relative to the
    foot wall
  • Caused by compressional forces
  • first wave at seismograph station is deflected
    upwards
  • Illustrate a reverse fault

17
Types of Faults
  • Thrust similar to a reverse fault in that the
    hanging wall still moves upwards relative to the
    foot wall but the angle of the fault plane is
    low less than fourty-five degrees (low angle
    fault plane)
  • Illustrate a thrust fault

18
Types of Faults
  • Strike-Slip has no hanging or foot walls all
    movement occurs horizontally along a vertical
    fault plane and can be classified as
  • right lateral strike-slip fault or
  • left lateral strike-slip fault
  • Illustrate these types of SS faults

19
Volcanic Explosions
  • Usually due to rapid depressurization of the
    magma because of the escaping volatiles
  • Can also be caused by the movement of the magma
    within the chamber seeking areas of low pressure
    (the surface)
  • These quakes are rarely felt over a wide area

20
Pressure Changes
  • A change in pressure can occur from pumping out
    such things as water or petroleum or pumping in
    such things as nuclear waste, waste fluids, etc.
  • Pressure changes can also be caused simple
    sedimentation over time

21
Lubrication
  • Associated with the pumping of liquid sludge
    waste into cracks in the ground (inactive faults)
    for disposal or storage

22
Effects of Earthquakes
  • Sounds
  • Cracks
  • Landslides
  • Destruction By Fire
  • Tsunami
  • Loss of Life

23
Landslides
  • When regolith or other materials have become
    steepened over time or whose pore spaces have
    become waterlogged (acts as a lubricant) and are
    subjected to shaking they tend to slide downslope
    under the influence of gravity

24
Destruction by Fire
  • Gas mains are ruptured by breakage and fires
    result water mains are also ruptured so the
    fires cant be fought
  • only 5 of the devastation of the 1906 San
    Francisco quake was caused by the actual shaking
    the rest (which leveled countless city blocks)
    was from fire

25
Loss of Life
  • People are able to check out in many different
    ways during an earthquake most die from man-made
    structures collapsing on them
  • From earliest recorded history over 16 million
    folks have checked out due to earthquake activity

26
Tsunami
  • Caused by rapid movement of the ocean floor
    these waves appear as a simple rise in sea level
    and are not noticed by ships at sea they only
    become visible when they pile up as the wave
    comes ashore as the wave bunches up, the water
    recedes for miles to come crashing back
  • Illustrate tsunami formation

27
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28
Earthquake Measurement
  • Earthquakes generate waves we can measure these
    waves to estimate the ferocity of the earthquake
  • These waves are measured on seismographs...

29
Measurement Magnitude
  • When an earthquake occurs, a seismograph is able
    to record a measure of the total seismic energy
    released in the form of earth waves producing a
    seismogram...

30
Types of Seismographs
31
Seismograph Vs Seismogram
  • Remember that a seismograph is the machine that
    records the data and the data that is recorded is
    the seismogram

32
Earthquake Waves
  • Movement originates deep within the earth at a
    point from this point, the waves caused by the
    movement travel outwards in all directions the
    point where movement first occurs deep within the
    earth is the focus the point directly above the
    focus on the earths surface is the epicenter

33
Earthquake Waves
  • The waves generated are of two different types
  • BODY WAVES and
  • SURFACE WAVES

34
Body Waves
  • P waves Primary Pressure arrive at a given
    seismograph station first, can be transmitted
    through solids, liquids and gases
  • S Waves Secondary Shear arrive at a given
    seismograph station second, can only be
    transmitted through solids

35
Surface Waves
  • Rayleigh waves and Love Waves arrive at the
    seismograph station thirdly, following the P and
    S waves these surface waves cause the most
    destruction to man-made structures and cause the
    surface of the earth to roll like ocean waves...

36
Seismogram of 06 SF Quake
37
Earthquake Measurement
  • Earthquakes can be measured in two ways
  • Intensity the strength of the quake
  • Magnitude the amount of energy released during
    the quake

38
Measurement Intensity
  • The intensity is the strength of the earthquake
    it is a persons measure (opinion) of how the
    earthquake affects that individual and the
    earths surface (primarily man-made structures)

39
Measurement Intensity
  • A number is assigned to different intensity
    levels, but it should be noted that the effects
    of shaking are different at different locations
    so one earthquake can have many different
    intensities
  • An Italian seismologist named Mercalli proposed
    the scale that we still use to classify
    Intensities

40
Measurement Magnitude
  • The total energy released during an earthquake is
    the magnitude while there are many intensities
    for one given earthquake (depending upon
    location) , there can be only one magnitude
  • The scale we use to classify an earthquakes
    magnitude is the Richter Scale (allows world-wide
    comparison)

41
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