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ES5001- Natural Hazards and Society > Week 3 > Flashcards

Week 3 Flashcards

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1
Q

What are the three types of faults

A
  1. Normal Fault
  2. Reverse/ Thrust Fault
  3. Strike-Slip Fault
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2
Q

What is a normal fault

A
  • occurs at the divergent plate boundary
  • stretching the two plates away from each other (extensional force)
  • e.g: the fault that cause a big earthquake in 1954 in Nevada, USA
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3
Q

What is a reverse/ thrust fault

A
  • occurs at the convergent plate boundary
  • compression force
  • e.g: 1999 Chi-Chi earthquake, Taiwan Mw 7.6
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4
Q

What is strike slip fault

A
  • occurs at the transform plate boundary
  • the walls move sideways
  • e.g San Andreas Fault
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5
Q

What is right lateral and left lateral in strike slip faults

A

movement of the plate from the side that we are facing

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6
Q

What is the cause of earthquakes

A
  • Due to stress and strain
  • With increasing stress, a rock deforms elastically, then plastically, before ultimately failing or breaking in an earthquake
  • Completely brittle rock fails at its elastic limit
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7
Q

Summary of the elastic rebound theory

A
  • As the earth’s crust deforms , the rocks on opposing sides of a fault are subjected to shear stress
  • Slowly they deform, until the rock strength is exceeded
  • Then they separate with a rupture along the fault
  • The sudden movement releases accumulated energy and the rock snaps back almost to its original shape
  • The previously solid mass is divided between the two slowly moving plates
  • The energy is released through the surroundings in a seismic wave
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8
Q

What are body waves

A
  • waves that travel through the entire body of the earth
  • two types
    1. P-waves
    2. S-waves
  • the velocity of a P or S wave is related to the bulk or shear moduli (respectively) of the material through which they travel
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9
Q

What are P-waves

A

the quickest and have a compressional particle motion parallel to the direction of travel

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10
Q

What are S-waves

A

quicker than surface waves, and have a shearing particle motion perpendicular to the direction of travel

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11
Q

What are surface waves

A
  • forms on the free surface
  • amplitude decays exponentially with depth
  • restricted to propagation close to the free surface
  • Two types
    1. Love waves
    2. Rayleigh waves
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12
Q

Other things that seismic waves can be used for

A
  1. To find oil and gas
  2. Medical scan (e.g CT)
  3. Nucleation test monitoring
  4. Building damage examination
  5. Earthquake early warning
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13
Q

Factors of an earthquake

A
  1. Rupture size
  2. Length of rupture
  3. Width of rupture
  4. Amount of Slip
  5. Dynamics
  6. Direction of rupture
  7. Impulsive or slow
  8. Onset
  9. Tectonic Occupation
  10. Geographic Location
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14
Q

Seismic moment

A

length x width x slip x shear modules

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15
Q

What is shear modulus

A

a measure of the resistance a substance provides to shearing deformation

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16
Q

Moment magnitude

A

2/3Log10Mo - 10.7

17
Q

What is a Hypocenter

A

The point where an earthquake or underground explosion originates

18
Q

What is an epicenter

A

The point on the earth surface directly above a hypocenter or focus

19
Q

What is a fault scarp

A

A planar geomorphic feature formed by the offset of Earth’s surface by one or more earthquake

20
Q

What is a wavefront

A

A surface over which time of the wave have been propagated away from the hypocenter is the same

21
Q

Cross section of the lithosphere

A
  • Earthquakes occur when cold rocks break
  • Cold means temperature of 300 - 400 degrees C
    -This is because two prominent minerals that make up much of the earth’s crust breaks when they are colder than these temperatures but flow like taffy when they are warmer than this
22
Q

Why do subduction zones produce the biggest earthquakes

A
  • Faults dip more shallowly, like thrust faults and megathrust faults, rupture with greater widths, because they angle into the crust at a shallower angle and carry cold crust down into the mantle
  • Normal faults have thin widths
  • Strike Slip faults have relatively short widths

ES5001- Natural Hazards and Society (12 decks)

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