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Geography - C - Tectonics > Earthquakes, Processes, Hazards + Their Impacts > Flashcards

Earthquakes, Processes, Hazards + Their Impacts Flashcards

1
Q

Define earthquakes

A

Violent shaking of the ground, caused by movements of the Earth’s crust usually along pre-existing faults

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2
Q

Where do earthquakes occur?

A
  • Mainly: along plate boundaries

- Also: locations where human activity causes low magnitude earthquakes (e.g result of fracking or nuclear explosions)

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3
Q

What percentage of earthquakes occur along the Pacific Ring of Fire?

A

80%

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4
Q

What type of plate boundaries can earthquakes occur at?

A

All

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5
Q

Outline how earthquakes are formed at converging (destructive) plate boundaries

A

Most common earthquake location
Varying foci depth
- Caused by friction along the Benioff Zone as slab pull occurs which triggers build up then release of stress

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6
Q

Outline how earthquakes are formed at diverging (constructive) plate boundaries

A

Shallow focus

- Caused by build up and release of stress at transform faults

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7
Q

What are transform faults?

A

Faults that open up near the main fault due to plate movements (occur at diverging plate boundaries)

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8
Q

Outline how earthquakes are formed at converging collision plate boundaries

A

Shallow focus

- Cause by build up and release of stress as plates move together as orogenies occur

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9
Q

What are orogenies?

A

Mountain building

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10
Q

Outline how earthquakes are formed at conservative plate boundaries

A

Can cause strong earthquakes
- Caused by: lateral movements cause friction, causing tension to build up then be released when plates slip past each other

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11
Q

Outline how earthquakes occur

A
  • As crust moves, pressure builds up in rocks in underground fault zones
  • Pressure becomes so great that rock shifts violently and deforms (internal deformation)
  • When the rock deforms, seismic waves are released from the focus
  • Afterwards, the rock rebounds to its original shape, but in a new geographical position (elastic rebound)
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12
Q

Define fault zones

A

The location deep underground where pressure builds up in rocks due to crust movement

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13
Q

Define internal deformation

A

When pressure in rocks becomes so great that the rock deforms and releases shockwaves

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14
Q

Define elastic rebound

A

When deformed rock rebounds to its original shape in a new geographical position

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15
Q

Define focus

A

The point of rock deformation, which seismic waves are released from

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16
Q

What is a ‘shallow focus’ depth?

A

70km or less

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17
Q

What is an ‘intermediate focus’ depth?

A

70km -> 300km

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18
Q

What is a ‘deep focus’ depth?

A

Over 700km

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19
Q

Define epicentre

A

The projection of the focus onto the Earth’s surface

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20
Q

What causes a series of small magnitude earthquakes?

A

When pressure is released in stages

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21
Q

What causes one major earthquake?

A

When pressure is released all at once

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22
Q

Define seismic waves

A

Waves released from earthquakes

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23
Q

What are the four types of seismic waves?

A
  • P waves (Primary)
  • S waves (Secondary)
  • L waves (Love)
  • R waves (Rayleigh)
24
Q

What are the two ‘body waves’?

A
  • P waves (Primary)

- S waves (Secondary)

25
Q

What are the two ‘surface waves’?

A
  • L waves (Love)

- R waves (Rayleigh)

26
Q

What are ‘body waves’?

A
  • P + S
  • Travel through Earth’s interior
  • High frequency
  • Less damaging
  • Arrive before surface waves
27
Q

What are ‘surface waves’?

A
  • L + R
  • Travel through Earth’s crust/surface
  • Low frequency
  • More damaging
  • Arrive after body waves
28
Q

List the properties of P waves (Primary)?

A
  • Body wave
  • Fastest/first to arrive
  • Less damaging than S waves
  • Can move through: solids + liquids
  • Pattern: compressions + expansions of rock particles (longitudinal)
29
Q

List the properties of S waves (Secondary)

A
  • Body waves
  • Arrive after P waves but before surface waves
  • More damaging than P waves
  • Can move through: solids
  • Pattern: rock particles move at right angles to wave travel (transverse)
30
Q

List the properties of L waves (Love)

A
  • Surface wave
  • Faster than R waves, slower than body waves
  • Often most damaging
  • Pattern: rock particles moved horizontally from side to side
31
Q

List the properties of R waves (Rayleigh)

A
  • Surface wave
  • Slowest wave, arriving last
  • Can be largest, resulting in most shaking felt
  • Pattern: rock particles moved elliptically, so ground moves horizontally + vertically
32
Q

List the 4 seismic waves from fastest to slowest

A
  • P waves
  • S waves
  • L waves
  • R waves
33
Q

What are the two key uses of seismic waves?

A
  • To locate Moho Discontinuity

- To locate earthquake’s epicentre

34
Q

Outline how seismic waves have been used to locate the Moho Discontinuity

A
  • Seismographs record body waves
    At the discontinuity…
  • P waves: refract, slower velocity in mantle (partially liquid)
  • S waves: don’t pass through the mantle
  • This point of P waves refracting + S waves stopping is recorded
35
Q

What is the Moho Discontinuity?

A

Boundary between crust + mantle

36
Q

How can seismic waves be used to locate an earthquake’s epicentre?

A
  • Record time taken for waves to reach seismograph station
  • Already know speed of each type of wave
  • Do speed x time to work out distance (between epicentre + station)
  • Can work out where epicentre is by triangulating the distance circles of three seismograph stations
37
Q

Define a primary impact of earthquakes

A

A direct result of the ground shaking

38
Q

List some examples of primary environmental impacts of earthquakes

A
  • Destruction of physical environment: e.g. treefall

- Destruction of built environment: e.g. collapsed buildings

39
Q

List some examples of primary social impacts of earthquakes

A
  • Deaths

- Injuries

40
Q

Define secondary impacts of earthquakes

A

An impact caused indirectly as a result of the ground shaking

41
Q

What hazards can be triggered by earthquakes - causing secondary impacts?

A
  • Liquefaction
  • Landslides, Avalanches, Rock falls (MASS MOVEMENTS)
  • Tsunamis
42
Q

List some examples of secondary environmental impacts of earthquakes

A
  • Flooding
  • Damage of buildings + infrastructure after the earthquake, as a result of secondary hazards
  • Pollution (e.g. atmospheric pollution from fires triggered)
43
Q

List some examples of secondary social impacts of earthquakes

A
  • Homelessness (due to loss of buildings)
  • Unemployment (due to loss of business buildings + infrastructure)
  • Spread of diseases from contaminated water + conditions in temporary camps (e.g. cholera)
  • Lawlessness
  • Lack of education + health facilities (due to loss of trained staff)
44
Q

List some examples of secondary economic impacts of earthquakes

A
  • Need for costly repairs
  • Costs of aid (often comes from abroad)
  • Loss of businesses + lower economic activity lowers GDP
45
Q

Define liquefaction

A

Water-saturated material loses strength + behaves as a liquid when subjected to ground movement

(A secondary hazard triggered by earthquakes)

46
Q

How does liquefaction occur?

A
  • Ground shakes
  • Increase in pressure on ground
  • Water forced from pore spaces when under pressure
  • Cohesiveness of ground’s internal structure decreases
  • Ground material is able to move as a liquid
47
Q

What can liquefaction cause?

A

Structural instability in buildings, as their foundations sink + they collapse

48
Q

What happens to liquefacted land post-earthquake?

A

Water sinks back into ground + surface firms

49
Q

Give an example of the secondary hazard liquefaction

A

Christchurch earthquake (2011)

  • Liquefaction caused buildings to collapse
  • About 20,000 residential properties had severe damage due to this
50
Q

Define landslides/avalanches/rock falls

A

Mass movements that occur after land shakes in earthquakes

A secondary hazard triggered by earthquakes

51
Q

How do earthquakes trigger mass movements?

A
  • Ground shakes
  • Stresses are created
  • Natural slopes weakened by the stresses + collapse in mass movement
52
Q

What do mass movements cause?

A

A significant hinderance in rescue efforts, as accessibility is usually reduced

53
Q

What influences the chances that the secondary hazard of mass movements is triggered?

A
  • Rainfall
  • Relief of land
  • Land use
  • Geology
54
Q

Give an example of a secondary hazard mass movement

A

Alps (often)

- Avalanches often triggered by earthquake activity

55
Q

Define tsunamis

A

?

Geography - C - Tectonics (2 decks)

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