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

Earthquakes, Processes, Hazards + Their Impacts Flashcards

(55 cards)

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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?

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

What are the two ‘body waves’?

Study These Flashcards
A
  • P waves (Primary)

- S waves (Secondary)

25
What are the two ‘surface waves’?
- L waves (Love) | - R waves (Rayleigh)
26
What are ‘body waves’?
- P + S - Travel through Earth’s interior - High frequency - Less damaging - Arrive before surface waves
27
What are ‘surface waves’?
- L + R - Travel through Earth’s crust/surface - Low frequency - More damaging - Arrive after body waves
28
List the properties of P waves (Primary)?
- Body wave - Fastest/first to arrive - Less damaging than S waves - Can move through: solids + liquids - Pattern: compressions + expansions of rock particles (longitudinal)
29
List the properties of S waves (Secondary)
- 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
List the properties of L waves (Love)
- Surface wave - Faster than R waves, slower than body waves - Often most damaging - Pattern: rock particles moved horizontally from side to side
31
List the properties of R waves (Rayleigh)
- 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
List the 4 seismic waves from fastest to slowest
- P waves - S waves - L waves - R waves
33
What are the two key uses of seismic waves?
- To locate Moho Discontinuity | - To locate earthquake’s epicentre
34
Outline how seismic waves have been used to locate the Moho Discontinuity
- 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
What is the Moho Discontinuity?
Boundary between crust + mantle
36
How can seismic waves be used to locate an earthquake’s epicentre?
- 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
Define a primary impact of earthquakes
A direct result of the ground shaking
38
List some examples of primary environmental impacts of earthquakes
- Destruction of physical environment: e.g. treefall | - Destruction of built environment: e.g. collapsed buildings
39
List some examples of primary social impacts of earthquakes
- Deaths | - Injuries
40
Define secondary impacts of earthquakes
An impact caused indirectly as a result of the ground shaking
41
What hazards can be triggered by earthquakes - causing secondary impacts?
- Liquefaction - Landslides, Avalanches, Rock falls (MASS MOVEMENTS) - Tsunamis
42
List some examples of secondary environmental impacts of earthquakes
- Flooding - Damage of buildings + infrastructure after the earthquake, as a result of secondary hazards - Pollution (e.g. atmospheric pollution from fires triggered)
43
List some examples of secondary social impacts of earthquakes
- 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
List some examples of secondary economic impacts of earthquakes
- Need for costly repairs - Costs of aid (often comes from abroad) - Loss of businesses + lower economic activity lowers GDP
45
Define liquefaction
Water-saturated material loses strength + behaves as a liquid when subjected to ground movement (A secondary hazard triggered by earthquakes)
46
How does liquefaction occur?
- 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
What can liquefaction cause?
Structural instability in buildings, as their foundations sink + they collapse
48
What happens to liquefacted land post-earthquake?
Water sinks back into ground + surface firms
49
Give an example of the secondary hazard liquefaction
Christchurch earthquake (2011) - Liquefaction caused buildings to collapse - About 20,000 residential properties had severe damage due to this
50
Define landslides/avalanches/rock falls
Mass movements that occur after land shakes in earthquakes | A secondary hazard triggered by earthquakes
51
How do earthquakes trigger mass movements?
- Ground shakes - Stresses are created - Natural slopes weakened by the stresses + collapse in mass movement
52
What do mass movements cause?
A significant hinderance in rescue efforts, as accessibility is usually reduced
53
What influences the chances that the secondary hazard of mass movements is triggered?
- Rainfall - Relief of land - Land use - Geology
54
Give an example of a secondary hazard mass movement
Alps (often) | - Avalanches often triggered by earthquake activity
55
Define tsunamis
?

Geography - C - Tectonics (2 decks)

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