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AQA A-Level Physical Geography > 🌋3.1.5.4 - Seismic Hazards > Flashcards

🌋3.1.5.4 - Seismic Hazards Flashcards

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1
Q

What are seismic hazards?

A

Earthquakes, tsunamis, landslides and liquefaction

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2
Q

What is seismicity?

A

The Earth’s shaking, can be human induced or natural

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3
Q

How are seismic waves formed?

A

Pressure builds up at a point where plates meet
Sudden release due to rock failure creates waves
The waves cause the ground to shake
Intensity of the shaking is dictated by the depth of focus and energy release

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4
Q

What are tsunamis caused by?

A

Earthquakes under the sea, moving a column of water above it, displacing it

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5
Q

What are the characteristics of tsunamis?

A

Waves less than 3ft tall, but are compress towards land, gaining height. A wave train which propagates form the earthquake.

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6
Q

What is liquefaction?

A

The mixing of sand or soil with groundwater during the shaking of a moderate or strong earthquake. Ground becomes very soft and similar to quicksand.

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7
Q

When is land susceptible to landslides?

A

It has experienced heavy rain
Fractured or unconsolidated rock
Fold mountains, unstable plate boundary
Steep relief

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8
Q

How can earthquakes be predicted?

A

Past seismic events
Remote sensing
Radon gas emissions

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9
Q

How can past seismic events be used to predict earthquakes?

A

Looking into past frequencies and magnitudes to infer future events can be used for prediction

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10
Q

How can remote sensing be used to predict earthquakes?

A

GPS can be used to monitor the smallest of movements by the plates, stationary plates suggest build up of pressure

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11
Q

How can radon gas emissions be used to predict earthquakes?

A

Radon escapes form cracks in the earth’s crust and a sudden increase may suggest that an earthquake may be imminent

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12
Q

Are earthquakes predictable?

A

No

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13
Q

What type of boundary to most earthquakes originate from?

A

Destructive - at subduction zones

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14
Q

Where is liquefaction a particularly dangerous hazard?

A

In areas where groundwater is near the surface and the soil is sandy

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15
Q

What is subsidence?

A

When the ground surface is lowered often during earthquakes

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16
Q

What are the characteristics of P waves?

A

Fastest waves
Earth moves backwards and forwards but surface stays flat
Moves through solids and liquids

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17
Q

What are the characteristics of S waves?

A

A ripple, up and down movement
Water wave, surface doesn’t stay flat
Shakes earth at right angles

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18
Q

What are the characteristics of Rayleigh waves?

A

Up and down movement and side to side, moves like a snake
Low frequency, rolling motion
Radiate along the surface

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19
Q

What are the characteristics of Love waves?

A

Slowest waves, surface
Causes sideways motion and most damage
One pulse, up and down and some side to side

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20
Q

What is a seismograph used for?

A

To measure ground movement

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21
Q

How does a seismograph work?

A

Pen attached to weight to track movements

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22
Q

What is a seismometer used for?

A

Recording ground movement data digitally

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23
Q

What are the issues with a seismometer?

A

So small that waves must be amplified

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24
Q

What does the Mercalli scale range from and to?

A

1-12

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25
Q

What is a 1 on the Mercalli scale?

A

Instrumental - not felt by many people unless in favourable conditions

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26
Q

What is a 12 on the Mercalli scale?

A

Cataclysmic - total destruction

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27
Q

What are the positives of the Mercalli scale?

A 
Can be used for damage comparison
Relates to epicentre location
No equipment required
Idea of damage done, builds a picture
Perfect for response planning
Allows links for human need
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28
Q

What are the negatives of the Mercalli scale?

A

Subjective, qualitative measure
Uncertainty and bias
Location of observer alters results
Compares effects, not the event

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29
Q

What does the Richter scale measure?

A

Ground deformation and energy release

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30
Q

What type of scale does the Richter follow?

A

Logarithmic

31
Q

What is the highest recorded value on the Richter scale?

A

8.9

32
Q

Seismicity

A

Earth shaking
Can be human induced through fracking, mining and reservoir construction

33
Q

Earthquake Formation

A

. Friction along margins = stress in lithosphere
. Stress suddenly overcome
. Plates fracture along faults
. Sends a series of shock waves to the surface
. Tremors can be followed be several weeks of after shocks whilst crust settles

34
Q

What factors make the damage done by an earthquake worse?

A

Time of day
Depth of focus
Population density
Level of development
Building quality

35
Q

P Waves

A

Fast moving, first to reach the surface
Travel through solids and liquids (crust, mantle, core)
High frequency

36
Q

S Waves

A

Second waves to reach the surface
Travel through liquids (mantle)
Sideways movement, shaking earth at 90° to direction of travel
Do more damage than P waves

37
Q

Love Waves

A

Slowest moving
Do most damage because of sideways movement

38
Q

Rayleigh Waves

A

Radiate from epicentre in complicated, low frequency rolling motions

39
Q

Tsunami

A

Large sea wave generated by earthquakes on the ocean floor, large landslides and submarine volcanic eruptions

40
Q

Tsunami Formation

A

. Pressure between 2 plates suddenly released
. Large waves of energy displace water
. Water train created, spreads in concentric circles to shore
. Upon reaching shore, wave shoaling occurs (friction = highly destructive wave)
. Wave retreats taking debris, forming the next wave

41
Q

What factors make the damage done by a tsunami worse?

A

Distance travelled
Focus depth (shallower = larger)
Population density
Level of development
Warning given

42
Q

Landslide

A

Movement of rock, debris or earth down a slope

43
Q

Landslide Formation

A

Ground shaking due to earthquake destablishes cliffs and steep slopes
Causes material to quickly move down slope

44
Q

What factors make landslides worse?

A

Steep gradient
High relief rainfall (saturates ground = unstable)
Shallow soil
Unstable rock

45
Q

Liquefaction

A

Jelly like state of silts and clays resulting from intense ground shaking

46
Q

Liquefaction Formation

A

Sand or soil mixes with ground water
Becomes very soft, causing subsidence and building collapse

47
Q

What factors make liquefaction worse?

A

High ground water
Reclaimed soil
Sandy soil (loosely packed grain = more pore spaces to fill with water)

48
Q

Richter Scale

A

Logarithmic
1 to 10+
Easy comparison between disasters
Quantitative

49
Q

Modified Mercalli Scale

A

Qualitative
0 to XII
Different levels for different areas
Only useful with buildings around

50
Q

Preparedness: Name some of the events that occur in the minutes before an earthquake

A

Microquakes before main tremor
Magnetic changes in local rock
Unusual animal behaviour

51
Q

Prevention: Although almost impossible to prevent, what have some scientists suggested?

A

Putting water and oil in margins
Lubricates movement
Plates will slide not stick

52
Q

Adaptation: What form does protection mainly take?

A

Preparation by modifying the human and built environments to decrease vulnerability and reduce loss

53
Q

Adaptation: 2 features of hazard resistant structures

A

Concrete weight on roof- moves in opposite direction to force of earthquake, counteracting stress
Rubber shock absorbers in foundations- allows some movement

54
Q

Adaptation: What can people in old buildings do?

A

Retrofit them to make them more aseismic

55
Q

Mitigation: How does education help?

A

Minimises loss of life, through earthquake drills

56
Q

Adaptation: 2 ways fires can be prevented

A

Smart meters- cut off gas in an earthquake over a certain magnitude
Tokyo gas companies- switch off pipelines, reducing the number of fires

57
Q

Adaptation: 2 ways of protecting against tsunamis

A

Tsunami warning systems
Build 12m high tsunami walls (ineffective)

58
Q

Protection: How can the emergency services be ready?

A

Heavy lifting gear available
Carefully organised and planned response
People in communities given first aid training to treat injured before help arrives

59
Q

Mitigation: Why are people urged to take out insurance in richer countries?

A

To cover their losses- expensive

60
Q

Adaptation: Land use planning

A

Schools and hospitals built in low risk areas
Green space put into high risk areas, forming a safe area away from fires and aftershock debris + distribution areas

61
Q

Prevention: How can any impacts from liquefaction be prevented?

A

Authorities preventing building on land prone to liquefaction

62
Q

Mitigation: How to earthquake and tsunami warning systems reduce damage caused?

A

Detect weak shockwaves
TV / SMS warnings given
Aids evacuation

63
Q

Predicting earthquakes: past seismic events

A

. Seismic gap theory
. Regular pattern can help predict the next earthquake
. The seismic gap states that earthquake hazard increases with time since the last large earthquake on certain faults or plate boundaries

64
Q

Animals in prediction

A

. They may detect seismic activity and notice smaller vibrations and exhibit unusual behaviour
. They may sense ionisation of air caused by the large rock pressure in earthquake zones in their fur
. May smell gases

65
Q

Lazar beams

A

Can detect plate movement by directing the beam across the fault line

66
Q

Pros of mercalli scale

A

. Useful in determining damage caused to an area and responses can be planned
. Structural engineers contribute information for assigning values of VIII which is useful for rebuilding phases

67
Q

Cons of mercalli scale

A

. Can only measure earthquakes in inhabited ares
. Not very scientific
. Damage caused may not accurately reflect an earthquake’s strength
. Only measure effects not energy released
. Witnesses that scale is based on may not be accurate

68
Q

Mercalli scale vs Richter scale

A

. Unlike the mercalli scale which looks at damaged caused the Richter scale measures ground deformation and energy released
. In richter as you move up the magnitude frequency decreases
. Large earthquakes are rare as it takes many years for the pressure and energy to build up

69
Q

Do scientist prefer the Richter scale or Mercalli scale?

A

Scientists prefer the Richter scale as it is more scientifically based, logarithmic scale, rather than human observation

70
Q

Steps to seismic waves

A

1) Pressure builds at the point where 2 plates meet
2) Sudden release (due to rock failure creates waves)
3) The waves cause the ground to shake
4) The intensity of the shaking is dictated by the depth of the focus and the energy release
5) The result of this is the earthquake hazard

71
Q

P-waves (primary)

A

Fastest waves, moving through solid and liquids causing the earth to move backwards and forwards

72
Q

S-waves (secondary)

A

Slower waves which move through a sideways motion, shaking the Earth at right angles to the direction of travel. Can’t move through liquids but do much more damage then P-Waves.

73
Q

Love waves

A

Surface waves which are the slowest. Cause a sideways motion and the most damage.

74
Q

Rayleigh waves

A

Radiate along the sirface in a low-frequency rolling motion.

AQA A-Level Physical Geography (28 decks)

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