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Geography (Physical) - 3. Hazards > Seismic Hazards > Flashcards

Seismic Hazards Flashcards

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1
Q

What are earthquakes? What is seismicity? - Seismicity

A

Earthquakes are a primary hazard produced by friction after the movement of tectonic plates in the lithosphere. Pressure builds up as plates attempt to move, and produces tremors when this is released.
Seismicity is the movement of plates in the Earth.

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2
Q

What form of earthquake occurs at destructive subduction/destructive collisional margins? - Seismicity

A

Destructive subduction - shallow or deep earthquake of significant magnitude.
Destructive collisional - shallow focus earthquakes occur when plates push against each other.

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3
Q

What forms of earthquake occur at constructive margins/conservative margins? - Seismicity

A

Constructive - shallow focus earthquakes occur as plates move apart.
Conservative - shallow earthquakes occur as 2 plates move alongside each other.

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4
Q

What is an earthquake’s focus? What is an earthquake’s epicentre? - Seismicity

A

Focus - a point within the crust at which pressure realise occurs.
Epicentre - a geographical position at the centre of seismic activity.

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5
Q

What form of earthquake cause the greatest damage? - Seismicity

A

Shallow focus earthquakes cause the greatest damage.

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6
Q

What is elastic rebound theory? - Seismicity

A

Elastic rebound theory is where 2 plates building pressure and energy exceed the strength of the rock, causing a rupture and the release of energy. After this energy is released, the rocks rebound to an undeformed shape.

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7
Q

What are seismic waves? What are the 4 types of wave? - Seismicity

A

Seismic waves are waves released following a seismic event, travelling through the Earth’s crust.
The 4 types of waves are primary waves, secondary waves, Love waves and Raleigh waves.

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8
Q

What are body waves? What 2 types of wave fall under this category? - Seismicity

A

Body waves are waves which travel through the Earth, divided into primary and secondary waves.

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9
Q

What are surface waves? What 2 types of wave can these be divided into? - Seismicity

A

Surface waves are waves which travel along the surface of the Earth, divided into Love and Raleigh waves.

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10
Q

Describe the characteristics of P waves and S waves respectively (speed, substances they can travel through) - Seismicity

A

P waves - fast, travel through gas, solid and liquid, compressional
S waves - slower, only travel through solids

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11
Q

Describe the characteristics of Love and Raleigh waves respectively (movement style, speed, damage- Seismicity

A

Love waves - horizontal movement, slow moving, high damage

Raleigh waves - rolling movement, faster moving, highly damaging

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12
Q

What is the Benioff Zone in relation to earthquakes? How does it impact the magnitude of earthquakes? - Seismicity

A

The Benioff Zone is the area in which a denser plate subducts beneath a lighter one, causing friction between the two. This friction creates earthquakes, with the further down a plate friction occurs, the smaller the magnitude of an earthquake.

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13
Q

What % of earthquakes occur at plate boundaries? What % occur intraplate? - Seismicity

A

90% of earthquakes occur at plate boundaries? 10% occur intraplate.

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14
Q

What causes earthquakes at intraplate locations? - Seismicity

A

Earthquakes at intraplate locations can be caused by movement of old fault lines, as well as human activities (mining, fracking or reservoir building).

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15
Q

Describe the moment magnitude scale. What does it measure and how? - Seismicity

A

The moment magnitude scale measures the amount of energy released by an earthquake relating to the movement of rocks. It uses a logarithmic scale to measure quake. Since it measures something physical, these quakes may be compared.

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16
Q

What is the Mercalli Scale? What does it measure and how does it do this? - Seismicity

A

The Mercalli Scale measures observable change caused to an environment, based around subjective data and varies based on location of measurement following an earthquake. MEASURES IMPACT AND INTENSITY OF THIS.

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17
Q

What is the Richter scale? What does it measure and how does it do this? - Seismicity

A

The Richter scale measures the amplitude of the largest wave produced by an earthquake, recorded by a seismograph a distance from the epicentre of an event. Does not measure total energy released. Logarithmic scale.

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18
Q

What are the 2 primary impacts of earthquakes? - Seismicity

A

Earthquakes lead to ground shaking and ground rupture (the visible fracturing and breaking of the ground).

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19
Q

What recent developments have increased the risk from seismic events? - Seismicity

A

Rapid and unregulated urbanisation has led to more high-rise buildings/weak housing and increased urban populations, leading to these being at greater risk than would be the case in less urbanised environments.

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20
Q

What short-term impacts exist from infrastructure damage caused by earthquakes? - Seismicity

A

Infrastructure may be damaged in the form of broken gas pipes, contaminated water supplies, landslides, tsunamis, fires and liquefaction

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21
Q

What long-term social and economic infrastructure damage is created by earthquakes? - Seismicity

A

Social - homelessness, health service pressures

Economic - reconstruction and repair of services, loss of farmland

22
Q

Describe the process of liquefaction. What consequences are there of this? - Seismicity

A

Liquefaction occurs when once stable soil is destabilised by the movement of water through it during earthquakes. Water rises during earthquakes and fills gaps between particles, causing sands and soils to act as if fluid during earthquakes.
This causes buildings atop this soil to collapse during earthquakes.

23
Q

What are landslides? What causes them? What are their impacts? - Seismicity

A

Landslides are the downward movement of rocks and soils under the movement of gravity, often caused by seismic activities. Earthquakes can cause soils to rapidly move downhill. These have been known to block roads, cause death and damage buildings/infrastructure.

24
Q

What are tsunamis? What causes them? - Seismicity

A

Tsunamis are extreme waves caused by the uplift of the lighter plate at a subduction margin and other seismic activity.

25
Q

What happens to a tsunami as it begins to reach the coast? - Seismicity

A

As a tsunami reaches the coast, it slows down but increases in height. Furthermore, the waterline suddenly retreats, exposing the seabed.

26
Q

Can earthquakes be predicted? What warning signs exist? - Seismicity

A

Earthquakes cannot generally be predicted as they are very sudden events with few warning signs that they are about to occur. However, raised ground levels and increased argon in soils/radon in water, as well as historical records, can indicate that an earthquake may occur.

27
Q

What are seismic hazard maps? What can they display? How are they useful? - Seismicity

A

Seismic hazard maps are maps which display potential hazards that may impact a certain area based on previous events, the conditions/built environment at a location and the behaviour of seismic waves in that area. They can plan emergency responses, land-use planning and mitigation.

28
Q

What are seismic hazard maps produced based on? - Seismicity

A

Seismic hazard maps are produced on the basis of the likelihood of shaking, the magnitude of any shaking, land use in a given area, building type/value/age, population density, underlying soil/local geology.

29
Q

What is seismic gap theory? How is it used to predict the occurrence of earthquakes? - Seismicity

A

Seismic gap theory is the idea that plates that have not slipped for a prolonged period are likely to be most vulnerable to a future earthquake. This is especially the case when there is a gap in the displacement of different parts of a fault.

30
Q

What are short term responses to seismic hazards? - Seismicity

A

Short term responses occur in the immediate aftermath of an event. This usually involves supplying emergency aid, evacuating people from affected areas, saving people from collapsed structures and setting up medical centres.

31
Q

How can seismic events be mitigated through prediction? - Seismicity

A

Locations of earthquakes may be predicted due to knowledge of tectonics and previous history, although timing is difficult to predict. Hazard zone maps can help to predict.

32
Q

How can seismic events be mitigated through prevention? - Seismicity

A

It is impossible to prevent earthquakes (although some experimental efforts aim to use lubricants to reduce friction at plat margins). Some secondary impacts can be prevented, such as fires, which may be limited through using smart meters which cut off gas supply when an earthquake hits.

33
Q

How can education be used to mitigate the impacts of seismic hazards? - Seismicity

A

Public education and practices prepare a population for the impacts of a seismic hazard. Japan and the US carry out regular earthquake drills. Guidance is also offered on how to assemble earthquake kits and sort evacuation routes.

34
Q

How can emergency responses be crucial in preventing the impacts of earthquakes? - Seismicity

A

Emergency responses can prevent fatalities by rescuing people from rubble. It can also set up medical centres to deal with immediate medical emergencies.

35
Q

How can mitigation of the impacts from earthquakes be achieved through adaptation? - Seismicity

A

Buildings can be engineered to prevent collapse during seismic events, with some reinforced with deeper foundations and made to absorb shocks. Some buildings have even been built atop shock springs and ball bearings to act as shock absorbers.

36
Q

What are significant examples of buildings that have been reinforced to prevent collapse during earthquakes? - Seismicity

A

Taipei 101 shopping centre in Taiwan has a pendulum which can combat any swinging of the building during earthquakes.
Furthermore, the Transamerica Pyramid in San Francisco has been fitted with 50 foot deep foundations and steel bracing.

37
Q

When did the Nepal earthquake take place? What was the magnitude of this earthquake? - Seismicity

A

The Nepal earthquake took place in April 2015, with it being a 7.8 magnitude earthquake.

38
Q

How far away from Kathmandu did the Nepal earthquake take place? What direction? - Seismicity

A

The Nepal earthquake took place 80km from Kathmandu in a NE direction.

39
Q

What 2 plates made up the Nepal earthquake boundary? What type of plate margin is this? - Seismicity

A

The Nepal earthquake boundary is made up of the Indo-Australian Plate and the Eurasian Plate. This is a destructive margin.

40
Q

How did Kathmandu’s geology and built environment contribute to the impacts of the earthquake? - Seismicity

A

Geology: built atop river sediments, which amplify the shaking and cause liquefaction.
Built environment: the infrastructure in Kathmandu is poorly built and vulnerable to shaking.

41
Q

How many people were killed by the Nepal earthquake? How many were injured? - Seismicity

A

9,000 killed

23,000 injured

42
Q

How many houses in Nepal were damaged or destroyed? - Seismicity

A

700,000 houses in Nepal were damaged or destroyed.

43
Q

What was the value of damage caused by the Nepal earthquake? (In dollars) - Seismicity

A

The Nepal earthquake caused $5.17bn worth of damage.

44
Q

How many landslides were caused by the Nepal earthquake? How many people died in an avalanche on Everest? - Seismicity

A

5000 landslides were caused by the Nepal earthquake, with 19 dying on Everest.

45
Q

How many people were still in substandard accommodation a year after the earthquake? - Seismicity

A

A year after the earthquake, 4 million people lived in substandard accommodation.

46
Q

What general impacts were there from the Nepal earthquake? (Health, tourism, agriculture) - Seismicity

A

Health: clean drinking water availability fell in rural areas.
Tourism: loss of tourism revenues
Agriculture: damage to agricultural production

47
Q

How much financial aid did the UN give to Nepal? How much did the UK give? - Seismicity

A

UN: $15m
UK: £73m

48
Q

What % of Nepal’s military was deployed in response to the Nepal earthquake? - Seismicity

A

90% of Nepal’s military was deployed in response to the earthquake.

49
Q

What involvement did NGOs have in supplying emergency aid to Nepal? - Seismicity

A

NGOs brought emergency supplies, such as UNICEF supplying hygiene kits, water purification tablets and nutritional foods. Also helped evacuate and save people from fallen structures.

50
Q

How much money did the World Bank grant to Nepal? How many families did this assist in rebuilding houses? - Seismicity

A

The World Bank granted $200m to Nepal, allowing 100,000 families to rebuild houses.

51
Q

How did Oxfam contribute to the long-term responses to the Nepal earthquake? - Seismicity

A

Oxfam set up ‘cash for work’ schemes which paid local people for undertaking reconstruction work and the rebuilding of infrastructure.

Geography (Physical) - 3. Hazards (6 decks)

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