Geography Physical > Hazard Post Mocks > Flashcards

Hazard Post Mocks Flashcards

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1
Q

Explain the formation of an island arc

A

Form at destructive plate boundaries (where plates move towards one another)
Convection currents act as a conveyor belt with magma sinking at this boundary
Intense heating occurs (due to friction)
Less dense magma rises and forms volcanos which make islands, often in an arc

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2
Q

Example of an island arc

A

Ryuku Islands, South of Japan

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3
Q

Where are the Ryukyu islands

A

In the Ryukyu trench north of Japan

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4
Q

Which two plates caused the Ryukyu islands to form

A

Philippine Oceanic plate subducted under the Eurasian plate

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5
Q

What is an earthquake

A

Build up of stress between the constantly moving tectonic plates of the crust. When the stress is released, it causes an intense shaking motion

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6
Q

What is the focus of an earthquake

A

Point of pressure release within the crust

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7
Q

What is the epicentre of an earthquake

A

The point on the earths surface immediately above the focus

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8
Q

Characteristics of a shallow focus earthquake

A

0-70km

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9
Q

Characteristics of a intermediate focus earthquake

A

70-300km

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10
Q

Characteristics of a deep focus earthquake

A

300-700km

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11
Q

Where experiences the most shaking in an earthquake

A

The epicentre

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12
Q

What happens the further you go from the epicentre of an earthquake

A

Shaking becomes less intense

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13
Q

How long can the shaking last in an earthquake

A

Less than a minute and often followed by aftershocks where the crust settles up to several weeks later

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14
Q

What is the example of an earthquake with a far away epicentre still doing lots of damage

A

1985 in Mexico City

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15
Q

How far away was the epicentre in the 1985 earthquake in Mexico City

A

350km south on the coast

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16
Q

Why was the damage os bad in the 1985 earthquake in Mexico City

A

It is built on a former lake made up of soft unconsolidated sediment (led to liquefaction)

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17
Q

What are the characteristics of Primary/Pressure seismic waves

A

Fastest and reach the surface first
High frequency
(compressions and rarefactions of the crust, mantle and core)

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18
Q

What are the characteristics of Secondary/Shear seismic waves

A

Half as fast as P waves and second highest frequency (Shake only through the crust and mantle)

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19
Q

What are the characteristics of Surface Love seismic waves

A

Horizontal to ground motion
Often cause the most destruction
Slower than P and S waves

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20
Q

What are the characteristics of Rayleigh seismic waves

A

Form when P and S waves interact at the surface
Travel very far
Slowest of all waves
Both side to side and up and down
Similar to ocean waves

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21
Q

What are the 3 different earthquake magnitude scales

A

Mercalli Intensity
Richter magnitude
Moment magnitude

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22
Q

How does the Mercalli intensity scale measure earthquakes

A

Described in terms of what nearby residents felt and the damage that was done

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23
Q

How does the Richter magnitude scale measure earthquakes

A

Uses a seismometer to measure the magnitude of the largest jolt of energy released by an earthquake

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24
Q

How does the Moment Magnitude scale measure earthquakes

A

Measures total energy released by an earthquake
Calculated from the area of the fault that is ruptured and the distance the ground moved along the fault

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25
How is the Richter scale measured (description)
Logarithmic scale
26
How is the Mercalli scale measured (description)
Measures effects from 1-12 (often roman numerals)
27
Advantages and Disadvantages of the Richter Scale
Objective Absolute (not relevant to development) Can over-represent if there is only 1 large shockwaves Quantitative Best recognised Physical approach Quality of seismographs varies globally
28
Advantages and disadvantages of the Mercalli scale
Linear so easier to interpret Based on effects (more usable by normal people and reflects the local context) Uses damage reports and eyewitnesses Qualitative Human approach
29
What is soil liquefaction
Violent shaken soils with a high water content lose their mechanical strength and begin to behave as a liquid
30
What is a landslide or avalanche caused by (seismic hazard)
Slope failure as a result of ground shaking
31
How is a Tsunami a seismic hazard
Giant sea waves generated by shallow focus underwater earthquakes involving movements of the sea bed
32
How are fires seismic hazards
Resulting from broken gas pipes and collapsed electricity transmission systems
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What are the effects on people and the built environment from seismic hazards
Buildings collapse Roads destroyed Communications services destroyed Flooding -> disease Blocked roads make it harder to receive aid Economics impacts
34
Describe liquefaction in detail
Surface material of fine grained sands, alluvium and landfill with high water content start to behave like a liquid They lose their mechanical strength and river banks collapse structures tilt and slip as foundations give way
35
What is foundation failure
Liquefaction causes buildings to tilt, sink or even collapse
36
What is lateral spreading
Liquefaction abuses structures to shift downhill/sideways
37
What is settlement and ground deformation (seismic effect)
Liquefaction causes ground to settle unevenly and it causes cracks
38
Outline liquefaction
During an earthquake, violent shaking occurs Saturated soil Particles get rearranged and the shaking makes them behave like a liquid Some buildings may undergo foundation failure and sink into the ground E.g. Christchurch 2011 NZ
39
Where is the liquefaction small case study
Christchurch 2011 New Zealand Foundation failure so buildings sank into the ground
40
Size of a tsunami info
Initially a low wave but can get big at the shore (1m -> 25m)
41
What creates a Tsunami
Seimsic activity (typically earthquake but can be created by underwater landslides)
42
What is the speed of a Tsunami
640-960km/h
43
Where are most Tsunamis
90% in the ring of fire
44
What impacts do Tsunamis have
Sweeps away victims Destroys poorly constructed buildings Washes boats 100s of metres inland
45
Example of underwater landslide and its impacts
In 1998, 2,200 bukkagers living in Papua New Guinea were killed by a local underwater landslide causing a Tsunami after an earthquake.
46
Specific details of why underwater landslides leading to tsunamis are more dangerous
Very localised and very little warning so no mitigation
47
Why are underwater landslides different from terrestrial ones
They are far larger than on land We don’t know where they happen They only need a 1-5 degree slops
48
Example of terrestrial landslide leading to on land damage from an earthquake
Northern Italy in 1963 Hillside above the Vaiont reservoir collapsed, generating a 100m wave, drowning 30k people
49
How and where do most underwater landslides occur
At subduction zones (they displace water)
50
How can submarine landslides be mitigated
OBS to measure seismic activity
51
What is OBS that measures underwater seimsic activity
Ocean Bottom Seismometer
52
What is prediction in terms of hazards
Ability to give warnings so that actions can be taken to reduce the impacts of a hazardous event
53
How can a hazard map be used to reduce risk (warnings)
Improved monitoring, information and comms tech to issue warnings ASAP Advance in comms couples with globalisation to spread the message faster
54
How can a hazard map be used to reduce risk (prediction)
Very hard: at risk regions can be identified by plate tectonics but anything more than a few hours is a questionable guess
55
What are hazard maps best for (which hazard)
Volcanoes are better because the location is almost always known before the eruption, whereas earthquakes are just a guess
56
What can be used to make a hazard map
GPS predictions to show high risk areas They aid urban planning and development
57
What tech is used to make hazard maps
Satellite remote sensing Preliminary tremors Release of Radon Gas Subs surface hydrological changes (e.g. the water table)
58
How does satellite remote sensing work
Detects changes in the earths surface like ground deformation
59
What is the scale of satellite remote sensing
Pixels can be a small as 1m so quite accurate but not specific enough for very local things
60
Advantages of satellite remote sensing
Broad overview of anywhere Helps map active fault lines
61
Disadvantages of satellite remote sensing
Extremely expensive initially (but cheap after that and there’s even free data) Requires complex data processing Cannot see underground
62
How does measuring of preliminary tremors work
Seismographs used to record small foreshocks
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Scale of preliminary tremors
Local
64
Advantages of measuring preliminary tremors
Can use established seismograph networks Foreshocks are usually telltale signs of earthquakes
65
Disadvantages of measuring preliminary tremors
Many large earthquakes don’t have foreshocks Can lead to false alarms and/or public panic
66
How can escape of radon gas be used to predict an earthquake
More radon gas = more likely to be an earthquake because it gets released from within the crust
67
What is the scale of escape of radon gas as a means to measure likelihood of seismic hazards
Local, very site specific
68
Advantages of using escape of radon gas as a means to measure likelihood of seismic hazards
Chemically inert so its presence is an indicator of new fractures opening up
69
Disadvantages of using escape of radon gas as a means to measure likelihood of seismic hazards
Radon levels vary naturally anyway due to tides and weather Not all earthquakes release radon gas Hard to monitor over large areas
70
How can sub surface hydrological changes be used to measure likelihood of seismic events
Changes in groundwater indicate stress in the earths crust E.g. measuring wells to see change to the levels
71
Scale of sub surface hydrological changes being used to measure likelihood of seismic events
Local
72
Advantages of sub surface hydrological changes being used to measure likelihood of seismic events
Monitoring wells are very cheap Changes in water pressure occur directly as a result of tectonic stress
73
Disadvantages of sub surface hydrological changes being used to measure likelihood of seismic events
Gorundwater can change due to rainfall, irrigation or human use so the data is full of “noise” that is hard to control for
74
Why is it hard to predict magnitude of earthquakes
It depends on total amount of accumulated elastic strain which we can’t measure directly from 10-700km Also, a small earthquake can lead to a runaway effect which can cascade into a larger rupture so its impossible to guess the magnitude
75
Why is the timing of an earthquake hard to estimate
They don’t happen at regular intervals, they are not exactly “due” to erupt on a regular basis, when the rock fails is not consistent All precursor signals are very unreliable and not necessary for an earthquake to happen and vice versa
76
Why is the location of an earthquake hard to estimate
We can identify rough zones of high risk (ring of fire) Pinpointing epicentres is impossible since most faults are blind and hidden deep under sediment Stress can be transferred along a fault system so where the initial stress is the earthquake might not even happen so its just a guessing game
77
What happens in Japan for planning for earthquakes (whole population)
National Disaster Prevention Day on September 1st
78
What else does Japan do for earthquake preparation
In 2008 the whole army did emergency drill training which involved 18k participants across 22 towns
79
How did the planning in Japan beat Haiti in the 2010 earthquakes (education)
Nationwide awareness and military drills VS No public education or drills before their 2010 earthquake
80
How did the planning in Japan beat Haiti in the 2010 earthquakes (infrastructure)
Japan had world leading infrastructurecure with semisic building codes so that high rise buildings were flexible VS Haiti had rapid and unregulated urbanisation with heavy and unreinforced masonry which lacked any seimsic resilience
81
How did the planning in Japan beat Haiti in the 2010 earthquakes (monitoring )
Japan had advanced nationwide mointoring for P waves to provide phone alerts as early warnings VS Haiti had NO seismic monitoring or early warnings
82
How did the planning in Japan beat Haiti in the 2010 earthquakes (mobilise public servants)
Japan is an HIC with a military which had large scale disaster responses VS Haiti was an LIC with political instability so no investment or mobilisation was made into mitigation
83
What seismic phenomenon damages buildings most during seismic events
The initial shaking of the ground
84
What is seismic retrofitting
Provides existing structures a way to improve resistance to seismic activity Typically involves strengthening weak connections of walls to roofs shear walls and the roof diaphragm
85
what is a shear wall (seismic retrofitting)
Vertical, stiff panels (concrete, masonry or wood) that acts as a cantilever which absorbs horizontal shear forces
86
What is a roof diaphragm (seismic retrofitting)
Horizontal plates of concrete, metal or wood) that collects and distributes lateral forces They span between shear walls to transfer the earthquake force downward
87
Examples of hard engineering on buildings to withstand small earthquakes
Rolling weights on the roof to counteract shock waves Rubber shock absorbers between foundations and superstructure Reinforced lift shafts with tensioned cables
88
How do shock absorbers work in earthquake proof buildings
Also called base isolation Rubber and steel bearings placed between foundations and the building to absorb seismic waves The building moves but the structure doesn’t
89
How do dampers work in earthquake proof buildings
Large, tuned mass dampers act like a cars suspension, they counter the buildings swaying motion by moving the opposite direction, dissipating energy
90
Example of soft engineering to reduce the damage from earthquakes to buildings
Bamboo can be used due to its strength to weight ratio and low cost This allow structures to bend and sway rather than shatter
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