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Geography A-level > Seismic hazards > Flashcards

Seismic hazards Flashcards

1
Q

Earthquake

A

A sudden and violent movement or shaking within the rocks of the earths crust, causing surface vibrations which only last a few seconds

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2
Q

Intraplate earthquakes

A

The small 5% of eqs which occur away from plate boundaries due to build up in crustal stresses in old fault lines overtime which eventually release without warning

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3
Q

Alpine collision zone

A

23% of global eqs
shallow focus eqs
killed more than 10,000 people since 1990 (nepal 2015, turkey - syria 2023)

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4
Q

Impact of turkey eqs?

A

Turkey 1999- 12mit 20,000 deaths identifying how poorly prepared country were
Turkey 2023 - 60,000 deaths tripled!#

Govt introduced disaster tax in turkey to help them prepare for next event raised 3 billion yet tripled deaths

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5
Q

Spatial distribution of eqs

A
  • 95% at plate margins
  • Ring of fire 75%
  • 23% alpine himalyan collision zone
  • Some pm more seismaclly active but occur at all
  • Most powerful at destructive
  • Intensity and depth depends on pm
  • Benioff zone = deep focus eqs at destructive and shallow focus at conservative
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6
Q

Benioff zone

A

Found at destructive plate margins where subudcting oceanic plate melts into the mantle 330-700km below the surface

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7
Q

Deep focus

A

Greater spatial impact

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8
Q

Shallow focus

A

Less spatial impact

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9
Q

EQS at constructive?

A

Shallow focus eqs, caused by tensional forces in the crust
Occur at mid-ocean ridges
Little threat to people
Low magnitude

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10
Q

EQS at destructive

A

Deep focus created within the benioff zone
High magnitude and major threat to people

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11
Q

EQs at Conservative E

A

Shallow focus, mid-high magnitude, caused by friction due to sliding can be disastorous e.g. san fransisco 1989

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12
Q

What are eqs caused by?

A
  • Stress and friction as plates subduct, diverge or slide within the lithosphere
  • When rocks in crust move they fracture along faults sending out shockwaves from focus
  • Last few seconds
  • Produce aftershocks
  • Intraplate eqs caused by human activity e.g. fracking
  • eq fault lines reack 10km down cause stresses
  • Eq can be caused by human acitivty such as mining, fracking or resivoir construction
    *
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13
Q

Focus

A

The point of origin of the eq

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14
Q

Epic centre

A

The point above the focus where most damage tends to occur

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15
Q

Focal depth

A

The distance between the focus of the eq and the epic centre
The depth can disspate or amplify eq energy

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16
Q

Primary pressure waves

A
  • Fastet waves and reach surface first
  • like soundwaves, high frequency push through the mantle, core crust
  • Faster in dense rocks slower in fluids
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17
Q

Secondary shear waves

A

Half as fast
reach sufrace next
high frequency but shake through crust adn mantle
affect buildings
shadow zone

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18
Q

Surface love waves

A

slowest waves and cause most damage
move side-side
dont penetrate interior or surface

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19
Q

Rayleigh waves

A

Radiate from epic cntre in complicated low frequency rolling motion

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20
Q

Amplificattion

A

seismic waves are amplified as they pass from the focus through basin filled with sedimentary unconsolidated rock
eqs impact will be even greater on the surface

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21
Q

Seismometer

A

The instrument used to detect and monitor earthquakes

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22
Q

Seismograph

A

Produces the reading of the EQ

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23
Q

The richter scale

A

Measures the magnitude of EQS

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24
Q

The Mercalli

A

Measures the earthquakes intensity (impact/effect)

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25
Q

Key facts about the RICHTER SCALE:

A
  • Measures the magnitude of the EQ
  • Devised in 1935
  • Logarithmic scale measuring strength of the seismic waves
  • Starts at 0 and each number is 10x the magnitude (slight increase is an enormous effect on the ground
  • Destructive reported eqs 67
  • 9.5 in chile in 1960 is the largest ever recorded
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26
Q
A
27
Q

Moment magnitude scale

A

devised in 1997 considers both magnitude and ground movement used more frequently

28
Q

The modified mercalli intensity

A
  • Measures impact on people, enviroment and structures
  • Based on observations of the ground of the actual impact of the EQ
  • Devised in 1900
  • Not logaraithmic
  • A subjective measure of impact
  • 12 point scale from I TO XII
  • I =
  • XII = Catastrophic complete destruction
  • Less reliable than richter scale
29
Q
A
30
Q

Tsunami

A

Harbour wave caused by tectonic activity and a series of larger than normal waves
Displaced huge amounts of water

31
Q

Where do tsunamis occur?

A
  • Close to major fault zones
  • Countries located around pacific ring of fire 90%
32
Q

What are tsunamis caused by?

A
  • Ocean floor earthquakes
  • Megathrust earthquakes
  • Submarine volcanic eruptions
  • Massive landslides into sea
  • Submarine landslides
  • Metor
  • Asteroid strikes
33
Q

What are the features of a tsunami?

A
  • Low wave height less than 1 metre - reaching shore reach over 25km high
  • Wave length: 100-1000km
  • Wave period: 10-60 minutes
  • Wave speed: 640-960km per hour
  • Approaching coastline will slown down and pile up before inudating low lying areas
  • LOTS OF ENERGY = ACCUMULATES LOTS OF SEDIMENT AND MATERIAL
34
Q

Wave length of tsunamis

A

Long - 100-1000km

35
Q

Liquefaction

A

Unconsolidated, saturated sediments on or near ground surface lose strength in response to shaking of ground and begin to act like a liquid

36
Q

Salinisation

A

Soil increases its salt content from the inudation of sea water

37
Q

Shoaling

A

A vacumm effect created when first wave crest reaches the shore water is sucked out to sea and exposes a large amount of the sea bed (water then returns quickly as a series of waves)

38
Q

Retrofitting

A

Retrofitting is the process of upgrading existing structures to make them impervious against natural disasters

39
Q
A
40
Q

Wave height

A

low at 1m but can reach up to 25m by the time they reach the shore

41
Q

Speed of waves

A

High speed 640km - 960km per hour

42
Q

Wave period

A

Long: between 10 and 60 minutes

43
Q

Tsunamis by earthquakes

A
  • Created by megathrust earthquakes which displace the water in deep oceans
  • Earthqauke focus point of tectonic upthrust displaces huge quantities of water
  • Oceanic crust may remain displaced e.g. 2011 tokoyo earthquake
  • Both displacement of the crust anf seismic energy create larger waves (>1m) in open water which travels towards the coast increasing in height as the profile of the seabed changes (>25m)
  • Friction within sea bed and shallow depth causes wave to build up in height but speed to dramatically decrease resulting in wave train
  • Shoaling causes water to retreat from the coastline
44
Q

Tsunamis by volcanoes

A
  • During eruptions sides of volcanoes collapse, creating landslides that fall into the ocean
  • The material disrupts water causing a tsunami
45
Q

Tsunamis by meteorites

A
  • Meteorites that fall into the ocean can cause tsunamis
  • Larger the meteorite larger the tsunami
46
Q

Tsunamis in deep water

A
  • Wave height of <1m
  • Wave length >1000km
  • Speed >960km per hour can travel across the ocean in < than a day
  • Orbital movement in deep water
47
Q

Paul indonesia 2018

A
48
Q

Tsunamis in shallow water

A
  • Wave heigh >30m
  • Wave length reduces <1000km
  • Speed 36km per hour
  • Elliptical movement
  • Wave energy concentrated into smaller amount of water
49
Q

Social impacts of earthquakes

A

Primary:
* - Buildings collapse, killing/injuring people and trapping them.
Secondary:
* - Gas pipes
rupture, starting fires which can kill
- Water supplies are contaminated as pipes burst, spreading disease and causing floods
- Schools, unis closed
- Shocked hungry people
- Tsunamis which lead to damaging flooding

50
Q

Economical Impacts of seismic activity

A

Primary:
* - Businesses destroyed
Secondary:
* Economic decline as businesses are destroyed (tax breaks etc.)
- High cost of rebuilding and insurance payout
- Sources of income lost

51
Q

Political impacts

A

Primary:
* - Government
buildings
destroyed
Secondary:
* - Political unrest from food shortages or water shortages
- Borrowing money for international aid
- Can be initial chaos and ‘lawlessness’ e.g. looting

52
Q

Enviromental impacts

A

Primary:
* - Earthquake can cause fault lines which destroy th environment
* -Liquefaction

Secondary:
* - Radioactive materials and other dangerous substances leaked from power plants
- Saltwater from tsunamis flood freshwater ecosystems
-Soil salinisation

53
Q

Short term responses?

A
  • Depends on magnitude and vulnerability of the population
  • Priority is on saving lives - find people trapped in rubble
  • Evacuation
  • Deploying emergency services to provide first response treatment
  • International aid in form of first aid, food, tents, trained peronsell e.g. the army
54
Q

Long term responses

A
  • Involves longterm planning in future preparedness, mitigation,prevention and adaptation
  • Introduction of tsunami warning systems (japan costs 20 million per year), hazard mapping, evacuation plans to prevent future loss of life
  • Stockpiling of dood and water supplies for future loss
  • Rebuilding, retrofitting properties and structures
55
Q
A
56
Q

The seismic gap theory

A
  • Bilham conducted a detailed study of the historical recod of eqs in the himalaya over the past millenium and helps to assess ufture hazard potential
  • It identifies a seismic gap which is a segment of an active fault know to proudce signifcant eqs that has not slipped in a longtime
  • Any largr gap - fault segment likley to experience future eqs
  • Areas that experience lots of small eqs are unlikley to experience a big one
  • Areas not experienced in a long time are likley to experience a large eq
  • Predicting relative size and frequency of eqs in a given area
57
Q

What are stratergies for seismic preparation?

A
  • Education and public awareness campaigns - eq preparation checklists, practicing evacuation drills in schools and offices e.g. nz and usa
  • Evcaution routes
  • Retrofitting
  • Stockpiling food and medical supplies
  • Geographic information systems - used to create hazard maps which identify areas at greast risks
58
Q

Tsunami warning systems

A
  • Eqs can be detected and located using global seismic monitoring network
  • Warnings can be issues
  • Additional data from DART (deep ocean assesment +reporitings of tsunami ) buots in oceans via sattelite
  • A tsunami wanring station then interpets the data and issues an alert
  • Alert are increasingly app based text +traditional media
59
Q

The limitations of tsunami warning systems?

A
  • Ocean is an extreme enviroment; buoys often fail
  • Japans system has an annual maintence costs of us 20 million
  • If tsunami origin is close to land warning may be too short
  • Wave height estimates not very accurate
  • The system only saves lives alongside dissemination network and evacuate routes/safe places
60
Q

How do countries prepare?

A
  • Children instilled with “drop cover hold” practiced
  • Heavy items secured in place in homes, breakables at low levels
  • Families to create a communication group + emergency meeting point
  • Emergency supply kit to last couple of days
  • Structually sound houses
  • EQ insurance policy
61
Q

How do communities mitigate?

A
  • Early warning systems
  • Animal behaviour - acring unusual
  • Raisung/bulging ground levels
  • Microquake
  • Hazard resistant structures
  • Hard engineering e.g. japans walls now 5m cost 15bn so far
  • Soft engineering e.g. putting large concrete weight on top of building so it will move in opposite direction of force
  • Large rubber shock absorbers in the foundations
  • Insurance cover (only afforded by wealthy)
  • Tsunami protection - automated systems installed to give warnings (seabed pressure sensors) warning systems (klaxon) to warn population before waves reach land (Pacific tsunami warning +mitigation system co-ordinate by unnesco in hawaii)
  • Prevention walls up to 12m height e.g. japan 15m costing 9.1bn

E.g. eq early warning systems in japan aims to slow down trains immediatley controlling lifts enabling people to protect quickly

62
Q

How do communities prevent?

A
  • Cannot be prevented
  • Techniques such as lubricating active fault lines with oil and water when stuck
    E.g. attempted at the St Andreas Fault but had little success
    Nucleaur explosions at depth
63
Q

How do communities adapt?

A
  • Long term changes in peoples behaviour depends on economic development, education and national and regional priorities e.g. japan and usa can afford to adapt
  • Land use zoning e.g. life-safe buildings decrease vulnerability, identifying areas most at risk from a seismic event and regulating land use planning for those areas limiting how land can be used
  • Putting key buildings in low risk areas whilst open space in high risk areas
  • Including open spaces in plans to allow for safe areas away from fires and aferstock damage to buildings
  • Emergency services adaptt their organisation and planning to deal w events
  • A seismic building can be designed to be eq resistant - cross bracing tech using straw roofs in nepal
  • Retrofitting structures such as motorways E.g. highways in CA
  • Smart meters tokoyo the gas company recieve immediate seismic readings which allow employees to shut off major gas pipes which reduces the risk of fires
64
Q

Retro fitting

A
  • Large blocks on top to move in opposite direction to eq force
  • Rubber shock absorbers
  • Cross-bracing buildings to hold together when they shake
  • Older buildings retrofirred eq proof

Geography A-level (41 decks)

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