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Geography A-level > Seismic hazards > Flashcards

Seismic hazards Flashcards

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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

22
Q

Seismograph

A

Produces the reading of the EQ

23
Q

The richter scale

A

Measures the magnitude of EQS

24
Q

The Mercalli

A

Measures the earthquakes intensity (impact/effect)

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
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

Geography A-level (21 decks)

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