Earthquake Theory and Fieldwork

1) Earthquake theory

(i) What is an earthquake?

    

An earthquake is a sudden movement of the earth’s crust caused by the release of stress accumulated along tectonic plate boundaries or fault lines.

(ii) Why do earthquakes form?

The Earth’s surface is divided into pieces which all interlock each other like a jigsaw. 

These plates aren’t stationary. Below them there is hot liquid magma which makes plates move. When the plates move because of the hot magma underneath and make contact with another plate, energy is produced. The energy produced can be felt on the Earth’s surface through seismic waves. This is what we call an earthquake.

(iii) How do earthquakes form?

 The plates can interact with each other in four ways:

Boundary 

Plates Involved 

What Happens

Result 

Example

Destructive

Oceanic and Continental 

The denser oceanic plate subducts the continental plate causing hot molten rock to form and rise. This creates a volcano.

Volcano, Earthquakes and fold mountains

Nazca and South American Plates

Constructive

Oceanic and Oceanic 

Two plates move away from each other forcing hot magma to rise from underneath. 

Volcano and Earthquakes

North American and Eurasion Plates – Iceland

Collision 

Continental and Continental 

This is where two continental plates collide together and neither can sink hence forcing material upwards.

Earthquake and fold mountains 

Indian and Eurasion plates – Himalayas

Conservative 

Any 

Two plates slide past each other usually getting stuck. This builds pressure and when they finally release the pressure there is sudden movement.

Earthquake 

North American and Pacific Plates – San Andres Fault

(iv) Where are earthquakes usually found in the world?

The take place all over the world. They don’t just occur on plate boundaries, they also occur on minor faults. 80% of all tectonic activity take place on the boundary of the pacific plate. This includes; the Philippines islands, New Zealand, and Japan.

2. Earthquake fieldwork

(i) How can we measure the magnitude of an earthquake?

There are two ways of measuring the magnitude of an earthquake (i) the Mercalli scale and (ii) the Richter scale.

Mercalli scale

The Mercalli intensity scale is a numerical and subjective way of measuring the magnitude of earthquakes. It is a scale between 1-12; 1 being nothing being felt and 12 total destruction. The scale isn’t used very much today because it isn’t accurate because different will have different experiences which will reflect the different scores given to different earthquakes.

Richter scale 

The Richter scale is a numerical and objective way of measuring the magnitude of earthquakes. It is a scale between 1-10; it has a logarithm scale i.e. an earthquake measure 4 on the Richter scale is 10 times as big as one measuring 3.  This is the most popular way of predicting earthquakes today. It works by using seismometers to measure the seismic energy released.

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Test on global hazards

Use this test to make sure you know about global hazards. In addition, please look at the different ways of presenting hazard profiles.

  1. Define a natural hazard. (2)
  2. Identify and define with examples the four types of hazards. (8)
  3. State whether each of the events below is a hazard, if so what type and why is it/is it not   a hazard;
  • A drought in the South East of England. (3)
  • A flood in a rural area which floods the roads, but doesn’t affect any houses.(3)
  • An avalanche, high on mountain slopes, remote from any settlement. (3)
  • A tsunami 50 cm high off the coast of Japan. (3)
  • A volcano erupting on a remote unpopulated island. (3)
  1. Define a windstorm. (2)
  2. Name two case studies of each type of hazard;
  • Flood (2)
  • Earthquake (2)
  • Windstorm (2)
  1. How would Swiss Re define a disaster? (3)
  2.  What is a vulnerable population? (2)
  3. What is a quasi-natural hazard? Give an example with it. (3)
  4. What are the six indicators used to assess the impact of a hazard? (6)
  5. What is the risk equation? (3)

_______________________________________________________________________________________

Answers

  1. A natural hazard is a natural event or process, which involves people. (2)

Candidates may also give example e.g. loss of life, injury, disruption, economic damage or environmental degradation.

  1. Hydro-meteorological (1) — these are hazards caused by weather conditions & water (1)

Geo-physical (1) — these are hazards caused by processes of the earth. (1)

Geomorphic (1) — these are hazards caused by external earth processes involving mass movement (1)

Tectonic (1) — these are hazards caused by tectonic activity; earthquakes, volcanoes and tsunamis. (1) (to get 1 mark for tectonic hazards candidate is not required to give examples)

  1. a) It is a hydro-meteorlogical hazard (2) Chose one from the following 3 reasons;

– Because it will affect the agricultural yield for England. (1)

– Extreme heat may affect some people’s health. (1)

– There may also be concerns with water supply. (1)

b) Hydro-Meteorlogical hazard (2)-because it affects roads which affects people because they may be blocked from going to work or school and residents experience general disruption (1)

c) It is not a hazard because being remote it affects no one. (3)

d) Tectonic hazard (2) because it affects people living on the coast of Japan e.g. injury, loss of lives, economic damage etc (1) Candidates do not need to give an example to get one mark

e) It is not a hazard because there are no people involved. (3) It is just a natural event.

A storm with high or violent winds (1) with no or a little precipitation (1)

(a) (i) Boscastle August 2004 (ii) Mississippi flood 1993 (2)

(b) (i) Kobe earthquake January 1995 (ii) California earthquake 1989 (2)

(c) (i) Lady Lake tornado 2007 (ii) Windstorm Klaus January 2009 (2)

Candidates may pick other examples e.g. Haiti earthquake Jan 2010 – year it happened is required but month isn’t.

  1. A disaster, which caused at least 20 people to die (1), or insurance damage (1) of over US $16 million. (1)
  1. A vulnerable population is one that is susceptible to human or economic loss (1) because of the geography of where they live. (1)
  1. A quasi-natural hazard is a hazard, which is caused by a bi-product of human activity (especially while using natural resources) (2) . For example, in Indonesia (2006) a mud volcano erupted killing and disrupting many lives. It is claimed that a company called Lapindo Brantas caused it. (1) Candidates may use other examples.
  1. i) Duration (1) — Period of time over which it occurs
  2. ii) Area reliability (1) – Could you predict the area that was affected e.g. you can predict where a volcano will reach but you can’t for a

iii) Magnitude (1) — How big is it compared to the average

iv) Frequency (1) – How often-on average does the even happen?

v) Speed of onset (1) – Length of time between first appearance and peak e.g. lag time in flooding

vi) Area extent (1) – How big is the region affected?

(Note: Candidate do not need to give explanation to get the mark, the indicator on its own is fine)

10. Disaster risk = (Hazard x Vulnerability) / Capacity

A mark each for each part being in the right space.

Global Distribution of Cyclones

Cyclones

Quick Summary 

What are cyclones?

Cyclones are extreme versions of depressions. The pressure is so low that dangers caused by this weather system are deadly compared to a depression. Cyclones have other names e.g. the are called ‘hurricanes’ in the West, ‘Typhoons‘  in oriental Asia and ‘Willy willy’ in Oceania.

Why do they occur?

If we are looking at hurricanes in America then they tend to start off in places like the sub-Saharan African continent. Geographers  are not sure the exact cause but small disturbances in atmosphere over land and start of a low pressure system of thunderstorms. As this weather system travels west over the warm pacific ocean it gains energy and all the thunderstorms start swirling around the eye – the area with the lowest pressure. As this system moves on land it releases its energy through precipitation and strong winds up to crazy speeds like 176mph and even higher. However, it doesn’t last too long as it looses its energy on land as there is no warm water from the ocean evaporating.

What conditions are required for them to take place?

  1. Warm tropical oceans where sea temperatures are at least 27 degrees 
  2. Oceans where the depth is at least 60m.
  3. Late summer and early autumn where sea temperatures are at their highest
  4. The area of the trade wind belt between latitudes 5 degrees and 20 degrees on either side of the equator
  5. Wind speeds need to be constant between ground level and 12km above ground level.

How are they measured?

The Saffir-Simpson scale is used to measure hurricanes. It gives each hurricane a rating between 1 and 5. It basis the rating according to the wind speed, storm surge and damage. The rating each hurricane is given is called ‘category’. Hurricane Katrina was so intense that it had a rating of category 5 on this scale. Below I have put the rating table:

Category

Sustained winds (mph)

Storm surge

Damage

1

74-96

4-5 feet

Minimal

2

96-110

6-8 feet

Moderate

3

110-130

9-12 feet

Extensive

4

131-155

13-18 feet

Extreme

5

>155

>18 feet

Catastrophic

Where do they happen – the global distribution?

So it is quite clear the global distribution is limited because of the large criteria required for hurricanes to form. Hurricanes occur in equatorial areas in the latitudes of 5 degrees to 20 degrees to either side of the equator. This includes regions such as the Gulf of Mexico, the Bay of Bengal and the Indian Ocean. Any coastal area in this latitude which is surround by warm water is at risk of experiences cyclones.

When do they occur most often?

They occur in the months of late summer and early autumn. This usually in the months of July to November in the Northern Hemisphere and December to May in the Southern Hemisphere.

Dealing with climate change: Adaptation vs. mitigation

 

There are two approaches to dealing with climatic change: MITIGATION and ADAPTATION.

MITIGATION

Mitigation refers to policies that attempt to prevent further global warming and they are strategies which try to get rid of or reduce global warming e.g. using carbon tax to reduce the amount of greenhouse gases being emitted into our atmosphere.

ADAPTATION 

Adaptation refers to policies that attempt to cope/deal with climatic change. They are not strategies which try to get rid of global warming. They are trying to cope with the impacts of climatic change e.g. introducing drought resistant crops.

So Lets look at some of the policies…

Mitigation

Adaptation

Wind Farms – By producing more energy by wind farms we can use renewable fuels less which emit greenhouse gases and try and prevent global warming.

Coastal defence – Through climate change our coasts are increasingly becoming a risk especially as sea levels rise. So coastal defence can include things like a sea wall, rip-rap etc.

Transport reformation – By changing our modes of transports or how they are run e.g. switching to biofuels is another way in which we can cut of greenhouse gas emissions. This also includes creating incentives for people to use more public transport rather than private transport.

Diversify agriculture –  This includes things like exploring different plants to grow and in different areas. Global warming means temperatures in different places are changing so by diversifying crops we are sure to have some which can grow in the new conditions that climatic change presents.

Afforestation –By planting trees/plants we are offsetting the carbon we produce hence reducing the net greenhouse gas emissions. This is known as carbon sequestration.

House Design – Global warming means our houses are continually becoming at risk of a variety of hazards and more than before. So we have to design our houses in such as a way that they can cope with lets say increased flooding risks. Double glazing is one example of how we can protect our homes from increased hazards.

Solar Panel – So as you can see many of these methods include alternate energy productions. This is because this cuts the amount of energy we need from carbon fuels which heavily emits greenhouse gases.

GM Foods –  Just like why we have to diversify our agricultural range, we have to invest in genetically modified crops and plants because this means we can still get a high yield for our exponentially growing population as well as coping with increased risks of lets say droughts.

Congestion Charge – So this is a deterrent for people to stop using there private transport too much – again a method cutting emission of greenhouse gases.

Better warning/forecasting systems – So the key element here is that climatic change means that we all are at risk from increased number of hazards hence we need to be more prepared. One way of doing this is by investing in our warning and forecasting systems. (particularly in LEDCs)

Regulate burning/chopping trees/plant – this is part of carbon sequestration and by using more regulation we can limit the number of trees/plants this happens which 

 also reduce the net carbon emissions.

Emergency plans – This is similar to better warning/forecasting systems except here leaders need to devote time and funds to preparing emergency plans and enforce regulations to ensure people are prepared for any major hazard.

Energy efficient appliances – We can not only encourage the use of energy efficient appliances, we can invest in innovation and R&D of such green appliances.

Domestic efficiency – Again by becoming more efficient we are cutting the amount of greenhouse gas emissions we send to the atmosphere. This type of efficiency including insulation homes, double glazing etc.

So which is better adaptation or mitigation? Lets look at some of the benefits of each strategy…

Pro- Adaptation

Pro- Mitigation 

It is time consuming to get all the countries to multilaterally come to a decision about how to reduce carbon emissions let alone cease them.

We should reduce emissions immediately to avoid being a position where climate change is irreversible.

The time on trying to get countries to mitigate climate change means that it might get much worse before we see green shoots.

Unless we challenge global warming then change will never arise in our energy production and other aspects of our life.

Climate change has already happened e.g. melting Arctic ice so we have to react and manage the situation now.

Policies such as carbon sinks are easily achievable e.g. the government just needs to provide a couple of grants for afforestation.

Even if emissions were to cease today then greenhouse gases already present in the atmosphere would cause changes at least for the next century. CO2 has a life for 100 years!

Mitigation methods are politically recognized in developed nation hence this means they are important and the rest of the world should follow on.

The Earths absorbs CO2 slowly so even with increased carbon sinks ( e.g. afforestation) it will take time for all the excess CO2 to be absorbed.

It is claimed that cutting greenhouse gases adversely affects economic growth. However, this is not true. In Western countries emissions are constant or falling and economic growth is pretty strong so we should seek more mitigation strategies. 

Keeping carbons emissions at where they are at or reducing them is unrealistic especially with BRIC countries such as China and India which have rapid economic growth. Hence we need to adapt as we might be too late to mitigate!

REVIEW TEST

  1. Define Mitigation strategies
  2. Define Adaptation
  3. Give the two main ways in which we can mitigate climate change
  4. What is the main way we can adapt to climate change
  5. Give one advantage of adaptation policies and one of mitigation policies

Suggested Answers 

  1. Mitigation strategies are policies used to try and reduce/ get rid of climatic change.
  2. Adaptation are policies used to try and cope/deal with climatic change.
  3. The two main ways we can mitigate to climate change is by reducing greenhouse gas emissions through energy production and by changing lifestyles e.g. switching to public transport.
  4. The main way we adapt to climatic change is by preparing all aspects of out life for increased risks
  5. One advantage of mitigation strategies is that if we act now we might be able to prevent reaching a situation where climate change is irreversible. One advantage of adaptation strategies is that instead of trying to mitigate something which has probably happened (E.g. Arctic ice melting) we can fortify ourselves for the impacts and be prepared.

Compulsory case study: Africa

Africa compulsory case study 

AIM: To develop an understanding of the complexities of economic impacts across the African continent and how it could lead to disasters for poor and vulnerable people.

Background

  • 55 countries
  • 34% of the 15-24 year old population is illiterate 
  • African economies are on the brink of collapse thanks to international debt and to make things worse they are having to cope with some of the malicious impacts of climate change.
  • The continent as a whole is warmer by half a degree than in the 1900s.
  • Most African economies are heavily dependent on agriculture which is heavily on the environment. 
  • Water is already a scarce resource in Africa, in 2007 14 countries were officially declared as water stressed. So decreased rainfall has made conditions much worse than they were before.

What has global warming brought to Africa?

  1. Droughts 
  2. Rainy seasons are unreliable and overall rainfall is decreasing
  3. Rains are more localised – the rain that ended the 2005-2006 drought were not widespread across the whole of the continent

So why are these impacts a problem?

Firstly, the competition for water will increase and this can lead to conflicts especially since major freshwater stores such as the Nile cross countries. Not just conflict but people will become reliant on poor quality water stores which can lead to water-borne disease such as cholera.

How does this affect the economy?

Well as more people become prone to water-borne diseases this puts more stress on healthcare. This puts pressure on the governments budget to provide enough welfare for all these people. Also, if more people are ill then they won’t be able to work to their fullest and this will reduce productivity.

Physical and human impacts on Africa 

Physical Impacts

Human Impacts

Fragile impacts may not survive and 20-50% of species in Africa could face extinction

Reduction in food supply (climate change affects rainfall which affects crop production)

Many low-lying coastal countries in Africa are vulnerable to rising sea levels.

Malaria will increase due to increased humidity and rainfall. This puts pressure on  the health care system.

Coral beaching

Increased cyclones

Deforestation and desertification 

So why is Africa so vulnerable?

Well climate change brings a range of problems all over the globe. However, to make the situation worse Africa has a debt crisis. The have a debt to some of the world’s richest countries, the repayments of these sometimes exceed their entire GNP. In 2007 the G8 wrote off the debt to 18 countries but there is still the vast majority of countries which still have their debt.

One method of coping with this debt is by opening doors to international trade. This means by increasing the production of cash crops (crops sold for income rather than the country’s own food supply). However, this has led to much forest clearance.

According to Oxfam this clearing of forests is likely to worsen. Not just to write off debts but because of global warming.  They argue that extreme weather such as droughts will expose soils to erosion from the wind. The puts stress on land and this kind of stress can lead to desertification e.g. animals have to graze on a smaller piece of land leading to that area of land being over -grazed.

Put all these factors together and we learn that it is Africa’s food security which is under threat and that is a major concern for authorities there. 

Test your definitions…

define the following:

  1. Debt crisis
  2. Food security
  3. Cash crop
  4. Desertification
  5. Coral bleaching 

Answers

  1. This is where many African countries have become so heavily indebted that repayments sometimes exceed their entire GNP.
  2. This is the extent to which a country can rely upon food supplies e.g. upon weather or if unable to grow all its food then the extent that it can rely on imports.
  3. These are crops which are grown for income not domestic food supply.
  4. This is the process when fertile land turns into futile desert
  5. This is the whitening of coral due to stress induced death. There are many causes of this e.g. changes in water temperature

Rising Sea Levels & Bangladesh

RISE IN SEA LEVELS 

AIM:  To investigate how sea level rise may have a disproportionately bigger effect on some countries like Bangladesh.

Modelling the rise in sea levels 

There are various predictions for sea level rise for the future. The mode extreme one predicts a rise in sea level by 15m by 2100. This puts many places including London in peril. But how is this 15m going to be achieved?

  1. Melting of West Arctic ice sheet = 5m rise
  2. Complete melting of Greenland ice sheet  =  7m
  3. Collapse and melting of world’s glacier system = 2m
  4. Continual thermal expansion of oceans = 1m

So all four event equal a 15m rise in sea level.However, most models produce a rise of 1m. Nevertheless, it is important that we act fast because even if the probability is small the risk of sea levels rising is so great. There are 3 key fundamental reasons why it is so difficult to model sea level rise hence the vast set of results.

The first reason is that it is difficult to predict the quantity of future greenhouse gas emissions especially as that isn’t just based on us it is based on nature e.g. volcanic eruptions. The second is based on the concept of ceteris paribus which is the concept that all other things remain the same i.e. ‘business as usual’. Finally, it is difficult to predict the actual impacts of a rise in sea levels.

There are two types of changes involved when we are discussing sea level changes: EUSTATIC & ISOSTATIC. Eustatic changes involve changes in sea level due to the amount of water in oceans and isostatic changes involves movements of land in response to changes in sea levels.

So where are the most vulnerable places?

There are three types of area which are most vulnerable to changes in sea level rise.

  1. Land on river deltas e.g. Bangladesh
  2. Areas that lie close to sea level e.g. Netherlands, Eastern Britain
  3. Small low lying islands in the Pacific oceans e.g. Tebua

CASE STUDY: Bangladesh

Background

  • 70% of the country lies on flood plains, less than 6m above sea level
  • Faced by multiple varieties of hazards
  • Has a growing population 
  • It is an LEDC
  • It is the world’s most densely populated area
  • It is a mega-delta filtering 57 river including Ganges, Meghna and Brahmaputra. In addition it filters snowmelt from Himalayas, monsoon rains and high tides.

What happens if sea levels rise

  • It could loose up to 20% of its land
  • Displace 40 million people
  • Threaten food supply, drinking water and agricultural land
  • Increasing water temperatures can lead to increased number of water borne diseases such as Cholera
  • The biggest risk is being lost like Tebue which means that tens of millions of environmental refugees will have to seek livelihood in other countries.
  • Damage to coral reefs 
  • More risk of cyclones
  • Malnutrition
  • Child development and education will be negatively affected 
  • Loss of properties 

So how are Bangladesh acting right now?

  1. Technological solutions – In the 1990s, Dhaka the capital city – cleared 102km of drains and constructed 144km of drains. They also opened 633 channels to improve drainage
  2. Early warning/ flood predictions – This includes preparing people especially the vulnerable of floods e.g. allowing people to be evacuated to safer grounds quickly and effectively
  3. Behavioural – Changing land uses and food choices e.g. increase fishing more than arable farming. Bans have also been put in place to slow down urbanisation
  4. Managerial – e.g. improve sanitation and water management to prevent water-borne diseases.

The solutions presented in this post are one thing but Bangladesh only has limited funds and there is a limit to how much they can borrow or rely on international aid. They also have a large vulnerable population and protecting every single citizen isn’t easy. Bangladesh has to think ahead as climate change provide more extreme situations of flooding etc then they have prepared for.

REVIEW QUESTIONS

  1. Define Eustatic changes.
  2. Define Isostatic changes.
  3. What are the three reasons that make modelling difficult?
  4. What is extreme quantity of sea level rise predicted?
  5. What are three most vulnerable places in regards to rising sea levels
  6. State two facts about Bangladesh
  7. Name three impacts of rising sea levels in Bangladesh
  8. Name two solutions Bangladesh plans
  9. What are the two fundamental  problems with these solutions?
  10. What are the three main rivers of the 57 that make Bangladesh a mega-delta?

Suggested Answers

  1. Eustatic changes are changes caused by changes in the amount of water in oceans
  2. Isostatic changes are the responses of land to changes in sea levels
  3. It is based on the concept of ceteris paribus, it is hard to predict future greenhouse gas emissions and we do not accurately know the impacts of rising sea levels
  4. 15m 
  5. Large river delta e.g. Bangladesh, the Nile, places with low lying land such as Netherlands or Eastern Britain, small low lying islands in the Pacific or Indian ocean
  6. Almost 70% is a flood plain which lies on less than 6m above sea level and  has the world’s most densely populated area
  7. 40 million people will have to be displaced, risk of water borne diseases such as Cholera and risk to properties and livelihoods 
  8. Technological 633 channels to improve drainage and managerial improve sanitation and waste management
  9. Bangladesh does not have the funds and has a large vulnerable population
  10. Ganges, Meghna and Brahmaputra