Causes of Earthquakes and Volcanoes

There are clear patterns of TECTONIC activity around the earth. Both Volcanoes and Earthquakes tend to occur in certain places – and not in

other places. Where you get Volcanic activity, you often find Earthquake activity – and both tend to take place at the edge of the world’s Tectonic

Plates. Places far from tectonic margins (where 2 plates meet) get few earthquakes and/or volcanoes.

There are 4 main parts to the earth’s structure : an

Inner Core of iron, surrounded by an Outer Core.

The majority of the earth is the MANTLE. Inside

this Convection Currents are moving. In hot areas

the convection currents rise towards the Crust.

When they get there they spread apart – dragging

the crust in separate directions to give a

‘Constructive Margin’. As the convection currents

continue they cool and begin to sink back towards

the core. As they do they drag some of the crust

down where it collides with other crust to form a

‘Destructive Margin’.

Volcanoes and Earthquakes are a feature of the

edges of the plates because this is where plates

are either pulling apart (constructive margin) or

colliding (destructive margin).

CONSTRUCTIVE MARGIN : where plates are pulling apart. Frequently eruptingvolcanoes, frequent but gentle earthquakes as the plates are moving apart withvery little resistance.

DESTRUCTIVE MARGIN : Ocean plate collides with a Continental plate.(oceanic plate is denser and heavier so is driven beneath the oncoming plate).Occasional powerful Volcanoes and regular powerful earthquakes if plates havegot ‘stuck’. Plus deep ocean trench on sinking plate

COLLISION MARGIN : where 2 plates collide and are both continental plates.Neither ‘sinks’ so produce a collision zone of rising mountain ranges. Novolcanoes but infrequent powerful earthquakes as mountains re-adjust

CONSERVATIVE MARGIN : where 2 plates slide past each other in differentdirections or at different speeds. Friction causes them to ‘stick’ so pressure buildsup – and is released as frequent, possibly severe earthquakes

Volcanoes erupt at Destructive and Constructive margins – though they are often more explosive and powerful at Destructive

margins due to them starting deep within the crust. At Constructive margins they are more surface features as plates move apart.

In both cases the built-up pressure has a number of consequences.

Gas and steam emissions increase

Underground water becomes more acidic and hotter

Surface snow and ice may melt with rising ground temperatures

Trees and vegetation may die as roots are heated

Surface earth tremors are noticed as magma is forced up the vent

Small burrowing animals evacuate the area as soil temperatures rise

Small animals may die from rising carbon dioxide emissions close to the ground

Explosion of built-up steam and gas which disintegrates solidified vent from previous eruption

Ash cloud of pulverised rock, steam, and gas rises into the air. In sufficient quantities this can cover the surrounding area in a layer of hot ash which burns crops, vegetation and possibly people. Causes breathing problems in very young & old

Collapsing ash cloud can lead to a Pyroclastic flow of superhot steam, ash and gas rolling forward at up to 200mph which incinerates all in its path as it rolls downhilll.

Volcanic bombs of liquid lava are shot out by pressure of gases from erupting vent.

Streams of lava may pour out of main vent and secondary vents (called Magma when inside the crust & volcano)

Ash injected into upper atmosphere can be blown far and wide, disrupting air travel and reducing light and global temperatures for weeks and months.

Warning Signs of an Eruption

Sequence of Eruption Events

Volcanoes

Volcano Impacts Benefits Problems

Economic • Volcano Tourism

• Skiing industry

• Mineral mining (sulphur)

• Big yields of farm crops

• scientific researchers come to monitor the volcano

• Eruptions can cause tourists to cancel visits

• Lava flows can damage ski lifts

• Hot ash can destroy fields of crops

Social • communities have year-round jobs in tourism with summer volcano hikers and winter skiers.

• medical use of hot spa water and mud can improve health.

• Lava flows can stop movement if roads are blocked

• Air flights are delayed & diverted due to ash clouds

Environmental • Geothermal energy is a renewable energy source using steam from hot rocks near the surface.

• Farmland is supplied with mineral nutrients as ash is washed into the soil

• air contaminated with ash and acidic fumes causes breathing difficulties.

•water supplies contaminated with acidic lava and ash

• Global cooling can follow as ash spreads through the upper atmosphere.

Earthquakes

Seismic waves of energy move in all directions from the FAULT where theearthquake happens – the FOCUS. This may be near the surface or deep in the crustdepending on the type of plate margin. The place directly above the Focus on thesurface – which may receive the most shaking – is the EPICENTRE

Earthquakes are measured usingSEISMOGRAPHS which detect movements in theearth. The RICHTER scale is a measure of thestrength of earth movement, while the MODIFIEDMERCALLI scale measures the impact on people& surface features such as building & trees

Earthquake Event Primary Effect Secondary Effect

Ground shakes Homes collapse

Factories collapse

Shops collapse

Homeless refugees (social)

More unemployed (economic)

Looting from shops (political)

Ground shakes Gas pipes fracture

Water pipes broken

Leaking gas starts fires (social)

Fires can’t be put out (social)

Lack of fresh water(social)

Disease such as cholera from drinking contaminated water (social)

Ground shakes Liquefaction of tall office buildings

Lack of money made by business –less tax revenue for the city (economic)

Landslides Roads blocked Isolated areas are cut off and lack essential medical supplies (social)

Ground shakes Tunnels & bridges collapse Factories in other areas run out of key supplies (economic)

Tsunami Flooding of coastal areas by tidal wave

Riots in refugee camps with not enough aid (political)

The Haiti earthquake of January 13th 2010 was one of the largest casualty events of the last decade – but wasn’t the largest of

earthquakes. How far did Haiti’s poverty contribute to the death rate of almost 250,000 people?

Haiti is one of the poorest 20% of countries in the world. Whilst it hasn’t

suffered from any serious earthquakes for almost 200 years it is frequently

flooded with it lying in the main Atlantic hurricane path.

The earthquake of January 2010 registered 7.0 on the Richter scale – which

is a large event, though larger ones do take place each year around the

world. It occurred on a fault line running almost directly under the capital Port-

au-Prince so the epicentre was focused on the most densely populated parts

of the country. It was caused by the fracture of a Conservative margin as the

Caribbean plate slide one way, and the North American plate went the other

way.

LEDC Earthquake Haiti 2010

•No significant earthquake for 200 years – so the country was not prepared, nor were buildings earthquake-ready.

•Fault-line ran right under the capital city – Port au Prince, so it got maximum ‘shake’.

•Buildings were poorly constructed – with many slum dwellings, so they collapsed easily. Also the density of buildings in the city meant there was

no escape from falling debris.

•Corruption of officials and building constructors meant government buildings were made of weaker materials than expected. The presidential

palace and UN offices collapsed.

•Disruption of airport, port and roads meant there was a delay of over a week in organising rescue of trapped people. Planes didn’t land for 48

hours – took 5 days to get the port working

•Lack of army or emergency teams to put an after-earthquake plan in place until US army came

•Hospitals destroyed – so very little blood supplies for transfusions; medicines for those with on-going health conditions (heart pills) or to stop

injuries becoming infected.

•Water supplies disrupted – people forced to drink dirty water contaminated by broken sewage systems. Disease broke out rapidly in the tropical

heat with so many dead bodies unburied.

•Looters shot & lynched by survivors who felt they were stealing food from their neighbourhood

•Main jail broken open and 4000 criminals escaped to form violent gangs taking food from others with machetes, knives and guns.

•A month after the earthquake, 14 people are killed searching for tins of food in a damaged supermarket which collapsed on them.

• 9 months after, following heavy tropical storms, cholera breaks out in the refugee camps still with 1 million people in – 500 die due to poor

sanitation conditions, overflowing sewage ditches, poor hygiene and lack of clean water. 1 million refugees in tent cities have to be evacuated in

November 2010 as Hurricane Tomas tracks across Haiti bringing dangerously high winds and rainfall.

Why was the Haiti

earthquake so

devastating?

Location : the epicentre of the

earthquake was in the most

densely populated part of Haiti

so the capital city got most

‘shake’ from a ‘surface’ quake

Poor Building Construction :

many people live in self-built

homes, and low quality building

materials & lack of Building

Codes meant many buildings

collapsed at the first shaking.

Transport Disruption

- the main runway in

Haiti was put out of

action by the

earthquake for days

so little medical aid

could be flown in.

Public Disorder : lack of police meant

gangs took over the streets leading to

violence, looting and lynching of looters.

Refugee Camps : the slow arrival of food,

clean water and medical care meant some

survivors died from injuries. Months later the

poverty of Haiti meant many were still living in

camps with no proper toilets or clean water

leading to cholera deaths & hurricane danger.

Before

During

Months Later

Days Later

Hours Later

Where / When / Why : On January 17th 1995 a 7.2 magnitude earthquake hit the port city of Kobe on the south

coast of Japan – the largest earthquake in Japan for 47 years. Caused by the Philippine plate sliding under the

Eurasian plate it lasted 20 seconds where there was solid rock – but over 2 minutes on less solid reclaimed land

in Tokyo Bay.

Primary Effects :

• Over 6000 died. Many more injured

• 200,000 buildings destroyed including offices, factories, houses, and port facilities.

• Elevated roads collapsed and 130km of railway track put out of use.

• Gas and water pipes fractured and 300 fires broke out

Secondary Effects :

• It was the middle of winter so survivors had to be given refuge fast to avoid hypothermia

• There were over 700 after-shocks so many people left Kobe – not all returned.

• Some companies were forced to close as their factories were so badly damaged eg Mitsubishi

• The port was put out of action for 3 months – reducing the imports & export trade for the area

MEDC Earthquake: Kobe, Japan 1995

One of the positive aspects of earthquakes is if lessons are learnt which can reduce the impact of future earthquakes. As a result of the Kobe

earthquake in 1995 – these earthquake precautions were put in place in the following months and years. However they need either good

planning, and/or cost money – so are often out of the reach of LEDCs

Building zones : restricting the type of

buildings allowed on reclaimed land. New

housing has to be built on solid ground &

use fire-resistant materials.

Retro-engineering : putting a stronger support

framework around existing buildings – such as the

red girders around Kobe port tower

Rubber Shock Absorbers bridge

supports now have to have rubber pads to

absorb the shock waves are prevent bridge

& road collapse

Building Spacing Office blocks

have to be a certain distance apart

to stop a ‘domino effect’ if one

collapses

MEDC : JapanEarthquake of January 1995Kobe – port city6,436 deaths

LEDC : HaitiEarthquake of January 2010Port-au-Prince – capital city250,000 deaths

Before the Earthquake

Building codes mean buildings have to

be designed to withstand a certain

amount of earth tremor.

Strong building materials used – steel,

reinforced concrete, strengthened glass

etc.

Fire crews trained so they know what

to do in an earthquake. Residents

trained to hide under door frames.

No building codes. Many poorer people build

slum housing out of materials they can find.

Cheap building materials used to cut costs.

Weak cement and poor concrete fracture

easily.

No training of police, army or emergency

services of what to do in an earthquake

emergency

During the Earthquake

Few buildings collapse.

Most tunnels, bridges and elevated

roads absorb the earth movements

Thousands of buildings collapse

Many buildings are very close together so

people are crushed in narrow alleyways

between buildings and on streets by falling

debris

After the Earthquake

Thermal image equipment used to

locate trapped bodies. Powerful

equipment lifts debris off survivors.

Effective medical services treat the

injured rapidly

Gangs of looters cause violence on the

streets

Many survivors die trapped in ruins.

Lack of trained medical aid means people die

of injuries and disease

Follow up. Government emergency funds help

rebuild roads, power supplies and

buildings

Home insurance means people can pay

to rebuild their homes

Government has very little in funds.

Up to a million people are still living in tents

in refugee camps a year after the earthquake,

many dying from cholera in the hurricane

season 10 months after.

While earthquakes cannot be prevented from happening, it is possible to make preparation in advance. Residents can be given

advice on what to do during an earthquake, and the authorities can make sure injuries and damage are dealt with rapidly after an

earthquake.

Before an

earthquake

During an

earthquake

After an

earthquake

Building design : In Wellington, New Zealand, houses are built of wood so they ‘flex’ in an

earthquake and have light wooden roofs.

Retro-engineering / Retro-fitting : in China elevated roads and railways have been given extra

girders to prevent collapse.

Warning Advice : in New Zealand there are warning leaflets and adverts on TV to tell people what

to do in an earthquake : DROP, COVER & HOLD, and not run outside

Training Days : in Tokyo on the anniversary of the Great Earthquake of 1923 schools, workplaces

and communities spend the day practicing what they would do in an earthquake. The same was done

in California in October 2010 with 7m people.

Emergency Kits : in Wellington, New Zealand, the emergency services have kits with the main pieces

of after-care equipment they need to rescue people and stop earthquake injuries becoming fatal. They

practice using these in regular mock emergency training where police, fire and ambulance all co-

operate together.

After the Boxing Day Tsunami disaster of December 2004 when over a quarter of a million people died a lot of effort has gone into

trying to give earthquake warnings so people can prepare. This is especially important for people in coastal areas where an early

warning of an approaching tsunami following an undersea earthquake could save many lives.

To give Tsunami Warnings a series of seismographs have been placed on the Indian

Ocean sea bed. When they sense an earthquake a signal is sent to a transmitter

floating on the sea surface. This sends a signal to a satellite – which then informs

Warning Centres on land. They can then send out a warning to coastal residents telling

them to evacuate the coast and head inland and for higher land.

At the moment there is no

accurate way of predicting

when an earthquake might

strike. Work is being done to

see if there are patterns to

earth tremors which could

indicate a ‘big one’ is likley in

the near future.

In China people are told to watch for strange behaviour in animals – cats, dogs and cattle

seem to be able to sense a build up of stress in rocks and show strange behaviour.

Before the 2004 Tsunami working elephants in Thailand broke from their chains and ran

into the forests away from their keepers hours before the earthquake which caused the

tsunami.

Elephants: a low-

tech early

warning system

for earthquakes?

Earthquake Prediction

If you asked someone why they lived in an earthquake zone, they might say they were born and brought up there. It takes a lot

to give up your job, college, work, friends and community to move somewhere else because you think there ‘might’ be an

earthquake ‘one day’. But these are some answer people might give :Earthquake Date

Number Killed

February 2010 1

August 2009 1

June 2008 12

July 2007 11

March 2007 1

March 2005 1

October 2004 40

January 1995 6,434

June 1948 3,769

December 1946 1,362

“The risk of death or injury is really low –

I stand more chance of dying in a traffic

accident”

The figures show the number of deaths in

Japan for Earthquake deaths.

“The buildings in this city are built to be really safe. They will keep me

protected”

In San Francisco in California certain shaped buildings are not allowed because they

are more likely to collapse in an earthquake (4 diagrams), however buildings like the

TransAmerica Building in the centre of the city was designed in the 1970s to

withstand large earthquakes with :

• a pendulum in the top which sways into the hollow shoulders if the building

starts to ‘tilt’ to pull it back upright

• a pyramid shape – which is the most stable shape

• windows that fall in – not out onto the street

• deep foundations on rubber & spring shock absorbers

“I’ve been told what to do – like hide

under a table or a door frame. I’m sure I

would be OK”

Many cities have earthquake practice days,

warning leaflets and websites that tell you

how to be safe

Living in an Earthquake Zone