Tectonic hazards

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Distribution of earthquakes and volcanoes

Why is there a pattern in Earthquakes?

Earthquakes are a sudden and violent shaking of the ground

They are most commonly caused by sudden movement of rocks in the earths crust

They occur mainly at tectonic plate margins, here the plates are moving which builds up pressure that is released

COMPARING THE DISTRIBUTION OF VOLCANOES

Along the western coast of North and South Amercia there are lots of earthquakes and it is also where there is a plate margin

The occurence of Earthquakes along the Pacific Ocean follows the plate margins

Some Earthquakes do not occur at plate margins- this may be caused by human activity such as underground mining or oil extraction

TECTONIC PLATES

The earth's crust is split into a number of plates about 100km thick

There are two types of crusts- dense, thin oceanic crusts and less dense, thick continental crusts

Plates move in relation to each other due to convection currents from deep within the Earth

A denser oceanic plate may subduct (sink) beneath a less dense continental plate

Gravity pulls the oceanic plate into the mantle, dragging the plate away from the constructive margin

Tectonic activity at plate margins causes earthquakes and volcanoes

WHERE DO VOLCANOES HAPPEN?

Volcanoes form over a long period of time

Volcanoes occur along long belths that follow the plate margins- Around the edge of the Pacific Ocean- The Pacific ring of fire

There is also a belt of volcanoes through the middle of the Atlantic Ocean- The Mid- Atlantic Ridge

WHY IS THERE A PATTERN OF VOLCANOES?

Volcanoes are fed by hot molten roch deep within the Earth

The magma rises to the surface at constructive and destructive plate margins

Volcanoes also form at hot spots, where the crust is thin and magma can break through the surface

Hawaiin Islands in the Pacific Ocean are an example of a hot spot

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Physical Processes at Plate Margins

CONSTRUCTIVE MARGIN

At a constructive plate margin the two plates move apart

When the plate move apart magma forces its way to the surface

As it breaks the crust it causes mild earthquakes

The magma is very hot and fluid allowing the lava to flow a long way before cooling

Constructive plates often result in broad flat sheild volcanoes- e.g. Mid-Atlantic Ridge

DESTRUCTIVE MARGIN

At a destructive plate margin the two plates move towards each other

Continental plates

Where two continental plates meet there is no sunduction so no magma to form volcanoes

The crust crumbles and lifts to form mountains- e.g. Himilayas

Powerful earthquakes can be triggered

Oceanic plate and a continental plate

An example of a destructive margin is the West Coast of South America

Here the dense oceanic plate is subducted beneath the less dense continental plate

Friction causes strong earthquakes

The sinking oceaninc plate creates sticky, gas-rich magma

This results in steep-sided composite volcanoes which erupt violently

CONSERVATIVE MARGIN (transform margin)

At a conservative plate margin the two plates move past each other at different rates

Friction between the two plates build stresses and trgger earthquakes when they slip

There are no volcanoes because there is no magma

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The effects of earthquakes (case study- Chile and Nepal Earthquakes)

Primary effects (caused by the ground shaking) destroy buildings and infrastructure, and kill and injure

Secondary effects (resulting from the shaking) include fires and landslides

Responses include emergency care, support and long-term reconstruction

Wealth (GPD- Gross domestic product) and quality of life (HDI- human development index) indicators

GPD 38th out of 193

HDI 41st out of 187 countries

Cause of Earthquake

Nazca plate subducted beneath the South American Plate

Just off the coast Central Chile

Size

Magnitude: 8.8

Shallow focus (35km)

Primary effects

500 killed

12 000 injured

800 000 people affected

Significant destruction of buildings and infrastucture

Power, water and communications cut

$30 billion (US) damages

Secondary effects

Communities cut off by landslides

Coastal towns devastated by tsunami

Chemical plant fire near Santiago forced evacuations

Wealth (GPD- Gross domestic product) and quality of life (HDI- human development index) indicators

GPD 109th out of 193 countries

HDI 145th out of 187 countries

Cause of Earthquake

Indo-Australian Plate colliding with the Eurasian plate

Size

Magnitude: 7.9

Very shallow focus (15km)

Primary effects

9000 killed

20 000 injured

8 000 000 people affected

Widespread destruction of buildings and infrastructure

Power, water, sanitation and communication cut

$5 billion (US) damage

Secondary effects

Communities cut off by landslides and avalanches

Avalanches on Mount Everest killed at least 19 people

Flooding caused by (landslide) blocked rivers

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Responses to Earthquakes

Immediate response: search and rescue and keeping survivors alive by providing medical care, food, water and shelter

Long-term response: re-building and reconstruction, with the aim of returning people's lives back to normal and reducing risk

COMPARING RESULTS

chile

Chile Earthquake's are quite common

Local ommunities were prepared and knew how to respond quickly and effectively

Chile also had the money to support people and to rebuit

Nepal

Nepal Earthquake's are not uncommon

Scientists identified a pattern of large earthquakes in this region around every 80 years

Depsite the warnings and new building regulations, little had been done to prepare the city and people for when an earthquake struck

Immediate responses

Emergency services acted very quickly. International help supplied field hospital, satellite phones and floating bridges

Temporary repairs were made to the important Route 5 north-south highway within 24 hours, enabling aid to be transported from Santiago to affected areas

Power and water restored to 90% of homes within 10 days

A national appeal raised US$60 million- eniugh to build 30 000 small emergency shelters

Long-term responses

A month after the Earthquake the Chile government launched a housing reconstruction plan to help nearly 200 000 households affected by the earthquake

Chile's strong economy, based on copper exports, could be rebuilt without the need for much foreign aid

The president announced it could take 4 years for Chile to recover fully from the damage to buildings and ports

Immediate responses

search and rescue teams, water and medical support arrived quickly from countries such as the UK, India and China

Helicopters resued many people caught in avalanches on Mount Everest and delivered supplies to villages cut off by landlides

Half a million tents needed to provide shelter to the homeless

Financial aid pledged to support overcrowded main hospitals

300 000 people migrated from Kathmandu to seek shelter and support with family and friends

Social media widely used in search and rescue operations and satellites mapped damaged areas

Long-term responses

Roads repaired and landlides cleared. Lakes, formed by landslides damming river valleys, need to be emptied to avoid flooding

Thousands of homeless people to be re-housed, and damaged homes repaired. Over 7000 schools to be re-built or repaired

Stricter cotrols on building codes

In June 2015 Nepal hosted an international conference to discuss reconstruction and seek technical and financial support from other countries

Tourism, a major source of income, to be boosted- by July 2015 some heritage sites re-opened and tourists were starting to return

Repairs to Everest base camp and trekking routes- by August 2015 new routes had been established and the mountain re-opened to climbers

In late 2015 a blockade at the Indian border badly affected the supplies of fuels, medicines and contrcution materials

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Living With The Risk From Tectonic Hazards

The majority of tectonic hazards occur at plate margins some of which run through densely populated regions such as Japan, parts of China and southern Europe

WHY PEOPLE LIVE AT RISK FROM TECTONIC HAZARDS

Poor people have no choice- money, food and family are seen as more important

Earthquakes and volcanic eruptions are rare, so not seen as a great threat

Earthquake-resistant building designs reduce risk

Effective monitoring of volcanoes and tsunami waves allow evacuation warnings to be given

Plate margins often concide with favourable areas for sttlement and trade, e.g. flat, coastal areas

some people have no experience or knowledge of the risks

Volcanoes can bring benefits auch as fertile soils, rich mineral desposits and hot water

Earthquakes fault lines can allow water to reach surface area- important in arid regions

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Reducing The Risk From Tectonic Hazards

MONITORING

Volcanoes

All active volcanoes are modified using hi-tech scientific equipment including

Remote sensing- satelites detect heat increases

Seismicity- seismographs record microquakes

Groud deformation- laser beams measure changes in the shape of the ground

Earthquakes

​​​​​​​Earthquakes normally occur without warning. Lots of different events can happen before an earthquake strikes, but they are never certain warnings. The events that could happen are:

microquakes before the main tremor

Buldging of the ground

raised groundwater levels

PROTECTION

Volcanoes

Not much can be done to protect property

Earth embankments and explosives have successfully diverted lava flows

Earthquakes

Earthquake drills help keep poeple alert and prepared

Earthquake-resistant construction is the best way to reduce the risk

PREDICTION

Volcanoes

Monitoring now allows for accurate prediction and effective evacuations

Earthquakes

Accurate predictions are impossible due to a lack of clear warning signs

Historical records can help to determine probability and so help in planning for them

PLANNING

Volcanoes

Risks assesment and hazard mapping to identify areas to practise evacuation or restrict building

Earthquakes

Risk assesment and hazard mapping to identify areas to protect buildings and infrastructure