Earthquakes

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Earthquake focus

Shallow focus: 0-70km deep

Intermediate focus: 70-300km deep

Deep focus: 300-700km deep

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Types of wave

Primary waves: Faster wave, longitudinal (vibrate parallel to the direction of travel). Can pass through both solids and liquids but changes in density will cause them to refract

Secondary waves: Slower wave, transverse (vibrates at right angles to the direction of wave travel). Cannot pass through liquids but cause more damge than P-waves

  • Surface waves- both travel slower but cause more damage

Love waves: Cause the ground to move sideways 

Raleigh waves: Cause the ground to move up and down

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Ways of predicting earthquakes

Seismic records: Studing patterns of earthquakes and using these to predict the next event. Seismic shock waves are recorded on a seismometer which records ground motion. Research into fault system stress suggests that earthquakes are not random 

Radon gas emissions: Radon gas is an inert gas that is released from rocks such as granite at a faster rate when they are fractured by deformation

Groundwater: Deformation of the ground can cause water levels to rise (compression) or fall (tension)

Remote sensing: Evidence that electromagnetic disturbance in the atmosphere directly above areas about to have an earthquake can be detected

Low frequency electromagnetic activity: There are strong correlations between certain types of low frequency electromagnetic activity and the seismically active zones of the earth. A sudden change in the ionospheric electron density and temperature was recorded a week before a 7.1 magnituse earthquake that occured in Japan in 2004

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Ways of measuring earthquakes

Richter scale: Measures the magnitude of an earthquake which is the amount of energy released by the event. It's a logarithmic scale, with each unit representing a 10-fold increase in energy released

Mercalli scale: A 12-point seismic scale that measures the intensity of an earthquake according to the effects it results in. For example if the earthquake measures a 5 then the scale reads :Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.

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Protection from earthquakes

  • Making buildings more earthquake resistant: Many areas that are prone to earthquakes have strict building regulations to reduce damage. Such building structures could include multi-storey buildings having a soft storey at the base, such a car park, or the builting having a deep foundation built into the ground to prevent shaking. Examples of earthquake resistance buildings are in California and Japan, where high rise buildings are slightly elastic so the energy from the shock is disipated harmlessly. The Taipei 101 in Taiwan has a "mass damper"- a swinging 666-tonne pendulum hanging inside it from the 92nd floor that absorbs vibrations. 
  • Raising public awareness about disaster prevention via an education programme 
  • Improving earthquake prediction
  • Well planned out evacuation plans
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Effects of earthquakes

Tsunamis: Enormous sea waves most often generated by earthquakes and submarine landslides

Liquefaction: Where violent disruption of the ground causes it to become liquid-like when strongly shaken.Earthquake shaking often triggers an increase in water pressure to the point where the soil particles can readily move with respect to eachother. This can cause buildings to sink or slide.

Landslides and avalanches: Where slope failure occurs as a result of ground shaking 

Human impact: Primary: Buildings, roads and bridges collapse. Disruption to gas, electricity and water supplies Secondary: Fires from ruptured gas mains, low water supplies, loss of business 

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Northridge, USA (MEDC) Facts

Where: Northridge is a neighborhood of Los Angeles, California

Epicenter: Reseda

When: 4:30am, 17th January 1994

Magnitude: 6.7 

Duration: 10-20 seconds

2 aftershocks: 1st a minute after the event and 2nd 11 hours after event

Focus: 18.3km, shallow

Cause: A blind thrust fault miles below Northridge that was previously unknown to seismologists 

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Northridge, USA (MEDC) Primary effects

Deaths: 57 - this was limited due to the early hour as people were not in their office buildings and these high rise buildings were the worst hit

5,000 injured - Months after the earthquake 67% of adult survivers and 88% of children survivers had severe PTSD

Buildings collapsed because they were built on a blind thrust fault so the land buckled and this was not foreseen

11,000 homes destroyed

Lansides occured, blocking roads

9 underpasses collapsed

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Northridge, USA (MEDC) Secondary effects

Fires caused by broken gas lines

In San Fernando Valley, several underground gas and water lines were severed, causing some streets to experience simultaneous fires and floods. Water pressure dropped to zero in some areas, meaning fighting the fires was difficult

5 days after the earthquake, between 40,000 and 60,000 people were without public service water

Caused a breakout of Valley Fever - a respiratory disease thats caused by inhaling airbourne spores of fungus. 203 cases reported, 3 fatalities (10 times the normal rate). The spores were carried by seismically triggered landslides.

Postal service suspended for several days

Caused more than $40 billion in damage

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Northridge, USA (MEDC) Responces

Within a week the federal government issued a $7.5 billion aid package

The American Red Cross dispatched 15,000 trained relief workers to harbor 22,000 refugees in47 shelters and provide 1.7 million meals

Law was passed requiring all hospitals in California to ensure care units and emergency rooms would be in earthquake resistant buildings by Jan 1st 2005 - Many only managed to meet this by 2008-9

Building codes were already in place, but some structural specifications did not perform as intended, so they were revised.

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Haiti (LEDC) Facts

Where: Caribbean

Epicenter: 16 miles west of port-au-prince

When: 4:53pm, 12th January 2010

Cause: North American plate sliding past the Caribbean plate at a conservative plate margin

Magnitude: 7

Focus: 5 miles, shallow

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Haiti (LEDC) Primary effects

Deaths: 316,000

1 million made homeless

250,000 houses and 30,000 other buildings, including the presidents palace and 60% of government buildings, were destroyed or badly damaged

Transport and communication links were badly damaged

Hospitals (50+) and schools (1,300+) were badly damaged, as was the airport control tower

The main prison was destroyed, allowing 4,000 inmates to escape. 

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Haiti (LEDC) Secondary effects

The inmates that escaped stole weapons from guards and burned all evidence of their crimes, and returned to the slums they were arrested from. Rescue efforts and delievering of aid was decreased due to this as the inmates were shooting and robbing people from the moment they go out.

People squashed into shanty towns or on to the streets

1/5 people lost their job - Haiti's largest industry, clothing, was worst hit

Large numbers of deaths meant hospitals and morgues became full and bodies had to be piled on the streets - this meant diseases were very common

Difficult getting aid to some areas due to issues at the airport and poor management

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Haiti (LEDC) Responses

£100 million given by the USA, £330 million given by the EU 

810,000 people placed in aid camps

115,000 tents and 1 million tarpaulin shelters were provided

Lack of immediate aid through poor planning, management and access

Countries such as the United States, the UK, Israel and the Dominican Republic sent 1,000 military and disaster relief personnel each

The damage to the Haitian government ministries, all of which suffered varying degrees of facilitys' destruction and personnel deaths, impeded coordination of the disaster response.

Support for people without jobs - cash/food for work projects

Temporary schools created and new teacher training 

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Indonesian tsunami facts

When: 26th December

Focus: 30km below sea level, shallow

Epicenter: 160km off shore in the Indian Ocean

Cause: 9.1 magnitude Great Sumatra-Andaman earthquake. Occured at a subduction zone - Austrailian plate under the Burmeu plate. The sea floor was uplifted, displacing several billion tonnes of sea water. The waves reached height of 24m at Banda Aceh

Countries that suffered major casualties and damage: India, Indonesia, Malaysia, Maldives, Thailand, Sri Lanka, Myanmar, Somalia

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Indonesian tsunami Primary effects

60% of Sri Lanka destroyed

220,000 people lost - 180,000 definitely died (although this number greatly fluctuates with different health reports). 131,000 of these deaths were in Indonesia alone.

45,000 people injured

1.7 million homeless

1500 villages entirely destroyed in Sumatra (indonesian village) - serious damage to all roads, briges, buildings, ports, crops etc

60% of fishing infrastructure destroyed

Contamination of drinking supplies

Some damage to habitats: Mangroves, coral reefs, forests and coastal wetland 

8000 tourists from Australia, Europe and America were killed

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Indonesian tsunami Secondary effects

Unburied bodies increased the likelihood of diseases such as cholera, which killed 150,000 people in the refugee camps

Many survivers developed mental injuries as well as physical

Tourism decreased as people feared a repeat event

£5 billion in damages

Altered seabed in Malacca Strait, making shipping even more dangerous

Income lost due to destruction of fishing boats

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Indonesian tsunami Management

No warning of the tsunami, hit shores 30 minutes after earthquake so could not prepare

British public gave £330 million, which is greater than what was given by the British government. A lot of TV coverage may have been the reason for this

World food programme sent food for 1.3 million people

It took months to clear the debris before rebuilding could even start

Rapid burial and burning of bodies to prevent disease

5 million relocated into temporary refugee camps

Tsunami early warning system has been installed in the Indian Ocean at the cost of £20 million

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