Earthquakes
- Created by: Issy1998
- Created on: 02-06-16 10:46
Earthquake focus
Shallow focus: 0-70km deep
Intermediate focus: 70-300km deep
Deep focus: 300-700km deep
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
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
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.
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
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
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
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
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
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.
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
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.
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
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
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
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
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
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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