95% occours at plate margines. Many occour around the ring of fire.
What plate boundary does earthquakes occur at?
All plate margins. Most powerful and destructive ones occurs at destructive or collisions plate margins
What are intra-plate earthquakes?
They occur in the middle of plates- often a hotspots where a mantle lies over the mantle plume.
How does earthquake occurs?
They are sudden violent shaking of the ground, when tectonic plates move they become locked together and cause stress and pressure to build up. The stress builds up and the rock fractures and the pressure is released, causing intense ground shaking.
What is the focus?
Point where the earthquake starts below the earth surface. Where the energy is being released from.
What is the epicentre?
Point where the earths surface is directly above a focus
What is the magnitude of earthquakes at constructive margins?
Lower magnitude due to the plate margins moving away. Examples: Mid-Atlantic Ridge experiences many small earthquakes daily but all slow 3.0 magnitude
What is the magnitude at a destructive, conservative and collision margins?
Much higher magnitudes. Example: Tohuku earthquake in Japan occurred at a destructive margin had a magnitude of 9.0
How does an earthquake occur?
Tectonicplates move due to convectioncurrents and processes like slabpull and ridgepush
Plates get stuck and become locked together due to friction
This causes rocks to deform and leads to a build-up of stress and pressure
When the strength of the rock is exceeded, it fractures (breaks)
This releases the energy in a process known as elastic rebound
The point where the rocks fracture is known as the focus
Seismicwaves travel outward from the focus towards the Earth's surface, causing the ground to shake
The epicentre is the point on the Earth's surface directly above the focus
What are the types of seismic waves?
Primary,secondary and love waves
Primary waves
P waves. They are body waves and travel the fastest. They will reach the surface first and can travel through liquid and solids. causes backward and forward shaking. least damaging
Secondary waves
S waves. They are body waves and are slower than P waves. They only travel through solids and causes a sideways motion. These are more damaging
Love waves
L waves. They are surface waves and are the slowest. Causes a sided to sidemotion. Larger and energy is focuses on the surface and are most damaging.
What is liquidfaction?
Occurs when the ground shaking causes the saturates and loose soil to sink and allowing water to rise. Acts like a liquid and can cause damage to infrastructure. Example: 2011 Christchurch earthquake in new zealand caused significant liquefaction and 20,000 properties got damaged
What type of soils will liquefaction occur in?
Loose and saturated sandy soils. They are lowdensity and uncompacted.
What is a Tsunami?
Earthquake beneath the oceans causing a tsunami. example: 2011 Tohoku earthquake in japan triggered earthquake up to 40 metres high.
How does a tsunami occur?
When the sea beds jolts the water is displaced and forced upwards creating a wave. As the waves approaches the land they slow and the wavelength becomes compressed and leads to an increase wave height, reaching up to 30 metres They reach shore and a vaccumn is created and the water recedes rapidly leaving the sea bed exposed.
How are earthquakes measured?
moment magnitude scale which is measured by a seismograph. Scale from 1 being not felt by humans and 10 being the worse. It is a logarithmic scale.
How is earthquake intensity measured?
Mercalli scale which is on a scale from 1 to 12. It measures the impacts on people, built and natural environment.
How frequent are earthquakes?
Low magnitude earthquakes are much more frequent than high magnitude earthquakes. Around 20,000 earthquakes per year. Roughly 16 major earthquakes
What is the seismicgap theory?
If there has been no earthquake along a plate margin for a long time it is more likely to experience a large earthquake in the future. This is due to the stress building up for a longer period of time so more energy will be released.
How can we predict earthquakes?
Pre-cursor earthquakes/ foreshocks which can indicate a larger earthquake that will follow.
Deformation showing pressure building up. Groundwater levels which are measured using sensors.
Radon emissions which using radon sensors which can indicate a build up of radon gas which indicates an earthquake.
Animal behaviour which can signal an earthquake
What are the primary social impacts?
Death and injuries,
Displacement of people
Damage to properties and infractures
What are the secondary social impacts?
Mental health issues e.g. stress, anxiety, depression
Homelessness
Disruption to services such as healthcare and education
Loss of cultural heritage sites
What are the primary economic impacts?
Destruction of property and infrastructure leading to significant costs for repair and reconstruction
Disruption of trade and economic activity
Loss of income and employment
Costs of immediate responses e.g. food aid, temporary shelter, medical treatment
What are the secondary economic impacts?
Slower economic growth and development
Increased economic inequality as impacts are more severe for most vulnerable people
Increased costs of insurance and hazard management strategies
What are the primary environmental impacts?
Loss of vegetation and damage to natural environment through landslides and liquefaction
Contamination of water supplies
Tsunamis can cause flooding, erosion and damage to coastal ecosytems
What are the secondary environmental impacts?
Pollution as a result of the release of hazardous materials e.g. 2011 earthquake and tsunami in Japan caused the release of radioactive material from the Fukushima nuclear power plant
What are the primary political impacts?
Pressure on governments to co-ordinate emergency response
Social unrest and political instability
What are the secondary political impacts?
Conflicts over government response and food shortage
Changes in government policy and regulations to reduce future risk
What are the short term responses?
Search and rescue using sniffer dogs and sensors
Emergencyaid to provide food and shelter
Evacuation of danger zones for tsunami
Issue warning via TV, text and radio
What are the long term responses?
Building codes to increase resilience of buildings
Education and training to prepare communities though regular drills
Early warning systems can give people time to evacuate
Hazard mapping and land use zoning to identify the area with most risk
What characteristics does earthquake resilsacne buildings have?
Weights on the rood are controlled by computers
cross bracing in the steal frame
automatic window shutters to prevent falling glass
steak frames which can sway during earth movements
fire resistant buildings material
foundations sunk into bedrock avoiding clay
Examples of preventions?
Land use zoning in christchurch after the 2010 earthquake. 6000 hectares was declared a red zone
Examples of prepareness?
Monitoring and warning systems are sent out and education programmes in japan. Japans has an earthquake early warning system.
Example of mitigation?
Tsunami walls since 2011 earthquake and tsunami which are over 400km high
Earthquake resistant buildings
Examples of adaptations?
Emergency kits which are kept to hand with contents to hep with evacuation and survival