Seismic activity

• Where does majorities of earthquakes occur?

  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 hot spots 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?


  Tectonic plates move due to convection currents and processes like slab pull and ridge push

  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

  Seismic waves 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 side motion. 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 low density 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 seismic gap 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

  Emergency aid 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

  Evacuation routes and trained emergency service