Seismic Hazards Flashcards
What causes a tsunami
Sudden motion on the ocean floor from an earthquake, eruption or landslide
What causes most tsunamis
Earthquakes generated in the subduction zone
What causes subduction
Area where oceanic plate is forced down into the mantle by the less dense, thicker continental plate
Timeline of tsunami 5
- Plates subduct
- Energy accumulates over long period of time
- Builds until the frictional forces between between the plates are exceeded
- This sudden motion creates an earthquake
- Tsunami races away from epicentre
Why do waves build
As water is displaced, it rushes out of an area, energy is compressed forcing it to gain height
Areas susceptible to landslides
- Steep sloped cliffs
- Unconsolidated rock
- Loosened soil by rainfall
Areas susceptible for liquefaction
- Weak topsoil
- Large water table close to surface
- Heavy rain
Predicting earthquakes
- Previous history of area
- Remote sensing
- Radon gas emissions
More time between earthquakes indicate
Mounting pressure therefore greater magnitude
Remote sensing prediction
Laser beams can be used to detect plate movement, aided by seismometers to provide area of interest
Radon gas emission prediction
- Radon gas found in the centre of earth from radioactive decay
- Cracks in Earth indicate low pressure/stress, releasing radon gas therefore low earthquake risk
Measurements for earthquakes
- Richter scale (Universal)
- Mercalli Scale (subjective)
Mercalli scale usage
- Provides context into impact to an area in terms of damage and deaths
- Ineffective In determining the actual scale of an earthquake
- Difficult to compare earthquakes but is to compare effects, assessing damage but doesn’t account for preparedness
Richter scale
- Measures the ground deformation and energy release by an earthquake
- Numbers on scale increase by 10x in magnitude
- Not open to interpretation
What causes subduction
When the denser, thinner oceanic plate sinks beneath the thicker but less dense plate, creating pressure, releasing magma, and creating vibrations
Properties of oceanic plate
Composed of basalt rock 6km
Properties of continental plate
Dominated by granite rock 20-200km
What causes an earthquake to occur
Caused by a sudden slip or break in a rock on a fault when pressure exceeds what can be supported by the rock
Nepal background info 7
- Occurred 2015 7.9 magnitude
- Epicentre between the capital of Kathmandu and Pokhara the countries two main areas
- Indian tectonic plate was subducted under Eurasian, moving 4-5cm
- Landlocked surrounded by rough mountains
- Prone to mass movements of sediment
- Neighbours also LICs/NEEs
- 114th on prosperity index
Primary effects of Nepal 5
- Triggered avalanches and rockfall
- Killed 8000, 14500 injured, 2.8 million homeless
- 45000 classrooms destroyed
- Hospitals overwhelmed treating In streets
- Aftershock magnitude of 6.9
Secondary effects Nepal - ECONOMIC 5
- Areas isolated by damaged roads
- Destruction of 900,000 buildings
- Loss of tourism, infrastructure and trust
- Affected half of $20 billion GDP
- Dependance on aid/international support
Secondary effects Nepal - SOCIAL/POLITICAL 4
- Loss of trust in government = was warned of potential event
- Country destabilised
- 1.1 million children lost a normal childhood and denied education
- Food insecurity rose as a result of disruption to rice season
Secondary effects Nepal - ENVIRONMENTAL 3
- Pollution of waterways due to destruction of sewage systems
- land lost in devastation
- Avalanched destroyed crops and trees
Nepal short term responses
- Aid provided by US, UK, India total of £1.4 billion
- Aid agencies already in Asia
- UK raised £41 million
- Temporary schools for 11 million (school in a box rolled out by UN)
- Land clearing machinery moved in from neighbours
- India mobilised in 11 minutes
Nepal long term responses 5
- Long term plan to rebuild homes over 5 years = 76% completed 4 years later
- Medical Teams remain to provide psychological support
- Construction and repairs conducted according to international guidelines
- Earthquake safety in school curriculum
- $500 million of aid donated by India
