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
