Seismic Hazards Flashcards
What are earthquakes caused by?
Tension built up at all three types of plate margin. When the plates jerk past each other it releases shockwaves causing an earthquake.
What is the focus?
Where the shockwaves spread out from. Isn’t always a singular point can be an entire fault line. Near the focus waves are stronger and cause more damage.
What is the epicentre of an earthquake?
The point on Earths surface where the earthquake s felt first and is straight above the focus.
What are the three scales earthquakes can be measured?
- The Richter scale
- The Movement Magnitude scale
- The Mercalli scale
Describe the Richter scale.
Measures the magnitude of an earthquake. It’s logarithmic. Eg: 5 is 10x bigger than 4.
Major earthquakes score above a 7.
Describe the Movement Magnitude scale.
Based on the amount of energy released by an earthquake.
Logarithmic and is more accurate than the Richter scale.
Describe the Mercalli scale
Measures the impacts of an earthquake using observations of the event. Eg: Reports and photos.
Scale is between 1-12
12= total destruction.
What other seismic hazards can an earthquake cause?
- Tsunamis
- Landslides
- Soil Liquefaction
Describe the features of a tsunami.
Large waves caused by the displacement of large volumes of water.
They can be triggered by underwater earthquakes and are more powerful if it starts closer to the coast, as the waves energy as they travel towards land.
Travel very fast in deep water
= not much warning and high death toll.
Describe the features of a landslide and what they are caused by.
Shaking of the ground can dislodge rocks that move downslope.
Water can also infiltrate the rocks and the extra weight can trigger landslide even after the earthquake has stopped.
Describe the features of soil liquefaction and how it is caused.
When soil is saturated with water, the vibrations of an earthquake make it act like a liquid.
= more likely to subside especially when there is weight on it (building)
What three factors affect the nature of an earthquake?
1) Margin type
2) Rate of Movement
3) Depth of Focus
How does margin type affect the nature of an earthquake?
Biggest earthquakes occur at destructive plate margins. The subduction of a plate causes massive pressure to build.
Constructive margins tend to have a lower magnitude.
How does the rate of movement affect the nature of an earthquake?
Tectonic plates move at different rates, this can affect the frequency of earthquakes.
How does depth of focus affect the nature of an earthquake?
Focus close to surface= Lower magnitude but higher damage
Focus deep below surface= higher magnitude but do less damage because waves have to travel further to surface.
