Seismic Hazards Flashcards
Earthquakes, a primary hazard caused by seismic activity
Caused by the tension that builds up at plate margins
Plates jerk past each other, send shockwaves
Shockwaves spread out from the focus.
Epicentre is the point on the earths surface where the earthquake is felt first.
How can an Earthquake be measured?
1) Richter Scale - measures magnitude, logarithmic.
2) Moment Magnitude Scale MMS - based on the total amount of energy released by an earthquake. Logarithmic, more accurate.
3) Mercalli Scale - measures impacts using observations, scale of 1-12.
What other seismic hazards can earthquakes cause?
Tsunamis
Landslides/ Avalanches
Soil liquefaction
What are Tsunamis?
- Large waves caused by the displacement of large volumes of water.
- Triggered by underwater earthquake, waves radiate from epicentre.
- Generally more powerful if they occur near coast, as they lose energy as they travel towards land.
- Waves travel fast in deep water
- Hit without much warning, cause high death tolls.
What are Landslide and Avalanches?
- Shaking of the ground displaces soil or snow.
- Shaking can loosen ground material, easier for water to infiltrate. Can trigger landslide after eruption has stopped.
What is Soil liquefaction?
- When soil is saturated with water, vibrations cause it to act like a liquid.
- Makes soil weaker and easier to deform, more likely to subside.
Nature of earthquakes and magnitude affected by?
Margin type
Rate of Movement
Depth of Focus
Margin Type affect?
- Biggest earthquake occurs at destructive plates, at subduction zones.
- At constructive plates, lower magnitudes
Rate of Movement?
Tectonic plates in relation to each other, between 1-15cm per year.
No clear relationship
Depth of Focus?
Deep focus tend to have higher magnitude.
Deep focus generally do less damage as the distance to the surface reduces the power.
Magnitude and Frequency?
Low magnitude but frequent seismic hazards occur.
Radom occurance
Predictability is difficult
