Explaining The Causes Of Tectonic Hazards Earthquakes Flashcards
What causes earthquakes?
Occur by sudden movements
Movements are proceeded by a gradual build up of tectonic strain
When the pressure exceeds the strength of the fault the rock fractures
This produces a sudden release of energy creating seismic waves that radiate form the fracture
The crust then rebounds either side of the fracture which is the ground shaking
What is the focus
The point where strain is released within earths crust
What is the epicentre
The point directly above the focus on the surface
What are the several types of seismic wave
Primary waves
Secondary waves
Surface waves - Rayleigh and love
Describe primary waves
Arrives first- fastest 8km a sec
Compression and extension movement
Short wave length
Travel through solid and liquid rock
Describe secondary waves
Arrive shortly after primary waves. 4km a sec Longer wavelength Vibrate at right angles to direction of travel (up and down) Only travel through solid rock
Describe Rayleigh waves (surface)
Only travel on the surface Travel in a rolling motion Side to side and up and down Long wavelength Responsible for most shaking felt by people
Describe love waves (surface)
Faster than Rayleigh waves
Move side to side (horizontal)
Most shaking felt by us on the surface
What is liquefaction
When there are air pockets in soil and an earthquake begins the air pockets act like pumps pulling ground water up onto the surface making solid act like a liquid and can leave objects set in the ground after the earthquake has finished
What is a landslide and how do they occur
The downslope movement of material under the affect of gravity
They occur when the natural stability of the slope in affected for example when there an earthquake
Landslide example is Kashmir 2005
What are tsunamis and how do they occur
When a submarine earthquake displaces the sea bed vertically
May be small in middle of the ocean but can become 30 metres high and travel 700km/h
