8. Earthquakes Flashcards
What is the focus also known as?
The hypocentre
What percentage of earthquakes occur along tectonic plate tectonic plate boundaries
95%
What is earthquake energy released as?
seismic waves
What are primary waves?
Arrives first, fast, moves through solid rock and fluids, pushes and pulls in the direction of travel
Only damaging in most powerful earthquakes
What are secondary waves?
Slower than p waves, only moves through solid rock, up and down movement.
What are Rayleigh waves?
Only travels through the surface of the crust in a rolling motion, the ground is moved up and down and side to side.
Responsible for most of shaking felt by people
What is a love wave?
Only travels through the surface of the crust, fastest of the surface waves and moved from side to side as it moves forward.
They are the slowest but cause the most damage.
How can human activity cause earthquakes?
- Building reservoirs which puts pressure on underlying rocks
- Fracking
Why is the Moment Magnitude Scale generally preferred?
It’s accurate and better at measuring large earthquakes
What does the Moment Magnitude Scale measure?
- size of seismic waves
- amount of slippage or rock movement
- area of the fault surface broken by the earthquake
- resistance of the affected rocks
What does logarithmic mean?
Each number is 10x the magnitude of the number before
What is the Modified Mercalli Intensity Scale used to measure?
An earthquake’s effect on people, structures and the natural environment
What cannot be predicted of earthquakes?
frequency and regularity
What events have scientists identified that occur before an earthquake strikes?
- micro-quakes before main event
- bulging of the ground
- decreasing radon concentrations in groundwater
- raised groundwater levels
- electrical and magnetic changes within local rocks
- increased argon gas content in soils
- curious animal behaviour
What are the physical factors that affect earthquakes?
- magnitude
- depth of hypocentre
- distance from epicentre
