3a + b- Earthquakes + Hazards Flashcards
Why do earthquakes happen
- plates constantly moving but locked at plate boundaries due to friction
- pressure builds up in lithosphere + crust
- stress reaches threshold (limit where rock cracks)= stress released + plates slip
Where do earthquakes happen (3 points)
- at boundary’s between plates
- at hotspot volcanos
- human activity (fracking)
What are the 3 main features of a earthquake
- focus
- epicentre
- seismic waves
What is the focus
- point where shockwaves/ energy released originate from
- where stress builds up
What is the epicentre
- location on earths surface directly above focus
What are seismic waves
- the energy released travels as waves
How does depth of focus affect Dailey damage
- deeper the focus = less damage as more energy dissipated
What is the Benioff zone
- zone on subduction margin of plate
- experiences earthquakes
What does the Richter scale measure and how
- magnitude (energy)
- amount of energy released ( logarithmic scale with increments of 10x)
- scale from 1-9
What does the Mercalli index measure and how
Magnitude = Damage to people and buildings
- descriptions of damage experienced (12 categories)
= can be more useful than other scales as they do not include impacts
What does the “Moment Magnitude scale” measure and how
- magnitude = Physical movement/ Shaking
- how much ground shaking occurs to measure the intensity
- scale of 1-9
Properties of shallow focus earthquakes
- most common
- often occur in cold brittle rocks
- usually low energy but a high energy shallow earthquake can be severe
0-70km
Properties of deep- focus earthquakes
- increases in depth = higher pressure + temp
- less frequent but more powerful
70-700km
What are primary waves (P waves)
- fast travelling
- vibrate in the direction they travel
What are secondary waves (S waves)
- slower (half the speed of P)
- high frequency + vibrate at right angles to the direction of travel
What are surface waves (L waves)
- slowest waves
- low frequency
- Rolling movement that moves the surface vertically
- often moves the ground at right angle to direction of movement
What physical factors can affect damage caused by earthquake
- focus
- built environment
- geology = loose sands = more shaking
- duration
Human factors affecting damage of earthquake
- time of day
- population density
- distance of epicentre from town centre
- poverty
Effective governance / ability to respond to hazard
Time of year = summer , toursists
Ground shaking + ground displacement as earthquake hazard
- vertical + horizontal moving of the ground
- severity depends on magnitude, distance from epicentre + geology
- can cause collapse of buildings + disrupt natural drainage (rivers)
Liquefaction as earthquake hazard
- saturated solid when highly shaken act as a fluid
- houses may sink
- can be very destructive
Landslides + avalanches as earthquake hazard
- slope failure as result of ground skiing
- may lead to disruption of transport routes or drainage systems = flooding
Flooding as a earthquake hazard
- can be caused in may indirect ways eg: tsunami or destroying dams
Tsunami as a earthquake hazard
- giant sea wave generated from underwater earthquake
- low wave height in open ocean but can get to 25m in shallow water
- high speed = 7000 km/hr
How are rift valleys formed
- rising mantle pushes crust into bulge
- plates move apart
- spreading off plates causes faults in rock + stretches dome
- dome from rising lava subsides (sinks) forming steep sided valley
How does fracking cause earthquakes
Injecting of Fluids can Lubricate the fault causing it to slip = Earthquake
How fast can Tsunamis travel
7000 km/hr
2 ways tsunamis can form
Volcanos = Water displaced quickly by collapse of material /Caldera
Earthquake = Underwater earthquake can cause sea bed to rise vertically displacing water above
- Powerful waves spread out from epicentre/Volcano
