3a + b- Earthquakes + Hazards

Question 1

Why do earthquakes happen

Answer 1

• 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

Question 2

Where do earthquakes happen (3 points)

Answer 2

• at boundary’s between plates
• at hotspot volcanos
• human activity (fracking)

Question 3

What are the 3 main features of a earthquake

Answer 3

• focus
• epicentre
• seismic waves

Question 4

What is the focus

Answer 4

• point where shockwaves/ energy released originate from
• where stress builds up

Question 5

What is the epicentre

Answer 5

• location on earths surface directly above focus

Question 6

What are seismic waves

Answer 6

• the energy released travels as waves

Question 7

How does depth of focus affect Dailey damage

Answer 7

• deeper the focus = less damage as more energy dissipated

Question 8

What is the Benioff zone

Answer 8

• zone on subduction margin of plate
• experiences earthquakes

Question 9

What does the Richter scale measure and how

Answer 9

• magnitude (energy)
• amount of energy released ( logarithmic scale with increments of 10x)
• scale from 1-9

Question 10

What does the Mercalli index measure and how

Answer 10

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

Question 11

What does the “Moment Magnitude scale” measure and how

Answer 11

• magnitude = Physical movement/ Shaking
• how much ground shaking occurs to measure the intensity
• scale of 1-9

Question 12

Properties of shallow focus earthquakes

Answer 12

• most common
• often occur in cold brittle rocks
• usually low energy but a high energy shallow earthquake can be severe

0-70km

Question 13

Properties of deep- focus earthquakes

Answer 13

• increases in depth = higher pressure + temp
• less frequent but more powerful

70-700km

Question 14

What are primary waves (P waves)

Answer 14

• fast travelling
• vibrate in the direction they travel

Question 15

What are secondary waves (S waves)

Answer 15

• slower (half the speed of P)
• high frequency + vibrate at right angles to the direction of travel

Question 16

What are surface waves (L waves)

Answer 16

• slowest waves
• low frequency
• Rolling movement that moves the surface vertically
• often moves the ground at right angle to direction of movement

Question 17

What physical factors can affect damage caused by earthquake

Answer 17

• focus
• built environment
• geology = loose sands = more shaking
• duration

Question 18

Human factors affecting damage of earthquake

Answer 18

• time of day
• population density
• distance of epicentre from town centre
• poverty
  Effective governance / ability to respond to hazard
  Time of year = summer , toursists

Question 19

Ground shaking + ground displacement as earthquake hazard

Answer 19

• vertical + horizontal moving of the ground
• severity depends on magnitude, distance from epicentre + geology
• can cause collapse of buildings + disrupt natural drainage (rivers)

Question 20

Liquefaction as earthquake hazard

Answer 20

• saturated solid when highly shaken act as a fluid
• houses may sink
• can be very destructive

Question 21

Landslides + avalanches as earthquake hazard

Answer 21

• slope failure as result of ground skiing
• may lead to disruption of transport routes or drainage systems = flooding

Question 22

Flooding as a earthquake hazard

Answer 22

• can be caused in may indirect ways eg: tsunami or destroying dams

Question 23

Tsunami as a earthquake hazard

Answer 23

• 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

Question 24

How are rift valleys formed

Answer 24

• 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

Question 25

How does fracking cause earthquakes

Answer 25

Injecting of Fluids can Lubricate the fault causing it to slip = Earthquake

Question 26

How fast can Tsunamis travel

Answer 26

7000 km/hr

Question 27

2 ways tsunamis can form

Answer 27

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