Seismic Hazards

Question 1

What is the focus?

Answer 1

The point in the Earth’s crust where an earthquake occurs

Question 2

What is the epicentre?

Answer 2

The point on the surface directly above the focus

Question 3

What are the two types of focus?

Answer 3

Shallow and deep

Question 4

What causes an earthquake?

Answer 4

Seismic waves in the crust (earthquake is the primary hazard)

Question 5

What are the primary hazards of an earthquake?

Answer 5

• Ground shaking
• Ground rupture

Question 6

What are the main secondary hazards of seismic activity?

Answer 6

• Shock waves
• Tsunamis
• Liquefaction
• Landslides

Question 7

How is an earthquake caused?

Answer 7

1. Movement within the crust causes pressure to build up
2. If pressure exceeds the strength of the rock it will fracture
3. Pressure released as seismic waves
4. P-waves and S-waves spread out from the focus
5. The ground shakes

Question 8

What is a P wave?

Answer 8

• Primary wave
• Travels through S and L
• 6-7 km/s

Question 9

What is an S wave?

Answer 9

• Secondary wave
• Travels through S
• 3-4 km/s

Question 10

How is a tsunami generated?

Answer 10

Oceanic crust is jolted by a shallow focus earthquake, causing water to be displaced and creates a large wave which can make landfall

Question 11

What is liquefaction?

Answer 11

Ground shaking causes saturated soils to lose mechanical strength and behave as a fluid

Question 12

How are landslides caused?

Answer 12

Slope failure as a result of ground shaking

Question 13

What plate boundaries experience earthquakes?

Answer 13

All three

Question 14

How is seismicity often measured?

Answer 14

Richter scale (logarithmic)

Question 15

How can earthquake intensity be measured?

Answer 15

Mercalli Scale (1-12)

Question 16

What is the difference between constructive and destructive boundary earthquakes?

Answer 16

Constructive boundaries have shallow focus earthquakes whereas destructive boundaries have deep focus earthquakes

Question 17

What is the regularity and predictability of earthquakes?

Answer 17

No pattern and impossible to predict

Question 18

What are the social impacts of seismic hazards?

Answer 18

• Loss of life
• Buildings collapse
• Homelessness
• Gas and water pipes burst (fires and disease)

Question 19

What are the economic impacts of seismic hazards?

Answer 19

• Businesses destroyed
• Economic decline
• Loss of tourism
• High rebuilding and insurance cost

Question 20

What are the environmental impacts of seismic hazards?

Answer 20

• Fault lines
• Liquefaction silt
• Radioactive material leakage from power plants
• Soil salinisation from tsunamis

Question 21

What are the political impacts of seismic hazards?

Answer 21

• Government buildings destroyed
• Food and water shortages
• Borrowing money for international aid
• Looting and lawlessness

Question 22

What are examples of mitigation/preparedness strategies

Answer 22

• Coastal engineering to reduce tsunami damage
• Hazard resistant structures (e.g. cross-bracing buildings)
• Land use planning
• Hazard mapping
• Education and safety drills