Seismic Hazards

Question 1

Explain how an earthquake occurs in 6 steps?

Answer 1

• Earthquakes occur due to stress release along faults caused by plate movements.
• The focus is the point underground where the earthquake starts.
• The epicentre is the point directly above the focus on the surface.
• Large amounts of energy are released.
• Much of this energy is transferred vertically to the surface and then moves outwards from the epicentre (point on surface above the focus) as seismic waves
• After the moment of fracture, rocks may regain their original shape but in a new position.

Question 2

What are the 2 primary hazards of earthquakes?

Answer 2

• Ground shaking: Causes buildings to collapse.
• Crustal fracturing: The Earth can visibly separate and deep fissures in the ground can be created.

Question 3

What are the 3 secondary hazards of earthquakes?

Answer 3

• Liquefaction: Saturated ground behaves like a liquid, causing buildings to sink.
• Landslides: Triggered by ground movement on steep slopes.
• Tsunamis: Caused by undersea earthquakes displacing water.

Question 4

How do tsunamis form in 5 steps?

Answer 4

• Underwater earthquakes cause seafloor displacement -> pushing water upwards -> Waves travel fast in deep water -> slow in shallow water -> increasing height.

Question 5

What are the 3 impacts of tsunamis?

Answer 5

• Widespread coastal flooding.
• Infrastructure destruction (homes, roads, power lines).
• Loss of life due to fast-moving waves.

Question 6

When and where did the Gorkha earthquake occur?

Answer 6

• 25 April 2015
• Epicentre near Kathmandu, Nepal.

Question 7

What were the 3 primary impacts of the Gorkha earthquake?

Answer 7

• 9,000 deaths, 22,000 injuries.
• 600,000 buildings destroyed.
• Landslides and avalanches blocked roads and buried villages.

Question 8

What were the 3 secondary impacts of the Gorkha earthquake?

Answer 8

• Tourism decline (Everest climbing season cancelled).
• Food and water shortages due to damaged infrastructure.
• Aftershocks continued to cause damage.

Question 9

What were the 3 immediate responses to the Gorkha earthquake?

Answer 9

• Search and rescue operations by Nepalese army.
• International aid sent (e.g., India and Indonesia provided relief supplies).
• Tents and temporary shelters set up for displaced people.

Question 10

What were the 3 long-term responses to the Gorkha earthquake?

Answer 10

• Stricter building codes to make infrastructure earthquake-resistant.
• Rebuilding efforts with international funding.
• Improved disaster preparedness through early warning systems.

Question 11

What are the 3 ways in which earthquakes be predicted?

Answer 11

• Seismometers detect small tremors.
• GPS monitoring tracks crustal movements.
• Historical data helps identify high-risk areas.

Question 12

What 3 strategies can reduce earthquake damage?

Answer 12

• Earthquake-resistant buildings (shock absorbers, flexible materials).
• Land-use zoning (keeping critical infrastructure away from fault zones).
• Education and drills (teaching people what to do during an earthquake).

Question 13

What is the focus?

Answer 13

where the pressure is released underground and where the energy radiates out from.

Question 14

What is so special about the focus?

Answer 14

This is the place with the strongest waves that cause the most damage.

Question 15

What is the epicenter?

Answer 15

the point directly above the centre of the earthquake on the earth’s surface.

Question 16

What are seismic waves?

Answer 16

when energy is released from the focus in shock waves.

Question 17

What are the 3 types of earthquakes?

Answer 17

1) Shallow-focus
2) Deep-focus
3) Underwater

Question 18

What are shallow-focus earthquakes?

Answer 18

Earthquakes in which the focus is 0-70km under the Earth’s surface.

Question 19

What are deep-focus earthquakes?

Answer 19

when an earthquake has a focus which is 70-700km under the Earth’s surface.

Question 20

How are deep-focus earthquakes caused?

Answer 20

Deep-focus earthquakes are caused by previously subducted crust moving towards the core, heating up or decomposing.

Question 21

What do deep-focus earthquakes tend to be like?

Answer 21

They are generally less damaging than shallow-focus because the shock waves have to travel further and so cause less shaking at the surface.

Question 22

What is so special about underwater earthquakes?

Answer 22

They move the seabed, which causes water to get displaced. If enough water is displaced, tsunamis (series of enormous waves) can happen.

Question 23

Are underwater earthquakes deep or shallow focus?

Answer 23

They can be shallow- or deep-focus. The deeper the focus, the bigger the tsunami.

Question 24

What are the 3 types of waves?

Answer 24

1) P-waves
2) S-waves
3) L-waves

Question 25

What are P-waves?

Answer 25

P-waves are the fastest waves but they cause the least damage.

Question 26

What are S-waves?

Answer 26

Waves that make the ground shake violently.

Question 27

What are L-waves and describe how they occur?

Answer 27

The waves that create significant damage, including crustal fracturing. They only travel across the surface and have a large amplitude.

Question 28

Describe the process of liquefaction in 2 steps?

Answer 28

- Earthquakes compact loose sediment of silts, sand and gravel that are waterlogged. - The compact ground forces water to rise to the surface and damage to buildings and infrastructure is common.

Question 29

What are the 5 characteristics of tsunamis?

Answer 29

1) Long wavelength at sea 2) short amplitude at sea 3) velocity 4) drawback 5) wave-train

Question 30

What is wavelength?

Answer 30

the distance measured between two identical points of a wave.

Question 31

Can you give a stat for long wavelength at sea in a tsunami?

Answer 31

The wavelength is often over 100km long

Question 32

Can you give a stat for short amplitude at sea in a tsunami?

Answer 32

They are usually 1m in height and are barely noticeable but when they reach land, their height can increase to over 25m in some cases

Question 33

Can you give a stat for velocity in a tsunami?

Answer 33

They move quickly in deep water and can reach speeds of up to 700 kph but they slow down as they reach shallow water

Question 34

What is a drawback?

Answer 34

When there is a localized drop in sea level

Question 35

What is a wave-train?

Answer 35

The way that a tsunami hits a coastline is like a series of waves

Question 36

What was the magnitude of the gorkha earthquake

Answer 36

magnitude 7.8

Question 37

Why does the geological structure of Nepal increases the risk of earthquakes? (Give 4 chains of reasoning)

Answer 37

- Pre-historic lakes filled many of the valleys so the sediment is soft ->The depth of soft sediment reaches 600 m deep in the Kathmandu valley -> So seismic waves that pass through this material are amplified -> causing structures to swing violently.