Tectonics Pack E

Question 1

What is an earthquake?

Answer 1

The movement of the Earth’s crust, usually along pre-existing faults

Question 2

What is a fault?

Answer 2

• A fracture or zone of factures between two blocks of rock
• Along blocks to move relative to each other
• Range in length from milimetres to thousands of km

Question 3

How do earthquakes form?

Answer 3

• Result of a gradual build-up of stress due to crustal movement
• Rocks spanning plate margins are subjected to stresses and gradually deform
• When deformation is too great, the rock fractures
• This movement release stored up elastic strain energy as seismic waves
• Seismic waves propagate through the Earth and cause the ground to shake

Question 4

What is elastic rebound?

Answer 4

The bending of the plates and subsequent catching up of the crust

Question 5

What are the simple steps of earthquake formation?

Answer 5

1. Slide past
2. Friction
3. Stuck
4. Pressure
5. Jolt apart

Question 6

Where does an earthquake start?

Answer 6

• At the hypocenter/focus
• The point within the Earth where a rocks fracture and earthquake rupture starts

Question 7

What is the epicentre?

Answer 7

The point directly above the focus at the surface of the Earth

Question 8

What are the different depth of earthquakes?

Answer 8

• Shallow earthquakes are between 0 and 70km deep
• Deep earthquakes are 70+ km
• All deep earthquakes are localised in great slabs of lithosphere that are sinking into the mantle

Question 9

What are the hazards associated with earthquakes?

Answer 9

• Ground shaking
• Liquefaction
• Landslides
• Tsunamis

Question 10

What is ground shaking?

Answer 10

• Shaking of the ground caused by the passage of seismic waves
• Greatest hazard to humans due to collapsing structures and infrastructure destruction
• Intensity depends on earthquake intensity, duration, distance from epicentre, geology (as solid bedrock is less subject to shaking than loose sediment)

Question 11

What is liquefaction?

Answer 11

• Loose sediments (e.g. sand or silt) combine with groundwater and behave like a fluid or quicksand
• Causes the foundations of building to sink causing them to collapse
• After the earthquake, water sinks deeper into the ground and surface firms

Question 12

How are tsunamis formed?

Answer 12

• Shallow focus, undersea earthquakes at plate margins
• Creates a sudden rise of fall in ocean floor
• Displaces water above it
• Wave height is low in the ocean but increases as water depth near land decreases
• Over 80% of tsunamis are within the Pacific Ring of Fire
• Ocean waves spread out in all directions form epicentre

Question 13

How are landslides formed?

Answer 13

• Earthquakes creates stresses that make weak slopes fail
• Triggers landslides, rockfalls and avalanches
• Significantly increases death toll and hampers rescue efforts

Question 14

What are body waves?

Answer 14

• Travel through the interior of the Earth
• Higher frequency and arrive before surface waves
• P and S waves

Question 15

What are P waves (primary)?

Answer 15

• Fastest and arrive first
• Can move through solid rocks and liquids
• Caused by compression, pushing and pulling the rock as it moves

Question 16

What are S waves (secondary)?

Answer 16

• Slower
• Only move through solid rock
• Move rock particle at right angles to the direction of wave travel
• Second wave to arrive
• Responsible for much damage

Question 17

What are surface waves?

Answer 17

• Travel only through the crust
• Lower frequency and arrive after body waves
• L and R waves

Question 18

What are L waves (love)?

Answer 18

• Fastest surface waves
• Move the ground horizontally from side to side
• Often cause the greatest damage

Question 19

What are R waves (Rayleigh)?

Answer 19

• Follow an elliptical motion which moves the ground up and down and side to side
• Can be larger than other waves
• Result in most of the shaking that is felt