Tectonics Lesson 6: Causes of Earthquakes

Question 1

How is energy from the release of pressure at boundaries seen as?

Answer 1

Seismic waves causing the ground to shake

Question 2

Where are seismic waves released from?

Answer 2

Inside the Earth’s crust along a falutline

Question 3

What is the hypocentre?

Answer 3

The point inside the crust from which pressure is released along a fault

Question 4

What is the epicentre?

Answer 4

The point on the surface directly above the hypocentre

Question 5

Describe P waves

Answer 5

Body waves
Fastest at 8km/s and first to reach the surface
Through both solids and liquids
Backwards ad forwards motion with compressions and rarefactions
Damaging in the most powerful earthquakes

Question 6

Describe S waves

Answer 6

Body waves 
Slower at 4km/s 
Solids only
Up and down motion, perpendicular to the direction of travel
More damage than P waves

Question 7

Describe L waves

Answer 7

Surface waves
Slowest of all waves
Side to side motion, perpendicular to direction of travel
Larger and cause the most damage

Question 8

Can earthquakes be predicted? What can be done?

Answer 8

No there aren’t any methods for predicting

Can only forecast where an earthquake may happen by looking at past data

Question 9

What are methods of forecasting earthquakes?

Answer 9

Research focuses on precursors which can suggest e.g. foreshocks
Gaps along a fault which have not earthquakes are likely to have activity as friction in that area has not been released and is building up.

Question 10

What are some of the physical effects of an earthqauke?

Answer 10

Magnitude (size of seismic waves)
Depth (deeper hypocentre more energy dissipated)
Distance (closer to epicentre the stronger)
Geology (less resistant rocks can amplify shaking)

Question 11

What are some of the human effects of an earthquake?

Answer 11

Level of development
Population
Level of preparation 
The effectiveness of the emergency response 
Impact of the secondary hazar`ds

Question 12

Define primary effects

Answer 12

Those that happen as a direct result of the earthquake

Question 13

Define secondary effects

Answer 13

Side effects of an earthquake that happen as a result of the primary effects, often causing more damage

Question 14

Ground Shaking (primary/secondary)?

Answer 14

Primary

Causes buildings, bridges, roads and infrastructure to collapse

Question 15

Crustal Fracturing (primary/secondary)?

Answer 15

Primary

When the Earth’s crust cracks due to the energy that is released

Question 16

Landslides or Avalanches (primary or secondary)?

Answer 16

Secondary

Slopes fail as the shaking places stress on them resulting in landslides, rock slides, mudslides and avalanches

Question 17

Tsunami (primary/secondary)?

Answer 17

Secondary

Underwater earthquakes generate a series of big waves

Question 18

Liquefaction (primary/secondary)?

Answer 18

Secondary
When the surface rock loses strength and becomes more liquid than solid. The subsoil loses its ability to support buildings/infrastructure foundations, so they sink or tilt

Question 19

Define aftershocks

Answer 19

Result of the Earth’s ‘settling down’ or readjusting along the part of the fault that slipped originally. Occur in the general area of the original earthquake

Question 20

When can aftershocks occur?

Answer 20

Weeks, moths or years after an earthquake

The larger the earthquake, the larger and more numerous the aftershocks

Question 21

What are the problems with aftershocks?

Answer 21

Capable of causing additional damage as well as hampering recovery efforts

Question 22

Example of an aftershock which caused more damage

Answer 22

Christchurch 2011 at 6.3 magnitude

Caused more damage and loss of life than the original

Question 23

When was the Loma Prieta earthquake?

Answer 23

17th October 1989 5:04

Question 24

Magnitude of Loma Prieta?

Answer 24

6.9 magnitude

Question 25

Why did the geology make the LP earthquake worse?

Answer 25

Built on man-made landfill, with soft, sandy soil which amplified the ground shaking. This increased the level of damage sustained

Question 26

What were the effects of the LP earthquake?

Answer 26

Mariana District the worst affected with much damage
Liquefaction of buildings due to the soft soil
Part of the 2 level Cyprus freeway collapsed causing 42 of the 67 deaths

Question 27

What caused the Cyprus freeway to collapse?

Answer 27

Part of it was built on soft mud whilst the adjoining parts were built on firmer ground and remained standing

Question 28

When was the Christchurch earthquake?

Answer 28

4th September 2010 at 4:35am

Question 29

What caused the Christchurch earthquake?

Answer 29

The Greendale Fault - the subducting of the Australian plate under the Pacific plate came under friction causing a locked fault.

Question 30

Magnitude of CC

Answer 30

7.1 magnitude

10km below the surface - shallow

Question 31

Social impacts of CC earthquake

Answer 31

2 people seriously injured + many less serious
Aftershocks caused 185 deaths in 2011
Water supplies damaged led to contamination
Power outages
Airports, businesses and schools closed

Question 32

Economic impact of CC earthquake

Answer 32

Cost $10-15 billion in damages

Question 33

Environmental impacts of CC earthquake

Answer 33

Sulfur released into the atmosphere from gas leaks

Sewers and water pipes damaged releasing toxic substances into the environment

Question 34

What were some of the response to the CC earthquake?

Answer 34

16 ambulances in operation in 30mins
Curfew from 7am to 7pm for the CBD
New Zealand RAF bought in for search and rescue and to maintain restrictions
Government provided an initial fund of $5 million
Benefit concert, Band Together, on the 23rd October 2010 at Hagley Park to raise money for recovery