Tectonics Lesson 6: Causes of Earthquakes Flashcards
How is energy from the release of pressure at boundaries seen as?
Seismic waves causing the ground to shake
Where are seismic waves released from?
Inside the Earth’s crust along a falutline
What is the hypocentre?
The point inside the crust from which pressure is released along a fault
What is the epicentre?
The point on the surface directly above the hypocentre
Describe P waves
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
Describe S waves
Body waves Slower at 4km/s Solids only Up and down motion, perpendicular to the direction of travel More damage than P waves
Describe L waves
Surface waves
Slowest of all waves
Side to side motion, perpendicular to direction of travel
Larger and cause the most damage
Can earthquakes be predicted? What can be done?
No there aren’t any methods for predicting
Can only forecast where an earthquake may happen by looking at past data
What are methods of forecasting earthquakes?
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.
What are some of the physical effects of an earthqauke?
Magnitude (size of seismic waves)
Depth (deeper hypocentre more energy dissipated)
Distance (closer to epicentre the stronger)
Geology (less resistant rocks can amplify shaking)
What are some of the human effects of an earthquake?
Level of development Population Level of preparation The effectiveness of the emergency response Impact of the secondary hazar`ds
Define primary effects
Those that happen as a direct result of the earthquake
Define secondary effects
Side effects of an earthquake that happen as a result of the primary effects, often causing more damage
Ground Shaking (primary/secondary)?
Primary
Causes buildings, bridges, roads and infrastructure to collapse
Crustal Fracturing (primary/secondary)?
Primary
When the Earth’s crust cracks due to the energy that is released
Landslides or Avalanches (primary or secondary)?
Secondary
Slopes fail as the shaking places stress on them resulting in landslides, rock slides, mudslides and avalanches
Tsunami (primary/secondary)?
Secondary
Underwater earthquakes generate a series of big waves
Liquefaction (primary/secondary)?
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
Define aftershocks
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
When can aftershocks occur?
Weeks, moths or years after an earthquake
The larger the earthquake, the larger and more numerous the aftershocks
What are the problems with aftershocks?
Capable of causing additional damage as well as hampering recovery efforts
Example of an aftershock which caused more damage
Christchurch 2011 at 6.3 magnitude
Caused more damage and loss of life than the original
When was the Loma Prieta earthquake?
17th October 1989 5:04
Magnitude of Loma Prieta?
6.9 magnitude
Why did the geology make the LP earthquake worse?
Built on man-made landfill, with soft, sandy soil which amplified the ground shaking. This increased the level of damage sustained
What were the effects of the LP earthquake?
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
What caused the Cyprus freeway to collapse?
Part of it was built on soft mud whilst the adjoining parts were built on firmer ground and remained standing
When was the Christchurch earthquake?
4th September 2010 at 4:35am
What caused the Christchurch earthquake?
The Greendale Fault - the subducting of the Australian plate under the Pacific plate came under friction causing a locked fault.
Magnitude of CC
7.1 magnitude
10km below the surface - shallow
Social impacts of CC earthquake
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
Economic impact of CC earthquake
Cost $10-15 billion in damages
Environmental impacts of CC earthquake
Sulfur released into the atmosphere from gas leaks
Sewers and water pipes damaged releasing toxic substances into the environment
What were some of the response to the CC earthquake?
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
