Seismic Hazards Flashcards
Explain how an earthquake occurs in 6 steps?
- 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.
What are the 2 different types of seismic waves?
- Primary (P) waves: Fastest, compressional waves that move through solids and liquids.
- Secondary (S) waves: Slower, only move through solids, cause more damage. Surface waves: Move along Earth’s surface, most destructive.
What are the 3 different types of faults that cause earthquakes?
- Normal faults: Occur at divergent boundaries, crust pulls apart.
- Reverse (thrust) faults: Occur at convergent boundaries, crust is compressed.
- Strike-slip faults: Occur at transform boundaries, plates slide past each other.
What are the 2 primary hazards of earthquakes?
- Ground shaking: Causes buildings to collapse.
- Surface rupture: Cracks and displacement of land along faults.
What are the 3 secondary hazards of earthquakes?
- 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.
How do tsunamis form? (Mention 2 things)
- Underwater earthquakes cause seafloor displacement, pushing water upwards.
- Waves travel fast in deep water and slow in shallow water, increasing height.
What are the 3 impacts of tsunamis?
- Widespread coastal flooding.
- Infrastructure destruction (homes, roads, power lines).
- Loss of life due to fast-moving waves.
Where do most earthquakes occur? (Mention 2 things)
- Along plate boundaries, particularly in convergent and transform zones.
- The Pacific Ring of Fire is the most seismically active region.
Can earthquakes occur away from plate boundaries? (If so give an example)
Yes, intraplate earthquakes happen due to ancient fault lines and mantle hotspots (e.g., New Madrid Seismic Zone, USA).
When and where did the Gorkha earthquake occur? (Mention 2 things)
- 25 April 2015, magnitude 7.8.
- Epicentre near Kathmandu, Nepal.
What were the 3 primary impacts of the Gorkha earthquake?
- 9,000 deaths, 22,000 injuries.
- 600,000 buildings destroyed.
- Landslides and avalanches blocked roads and buried villages.
What were the 3 secondary impacts of the Gorkha earthquake?
- Tourism decline (Everest climbing season cancelled).
- Food and water shortages due to damaged infrastructure.
- Aftershocks continued to cause damage.
What were the 3 immediate responses to the Gorkha earthquake?
- Search and rescue operations by Nepalese army.
- International aid sent (e.g., India and China provided relief supplies).
- Tents and temporary shelters set up for displaced people.
What were the 3 long-term responses to the Gorkha earthquake?
- Stricter building codes to make infrastructure earthquake-resistant.
- Rebuilding efforts with international funding.
- Improved disaster preparedness through early warning systems.
How can earthquakes be predicted? (Mention 3 things)
- Seismometers detect small tremors.
- GPS monitoring tracks crustal movements.
- Historical data helps identify high-risk areas.
What 3 strategies can reduce earthquake damage?
- 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).
What is the focus?
where the pressure is released underground and where the energy radiates out from.
What is so special about the focus?
This is the place with the strongest waves that cause the most damage.
What is the epicenter?
the point directly above the centre of the earthquake on the earth’s surface.
What are seismic waves?
when energy is released from the focus in shock waves.
What are the 3 types of earthquakes?
1) Shallow-focus
2) Deep-focus
3) Underwater
What are shallow-focus earthquakes?
Earthquakes in which the focus is 0-70km under the Earth’s surface.
What are deep-focus earthquakes?
when an earthquake has a focus which is 70-700km under the Earth’s surface.
