Plate Tectonics (Factor of EQ, Hazards of EQs, risks and benefits of volcanoes) KQ2 Flashcards
Factors affecting extent of EQ damage
1) Magnitude
2) Level of Preparedness
3) Population density
4) Distance from Epicenter & depth of focus
5) Type of Soil
6) Time of Occurrence
How does Level Of Preparedness affect damage of EQ?
Def: amt of preparations takes by authorities and citizens
-Makes EQ more manageable and people are better prepared.
e.g. Tohoku EQ, 9.0 mag, 2011, Japan - 28,000 deaths
Haiti EQ, 7.0 mag, 2010, Carribeans - 300,000 deaths
How does magnitude of EQ affect damage of EQ?
Greater Magnitude, larger extent of damage and destruction
How does Population density affect damage of EQ
Def: Number of people living in the affected area
- Sparsely populated: less affected
- Densely populated: heavily affected, mass casualties and damage
How does distance from epicenter affect damage of EQ?
Epicenter Def: Directly above focus on surface
- Closer the area to epicenter, the more severe the damage
How does depth of focus affect damage of EQ?
Focus def: Origin of EQ in crust
-Affects magnitude of EQ
1) Deep Focus
- 70 - 700km below surface
- Seismic waves take longer time to reach surface = smaller impact
- Most energy lost to surroundings
- Lower magnitude
2) Shallow Focus
- 0-70km of crust
- Seismic waves reach land surface more quickly
- Less energy loss
- Higher magnitude
How does timing of EQ affect damage of EQ?
- Time determines where people are and what they are doing
- Affects chance of survival
-Night: Sleeping = trapped = more casualties - Day: Active = Quick responses = more survive
e.g. 2,400 deaths aft 1999 Sun Moon Lake EQ in Taiwan aft midnight.
How does type of soil affect damage of EQ?
-Loose, unconsolidated soils amplify seismic wave vibrations = greater mg
- Saturated and unsettled sediments liquify under vibrations = sinking of infra (Liquifaction)
e.g. 2011, Christchurch, NZ.
Tsunamis
Def: Large sea-waves formed by high-energy tectonic activities displacing large masses of water.
1) Seismic energy displaces huge volumes of water
2) Starts at heights of less than 1m, length of 100-150km and speeds of 800km/hr
3) When reaches shallower waters = greater friction = slow down = height increase
4) Reach heights of 15m and speeds of 30-50km/hr
5) Sea may retreat to fill void caused by movement of seafloor.
Tsunami example
2004, 9.2 mag EQ, Indian ocean.
-Tsunami damaged coasts of 12 countries
- heights of up to 40m, reaching 10km inland
Effects of Tsunamis and EQs
1) Disruption of services
2) Destruction of Infra
3) Destruction of property
4) Fires
5) Landslides
6) Loss of Lives
How are services disrupted during tsunami/EQ?
Def: Disruption of essential services such as electricity, gas and water, affecting large areas
- snap pipes, break cables, affect communication and power networks.
Disruption of services (Tsu/EQ) example
Kobe EQ, Japan, 1995
-Damaged pipes, and transmission lines, affecting power gas and water
-Affected 1.4 million residents
-Burst gas pipes caused city wide fires
Fires during EQ/tsu
- Gas pipes burst, petrol gas escapes
- Exposed cables may spark, setting flammable materials on fire
- Fire can spread easily and quickly over large areas.
- Causes injury and death
Fires (EQ/tsu) example
Kobe EQ, Japan, 1995
-Toppled appliances sparked fires
- Firemen unable to manage fires due to no water supply, strong winds, extensive fuelling and fast spreading of fires.
How are landslides caused during EQ/tsu
Def: Rapid downslope movement of soil, rock and vegetation debris from a slope
- Vibrations destabalise soil
- slopes weaken and sediments slide
- Can reach speeds of 40 - >80km/h and stretch for a few km wide
-Mudflows occur when soil is saturated
Landlisde (EQ/Tsu) example
Peru EQ, 1970
-Destabalised Mount Huascaran
-Landslides >160km/h
-Flattened town of Ranrahirca
-Killed, >18,000 people and only 200 survived.
