14.3 Hazards generated by seismic activity Flashcards
What is an earthquake?
A release of stress that has built up within the earth’s crust caused by tension
What is the focus?
Point in the Earth’s crust where rocks fracture, releasing energy
What is the epicentre?
Point at the surface directly above the focus
How many people were killed by earthquakes between 2000-2015?
800,000-900,000
What types of hazards are associated with earthquakes?
- Ground shaking and ground displacement
- Liquefaction
- Landslide/avalanches
- Tsunamis
Ground shaking: what does the severity depend on?
Earthquake magnitude
Distance from the epicentre
Local geology
Ground shaking: what areas will experience extreme ground shaking x4 + example:
Locations close to the epicentre of a high-magnitude quake and where surface layers are unconsolidated with a high-water content
Eg Kobe earthquake 1995
Ground shaking: what are the major hazards?
- rip apart pipelines/sewers,
- sever railways
- cause building collapses (can withstand vertical movements better than horizontal ones)
- divert rivers away from groundwater supplies
Liquefaction: what is it?
When an earthquake strikes an area that consists of fine-grained sands, alluvium, and landfill with a high water content, the vibrations cause materials to behave like liquids
Liquefaction: what happens as a result?
Materials lose their strength causing slopes to collapse and foundations to give way
Liquefaction: example
1995 Kobe earthquake – much of the port had been built on reclaimed land in Osaka Bay destroying 200 berths = world trade affected
Landslides and avalanches: what areas are susceptible?
Steep slopes in mountainous regions eg Himalayan range
Landslides and avalanches: what are 3 consequences?
- Transport routes can be blocked where accessibility is already limited
- Rivers can be blocked creating temporary lakes which can threaten areas downstream with catastrophic floods eg 2005 in Kashmir
- Displacement of water in a reservoir could overtop a dam eg 1963 northern Italy, hillside collapsed above Vaoint reservoir generating a 100m wave that drowned 3000 people
Tsunamis: how do earthquakes cause them?
Underwater earthquakes cause the seabed to rise vertically, displacing the water above which produces powerful waves at the surface which spread out at a high velocity
Tsunamis: height and wavelength at sea?
1m high and 200km long
