Basics of seismic hazards Flashcards
Occur along
All types of plate boundaries
Focus
Point of pressure release in the crust
Epicentre
Point above focus on crusts surface
Types of shockwaves
longitudinal and transverse
Features of a longitudinal wave
Faster
Travels through solids and liquids
Vibrates in direction of travel
Features of transverse wave
Slower
Travels through solids only
Vibrates at right angles
Primary hazards of an earthquake
Ground shaking
Ground rupture
Secondary hazards of an earthquake
Liquefaction Landslides Tsunamis Fires - from broken gas mains Collapse of buildings
Explanation of a tsunami
Giant sea waves
Generated by shallow focus underground earthquakes
Low wave height at sea
High wave height at shore
Immediate reduction in sea level - called drawdown
E.g of Tsunami
Tohoku, Japan 2011 Earthquake 70km offshore Magnitude of 9.0 40m height Penetrated 10km inland 16,000 deaths 127,00 buildings destoryed Fukushima nuclear power plant damaged
Explanation of Liquefaction
Loose waterlogged sediment lose strength in response to ground shake
E.g. of liquefaction
Mexico city
Lies on a lake bed
E.g of landslide
Laguna Miguel in California, USA
Management strategies
Hazard resistant structures - retrofitted, roof weights, shock absorbers, birdcage structures
Education - kits and instruction
Fire protection - gas cut offs
Emergency services - 1st aiders, computer modelled aid maps
Land use - schools & hospitals in low risk areas, open spaces
Insurance - for rich areas
Aid - availability of water, medical supplies, tents
Tsunami detection - automated systems on buoys
Measured using (3)
Richter scale
Mercalli scale
Moment magnitude scale
