Primary and Secondary Hazards of Earthquakes & Impacts Thereof Flashcards
What is ground movement as a hazard?
Surface seismic wavs cause the most severe hazards to humans; buildings collapse, gas and water pipes severed.
Near the epicentre, which waves do the most damage?
S and P. Unconsolidated sediment can amplify shaking and differential damage can happen as a result of different surface materials, such as San Francisco topography.
In the 1989 Loma Prieta earthquake, what was the impact of ground shaking?
It was a MM 7.1 with 98% of economic loss due to ground shaking.
41 of the 67 dead were due to a freeway which collapsed due to its construction on mud.
Which types of building are most dangerous?
Poorly buik, unreinforced structures with heavy tiled roofs are most dangerous.
What happened in the 1988 Armenia earthquake?
88% of buildings destroyed within 5km, but 95% destroyed within 35km due to soft foundations and no earthquake proofing.
What is liquefaction?
Loose sediments can become water-saturated and act as a fluid, increasing pore water pressures. Poorly compacted sands and silts below 10 metres the surface are most affected.
This caused buildings to collapse in the Christchurch NZ earthquake.
How are landslides, rockslides and avalanches secondary hazards?
Severe ground shaking causes slopes to weaken and fail, causing slides. Especially dangerous in mountainous areas (48 dead on Mt Everest in Nepal quake). Post-earthquake landslide risk varies with topography, rainfall, soil and forestry.
What happened in the Peru 1970 earthquake?
Rock avalanche formed a 50m high wave at 70 m/s, killing 18,000 in 4 minutes.
How are tsunamis formed?
They are the most destructive secondary hazard. Generated at subduction margins, and need a 6< earthquake with vertical displacement, causing ocean waves that spread out and take debris towards land, gaming power in the process.
How many have died from tsunamis since 1900?
500,000, with over half of that as a result of the 2004 Indian Ocean tsunami.
What are the 4 factors in severity of an earthquake?
Wave energy, water depth, coastline and topography.
What are primary effects?
Immediate consequences, damage from shaking and deaths from people hit by tiles. From 2000-2017, over 800,000 died to primary effects.
What changes in environment can result from landslides and tsunamis?
Land can be uplifted or subside. The 1976 Alaska earthquake saw some areas uplifted by 9 metres.
What are secondary effects?
Effects in the days following, such as air pollution from fires or combustion from leaking gas mains. Contamination from sewage resulted in 739,000 cholera cases in the 2010 Haiti earthquake.
Physical infrastructure can be destroyed.
What does recovery mainly depend on?
The economic status of an area, in a HIC there are management plans in place and financial contingency plans allocated.