Seismic Hazards Flashcards
How deep is a shallow focus?
0-70km
How deep is an intermediate focus?
70-300km
How deep is a deep focus?
300-700km
How is an earthquake measured?
Richter scale or Mercalli scale
What are the primary effects of earthquakes?
Ground shaking
Ground rupture - visible breaking and displacement of the earths surface
What are the primary effects of earthquakes?
Soil liquefaction - violently shaken soil with high water content lose their mechanical strength and behave like a liquid
Landslides/avalanche
Tsunamis
Fires
What is the width and height of a tsunami?
Very long wave length - over 100km
Low wave height - under 1 metre
(When reaching shallow water bordering land they increase rapidly in height - excess of 25m)
What is the speed of a tsunami?
700km/h
How do people know a tsunami is approaching?
The wave trough in front of the tsunami results in a reduction in sea level, known as a drawdown.
What do the effects of a tsunami depend on?
The height and distance travelled of the waves Length of event Extent of warnings Coastal physical geography Coastal land use and population density
What caused the 2004 Boxing day tsunami in Sumatra?
9.0
25km shallow epicenter
How many people were killed in the 2004 Boxing day tsunami in Sumatra?
300,000 people
What were the main effects of the 2004 Boxing day tsunami in Sumatra?
Damage to infrastructure and economies
Cost less than $5 bilion
What was the response to the 2004 Boxing day tsunami in Sumatra?
A warning system was set up among countries in the Indian Ocean
What caused the 2011 Japan tsunami?
70km offshore earthquake with a magnitude of 9
What was the effects of the 2011 Japan tsunami?
16,000 deaths
6,000 injuries
127,000 buildings destroyed
$235 billion cost
How can we predict a seismic hazard?
Areas at risk can be identified through plate tectonics
Monitoring groundwater levels
Release of radon gas
Animal behaviour
Close studies of fault lines can often indicate next earthquake (studies of san andreas showed a seismic gap in Loma prieta)
How can we prevent a seismic hazard?
Studies into lubricating the movement between the plates so that they don’t get stuck and cause an earthquake
But it’s almost impossible to prevent a seismic hazard
How can we protect against a seismic hazard?
Hazard resistant structures Education (e.g. disaster prevention day - drills) Preparing emergency services Land use planning Insurance Tsunami protection
What is tsunami protection?
Automated systems to give warnings
Pressure sensors under buoys to measure the pressure under the water
Warning systems like klaxons
How can we make hazard resistant structures?
-Large concrete weights on top of buildings which moves in the opposite direction to the force of the earthquake to counteract the stress
-Rubber shock absorbents in the foundations
-Cross bracing to the structure to hold it together better
Older buildings can be retrofitted
What was the cause of the Haiti 2010 earthquake?
7 magnitude
13km epicenter
25km west of Port-au-Prince
What was the risk and vulnerability of the Haiti 2010 earthquake?
Port au prince lies on the junction of the North American and Caribbean plates
Experienced several storms prior to the earthquake causing damage and 800 deaths
Poorest country in the western hemisphere
What were the major effects of the Haiti 2010 earthquake?
160,000 deaths
300,000 injuries
250,000 houses destroyed
Vital infrastructure destroyed (meaning it was harder to reach injured people)
All hospitals in Port au Prince were destroyed
Damage to communications
Education system collapsed - 1,300 schools destroyed
Spread of disease - over 8,000 died in a cholera outbreak
