Tectonic Hazards Flashcards
1
Q
what are P waves?
A
- fastest wave, first on seismogram
- compression and expansion of waves
- passes through solids, liquids and gasses
2
Q
What are S waves?
A
- transverse waves, sideways movement
- second fastest
- passes through solids but not liquids
3
Q
What are L waves?
A
- Surface waves
- responsible for all the damage
- High amplitude
- slowest type of wave
4
Q
what is the Richter scale?
A
- ranks magnitude from 1-10, measuring the amount of energy released
- works logarithmically (each increase in magnitude is 30x more energy released)
- 0-1 = cannot feel these
- 5 = damage done to weak buildings in epicentre
- 9 = rare but causes unbelievable damage
5
Q
What is the Mercalli scale?
A
- measures from 1-12 in Roman Numerals
- based on observations about the strength of earthquakes in different locations, by damage caused and life lost
- light - felt in doors by many, and outdoors by few
- violent - general panic, very weak constructions collapse
6
Q
What is the Moment Magnitude scale
A
- Updated version of Richter scale
- 32x increase in the amount of energy released between levels
7
Q
what are the primary hazards of earthquakes?
A
- ground shaking
- surface faulting
8
Q
what are the secondary hazards?
A
- Ground failure + liquefaction
- landslides and rockfalls
- Debris flow + mudflow
- Tsunamis
- avalanches
9
Q
What are the impacts of hazards?
A
- loss of life and livelihood
- total/partial destruction of buildings
- interruption of water supplies
- breakage of sewage systems
- loss of public utilities (gas, energy, etc.)
- floods from collapsed dams
- release of hazardous materials
- fires
10
Q
Factors affecting earthquake damage
A
- strength and depth of earthquake and number of aftershocks
- population density
- type of buildings
- time of day
- distance from epicentre
- type of rocks/sediments
- secondary hazards
- economic development
11
Q
what is ground shaking and displacement?
A
- the horizontal and vertical movement of the ground
- settlements close to epicentre and the geology is unconsolidated with a high water content will experience the greatest shaking
- ground movements cause the displacement of rocks along fault lines
12
Q
what is liquefaction?
A
- occurs when waterlogged sediments are agitated by seismic shaking
- separates the grains from each other which reduces the load-baring capacity and acts like a liquid
- can leave large areas covered in a deep layer of mud
13
Q
how do Tsunamis occur?
A
- earthquakes that occur underwater can cause the sea bed to rise, leading to the displacement of water
- when the ocean is deep the waves have a height of less than 1m and have a wide wavelength of up to 200km meaning they can go undetected
- wave height increases rapidly when it approaches shallow water
- water in front of the wave is pulled back out to sea which is called drawdown
14
Q
factors affecting Haiti’s vulnerability to 2010 earthquake
A
- Poor building – houses with no earthquake resistance.
- Poorest country in western hemisphere – 70% on less than $2 a day.
- Life expectancy – 60yrs old
- IMR – 86 per 1000
- GNI - $660 pa
- Long history of unstable governments.
- 86% of people in Port-au Prince lived in slum conditions
- Lack of awareness and coherent emergency plan.
15
Q
Factors affecting Christchurch’s limited vulnerability to earthquakes
A
- Having access to preparation measures:
- hazard mapping
- Education
- Monitoring of seismic activity
- Greater building regulations
- Evacuation orders
- close political ties with other HICs (being member of commonwealth)
16
Q
immediate responses to Boxing day tsunami
A
- fresh water, water purification tablets, food, sheeting and tents came in aid
- medical teams and forensic scientists arrived
- UK government promised £75 million and public donations of £100m followed
17
Q
long term responses to boxing day tsunami
A
- £372m donated by British public a year later - only £128m had been spent by the DEC due to organisational issues
- rebuilding - DEC spent more than £40m on projects in Sri Lanka and Indonesia - plans to spend a further £190m the following year building 20,000 houses
- Indian ocean tsunami warning system set up in 2006 - none previously
18
Q
Earthquake prediction
A
- looking for patterns (relies on there being the same amount of slippage between each dislocation, the rate of deformation within the crust is constant and the friction along the fault line is constant)
- looking for deformation (strain meters, GPS measurements, Microcracks and Radon Gas, major slips)
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