EQ + Resultant Hazards Flashcards
1
Q
What is an earthquake?
A
- series of vibrations or seismic waves that originate from the focus (the point at which the plates release their tension or compression suddenly)
- a large earthquake can be preceded by smaller tremors known as foreshocks + followed by numerous aftershocks
2
Q
What occurs after an earthquake?
A
- two types of body waves occur = P-waves + transverse S-waves
- these are a series of oscillations at right angles to the direction of movement
- P-waves are travel by compression + expansion + able to pass through rocks, gases + liquids
- S-waves travel with a side to side motion + can only pass through solids
3
Q
What influences the pattern of shocks/vibrations?
A
- nature of rock + sediment beneath the ground
- unconsolidated material such as sand shake in a less predictable way than solid rock
- P-waves can turn solid sediments into fluids like quicksand by disrupting sub-surface water conditions (liquefaction)
4
Q
Primary hazards of earthquakes
A
- ground shaking
- surface faulting
5
Q
Secondary hazards of earthquakes
A
- ground failure + soil liquefaction
- landslides + rockfall
- debris flow + mudflow
- tsunamis
6
Q
Impacts of earthquakes
A
- loss of life, loss of livelihood
- total or partial destruction of building structure
- interruption of water supplies
- breakage if sewage disposal systems
- loss of public utilities e.g. electricity + gas
- floods from collapsed dams
7
Q
How are earthquakes caused?
A
- pressure created by moving plates
- this increases the stress on rocks = the rocks deform + eventually give way + snap
- the snapping is the release of energy
8
Q
What does the size of the earthquake depend on?
A
- thickness of descending slab
- rate of movement
- size of fault = determines amount of energy released
9
Q
How is the strength of an earthquake measured?
A
- Richter scale
- mercalli scale
10
Q
What is the Richter scale?
A
- measures the magnitude of an earthquake
- the scale is logarithmic = EQ of 5.0 is 10x more powerful than 4.0 and 100x more powerful than 3.0
11
Q
What is the mercalli scale?
A
- measures the magnitude of an earthquake, presenting the rate of destruction caused
- the scale has a definite end of 12
- the mercalli scale is subjective = sometimes disputed as it is dependent on human development being present rather than strength of the seismic waves
12
Q
Examples of mercalli scale
A
- 3 = slight, felt by people at rest, like a passing truck
- 5 = rather strong, dishes broken, bells rung
- 7 = very strong, noticed by people in autos, damage to poor construction
- 10 = disastrous, many buildings destroyed
- 12 = catastrophic, total destruction
13
Q
What does the magnitude of an earthquake depend on?
A
- depth of focus
- conservative boundaries have the shallowest boundaries, meaning they are closer to the epicentre + seismic waves are stronger
- convergent boundaries usually have deeper focuses, meaning the seismic waves are spread over a larger area before they reach the epicentre
14
Q
Characteristics of EQs
A
- frequency = occur everyday (smaller ones that can’t be felt not felt occur everyday, but larger ones are less frequent)
- regularity = follow no pattern + are random
- predictability = almost impossible to predict, microquakes may give some indication but the magnitude can not be predicted
15
Q
Primary + secondary environmental hazards
A
- Primary = fault lines which destroy the environment + liquefaction
- Secondary = radioactive materials + other dangerous substances leaked from power plants, salt water from tsunamis flood fresh water ecosystems, soil salinisation
16
Q
Primary + secondary economic hazards
A
- primary = businesses destroyed, immediate payout for response
- secondary = economic decline as businesses are destroyed (tax breaks etc.), high cost of rebuilding + insurance payout, sources of income lost
17
Q
Primary + secondary social hazards?
A
- primary = people killed or injured due to being trapped under collapsed buildings, homes destroyed
- secondary = gas pipe ruptures starting fires, water supplies contaminated as pipes burst = spreading diseases + causing floods, tsunamis which lead to damaging floods
18
Q
Primary + secondary political hazards
A
- primary = govt buildings destroyed
- secondary = political unrest from food or water shortages, borrowing money for international aid, can be initial chaos + ‘lawlessness’ e.g. looting
19
Q
Hazards caused by earthquakes
A
- shockwaves
- tsunamis
- land slide + avalanches
20
Q
How do earthquakes cause shockwaves?
A
- when two plates move side by side, friction builds up + pressure increases = this pressure is stored as potential energy
- it can not move, so the energy builds up + eventually the pressure becomes too much = plates move
- this built up energy is transferred into kinetic energy which is released + vibrates throughout the ground
- the further away from the focus, the weaker the shockwave as the energy is transferred into the surroundings
- this shaking alone causes many hazards e.g. builds + infrastructure collapsing
21
Q
How do earthquakes cause tsunamis?
A
- when an oceanic crust is jolted during an earthquake, all of the water above the plate is displaced
- the wave has a long wave length (100km +), high velocity (up to 800kph) + low amplitude (height)
- as it gets closer to the coast, the water becomes shallower due to friction with the bed = forcing the waves to become compressed into a smaller area
- this causes the wave to slow down + amplitude increases = creating a wall of water that is on average 10 feet high, but can reach 100 feet
22
Q
How do earthquakes cause liquefaction?
A
- during an earthquake shaking draws water up through capillary action to the surface
- soil becomes weaker + more likely to subside when it has large weight on it
- the saturated sand/soil/clay now acts like a liquid + buildings will sink into it
23
Q
How do earthquakes cause landslide + avalanches?
A
- movement in the soil or now will cause it to become unstable
- this can cause huge areas to give way, sending large amounts of debris or snow to tumble downhill
- this can damage infrastructure + buildings, damage the environment + pose a huge threat to life
24
Q
Japan 2011 EQ + Tsunami
A
- EQ magnitude = 9.0
- 180 km section of sea bed raised by 5-8m in less than 5 mins
- wave reached coast at a height of 10m+, travelling at 200 kph + travelled 10km inland
- peak height of 40.5 m
25
Q
Impact of 2011 Japan EQ
A
- 15,856 deaths —> 92.4% deaths caused by drowning
- world’s most expensive disaster = $309 bn
26
Q
Impact of liquefaction
A
- can cause ground pipes to fracture or vehicles to sink
- the main damage is to the foundations of buildings + can cause irreplaceable damage
