Hazards: Seismic Hazards (earthquakes) Flashcards
1
Q
What are the primary hazards to earthquakes?
A
ground rupture and ground shaking
2
Q
What are the secondary hazards of earthquakes?
A
Soil liquefaction, fires, building collapse, landslides/avalanches and tsunamis
3
Q
What are the 5 forms of seismic hazards?
A
- earthquakes
- shockwaves
- tsunamis
- liquefaction
- landslides
4
Q
What are earthquakes?
A
A sudden violent shaking of the ground, from the release of tension between plate margins
5
Q
What are shockwaves?
A
Vibrations sent out by the focus of the earthquake (what we feel as the ‘earthquake’)
6
Q
What are tsunamis?
A
Large waves caused by the displacement of large volumes of water
- can be triggered by underwater earthquakes and waves radiate out from the epicentre of the earthquake
7
Q
What is liquefaction?
A
Soil is saturated with water, the vibrations of an earthquake can act like a liquid (makes the soil weak and deform)
8
Q
What are landslides?
A
Shaking of the ground can dislodge rock, soil or snow causing landslides/avalanches that move downslope quickly
9
Q
What is the spatial distribution of seismic hazards?
A
- most occur along plate boundaries (e.g. destructive or constructive)
- faults produce earthquakes at conservative plate boundaries (e.g. San Andreas Fault is a complex zone of fractures of crust)
- however they can occur away from plate boundaries, reactivation of old fault lines or human activity (fracking)
10
Q
What is the magnitude and frequency of seismic hazards?
A
hundreds of low magnitude earthquakes happen globally everyday
earthquakes of high magnitude occur less often
11
Q
What is randomness vs regularity of seismic hazards?
A
seismic hazards don’t seem to follow any clear pattern or trend, occurrence is largely random
12
Q
What is the predictability of seismic hazards?
A
scientists can monitor the movement of tectonic plates to predict which areas are at risk
hard to tell when an earthquake will strike a particular place or the magnitude of it
13
Q
What is the case study of an earthquake in a place of low HDI?
A
Haiti earthquake 2010
14
Q
What are the characteristics of the hazard in Haiti?
A
- 7MMS
- destructive plate boundary
- focus was deep, 13km
15
Q
What is the evidence of a disaster of Haiti earthquake?
A
- 160,000 deaths
- 188,000 buildings collapsed or destroyed
- $11.5billion in damages (120% of GDP)
16
Q
What are the characteristics of the place/people in Haiti?
A
- unconsolidated geology and steep terrain
- corrupt government
- building codes not enforced
- dense, informal settlements
- poorest country in the western hemisphere
- high poverty (19% have access to sanitation)
- fatalistic attitudes
17
Q
What is the case study of an earthquake in a place of high HDI?
A
South Napa Earthquake, California 2014
18
Q
What are the characteristics of the South Napa earthquake?
A
- 6MMS
- conservative plate boundary
- shallow focus of 11km
19
Q
What is the evidence of a disaster of South Napa earthquake?
A
- 1 death and 200 injured
- only older buildings suffered damage despite being retrofitted (4 destroyed)
- fires broke out
- $362 million in damages
20
Q
What are the characteristics of the place/people in South Napa?
A
- stable government, building codes enforced including landuse planning
- well planned residential zones
- excellent emergency services
- adaptation perception
21
Q
What 3 things affect the magnitude of an earthquake?
A
- margin type
- rate of movement of the plate (this is slightly unclear)
- depth of focus (deep focus, 300-700km, tend to have a higher magnitude however the waves have to travel further
22
Q
Assess the methods of measuring earthquakes
A
- Richter scale measures the magnitude (how powerful the shaking is), no upper limit with a logarithmic scale allowing for quantitative data comparison
- Moment Magnitude Scale (MMS), measure the total release of energy, qualitative data of energy release, allows comparison between events, more accurate than Richter, however doesn’t tell us about impacts on humans
- The Mercalli Scale measures real world impact, qualitative data (meaningful description of hazard intensity), allows comparison, however doesn’t link damage to characteristics of place = weak understanding of the event
23
Q
What is the pattern of frequency and magnitude of seismic hazards?
A
Constructive plate boundaries have high frequency but low magnitude
Conservative have a moderate to high frequency with a moderate magnitude (more frequent earthquakes are lower magnitude, lower frequency earthquakes are high magnitude)
Destructive plate boundaries have a low frequency but a high magnitude
24
Q
Do seismic hazards show a relationship between frequency and magnitude?
A
- as frequency of seismic hazards increases the magnitude decreases
- for example constructive plate boundaries have a high frequency but low magnitude seismic hazards
- low magnitude earthquakes tend to have a high frequency
- high magnitude have a low frequency
- conservative plate boundaries are in the middle of this distribution
25
Do seismic hazards show a relationship between hazard intensity and areal extent?
- most earthquake hazards have a high hazard intensity but small areal extent
- primary hazards have a high hazard intensity and a low areal extent such as ground rupture
- some secondary hazards such as soil liquefaction and building collapse have a small areal extent but a larger hazard intensity
- landslides have a larger areal extent
- tsunamis are the exceptions to this pattern
26
What is the case study of a seismic hazard in a low HDI country?
Haiti earthquake 2010
27
What are the characteristics of the Haiti hazard?
```
7 MMS
destructive plate boundary
deeper focus (13 km)
```
28
What are the facts about the disaster in Haiti?
160 000 deaths (8000 died to due cholera outbreak)
188 000 buildings destroyed
Education system collapsed (1300 schools destroyed)
Collapse of sanitation, water supplies lost and unburied bodies led to spread of disease
$11.5 billion in damages (worth 120% of Haiti's GDP)
29
What are the characteristics of the place/people in Haiti?
- unconsolidated geology and steep terrain
- corrupt government
- building codes not enforced
- dense informal settlements
- poorest country in Western Hemisphere
- high poverty rate
- fatalistic attitudes
30
What is the case study for an earthquake in a country of high HDI?
South Napa Earthquake, California, 2014
31
What are the characteristics of the hazard in South Napa?
6MMS
Shallower focus (11km)
Conservative plate boundary
32
What are the facts about the disaster in South Napa?
- 1 death
- 200 injured
- older buildings damaged (some even retrofitted)
- 6 fires broke out
- damage to the wine industry
- $362 million to $1 billion costs
33
What are the characteristics of place and people in South Napa?
- unconsolidated geology and steep terrain
- stable government
- building codes enforced including land use planning
- well planned residential zones
- excellent public services (+ FEMA)
- adaptation perception
34
Q: Assess the factors that determine the impact of an earthquake?
- Characteristic of place or people determine impact the most
- Physical characteristics determine the impact the least (however, the energy released and depth of focus can influence extent of the shear and surface waves, causing the greatest damage to buildings)
35
Q: Assess whether the secondary seismic hazards are more dangerous than the primary seismic hazards?
- secondary impacts can be managed and mitigated
- primary impacts are a natural unstoppable force (ie. ground shaking)
- secondary impacts can be extremely dangerous (e.g. building collapse in Haiti earthquake killed 188000) but with proper management can have a reduces severity (e.g. evacuation for tsunamis following earthquakes in Japan and earthquake proof building constructed in Napa), however are only dangerous when there's no management
- extent of secondary hazards is determined by management
- ground can shake and nothing can happen (in rural areas) but human development causes secondary hazards to be dangerous
36
What are P waves?
Pressure waves
- push and pull waves
- fast
- do the least damage
- longitudinal waves
37
What are S waves?
Shear waves
- transverse waves
- slower
- cause significant waves
38
What are Surface waves?
Rayleigh waves
- ripple through the ground
- most dangerous
- low velocity, high amplitude
39
Management of seismic hazards: prevention?
- impossible
- however can prevent them being a large risk to human life, for example not building on land that's prone to soil liquefaction
40
Management of seismic hazards: prediction?
- predicting when an earthquake will occur is mostly very difficult
- however fault lines can be monitored, magnetic fields measured and predicting what the impacts may be by hazard zoning maps
- a seismic survey of the San Andreas fault predicted the October 1989 Loma Prieta earthquake due a 'seismic gap'
41
Protection/preparation: hazard resistant structures
- withstand earthquakes
- use strong/flexible materials or building foundations that absorb the energy or retrofitting older buildings
- The 1989 Loma Prieta earthquake killed 63 people (6.9 MMS) whilst the 1988 Armenian earthquake (6.8 MMS) killed 25000, mostly from collapsed buildings
42
Protection/preparation: education
- teaches people how they should respond during an earthquake and encouraging people to prepare themselves
- this includes school drills
- Government offices and many companies in Japan observe Disaster Prevention Day (1 September) which marks the anniversary of the Tokyo (Kwanto Plain) earthquake in 1923
- the American Red Cross issued a list of supplies that people should keep at hand in case of an earthquake
43
Protection/Preparation: fire prevention
- cutting off gas supply to homes when an earthquake strikes
- ‘Smart meters’ cut off gas automatically
- Tokyo, the gas company has a network that transmits seismic information to a computer which then informs employees where to switch off major pipelines
44
Protection/Preparation: Emergency services
- appropriate training, adequate resources and proper technology
- preparation in California involves the establishment of computer programs that will identify which areas the emergency services should be sent to first
45
Protection/Preparation: land use planning
Most hazardous areas in the event of an earthquake can be identified, putting schools and hospitals in areas of low risk
Including having sufficient open spaces, as this forms a safe area away from fires and aftershock damage to buildings
46
What are the short-term responses to seismic hazards?
Occur immediately before, during or after the hazard event
- these include: deploying emergency services, distributing aid, evacuation if threat of a tsunami, rescuing people from collapsed buildings etc
47
What are long-term responses?
aimed to mitigate the impacts of future hazards by managing the risks
48
What was the response to the earthquake in Haiti?
- major relief programme (international governments and agencies), little resources in the country, extremely difficult
- US deployed 3500 troops and UK sent out search and rescue teams
49
What happened in the post-disaster phase of Haiti earthquake?
- in 2014 170000 were still in displacement camps, 23% children not at primary school, 70% lack electricity and 600,000 food insecure
- extremely slow management back to normality
- however lots of debris is removed and new building codes are being enforced
- some of Haiti's debt has been written off
50
What was the response to the South Napa earthquake?
- 144 repairs to water mains
| - immediate emergency care in Valley Medical centre
51
What was the post-disaster response to the South Napa earthquake?
- building restored and renovated
| - geologists studied the event and pre warned the fault moving another 1.5cm in the next 3 years
52
Q: Evaluate the strategies to manage seismic hazards?
- The most effective strategies need to take place before the hazard
- shortens relief and recovery time period, normality is returned sooner
- Managing the hazard during and straight after the hazard is the least effective way
- however these can still save lives, e.g. evacuation for a tsunami
53
What will affect the impact of a tsunami?
- the height of the waves
- distance they have travelled
- length of event from source
- the extent to which warnings could be given
- coastal/physical geography, both offshore and on the coastal area
- coastal land use and population desnity
54
Q: To what extent do you agree that seismic events will always generate more widespread and severe impacts than volcanic events?
ALWAYS is the debate word
- earthquakes tend to have more severe impacts but volcanoes have more widespread impacts
- however the characteristics of the place affected can cause the impacts to vary from this pattern
