Tectonics Flashcards
Hazard Risk Equation
Risk = (Event x vulnerability) / Capacity to cope
Determine magnitude - Richter scales, P&S waves or moment magnitude
Determine intensity - Mercalli (amount of damage), which could be affected by local conditions
Look at the power/energy of the event, how much risk different people are at, and how well the event can be dealt with
What’s the effect of the earthquake on Japan?
- High damage made Japan economically vulnerable, and they were cut off from the global economy
- Globalisation affected the impact on Tohoku, and countries who import Japanese goods
- Poorer, low income people live in the high risk areas e.g. marshy land, hills, near rivers or volcanoes
What is the Pressure and Release Model? The relationship between hazard + wider context?
- Shows what we should tackle to reduce risk of disaster
- A good capacity to cope can still mean that a large disaster has a sudden, negative effect
- Wider context can change what’s happening in a certain area e.g. tectonic plates in Tohoku
What are the factors of the PAR model?
- Unsafe conditions: landslides block roads, concrete infrastructure, building structure and codes (physical env), specific groups at risk
- Dynamic pressures: population growth, deforestation and agricultural dependency, rapid urbanisation
- Root causes: less funding in rural areas (economic system), tension between governments means less aid (political system), no focus on aseismic construction
Park’s model
- Helps plan what to do and track what stage you’re at
1. Pre-disaster - modify cause and event
2. Hazardous event
3. Search, rescue and care
4. Rehabilitation, modify loss and national/international help
5. Reduce vulnerability and restore normality (rebuild infrastructure)
Park’s response curve for diff hazard events and diff stages of development
- Varies depending on size/timing of hazard event and the country it hits
- Need resilience and efficiency
- Kashmir: emerging country but developing area, Stage 3
- Christchurch: developed, Stage 5 (not prone to hazards, so limited prep)
- Tohoku: developed, Stage 1 (well prepared, but better architecture/tech)
Earth’s internal structure
- Crust, mantle, outer core (liquid metal swirls + movement creates earth’s magnetic field), inner core
- As you go deeper, pressure and temperature increase melting point (harder to melt)
- 90% of heat at depth from radioactive decay in mantle
- Some latent heat from core
Mantle convection
- Magma creates convection currents
- Closest to melting point at asthenosphere
- Partially melts due to decompression, closer to melting point as pressure decreases, forms magma chambers under divergent boundaries
Seafloor spreading
- New oceanic crust is formed through volcanic activity, then slowly moving away from the ridge
- Ridge push causes seafloor spreading
Ridge push and slab pull
Mid-ocean ridge slides away under gravity and forced apart in opposite directions
Slab pull - force behind tectonic plates, subduction zones pull the plate down
Lava flows and pyroclastic flows
- Molten magma viscosity depends on amount of SiO2, buildings can be burnt or covered
- Bubbles of magma in vent burst + eject hot gases/pyroclastic material (glass, pumice, crystals, ash), deposits cause secondary hazards
Ash falls and gas eruptions
- Carried into atmosphere, falls locally causing roof collapse, difficulty breathing, bury crops/vegetation and can disrupt flight paths (engine blade abrasion)
- H2O vapour means heavy rainfall, SO2 particles in stratosphere cause acid rain, fluorine concentration increases so contaminates farmland/water supply
Lahars
- Water with volcanic deposits flows along valleys
- Heavy rain or ash in humid air, then condensation
- Fast and carry lots of material (60km/hr and 50m deep)
Tectonic mega-disaster regional significance (Iceland)
- Ash cloud reached N Italy meant flight disruptions in Europe but reduced air/noise pollution
- Had to travel on land so more traffic + higher train prices
- Europe econ lost $5 million
What is the global significance of Iceland’s tectonic disaster?
- Affected as far as Japan and industries in Asia
- Kenyan flower industry lost $2 million of produce
Tectonic disaster economic and human impacts
- African economy lost $65 mil
- Airlines lost $1.1 billion
- Knock on effect from cancelled events
- Ash affected health in S Iceland
- Postponed political events
Strategies to modify event
- Need to monitor gas emissions, clouds and faultline strain
- Tilt-ometers measure ground deformation
What does land use zoning and hazard resistant design involve?
- Keep residential/commercial areas away from all volcanoes, but hard due to fertile soil
- Retrofit buildings and cross-bracing, but expensive and needs govmt legislation
Engineering defences and diversion of lava flows
- Sea walls/mangroves absorb tsunami wave energy, backup utility for hospitals/police stations, drain craters to prevent lahars
- Spray seawater to solidify lava and make basaltic rock
How tsunamis are caused at subduction zones due to seabed displacement (and slab pull)
- Oceanic crust goes beneath continental
- Reduced melting temperature in asthenosphere from seawater
- Pull is force behind plates, causing EQ
- Seabed thrusts up from sub-marine EQ, then tsunami occurs
How are tsunami waves formed?
- Water column creates tsunami waves, which radiate out at 800km/hr
- Get closer to coast, slow down from seabed friction to 40km/hr
- Wavelengths shorten, waves catch up, amplitude increases and wave breaks
Variables affecting tsunamis
- Distance from source (lose energy over distance)
- Offshore bathymetry (shallow/deep)
- Coastline orientation
- Shape of coastline (estuaries funnel and cause larger amplitudes)
- Coastal topography (height) and geology
- Extent of vertical fault displacement (therefore amt. of water displaced)
Benioff Zone
- Planar zone that corresponds with slab going down
- Speed/movement of rock produces EQs
- Locked faults create more frictional resistance (greater stress)
Focal depth
- Can be deep or shallow
- If deep, EQ may lose energy as it reaches the surface
What factors of EQs and slopes increase stress? (landslides)
- Change focal depth (higher moment magnitude)
- Change moment magnitude
- Higher slope (more avalanches/freeze thaw)
- Higher mountain uplift (more precipitation)
How EQs, volcanoes and slopes decrease strength (landslides)
- Amount of folding (steeper slope)
- Lava type (doesn’t flow far, making land steeper)
- More hydration melting (explosive and andesitic lava)
- EQ destroys vegetation
What is a multiple-hazard zone?
- Two or more natural hazards
- Sometimes simultaneously, producing a complex disaster
What do hydrometeorological hazards involve in the Philippines?
- Tropical monsoon climate in SE Asia’s typhoon belt
- Increased risk of storm surges, floods and landslides
- El Niño periodic droughts causes wildfires
What is the hydrometeorological contribution to tectonic disaster?
- Plate boundaries in Ring of Fire, coasts face Pacific Ocean so are tsunami prone
- Events leave steep rugged slopes and poor vegetation
Hazard management cycle
- Response - emergency services
- Recovery - fixing everything e.g. lava removal, sorting out housing
- Mitigation- reduce vulnerability (of people)
- Preparedness - capacity to cope, putting plans/infrastructure in place
What makes capacity to cope difficult (Catania)
- Each eruption is difficult - fractures in different places, lava viscosity and gas eruptions vary
- Unexpected timings of minor eruptions
- Computer modelling data may not always be accurate
- Crucial infrastructure is vulnerable - single road access to ski resorts, towns, and limited airport alternatives
- High financial cost in poor part of Italy
P Waves
- Short wavelength
- Travel fast through solid and liquid
- Push and pull in direction of travel
- Trigger warning systems and aid immediate response
S Waves
- Slower and longer wavelength
- Only move through solid rock
- At a right angle to the direction of travel
L Waves
- Slowest but most destructive
- Only move at surface
- Largest amplitude and shakes from side to side
How are crustal fracturing and ground shaking caused by EQ waves?
- The energy released cracks crust and vertically displaces land
- Shaking causes infrastructure collapse
Secondary hazards from EQ waves
- Liquefaction: shaking destabilises the soil, increasing space between grains, so soil flows like liquid
- Landslides: increased stress on rock slopes
Inequality of access to education influences vulnerability (Nepal)
- Difficult to access damaged school in a mountainous environment
- High illiteracy rates with 70% of men, 40% of women
How does access to housing influence vulnerability? (Nepal)
- Nepalese share inherited property, so tall thin houses are vertically split
- 5 mil crammed in shoddy, concrete buildings, narrow alleys and hillsides in Kathmandu
How does access to healthcare influence vulnerability? (Nepal)
- Close contact spreads disease/infection, worsened by undernourishment
- Rural areas have 3 hour walk through mountains to the hospital
- Patients develop drug resistance and need specialist treatments in the capital city
How do income opportunities influence vulnerability? (Nepal)
- Caste structure creates division
- Many live in stone/mud houses that collapse from EQ tremors
- Concrete dwellings often occupied by higher caste
Local, national and global governance for management (general strategies)
- local: Might organise evacuation strategies
- national: Finance emergency care or mandate education strategies
- global: Coordinate a tsunami warning system
How isolation, accessibility and degree of urbanisation influence vulnerability (Bam)
- Desert oasis located in isolated part of Southern Iran
- Nearest major town is 200km away, so difficult to get help quickly
- Links East and West civilisations (trade route to Pakistan) but not developed/urban itself
Spearman’s Rank
- When ranking pairs, if the variable number is the same, use the middle number of the ranks
- Degrees of freedom is n-2
- Rank coefficient must be above the critical value to reject null hypothesis
What does prediction and forecasting accuracy involve?
- Statistical projections
- Build models of magma movement/measure EQ stress
- Can’t have accurate location or timing
How does prediction depend on type and location of hazard?
- It costs to change city life
- Communication between scientists and government being unclear means they can’t do much
- Persuade govmt to have building regulations and evacuation plans
Strategies to modify vulnerability
- High tech monitoring: computer models of ground movement and disaster potential, sensors tag buildings as safe or not
- Prediction: ShakeAlert (SMS warnings)
- Education: annual Golden Guardian exercise to simulate EQ
- Community preparedness: California State Law means multiple people in charge
- Adaptation: emergency operations centre, 180 seismic retrofits
- Models forecasting impacts: interdependence between energy and utility systems to get them working asap
General EQ management strategies
- EQ proof buildings: more money to reinforce or just repair after collapse
- Insurance: high EQ chance so high premiums, or take chance to save up and rebuild after
- High econ cost is a problem, so need to map chance of EQ
- Move financial services onto internet to continue trading and business when buildings collapse
Who needs emergency, ST and LT aid in San Francisco?
800,000 residents 100,000 tourists 300,000 commuters 20% disabled population Homeless population
Insurance
- Premiums go up and are more than property value (just pay to rebuild after)
- Or premiums do not cover cost of damage so insurance companies have to pay for it
Role of NGOs in relief
- NGO volunteers can help fire department
- CARD (community agencies responding to disaster) connects nonprofit + private orgs to provide essential items
Role of media as an actor
- Media is a non-state actor, but provides short term response, as they provide news immediately and give updates over a few months.
- Mostly social media, so they need to grab attention quickly over a few seconds, because they are profit orientated
- Show statistics, damaged areas, and upset people (disaster capitalism)
Intra-plate EQs
Not on plate boundaries
Mantle plumes
- Occur at areas of mantle where magma and heat rises
- Increase in heat and decreased pressure melts lithosphere base (crust)
Hot spots
- Magma exploits cracks and accumulates, and sometimes the mantle plume is more intense than usual
- Volcanoes form and move away as tectonic plate moves over stationary hotspot
- Sea level rises and cover the volcanoes that have moved away, then fills the crater, growing vegetation and possibly forming coral reefs
- Leads to atolls, volcanic islands and seamounts
Trend in number of deaths, number of affected and econ damage since 1960
- More megacities so more people living in hazardous areas, but number of deaths decreasing
- 1960 population was less than 3 billion, but now 7.3 billion, so naturally more affected
- Increased economic costs with more development
- Main change is hydrometeorological and effects of climate change
What are issues with reliability of data to interpret complex trends?
- No agreed definition or how to measure
- Number of those affected is subjective
- Methods of reporting have changed so hard to compare with previous data
- Don’t consider informal economy
- Understated or overstated by govmt
What are factors of a hazard profile?
Magnitude, speed of onset, duration, areal extent, spatial predictability, frequency
Profile doesn’t usually include human geo but can choose to add it in
