seismic and storm hazards Flashcards
what is an earthquake?
- a sudden or violent movement within the earths crust followed by a series of shocks
how is an earthquake formed?
1) earthquakes are caused by the tension that builds up at all three types of plate margins ( destructive, constructive and conservative )
2) when the plates jerk past each other it sends out shockwaves, due to the release of energy
3) the shockwaves spread out from the focus, the focus doesn’t have to be a single point - e.g. it could be along a fault line, near the focus the waves are stronger and cause more damage
4) the earthquake is felt first at the epicentre
5) earthquakes cause the ground to shake, and sometimes to rupture along the fault
what is the epicentre?
- the point on the earths surface above the focus, where the earthquake is felt first
what is the focus?
- the place where the energy is released
- an earthquakes focus can be close to the earths surface or deep below it
- a deeper focus earthquake tends to have a higher magnitude that a shallow focus earthquake, however deep focus earthquakes do less damage than shallow as the shockwaves are generated deeper in the earth so have further to travel to reach the surface, so their power is reduced
where are the biggest earthquakes located?
- the biggest earthquakes occur at destructive plate margins, where one plate is forced beneath another at the subduction zone, e.g. Benioff zone, they are very powerful and can occur under the sea
- the subduction of a plate causes massive pressure to build up, causing a huge earthquake when released
- earthquakes at constructive margins tend to be shallower and less powerful and can occur along the mid-Atlantic ridges away from people and land
- earthquakes at conservative plates are shallow and focused as continental plates drag past one another causing high compressions, meaning they are very powerful and can be severe if they occur in densely populated areas
how can earthquakes be measured?
1) the Richter scale
2) the moment magnitude scale
3) the modified Mercalli scale
what is a Richter scale?
- the Richter scale- measures the magnitude of an earthquake ( how powerful the shaking is ), it is logarithmic meaning an earthquake with a magnitude of 5 has an amplitude ten times greater than one with a magnitude of 4
what is a moment magnitude scale?
- the moment magnitude scale- based on the total amount of energy released by an earthquake, it is more accurate than the Richter scale especially for large earthquakes so is more widely used
what is a modified Mercalli scale?
- the modified Mercalli scale- measures the impacts of an earthquake using observations of the event ( e.g. reports and photos ), the scale is between 1 and 12 with 1 being an earthquake that’s only detected by instruments and 12 being an earthquake that causes total destruction
- it is easier to understand and shows the effects of the earthquake on people e.g. people awakening, movement of furniture or total destruction
what are the 3 seismic shock waves?
1) primary pressure waves- these are the fastest and first waves to arrive at the surface
2) secondary / shear waves- these are slower than primary waves and reach the surface next, they have a higher frequency and can travel through the mantle
3) love waves- slowest waves and can cause the most damage as they move side to side
how do we prevent an earthquake?
- the majority of seismic hazards cannot be prevented however:
- liquefaction of soils can be prevented through soil stabilisation ( gravel columns can be put in the ground )
- avalanches can be prevented through controlled explosions
how can we prepare for earthquakes?
1) within homes, any heavy items,
( such as TVs, refrigerators and bookcases ) should be secured and breakable items stored at a low level
2) families should create a communication plat e.g. WhatsApp groups and establish emergency meeting routes and places
3) households should have an emergency supply kit to last a few days containing essential items, such as food, water, clothing, bedding, a first aid kit, toilet paper, a torch, a radio etc.
4) insurance such as house and health insurance should be updated in case of damage to property or injury
5) building structures need to be solid e.g. earthquake proof buildings, so they sway, as well as shutters on windows and shock absorbers to prevent buildings from collapsing
- building materials such as wood should be used as it can flex unlike brick
how can we mitigate against an earthquake?
1) early warning systems- these give people a short amount of time to put themselves into a safer position for when the earthquake hits e.g. in Japan the ‘earthquake early warning’ system aims to reduce earthquake-related damage by slowing down trains immediately, controlling lifts and enable people to stop, drop and wait
2) hazard-resistant structures- designed to be earthquake resistant e.g. putting shock absorbers in the foundations that will allow some movement of the building without structural failure
how does adaption relate to the economic development of a country?
- long term change in people’s behaviour depends on levels of economic development, education and national and regional priorities
- e.g. countries such as the USA and Japan are generally more able to adapt their environment than those in low income countries
how do we adapt against an earthquake?
1) land use planning- includes identifying areas most at risk from seismic events and regulating land-use planning for those areas
- putting key buildings, such as schools and hospitals in low-risk areas and open spaces, such as parks in more high-risk areas
- including open spaces in plans to allow for safe areas, away from fires and aftershock damage to buildings
2) emergency services adapting- must adapt their organisation and planning to deal with seismic events e.g. heavy lifting gear needs to be available and emergency service personnel should be first-aid trained to deal with any causalities
3) having a substantial amount of search and rescue and planning before hand on who goes where
what is the case study for seismic events?
- Lombok earthquake in Indonesia 2018
- this is when a series of seismic events took place between the 29th of July and the 19th of august 2018
where is Lombok located?
- the island of Lombok in Indonesia is part of the chain of Lesser Sunda Islands, along with Bali to the west and Sumbawa to the east
why is Indonesia a high risk place for seismic hazards?
- as Indonesia is a meeting point of several tectonic plates and is one of the most seismically active places on earth
- it is a typical island arcs where the Indo-Australian plate is moving northward towards, and subducting under, the south easterly moving Eurasian plate, which moves approximately six centimetres per year
- most of the earthquakes affecting Indonesia happen along the Sunda Arc subduction zone
what are the tectonic processes occurring near Lombok?
1) this earthquake happened at a destructive plate margin where there is the subduction of the Indo-Australian plate under the Eurasian plate, forming ocean trenches, this subduction zone is named the ‘Wadati-Benioff Zone’
2) volcanoes can occur here as the partial melting of the continental plate, causes magma, which rises as it it less dense than the surrounding rock. when the volcano reaches above sea level island arcs form
3) earthquakes form here due to the friction of the two plates moving towards each other, which also forms a build up of energy that is released when the plates are past one another, causing seismic vibrations / waves
what were some events that happened during the Lombok earthquakes and how did Indonesia respond to them?
29th July 2018 a 6.4 magnitude earthquake strikes Lombok- the Indonesian Red Cross allocates money from their emergency fund to enable them to meet the humanitarian needs of 1,000 households ( 4000 people )
30th July 2018- the local state governor declared a three-day state of emergency
5th August 2018 a second stronger earthquake of 7.0 magnitude and depth of 15km strikes Lombok- the Indonesian Red Cross launched an emergency appeal for funds to assist 80,000 people affected by earthquakes in Lombok for 18 months
September 2018- an earthquake hits elsewhere in Indonesia and funds and help are diverted away from Lombok
8th November 2018- the emergency appeal asks for further funds to deliver assistance to 20,000 households in Lombok for 30 months
what were the major impacts of the Lombok earthquake?
the Indonesian National Board for Disaster Management reported that:
- 564 people died
- 1,584 people were injured
- over 445,000 people were in makeshift shelters
- over 129,000 houses were damaged
- over 432,000 persons had been displaced and were living in 2,700 displacement sites
- 458 schools were damaged
- the total cost of the damage was estimated to be around $600 million
what are the primary hazards of an earthquake?
1) ground shaking- caused by shock waves travelling through the crust from the focus up to the surface and then radiating outwards
2) ground rupture- the visible breaking and displacement of the earths surface
what are the secondary hazards of an earthquake?
- soil liquefaction
- landslides and avalanches ( slope failure as a result of ground shaking )
- tsunamis
what are the environmental effects of primary seismic hazards?
- earthquakes can cause fault lines which destroy the environment
- liquefaction can occur which makes buildings unstable
what are the economic effects of primary seismic hazards?
- businesses are destroyed, so causes economic decline as people have no source of income
what are the social effects of primary seismic hazards?
- buildings collapse, killing/injuring people and trapping them
what are the political effects of primary seismic hazards?
- government buildings are destroyed
what are the environmental effects of secondary seismic hazards?
- radioactive materials and other dangerous substances leaked from power plants
- saltwater from tsunamis can flood freshwater ecosystems
what are economic effects of secondary seismic hazards?
- economic decline as businesses are destroyed ( tax breaks etc. )
- high costs of rebuilding and insurance pay out as sources of income are lost
what are the social effects of secondary seismic hazards?
- gas pipes rupture, starting fires which can kill
- water supplies are contaminated as pipes burst, spreading disease and causing floods
- tsunamis lead to damaging flooding
what are the political effects of secondary seismic hazards?
- political unrest from food and water shortages
borrowing money for international aid, so development of country decreases as money is earmarked for development may have to be spent on repairing damage - can be initial chaos and ‘lawlessness’ e.g. looting
what happens during soil liquefaction?
- during an earthquake shaking causes soil particles to move
- in waterlogged conditions such as below the water table, a loss of shear strength occurs due to the particles losing contact with each other
- therefore, the soil behaves as a liquid and the soil loses the ability to support it’s own weight and buildings tilt or even collapse
- on a slope liquefaction causes soil to move downwards
what is a tsunami and how is it formed?
- giant sea waves generated by shallow-focus underwater earthquakes involving movements of the sea bed, or landslides into the sea or volcanic eruptions, underwater debris and large landslides into the sea
- tsunamis have a long wavelength, sometimes over 100km, a low wave height ( under one metre ) and they travel at speeds of over 700km per hour
- 90% of the most damaging tsunamis occur in the pacific basin, generated at subduction-convergent plate margins
what is the formation of a tsunami?
1) tectonics upthrust in the form of earthquakes or floor volcanoes that cause vast dissipation of water
2) energy from the quake causes a train of simple, progressive waves to propagate over the ocean surface in ever-widening waves that reach speeds of 500 mph, as the wavelengths continue to grow
3) as the waves approach the coastline they slow down due to friction with the seabed, the velocity lessens but the amplitude increases
- wavelengths hit the shore and the outflow of water continues to cause damage
give an example of a major earthquake and it’s effects.
- march 2011, off the Pacific Coast of the Tohoku region of Japan
- the earthquake occurred 70km offshore and had a magnitude of 9.0, the most powerful earthquake ever recorded in Japan
- triggered waves of 40 metres high
- nearly 16,000 dead and over 6000 injured
- over 300,000 people were made homeless
- an estimated economic cost of Japan being £235 billion
how do we prepare for a tsunami?
1) tsunami warning systems- this is when sea bed pressure sensors are used to detect the sea pressure
- these send information to a surface buoy, which constantly measures the pressure of the overlying water column to warn the population before the wave reaches the land
what are tropical storms?
- tropical storms are huge spinning storms with string winds and torrential rain that develop over warm oceans (27 degrees)
- most begin 8-20 degrees north and south
what is the structure of a tropical storm?
- tropical storms are circular in shape, hundreds of km wide and usually last 7-14 days, they spin clockwise in the northern hemisphere and anticlockwise in the southern hemisphere
- at the centre of the storm, there is an area of low pressure called the eye where the weather is calm
- rising air spirals around the eye in the eyewall, where there is high pressure, cause strong wind and condensing, sinking air causes bands of rain
- near the top of the storm, there is an outflow of moisture-laden air, so cloud cover extends for a long distance either side of the eye
where do most cyclones, hurricanes and typhoons form?
cyclones- Indian ocean
typhoons- north west
hurricanes- south east ( Caribbean )
what conditions do tropical storms have to be under to occur?
temperature- ocean temps must be around 26-27°C and at least 50 metres deep, warm water provides the storm with energy
air pressure- must be in areas of unstable air pressure, usually where areas of high pressure and low pressure converge, so that warm air rises more readily and clouds can form
wind shear- winds must be present for the swirling motion to form, but not too strong or the storm system will be ripped apart in the early stages
rotation- tropical storms only form around the equator, but no less than 5 degrees on either side
what is the Coriolis effect?
- the effect of the earths rotation on weather events e.g. the storm spins because the earth is spinning; but there is no Coriolis effect at the equator
describe the formation of a tropical storm.
1) warm, moist air rises, leaving an area of low pressure below, this causes warm air from surrounding areas of higher pressure to move into this low pressure area and rise too
2) the warm air rises and cools condensing into a thunderstorm cloud
3) the whole system is spinning due to the Coriolis effect
4) the constant addition of energy from the warm air causes the storm to spin faster and generate higher wind speeds, at 39mph the storm is classed as a tropical storm
5) the eye of the storm is in the centre, this is an area spanning around 30 miles wide that is extremely low pressure, cool dry air descends in the eye, causing the weather to be calm and cloud free ( the more intense the storm the clearer the eye )
6) surrounding the eye is the eyewall ( the most intense and powerful area of the storm ), where warm, moist air rapidly rises with extremely high winds and torrential rain, when wind reaches 74 mph it becomes a hurricane / cyclone/ typhoon
7) when the tropical storm reaches the coast, the low pressure and high winds cause large amounts of sea water to be taken up and then released as a high wave called a storm surge
8) when the storm reaches land, it no longer has a supply of energy ( warm, moist air from the sea ) and the eye eventually collapses, and heavy rain can persist for days