HAZARDOUS EARTH EXAMPLES

DIVERGENT MARGINS - *Iceland*

* shield build up new layers over 1000s of years
* two plates that are diverging magma forced up into the cracks and fissure the plate leaves behind crating new lands
* also located on hot spot so strange - very high pressure magma forcing way through earths curst
* combination of upwelling and plume produce volcanoes of Iceland
* Iceland comes from mantel contain lost of basalt and moves freely - BASALTIC
* fissure magma finds way between divergent plates not explosive most effusive - contains lots of gravel and thick vicious liquid piles up either side creating spater cones
* graben formed when earth moves and paltes move apart area in between subsides and creates a graben steep sided depression

MOUNT ST HELENS (MAY 18TH 1980) VEI 5

* on pacific and North American plate destructive plate boundary
* 5 miles exclusion zone in place before eruption - outside area may camped etc. saw it as safe
* when erupted the glacier caved into the mountain and huge fraciotn opened everything to the north the mountain lost 1300ft
* massive landslide trigger pressure released and ash blew sideways
* explosion of gas steam
* pyroclastic flow 700 miles per hour 1000x energy of Hiroshima bomb
* sap in trees boiled and trees taken out
* mudflows 60ft 100 miles per hour
* 540 million tonnes of material erupted into the area
* areas 150 miles away dark
* 57 killed all but 3 well outside the exclusion zone

KILAUEA, HAWAII

* Hawaii worship volcanoes - fire goddess
* 1983 village of Kalapana was completely destroyed by lava - lave creeped closer over 7 years gradually families had to move

NYIRANGONGO, CONGO (2002)

* 7 miles from Goma
* 2002 surprise
* divergent plate boundary with low silica level lava (although ash cloud are produced due to water presence in the crater)
* erupted twice in last 40 years
* 6 lava lakes
* 1.2km diameter crater
* flowed 2 days city desotyed
* petrol station set on fire
* lava flowed 40km per hour
* only 45 people lost their lives but longer term effects left 12,000 homeless

Nyirangongo, impact on area

* invisible gases of CO2 toxic to children kill live stock - volcanic observatory trying to teach children on the impacts of these
* when 2002 eruption occurred much of homes destroyed (by fast running lava flow) left many people with out access to toilets this lead to condiotns of spreading of cholera
* another affect was in 1994 when 1 million Rwandaneses refuges arrived in Congo, the volcanic rock made it very difficult to build graves so was difficult to stop cholera spread
* shape life in villages such as Sake where crops are both destroyed by ash deposit as well as fertilise later (although Nyamuragaria erupts so regularly this is less impactful)
* high levels of fluoride in water health effects such as damaging teeth - around 100,000 affect by this
* volcanos lead to valuable minerals used in touch screen tech military groups use this to found operations as well as recruit young children to work in military role of volcanoes in spread of conflict (30,000 were involved in conflict)
* national park made sewing room widowed women giving their jobs earning incomes

prediction techniques used on Nyirangongo

* infra red cameras measure level of lava lake if significantly lower then likely eruption going to occur
* gas boxes detected levels fo sulphur dioxide if more gases likely to erupt (although limited by wind etc.)
* found that lava may be even lower silica content meaning flow faster then lava did in 2002
* sounds produce indicate the level of lava in the chamber so infrasound radars used to predict

Nyamuragira, congo (2011)

* in dangerous area of Congo only accessible with military helicopters means very explosive volcano is not monitored

Tongo (2022) VEI 5.7

* underwater mountain blew its top
* sent ash and water vapour half way to space and generating tsunami waves across the globe
* New Zealand mapped the volcano shows seafloor scoured and sculpted by violent debris flows out to a distance over 80km
* 9.5km4 material displaced during the event
* loss of submarine cable connecting Tonga to global internet
* a Tsunami hit Tonga several metres high destroying beach restorts in the process

Monserrat (1997)

* destructive margin
* although much of island now abandoned
* only 19 people were killed result of mounting massive evacuation programme and exclusion zones

Iceland why live near volcanoes

* grow rapseed oil
* farming fertile
* hot water to heat homes - volcanic activity thats bedrock above water permeates and turns to steam rises cools and falls to be heat again - low cost hot water for 100,000 people
* energy 1/3 price of the UK
* blue lagoon attracts 500,000 tourist every year

Iceland volcanoes

* 30 active volcanoes
* 500m fissure effusive touriste not that dangerous
* Haimey 1973, 5,400 evacuee 1:3 choose to return lava flow reshaped area (although some people stay behind created dam cooling the lava that then built up helped prevent damage to the area)
* E16 glacial outburst floods erupted cancelled 100,000 flights and many effects on the economy (local also clogged up farmed machinery destroyed crops etc.)

Prediction/Prevention in Iceland

* evacuation
* warning
* smooth eviction
* 3D images map the height and location of ash particles helpful for airplanes preiciotn of how the ash will move knowns as ash modelling
* flood routes so know where to build levees made channel of rivers narrower on deeper

Earthquakes San Fran (1989) 6.9MW

* bay bridge broken 5 miles of cars build up
* freeway collapsed
* liquidifaction

Mexico City (1985) 8MW

* shock wave - subduction plate boundary
* 500 buildings collapsed
* buildings should have been to earthquake code but were not
* 10,000 died
* city now 10 million bigger significant earthquake could have huge effects

Turkey 2023 7.8MW conservative margin

* 50,000+
* 18% population homeless
* general election pushed back (close call)
* 7.4 million sub standard building poor implementation of building codes
* 35 billion worth of damage
* lower turnout for election
* high rates of inflation 85.5%
* women are the most effected
* not helped by Syrian war some areas did not even have governments
* 100,000 building destroyed
* weather did not help storm made camps blow away
* 20% relocated returning to effected areas

Christchruch 2010/11

* rural area M=7.4 and urban area M=6.3
* extensive damage in urban areas poorly constructed buildings and liqudification

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November 2016 Karikoura earthquake M-7.8 NZ

* rupture of multiple faults
* no large scale los of life
* but los of tranpsortation infastucutre
* 1.5 billion damage
* NZ they use insurance home for hazards that provides money for rebuilding

Improving models

* current earthquake models assume earthquakes occur at regular intervals
* new models consider the strain (pressure build up) on whether earthquakes may arrive ahead of schedule
* as earthquakes that come early may not shake out all the strain
* tested on earthquakes in the past model gave much more accurate prediction of them happening
* this should help to better predict earthquakes

Deep shake

* model help give few seconds of warning for earthquakes
* should give time to hide for example protecting from building collapse

different types of lava

Pahoehoe - smooth

AaAa- gases trapped more explosive

DESTRUCTIVE MARGINS - MONSERRAT 1995

* Subduciotn zone as oceanic crust is melted by friciotn and pressure of the matnle creates silica rich acidic lava the process produces lots of gas when eruption happen highly explosive
* large periods of inactivity
* monserat hot acidic lava is very thick rather then running down the side piles up at the top extrude lava building a dome shaped volcano
* dome volcanoes pile up lava very hot and a lot of energy if outside unstable pieces of dome fall exposing hotter material escalating activity perhaps leading to collapse creating a pyroclastic flow
* eruption of monserat, ash fall, phyroclastic flow, over time thicker and thicker chaining shape of dome
* where altanic dives under carribean their is an 800km ocean trench
* covergent plate boundaries also form fold mountains like the alpes as plates move the sedimentary rocks crumpled forcing them upwards creating rock structures seen in mountains

CONSERVATIVE MARGINS - HAITI 7M

* close to port au prince
* no warns
* 200,000 people died
* subduction and also conservative boundary two plates moving sideways
* lead to very shallow earthquake
* frictions builds up pressure jolt releasing energy in form of an earthquake
* epicentre close to capital
* in San från less destroyed compared to Haiti 1/3 was destroyed

some volcanoes more hazardous than others - viscosity of magma

* temperatures – higher temperatures the lower the density of the magma and more easily it will flow 
* dissolved gases – the greater the amount of dissolved gases, the more fludd the mgama, gases remain dissolve in high tempartues 
* chemistry – higher silica more viscous the magma

→ basic v acidic magma (gases free movement)

some volcanoes more hazardous than others - plate margins

a.     divergent moving away magma produced by the partial melting of the mantle deep below the surface, it is basic type and therefore low viscosity enabling it to flow easily. Volcanoes at constructive margins, for exmapel along the Mid-Atlantic Ridge, are both central vent and fissure erupt frequently but not usually as violentaly 

b.     destructive – plates subduct intense pressure result in acidic magma very viscous and resistant to flow there often a huge build up of pressure, which result in very violent and dangerous eruption involving ash and pyroclastic

→ 75% volcanic matieral erupted at constucitve marigns most of the world activie voclneoes occur at destructive generally these are more dangerous 

→ some volcanoes not occur at all plate margins at conservative and collision no magma produced and no volcanoes and hot spot volcanoes such as Hawaii magma is basic and similar to those on constructive margins 

explosiveness of eruptions

VEI ranges form 0 to 8 the higher the VEI the greater the potential hazard 

→ eruption with value of 0 to 1 tend to have very localised effects 

→ eruptions of 2 and more have much greater effect and huge quantities of phyroclatics being erupted with the potential of affecting both the immediate area and through global atmospheric circulation systems parts much further away 

→  Mt st. Helens with VEI of 5 more potential to be more hazardous of Kilauea VEI of 0 

material ejected

non explosive mostly lava flows not such threat to people but will destroy farmland and buildings

→  only when large part of carter collapses when there is then a real danger to people Nyiragongo

→  explosive eruption much more dangerous magma viscous cool and solidified very quickly threats include:

a.     ash clouds – explsive eruption balst solid and molten rock framgents into thea air ash carried ten or even 100s of KM away – threat to aircrafts 80 aircrafts flown into ash clouds

b.     Phyroclastic flows – reach temps of 800 dgrees travley 200kph down the volanos flanks Mt st helens

c.     laharas – mudlfows of volcanic ash and water which can travel down river valleys at speed of up to 100kph can travel 300km massive threat e.g Mt Pinatubo eruption in 1991 killed many people

d.     Tsunamis – if volcanoe eutps out to sea huge waves called tusnamis can be generated often impact on commmunites far way from volcanoes who do not consider themselves to be at risk e.g Sunda start tsunami part of caldera collapse into the sea killed 400 people

proximity to population centres

→ Japan, Indonesia active near huge cities 

→ Naples with 1 million population few km from Mt Vesuvius 

→ several reasons why people live close to volcanoes e.g Japan island limited space no choice and fertile soil, materials and hot water

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 frequency of eruptions and preception of risk 

* Hawaiian volcanoes continuously threat to people minor due to nature of eruptions is real 
*  MT Etna is also attraction for tourists and hotels and cafes flank the mountain the risk is consider worth it 
*  many poepel live really close to dangeour volcones e.g Monserat had not erupted for 350 years until 1995 – less likely to worry if not erupted recently 

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Prediction, forecasts and reactions 

* satellites infrared radiation indicates rising magma and ground instruments measure gas emissions and ground deformation 
*  hazard maps identify areas at greatest risk 
* evacuate areas e.g Mt St Helens 1980 
* government don’t always respond to preidciotn Colombia Nevado ruiz failed to evacute 25,000 died in the laharas 
* Scientists do not always get it right reducing credibility in the eyes of the government making evacuation less likely if volcanoes was to erupt next time 

COMPARING HAZARDS

* earthquake 5x more common than volcanic
* Tsunamis 4% of tectonic disasters but 33% of deaths 1;12 chance of dieting compared to 1:237 in an earthquake
* risk = hazard x vulnerability / capacity to cope
* shallow are most destructive in Benioff zones vary few km to 100s of km deep: depth dissipates earthquake energy so very deep earthquake much lower ground-shaking at the surface compared to shallow focus ones
* liquidifaciotn risk greater in coastal areas or on flood plains occur when water rises to the surface
* mountain risk of landslides
* population level
* Sunda Strat Tsunami indonesia seismic 70,000 buildings destroyed volcanic 3,500
* volcanoes 85 deaths per year 4 named events account for 73% of deaths
* predictability White Island new Zealand 2019 22 people died when new 50% chance of eruption should have been closed

DEFINITIONS OF HAZARD DISASTER RISK VULNERABILITY

* hazard -Threaten both life and property
* Disaster - when a hazard has a significant impact on people – a realisation of a hazard
* Risk - the probability of a hazard occurring and leading to a loss of lives and/or livelihoods
* Vulnerability - the risk of exposure to hazards combined with an inability to cope with them (location, environment, governanceand/or people)
* Resilience - the degree to which a society can absorb a hazardous event and yet remain within the same state of organisation – its ability to cope with stress and recover.

 

HAWAI 2018

* 800 million damage to properties
* 700 homes destroyed
* only 24 injures
* destruction of marine reserve

AFGHAN V TAIWAN EARTHQUAKES 2022

* MAG AFGHAN 6.1 TAIWANN 6.9
* BUILDING DESTORYED AFGHAN gran 80% TAIWANN several
* deaths 100 comarped to 1
* in Afghanistan taliban govenrmetn disowed by many other countries
* remote so response poor

TOHOKU 2011 9MMS

* 16,000 known deaths, 3,000 missing and 6,000 injured 130,000 buildings were destroyed and 145,000 damaged
* The inundation caused massive damage to ports, factories and services in coastal areas – over 26 million tonnes of debris was created
* Economic losses amounted to US$300 billion
* A major secondary issue arose when a nuclear power station at Fukushima was flooded and failed – there were fears of a nuclear meltdown and severe pollution.

The immediate priority was search and rescue, and stabilisationand prevention of nuclear disaster

Temporary housing was provided in huge numbers, together with long-term evacuation of the zone around Fukushima

Later, a government report was commissioned to establish principles for recovery

The report focused on future safety measures (e.g. a higher tsunami wall), greater environmental awareness for future planning (e.g. avoiding flat coastal areas) and long-term compassionate support for those bereaved and affected.

 

INDONESIA 2018 TUSANAMI EARTHQUAKE EDC

* subduction earthquake
* 2,250 deaths
* liquefaction
* mudflows
* 200,000 refugees
* 29 other countries helped

GORKHA NEPAL 7.9M

 

* Situated in the middle of the collision zonewhere the Indo-Australian plate meets the Eurasian plate
* Epicentre 90 km north east of Kathmandu
* 9000 deaths, 22,000 injured
* Economic losses of US$5 billion
* 2.8 million displaced from the Kathmandu valley
* Landslides and avalanches 1 million needed food assistance.
* Terrain meant that relief aid was slow arriving
* Severe gender discrimination in receipt of aid with thousands ofwomen missing out.
* Nepalese government was hindered by political turmoil beforeand after the earthquake.
* Asian Development Bank providedUS$200 million of aid for reconstruction
* Further geopolitical issues arose as neighbouring countries (e.g.India and Indonesia) vied with each other for greater influence within Nepal)

 

 

FORMATION CONSERVATIVE BOUNDARIES

* tectonic plates move past each other side by side
* For example, in NW Iceland, there is a conservative plate boundary.
* The land to the south is moving eastward and the land to the north is moving westward.
* They move at a rate of about 10mm per year. In the south Icelandic seismic zone.
* where the river has cut down into the surface the bedrock beside it is faulted over time stress builds up on the faults and the area then experiences earthquakes.
* for example, there 5.9MW earthquake which removed boulders, houses were damaged.
* Common for conservative boundaries to produce large earthquakes.
* Most famously the San Andres fault in California has produced several large earthquakes in recent history.
* In the south Icelandic seismic zone. The boundary runs form east to rest but fault that produces earthquakes from north to south.
* The reason for this is bookshelf faulting where the bedrock is fractured like a stack of books so as the two sides of the fault move from east to west there is movement on faults that run from north to south as the faults are twisted. 

lava divergent boundaries

*  when magma reaches the surfaced still has a temperature of 1000 degrees – molten rock that reaches the surface is lava 
*   this lava cools and solidified to create basalt
*  90% of Iceland is basalt 
*   on divergent plate boundaries and hot spots, they have low VEI lava is very runny it flows as streams of molten rock 
* low viscosity creating gentle EFFUSIVE ERUTPIONS 
* greats shallow sloping sided shield volcanoes 
* builds up in layers of basalts like this when lava cools and solidifies 
*  basalt - when melted flows easily 

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lava convergent

* oceanic crust is subducted beneath continental crust 
*  high silica content lava which gives lava lighter colour and that’s thick 
* heat high viscous creates bubbles that are trapped gases find it much harder to escape
*   pressure of gases builds and builds until reaches breaking point 
*  as result these volcanoes erupt less frequently than divergent boundaries in the middle of oceans when they do far more explosive 
* blast the magma apart shatters and cools – how volcanic ash is formed
*  create volcanoes with thick viscous layers around a vent forming composite volcanoes or Strato volcanoes e.g., volcanoes Fuego in Guatemala large explosive eruption 2018 
* in cold environment combination of lava and ice also lead to explosive eruptions – Iceland e.g., if erupts below ice leads the lava to shatter and create large vol of ash 
* when melts water vapour bubbles become trapped in exploding lava and gas tries to escape 
* E16 2010 became explosive as result Phreatomagmatic eruption cancelation of 95,000 flights 

 

some deadly earthquakes

* India 2001, 19,998 deaths transform margin 7.7MW

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earthquake magnitude and depth

* stronger magnitude more serious affects most of the most deadly earthquakes over 8MW
* shallow occur close to surface tend to result in greater intensity associated with destructive margins and subjecting plates

nature of bedrock

* liquefaction vulnerability
* Mexico City liquefied

population density

* hazard when impacts on human activity
* if near massive cities such as LA Tokyo
* 10% of popualtion lies within n earthquake zones

buildings and structural vulnerability

* in wealthier more earthquakes proof less killed
* older building vulnerably explain Kobe high death toll of 6,300
* poor parts of world codes and design inadequate may not be followed Mexico CitY 1985
* Precatoin poorly understood if activity infrequent 1993 earthquake struck centre of India unexpected many tone houses collapsed killing 10,000 people four months later in 1994 a more powerful earthquake hit LA only 40 died

extent of earthquake preparedness

* frequency and development link to this
* California and Japan compared to Haiti
* regular earthquake drills informed about dangers
* emergency response better trained
* even so best laid plans can fail Kobe emergency teams reacted slowly
* poor countries less well prepared lack of money and investment
* sometime daily struggles more pressing then infrequent earthquakes

levels of development

* LEDCS V EDCS
* poor country with less rigourous building likely to lead to greater loss of life and longer reconstruction
* in recent years some of the greater earthquakes occurred in LEDCs such as Syria and Haiti
* but also Acs affected such as Japan Tohuku 16,000 died
* economic cost may be greater in developed countries such as Japan 100 billion

nyiragonog 2002

* divergent (East African Rift Valley)
* but massive lava flow
* killed 147 people
* 40,000 evacuated to Rwanda
* example of how divergent can be deadly
* lava is particularly runny - moving up to 40 mph - because of very low silica content to do with there also being hot spot below - super plume rising from considerable depth
* obverstation centre in Goma lost support of world bank due to allegations of imbellezments (more recent 2021)

nyiragonogo lake

* scientist worried since eruption in 2021 - magma flowing towards lake kivu underground
* eruption under the lake could release toxic gases expert fears
* this is known a limnic eruption
* A limnic eruption involves the release of dissolved gases that have accumulated at the depths of a lake.

Gases such as carbon dioxide (CO2) and methane can seep into lakes through volcanic vents.

To trigger the release of these gases from the water, a disturbance of some kind is needed. 

That disturbance could be an eruption

In theory, the magma could heat up the water, causing the dissolved CO2 to mix rapidly with upper layers of the lake and escape into the air.

High concentrations of CO2 can displace oxygen in the air and affect breathing.

* In 1986, Lake Nyos released dissolved CO2 into the air after a landslide. The cloud of CO2 asphyxiated an estimated 1,800 people in nearby villages.

fuego - Guatemala 2018

* 200 died
* pyroclastic flow 700km/h
* strato cone
* explosive constructive margin
* 12 mile radius volcanic ash
* 3,700 evacuated

JAPAN - LIVING WITH VOLCANOES

* 70% of land moutianes formed by volcanic activity
* follow strongly associated with volcanoes
* mount Fiji in many culture myth etc.
* subduction zone
* 1200 volcanic eruptions is past 2000 years
* more explosive less frequent
* Ontake - strato volcano
* 3000m snow covered - some phreatic eruptions
* tourist destination, climbings, spritual pilgrame
* 27th sept 2014, erupted without warning - SUPRISE even in Acs
* killed 63
* phyroclastic flow and ash fall as well as laharas
* Japanese P order the minatory to assist with emergency operations

INDONESIA - LIVING WITH VOLCANOES

* 80 volcanoes erupted in historic times
* 3/4 of inhabitants live within 100km of a volcano
* EDCs
* subduction of indo-asutrialian beneath the eursain plate - island archipelago
* explosive toba - lake toga falls caldera
* Merapi starto volcano 3000m dome developed in the Carter which eventually collapsed producing pyroclastic flows 3-4VEI
* in 2010 VEI4 pyrcoasltic flow
* lava bombs 4km from summit
* rainy season start so triggered laharas
* closure of Yogyakarta aiport for 2 weeks
* emmisons of sulphur dioxide caused acid rain to fall over large part of the region
* 367 people were killed, 277 injured
* 410,000 refuggees
* livestock killed
* destoyred infasrucutre, balding power lines and bridges

WHY LIVE IN TECTONICALLY ACTIVE LOCATIONS?

* Places for employment and burn gap familes
* often attachment just were we have been brought up
* poverty
* Indonesia and japan exist coz of tectonics limited choice - Java pop density is 1000 people/km2
* volcanic soil java 3 crops of rice a year
* intensive farming high population density on the sides of volcanoes - japan 13% of land area for farming but very intensively
* volcanoes terraced to allow farming
* colder climates farming less of a factor
* Iceland tourists
* White Island new Zealand 2019
* hot rocks so geothermal power - Indonesia hoping to grow currently 3% but new sarulla power plant
* minerals - sulphur extracted in East Java from crater of Ijen volcano directly with hands - PH 0.5 very acid often poisonous clouds of hydrogen sulphides and sulphur dioxide

IMPACTS OF EARTHQUAKE ACTIVITY JAPAN

* 400 every day
* subduction zone
* since 2000 23 7MW+
* offshore plate boundaries so risk of tsunamis
* 2011 9MW between pacific and north American plates
* six minutes long
* undersea
* moved Honshu island 2.4m east
* 400km stretch of coast dropped 0.6m
* sea bed rose by about 7m and moved westwards by 40-50m
* waves 40.5m 10km -melted ice in Antartica, California 10 million image
* 110,000 nesting birds in wildlife refuge

IMPACTS OF EARTHQUAKE ACTIVITY JAPAN - social

* 16,000 lives
* 2/3 over 60
* 90% due to drowning
* mass mortality meant tradicoanl funeral methods had to be waived - mass graves to stop disease
* 100,000 children effect
* 2000 children without parents
* 74//108 died in one school
* destruction of school moshing and health centres - relocate communities

IMPACTS OF EARTHQUAKE ACTIVITY JAPAN - economic 

* 200 billion dollars
* 230,000 vechiles destoryed
* 15 ports effected
* 4.4 million lost eeleciricy
* 11 nuclear reactors shut down
* Fukushima power planet - meltdown of reactor realse of radioactivity 30km evacuation zone - soils contaminated with radioactivity
* radioactivity condintue to seep into pacific effecting fishing
* power cuts eocnci cost
* 2 oil rehires court fire
* 23 statations swep away
* farmland flooded by sea water has been contained by salt and made uncultivable
* japan stock market feel Sony Toyota
* overseas supply chains effected

IMPACTS OF EARTHQUAKE ACTIVITY JAPAN - poltical  

* Japanese gov inject billions of yen into the economy, especially the finacial sector - to bring some stability
* this increased government debt at a time when its reduction was a prime poltical aim
* popular movement against nculcuer power enveloped after the tohomu earthquake
* concerns over safety standards and regulation fo the nuclear industry - political issues
* it emerged warnings against tsunami hazards risk made many years before
* anit nuclear lobby used it as argument in Germany

HAITI - 2010

* voclanic island arc
* mostly 4MW
* but the earthquakes on the Enriquillo fault much large east eh 2010 earthquake is
* conservative margin
* 7MW
* slip along 40km section of the enriquillo fault
* 12km focus
* no seismic network to record the earthquake

HAITI SOCIL IMPACTS

* around 200,000 deaths
* 22 gov buildings desotryed
* gov corrupt and weak
* 1.5 million living in camps
* 300,000 houses destroyed
* 30,000 commercial buildings destroyed
* many destroyed poorest areas of city built on slopes prone to landslides
* still 30,000 living cmaps
* before 50% no access to fresh water, over 1/2 had no basic healthcare
* natural resources exploitative over deforestation rapid depopulation of rural areas to urban areas - slums
* cholera epidemic 800,000 cases and 10,000 deaths
* 2009 149th in HDI now 169th
* number underounoursihed increased to 3.7million

HATITI ECONOMIC AND POLITICAL IMPACTS

* exploited for reduces destroying rainforest in past
* for independence instead on ocmepntion not repaid until 1947
* US support series of dictators that served there interests
* neo liberal under cut farmers
* all serving to undermine development
* largest income source remittances 25% of GDP
* next aid 20% of GDP

MORE ON RISK/HAZARD VULNERALIBTY/RESLISANCE ETC.

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hazard - events such as eruption becomeahzards when they pose a risk to people

risk = vulneralibty x frequency or mag of hazard/ capacity o population to cope and adapt

disaster - actual event loss of life and damage to the environment both human and natural

greater magnitude less frequently it occurs - reoccurrence interval lower

vulneralbity - ability of person or community to withstand exposure to and risks form hazard such as an earthquake or volcanic eruption

resilience - is an indication of the rate of recovery from a hazardous event - how able society able to function at an acceptable level when a forces effects them

10 most serious earthquakes

1. HAITI 2010 200,000
2. indonesia 2004 230,000
3. china 2008 90,000
4. pakistan 2005 86,000
5. sri lank 2004 35,400
6. iran 2003 26,800
7. india 2001
8. japan 2011
9. india 2004
10. neapl 2015

9/10 EDCs or LIDCS

10 most serious volcanic eruptions

1. Indonesia 2010 322
2. DRC 2002 200
3. Japan 2013 63
4. INdonesia 2014 32
5. Colombia 2008 16

manging tectonic hazards - modifying the event

not possible for earthquakes and mostly volcanic but

* lava diversion channels
* spraying Alva to cool it so it soldifies
* slowing lava by dropping concrete blocks

modifying peoples vulnerability

education → what to do when eruption occurs e.g evauciton, drills, open space, shelter under table

community preparedenss e.g budding of tsunami shelters and walls, strenghting of public budilenges e.g. hospital fir stations and schools

prediciotn of warning → increasing use of tencnolgoy to monitor paricturaly active locations e.g individual volcanoes

hazard-resistant building design → cross bracing of budliigns to support them during an eartqhuka;sttep sloping grooves to rpevent ash budilign up

hazard mapping → predicted lahara routes; gourd lielkyt to liquify in an earthquake

land use zoning to avoid budiogn in location indietfyed by hazard mapping

modifying peoples lose

emergency aid e.g. bottle water, medical supplies, tents, food packs

disaster response teams and equipment e.g. Helicopters and heavy lifting machinery. sears and rescue strategies

insurance

resources for rebuilding public services eg help to rebuild individual homes

Aseismic design

* steeped profiel stability against sacking
* soft sores may lead to collapse and assymertical can make them more susceptible to collapse
* budding on soft soils and slopes bad better to coat flats surfaces and do not have ehgih building densities on slopes
* steeled frame building
* deep foundations - on soft soils prevent effects of liquefaction
* shock absorbers - absorb energy (rubber tyres filled with stones also effective in EDCs)
* cross bracing

all dependent on how rigoursly budding codes are applied - Turkey

RETRO fitting expensive

important key buildings such as hospitals protected

INDONESIA - MODIFYING VULNERALBITY

* centre fo volcanology and geological hazard mitigation
* independent lead to potlcial tensions and violence among competing groups lead to little focus on volcanic
* 60 volcanoes monitored
* some gas emissions, inflation as magma rise dn earthquake e activity measured
* lahars threat high so larger seniors and close cirrus TV have been insulated to monitor areas are risk
* hazard risk map
* CVGHM works with lcoal govenremtns
* pamrenet settelement forbidden on the highest slopes of merpai
* encourage to relocate to safe zones in some cases receiving finacial assistance and even plots of land to incentivise the move

INDONESIA MODIFYING LOSS

* often famileis return rebuild and accept the risks (fatalism)
* lower middle income country resources limtied
* many farming communities affected have limited resouces
* some well trained and well equipped emergency services
* expreicenced mitlary in search and rescue
* temporary shelters in safe zones amiable in case of evacuation
* cleared river channels of volcanic material limit risk of flooding and laharas
* some of this material used to rebuild housing and facilities

IATLAY MODYIFING EVENT

* diversity lava flows with concrete blocks

ITALY MODIFYING VULNERALIBTY

* volcano risk service
* long term analysis of eruption patterns compared with international eruptions that are similar
* constant monitoring e.g seismometers, tilt meter, gas emissions satellite saver
* infra rad to detect heat and daily and weekly bulletins are issued
* well estlaibhes alert level sequence understood by emergency services - all levels of gov and local communities
* closure of airports and air space when threatened by ash
* work to identify houses at risk and offer affordable solutions such as adding pitched roofs to allow ash to fall off

MODIFYING LOSS - ITALY

* well pracise
* houses farmers and lemon groves destroyed in recent decades
* italy gov can compensate individuals and restore budliigns
* casualties minimal timely evauciotn based on accuarte data
* well trained public services
* but still if eruption like vesusvies close to Naples 600,000 in red zone survival rate ow and evuaciotn plans are pronely understood
* false alarm evacuation expensive and reduce effectiveness when they are necessary

HAITI - MODYIGFING VULVNERALIBYT

* focused more on frequent challenge of hrurainces meaning budding concrete buildings which are not very good for tectonic ahzrdds
* 15 seismic stations but non earthquake proof or 24 hours
* hazard maps showing risks ere soft sediment liable to liquifiaciotn
* no national disaster risk management plan; no Jpananeses style eudcioant programme
* inability to enforce Jeahtquk budding design been 12 PM since 2010
* Bureau of mines and energy whcih oversees earthquake surveillance has an annual budget of just 600,000 use 0.04% of national budget

HAITI modyfing loss

* NGOs
* 5.3 billion but 1% went to gov and 0.4% Haitian NGOs

Red Cross rehousing scheme:

* raised 486 million USD built 6 houses
* USAID planed to built 15,000 with 59 million built 900 construction sight was 130 miles away from capital
* number of 750 house/900 built to earhtquake standards 0
* US taxpayer money used to fix problems with 750 house 21 million
* 2/3 reamins in banks of NGoOS
* scandal around behaviour of senior NGO officials

JAPAN MODYIFYING VULNERALIBTY

* JMA
* warn gins
* detailed disaster palling for gov, medical services, fire mialtry, transport etc.
* aseismic design e.g steel frames, shock absrobers, deep foundations, counter weights on the roofs, suspension bridges capable of movement rather than rigid design, flexible pipes
* fire proofing older building which common in Japanese cities
* land use zoning that provides for open spaces were people can assemble after an earthquake
* controling budilng in locations suceptiobel to excessive ground shaking or liquefaction
* tsunami warning systems off the coasts
* refugee sites on permanent, stand-by equipped with tents, bottle water blankets
* community preparedness ongoing edcuaotin and training for all ages

JAPAN MODYIFING LOSS

* vast reduces
* well rehearsed recovery and reoncstuciotn
* regionala nd local levels
* action imemidaly
* aim to rebuild as quick as possible less long term damage perhaps

STRUCTURE OF THE EARTH

o   The core and mantle are separated by a distinct boundary at a depth of about 2900km.

o   The mantel curst boundary is marked by the Homoeroticism discontinuity (Moho)

* Its depth below the continent average around 35km to 5-15km below oceans

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*Asthenosphere* 

o   100km to 300km

o   Although solid flow under pressure 

*Lithosphere* 

o   Lying immediately above this is the lithosphere a right layer sandwiched between crust and the asthenosphere

o   Lithosphere varies in thickness 

o   As pressure increases with depth and the rock becomes less rigid and can flow 

o   Together the Lithosphere and curst make up oceanic and continental plates 

*Role of convection currents* 

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o   Within the asthenosphere convection currents exist caused by vast amounts of heat generated deep in the mantle – as a result the asthenosphere flows carrying with it the solid lithosphere and crust

CURST V MANTLE

 

Thickness

Density (kg/m3)

Mineral composition

Crust

Continental- Mean 35km 

Oceanic- 5-10km

Continental- 2.6-2.7

Oceanic- 3.0

Continental- Mainly granitic, silicon, aluminium 

Oceanic -Mainly basaltic, silicon and magnesium

mantle

To a depth of 2900km

3\.3 at Moho 5.6 at core

Rich in magnesium and iron 

SEA FLORR SPREADING

Biologically  similar fossils brachiopods found in Australia and India limestone, similar fossil animals in south America and Australia especially marsupials 

Geologically  fit of continents such as south America and Africa, evidence of glaciation in southern Africa, Australia, India suggesting they were joined, mountain chains and rock sequences continue across oceans e.g., Canada and northern Scotland 

*palaeomagnetism*

o   Accidently, Echo sounders used to locate submarines showed for the first time the existence of a mid-Atlantic ridge 

o   Subsequently a pattern of magnetisms was discovered in the basaltic rocks making up the ocean floor 

o   They showed mirror images of repeated stripes as you moved away from the mid-Atlantic ridge 

o   Igneous rocks cool the iron minerals within them would line up in such a way to indicate the north pole was at the time of their formation 

o   Rocks formed at the same time on either side of the Atlantic ridge pointed to different locations separated by thousands of kilometres 

o   These locations could be pulled together by closing the Atlantic Ocean – evidence for continental drift 

o   The stipes reflect the fact eh earth polarity was not constant every 400,000 to 500,000 years polarity changes (palaeomagnetism)

o   The width of each strip of ocean bd with the same magnetic orientation was found to correspond with time scale of each magnetic reversal 

o   The symmetrical pattern of geomagnetism reversals on either side of ridge indicated fresh molten rock form the asthenosphere reached the ocean bed and older rock was pushed away from the ridge 

o   SEA-FLOOR SPREADIN moves material across the ocean floors as a conveyor belt either side of the ridge eventually the sea floor reaches an ocean trench where material is subducted into the asthenosphere an becomes semi molten 

It was clear that the plates were moved by sea floor spreading from the mdi ocean ridges to subduction at ocean trenches this support Wegener’s findings 

mid ocean ridges

1\.     Plates are divergent 

2\.     Magma is rising through the asthenosphere and forcing its way to surface 

3\.     These plumes of rising material are especially notable at mid ocean ridges 

4\.     Mid ocean ridges consist of very long chains of mountains in places rising 3000m above the seabed 

5\.     Added together these submarine mountain chains have a combined length of 60,000 km 

6\.     They are not continuing and are broken into segments by transform faults These faults displace the ridge laterally by tens or in places hundreds of kilometres

7\.     Volcanic activity is absent along transform faults as it is on conservative margins, but as they slip, energy is released in the form of earthquakes 

8\.     The eruption of magma along divergent boundaries occurs mostly underwater. Magma erupting directly on to the seabed is cooled rapidly forming rounded mounds called pillow lavas

9\.     As magma rises to the surface the overlying rocks can be forced up into a dome 

10\.  The rigid lithosphere is place under greater stress and eventually fractures along parallel faults producing the underwater rift valleys found along mid-ocean ridges 

1\.     At mid ocean ridges sea water seeps into rifts and is superheated 

2\.     As it rises towards the surface it causes chemical changes in the basaltic rocks

3\.     Superheated jets of water sometimes re-emerge on the ocean floor containing metal sulphides

4\.     These features are commonly known as black smokers and support unique and highly specialised organism and ecosystems

OCEANIC-CONTINETIAL

 

1\.     The denser oceanic plate is forced under the continental plate = subduction 

2\.     deepening the ocean forming an ocean trench (long with depths of 6000-11000m)

3\.     the oceanic crust descends into the asthenosphere pulling the rest of the ocean plate with it = slab pull

4\.     Doing so means the leading edge of the continental plate is buckled forming a trench 

5\.     Sediment and rock develop on the oceanic plates  

6\.     As the oceanic plate converges on a continental plate these sediments and rocks crumple and are uplifted along the leading edge of the continental plate 

7\.     The continental crust is buckled, and uplifted, and significant amounts of molten material are injected into it 

8\.     Leads to mountain chains such as the Andes on the pacific coast of south America 

9\.     Oceanic plate subducts between 30-70 degrees as it descends it comes under intense pressure and friction = faulting and fracturing in the Benioff zone – realising lots of energy in the form of earthquakes 

10\.  Oceanic plates contain lots of water as subduction takes place the pressure and temperature increase dehydration occur triggering partially melting of the overlying plate 

11\.  this molten material rises toward the surface as plutons of magma

12\.  Huge intrusions of magma create further uplift of fold mountains 

13\.  Where rising magma reaches the surface, a volcano will form 

oceanic - oceanic

1\.     Two oceanic plates meet

2\.     older and denser one will subduct under the other creating a trench 

3\.     Dehydration take space causing partial melting of the mantle wedge

4\.     Magma rises to the surface forming chains of volcanic islands = island arcs 

5\.     EXAMPLE: the central Atlantic the north American plate is subducted beneath the smaller Caribbean plate forming Antilles Island arcs 

6\.     Large earthquakes are extremely common on these convergent boundaries 

7\.     80% of earthquakes are in Pacific Ocean as largely convergent 

8\.     Mariana trench 11,000m lies where the pacific plate subducted beneath the Philippine plate 

nature of vulcnaicity - explosive

o   Form strat0-volcanoes which are cone made up of layers of ash and acid lava have concave symmetrical profile 

o   Containing complex internal networks of lava flows which form minor igneous features such as sills and dykes 

o   Acid magma does not easily flow the vents often filled with a mass of solidified magma which prevents magma from rising freely form depth 

o   Enormous pressures can build up eventually it erupts explosively 

o   CALDERAS usually more than 2km diameter craters 

o   Develop when an explosive eruption destroys much of the cone with underlying camber of magma emptied – without the support of volcano collapse to form a caldera e.g., Krakatoa in Indonesia left a caldera 7km wide 

o   Convergent plate boundaries and explosive eruption often five rises to chains of Strato-volcanoes Indonesia has 130 along its archipelago 

o   Unpredictable and resist easy classification 

nature of vulcanicity - effusive

Lava plateaux

o   When basic magma erupts form multiple fissures, vast areas can be covered by free-flowing lava 

o   These events are known as flood basalts 

o   For example, the deccan plateau in central India which covers more than 500,000 km2 known as the large igneous province 

o   The Columbia Plateau in the NW USA cover 130,000km2 

o   However, millions of years of denudation have created more varied relief 

o   No large-scale flood basalt events have taken place in past 50 million years 

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o   When they do occur, they have a devasting impact on the atmosphere and hydrosphere and consequentially the biosphere 

eruptions hot spots

o   Formation due to existent e of hot spot 

o   Where there is a large magma plume rising though the mantle to the earth surface 

o   As the pacific plate has slowly move northwest over the Hawaiian hot sport vast amounts of basalt have accumulate don the ocean floor to produce the Hawaiian Islands 

o   The active volcanic peaks of Mauna Loa and Mauna Kea reach over 4000m above sea level 

o   Over millions of years the pacific plate will move away from the to spot and volcanoes will become extinct 

o   Older islands like Kauai are no longer active 

o   Weathering and erosion break down the volcanic rocks into fertile soils 

o   Volcanic islands may sink below the surface 

o   Currently Loihi is rising above the sea floor as it is directly above the host spot 

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o   In east Africa the crust has been uplifted and stretched causing tension within the local rocks resulting in rifting and magma forcing it ways to the surface Kilimanjaro was formed in this way 

sheila volcanoes

o   Effusive eruptions are usually found at divergent plate boundaries 

o   As these boundaries coincide with mid ocean rights most effusive eruptions are unseen in the ocean 

o   Iceland however is an exception it owes it formation to effusive volcanic activity and its eruptions of basic lava result in volcanoes with gently sloping sides 

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super volcanoes

o   A volcano that erupts more than 1000km3 of material in a single event 

o   The existence of giant calderas proves super volcanoes such as Yellowstone in Wyoming which caldera is 75km 

o   Most recent volcanic eruptions were 27,000 years ago in Taupo, North Island, New Zealand 

o   Impact massive ash layers impact plant, insect, and animal species 

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o   For example, when Yellowstone erupted during one of the largest one’s ashes was spread over much of the western half of North America while gases and tiny particulates were carried around the globe in the upper atmosphere – it is likely that this caused a noticeable through temporary decrease in global temperatures 

VEI

o   Makes it easier to compare eruptions since eruptions vary greatly form effusive to explosive and duration 

o   Magnitude – the amount of material erupted 

o   Intensity – speed at which material is erupted 

o   Volcanic Explosively index (VEI) combines magnitude and intensity into a single number from 0-8 the most explosive each number represent 10x increase in explosivity 

o   It considers several factors such as considering: the volume of erupted material, the height ejected material reaches, the duration in hours and various qualitative descriptions 

o   The VEI does not work for effusive eruptions such as those in Hawaii

LIPS

o   ‘hot spots’ such as the Hawaiian chain of islands and therefore cannot be explained by plate tectonics 

o   The largest of these intra-plate volcanic features are continental flood basalts and giant oceanic plateaus 

o   These are massive effusive outpourings of basalt that commonly erupt intermittently over very long period and typically cover areas between 2000-2500km 

o   One of the largest of them the Siberian traps has a total volume of 3 million km3 

o   formed by a mantle plume of solid material that rises form the junction between the mantle and the liquid outer core; same process that creates convection currents

o   The material making up the plume is mafic but changes chemically by the time that it reaches the surface depending on whether the last leg of the plume’s route to the surface is through oceanic curst or continental curst 

o   Millions of cubic kilometres of magma pond up below the lithosphere before periodically breaking through the lithosphere crust, erupting over several million years 

o   Strong correction between creation of LIPs and the earth’s climate history 

o   Might create global cooling initially but long term lots of Co2 emitted will mean warming, ocean acidification as well 

o   LIP events have been identified as possible causes of at least four major extinctions e.g., the Permian extinction 

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lava flows

o   Dependent on the type of lava 

o   BASALTIC = free-flowing and can run for considerable distances. On Hawaii in July 2015 a lava flow extended for 20km before stopping and in August the same year a flow was reported to have covered about 800m in a day 

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o   ACIDIC LAVAS (rhyolite) = are thick and pasty so do not easily flow everything in the path of lava will be either burned or buried – although lava destroy infrastructure property and crops, they rarely cause casualties 

pyroclastic flows

o   These are a combination of very hot gases (500 degrees+), ash and rock fragments travelling at high speed (100 km/h)

o   The follow the contours of the ground and destroy everything in their path 

o   The inhalation of such hot and poisonous gas and ash causes almost instant death 

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o   Pompeii was overwhelmed by a pyroclastic flow 

tephra

o   Describes any material ejected form a volcano into the air 

o   It ranges in size from very fine ash to large volcanic bombs 

o   It also includes lighter debris such as pumice 

o   Potentially can be very hazardous burying farmland in layers of ash and destroying corps 

o   Eruption columns can carry material into the stratosphere largely because the temperature of the ejected material is always much hotter than the surrounding airs, so it rises very fast in adding to the propulsion of the explosion itself 

o   Transport can be disrupted as it did after E16 erupted in 2010 leading to 100,000 flight cancelations

o   Buildings can collapse due to the wright of accumulated ash and people with respiratory disease may have difficulty breathing 

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emission toxic gases

o   such as CO, CO2 and SO2

o   these gases can pose a deadly threat to human populations 

o   when SO2 combines with water acid rain is produced this can damage crops and pollute surface water and soils 

lahars

o   a type of mud flow with the consistency of wet concrete 

o   snow and ice on a volcano summit melt during an eruption and flow rapidly down the cone 

o   rock fragments large and small as well as ash and soil are mixed 

o   lahars can travel up to about 50 km/h 

o   everything in their path is either destroyed or buried under thick layers of debris 

o   in 1984 following the eruption of Nevada Del Ruiz the Colombian town of Amero was overwhelmed by laharas resulting in the deaths of 23,000 people in places such as SE Asia ash cover slopes of volcanoes and generated lahar hazards after heavy rain 

o   Boulders can be swept along by the lahar 

o   Can travel distance up to 50km – very fast moving 

o   A very common cause is very heavy rain – vegetation and soil that normally stored in soil can be absorbed into the lahar flow 

o   Some volcanoes are covered in ice and show this can caused rapid melting of ice or snow to create lahars

o   For those places threatened evacuation is the only option  

floods

o   If volcanoes erupt beneath an ice field or glacier it causes rapid melting 

o   In Iceland several active volcanoes lie under the Vatnajokull ice field 

o   During eruption vast quantities of water accumulate until they find an exit from under the ice 

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o   Iceland E16 – melting of ice cape rushed down the side of volcano and flooding the valley 

Tsunami

o   The violent eruption of some island volcanoes can cause massive displacement of ocean water and tsunami waves capable of travelling at speeds of up to 600 km/h

o   In deep water they have a height that is usually less than 1, and a very long wavelength of up to 200km 

o   Approaching the shore tsunami waves increase rapidly in height and when they break transfer vast amounts of energy and water along the shore and inland 

o   The tsunamis created by the eruption of Krakatoa in 1883 are believed to have killed 36,000 people 

mega tsunami

o   700 miles of the northwest coast of Africa 

o   Less than 4 million years old 

o   Explosive eruption 

o   Eruption in the last 60 years have created a fault line running along a ridge in the island 

o   On the western side of the fault the land about a ¼ of island fell 13 ft and then gripped onto the side of the region – this could have created a Mega Tsunami 

o   Traced the fault for 9 miles along the island ride 

o   If the fault crack s open potentially 5 hundred billion tonnes of rock would fall into the sea

o   Calculated that the mass of rock would move at 220 miles per hour 

o   Displaced half a mile of water – a dome of water 3,000 feet high 

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o   After the rock falls, while the water attempts to return to equilibrium it oscillates and as the water rises and down sends waves out into the ocean.

long term impacts of volcanoes

o   emission of ash can have implication of longer-term climate change. 

o   Super volcanoes eruption such as Toba led to reductions in global temperatures as ash blocked sunlight and has been linked to the dramatic fall in global human population of the time.

o   The release of SO2 added to cooling mixing with water forming sulphuric acid which reflects insolation.

o   On an even larger scale the creation of LIPs provides explanation of global mass extinctions.

earthquakes

o   Earthquakes represent the release of stress that has built up within the Earth’s crust caused by tensions, compression, or the shearing of rocks 

o   In general earthquakes are more widely distributed and much less predictable 

o   There is a theory called elastic rebound theory which explains how energy is stored in rocks – rocks bend until the strength of the rocks is exceeded, rupture occurs, and the rocks quickly rebound to an undeformed shape, energy is released in waves that radiate outward form the fault 

o   FOCUS – the point within the Earth where faulting beings is focus or hypocentre

o   EPICENTRE – the point closest to the focus on the surface is the epicentre 

o   SEISMOGRAPHS - record earthquake events

o   At convergent boundaries focal depth increase along a dipping seismic zone called a Benioff zone 

o   Some earthquakes events are preceded by several fore shocks 

o   If these fore shocks have the same P and S waves profiles, they may be a signal that a large event is likely allowing a few hours to warn a population 

o   Later a series of after-shocks follows the main quake, which gradually reduce in intensity

o   Earthquake’s activity tends to be concentration one of four locations: 

 

1\.     MID OCEAN RIDGES – tensional forces associated with spreading processes and subsequent faulting and rifting 

2\.     OCEAN TRENCHES AND ISLAND ARCS – compressive forces associated with the subduction of one plate below another 

3\.     COLLISION ZONES – compressive forces associated with the grinding together of plates carrying continental curst 

4\.     CONSERVATIVE PLATE MARGINS – shearing forces associated with the intermittent movement of one plate past another 

 

o   80% of all earthquakes occur in the circum-Pacific belt 

o   15% occur in the Mediterranean-Asiatic belt 

o   Although the great majority of earthquakes occur on or close to tectonic plate margins, stress within the curst is widespread 

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o   As a result, earthquakes can occur anywhere – locations such as the UK which were tectonically active in the past, still preserve old fault lines along which movement can take place 

smic waves

o   Seismic waves can travel along the surface and through the layers of the earth there are three types:

1\.     Primary (P) waves – fast-travelling, low frequency compressional waves 

2\.     Secondary (S) waves – half the speed of P waves, high-frequency waves, they vibrate at right angle to the direction in which they travel – the second wave you feel after an earthquake 

3\.     Surface (L) waves – slowest of the three types, low-frequency waves. Some L waves have a rolling movement that moves the surface vertically, while others move the ground at right angles to the direction of movement – very damaging and destructive – but in deeper earthquakes the damage is reduced – love waves produce entirely horizontal motions – Rayleigh waves – they move up and downside to side and role 

o   L waves travel through the outer crust only, S waves cannot pass through liquids and cannot travel through the outer core 

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o   While P waves travel through the Earth’s interior (both solids and liquids)

shallow and deep focus

*shallow-focus earthquakes* 

o    Surface down to about 70km 

o    Shallow quakes occur in cold, brittle rocks resulting from the fracturing of rock due to stress within the curst 

o    They are very common, with many releasing only low levels of energy, although other high-energy shallow quakes are capable for causing severe impacts 

*deep-focus earthquakes* 

o    70 to 700 km 

o    deep quakes are poorly understood – with increasing depth, pressure and temperatures increase to very high levels 

o    minerals change type and volume, which may contribute to a release of energy 

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o    it is likely that dehydration of water in subducting plates plays a significant role in these events, but scientists continue to evolve their ideas about these less frequent but often powerful quakes