Structure of the Earth

Crust - Solid outer layer of the earth. Between 5 and 80km thick. Made up of two types of material, continental and oceanic crust in large segments called plates.
Oceanic- composed of silica and magnesium and layer consisting of mainly basalt. Averages 6-10km in thickness; deepest point of temperature 1200°C
Continental -composed of silica and aluminia and largely of granite can be up to 70km thick
Mantle - Layer between crust and the core. It is the thickest layer of the Earth, extends to 2900km where temperatures exceed 5000°C. Made up of liquid rock called magma, magma is made mostly of silicates, iron and magnesium. The high temperature generates convection currents which drive plate movement

Outer core - Upper part of the Earth's core. Extends to depth of 2300km, only liquid layer mainly made of iron and nickel mainly. Responsible for Earth's magnetic field.
Inner core - Inner most layer iof the Earth, extends to depth of 1200km, believed to be a solid ball composed of mostly iron-nickel alloy. Gives off great heat that rises through other levels- about 6200°C.(Hotter than surface of sun)
Lithosphere - Solid outer part of Earth. Includes brittle upper portion of mantle and crust. It is continental or oceanic.
Asthenosphere- upper part of the mantle located below crust of Earth. Part liquid, part solid. Starts when the crust heats up to 1300
°C - when crust begins to melt and move more as a liquid - convection currents which move tectonic plates

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Mechanics of plate tectonics

The Earth is made up of 7 major and 7 minor plates and many micro-plates. Some plates are largely continental - Eurasian plate. Some are continental and oceanic and some only oceanic - Nazca plate.

Rising limbs of convection cells move heat from the Earth's core towards the surface, spreading out either side of the ridge and carrying the plates with it. The plates 'float' on a lubricated layer called the asthenosphere. This layer allows the solid lithosphere to move over the upper mantle. 

Image result for convection currents

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Constructive margin

This is when two plates are moving away from eachother in opposite directions. As these plates move apart this leaves cracks and fissures, lines of weakness that allows magma from the mantle to escapes from the highly pressurised interior of the planet.This magma fills the gap and eventually erupts onto the surface and cools as new land. The lava erupting is Basaltic, so can travel long distances and creates gently sloping land features. This can create huge ridges of undersea mountains and volcanoes such as the Mid-Atlantic Ridge and where these mountains poke above the level of the Sea Islands are created. Both earthquakes and volcanoes can result at these margins, the earthquakes caused by the movement of magma through the crust. A really good example of this is the mid Atlantic Ridge, where the Eurasian plate moves away from the North American plate at a rate of around 4cm per year. Iceland owes its existence to this ridge.  

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Destructive margin

2 plates move  together and the Destruction of some of the Earth's crust results. These margins are mainly found around the edges of oceans and the majority are found around the Pacific Ocean in what is known as the Ring of Fire.An oceanic plate (denser) is pushed towards a continental plate (less dense) by convection currents deep within the Earth's interior. The oceanic plate is subducted (pushed under) the continental plate at what is called a subduction zone, creating a deep ocean trench. It is the Oceanic crust which sinks down into the mantle because it is denser (heavier).

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Conservative margin

At conservative margins mountains are not made, volcanic eruptions do not happen and crust is not destroyed. Instead, 2 plates either slide past each other in opposite directions, or 2 plates slide past each other at different speeds. As they move past each other friction builds as the plates snag and grind on one another, and parts of the fault line “LOCK”. When this stress energy is eventually released it sends shock waves through the earth’s crust. We know these shock waves as earthquakes, and a good example of this is the San Andreas Fault in California, where the Pacific plate is moving NW at a faster rate than the North American plate.Image result for conservative plate boundary diagram (http://www.discoveringgalapagos.org.uk/wp-content/uploads/2014/09/g2a1_conservative-edit-2.png)

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Collision margin

At these margins 2 plates of similar density are forced toward each other. Neither plate descends into the mantle because of the similar density of the plates. Instead, the 2 plates crumple into one another and fold upwards into fold mountains. At these margins we get fold mountains and earthquake activity, and a fantastic example of this is the Himalayan mountains. Here, the Indo Australian plate is colliding with the Eurasian plate and has done so for millions of years.

Image result for collision plate boundary diagram (http://geography.parkfieldprimary.com/_/rsrc/1472778030599/hazards/plate-tectonics/foldmountains.png)

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Oceanic  hotspots occue where plumes of magma are rising from the asthenosphere. If the crust is thin or weak, magma may escape onto the srface as a volcanic eruption. Lava may build up over time until it is above the present day sea level causing basaltic sheild volcanoes. It also causes minor earthquakes. An example of this is the Hawaiian island chains or the Galapagos Islands.

Continental hotspots cause colossal rhyolitic mega-eruptions. An example is Yellowstone 'supervolcano' USA.

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Global distribution of Earthquakes

The zones of earthquakes/seismic activity can be divided into four plate settings.

  • Constructive  boundaries along the ocean ridges. Earthquakes here are mainly shallow, and result from tensionaltransform faults in the crust and from shaking during volcanic activity.
  • Destructive boundaries where oceanic crust is being subducted into the mantle beneath a continental plate or where two oceanic plates collide in island arc zone. These are subject to frequent earthquakes, including high magnitude ones and represent areas of major hazard.
  • Destructive boundaries where continental crust is colliding to produce fold mountain belts. Shallow earthquakes occur in a realtively broad zone, resulting in a high hazard risk with the occasional deep-seated earthquake.
  • Aread of lateral crust movement (transform) in the continental regions produce mainly shallow earthquakes of high magnitude.

Intra-plate earthquakes can occur. These are caused by stresses created in crustal rocks, usually by movement along ancient fault lines, a process knows as isostatic recoil. These quakes are more dangerous because they are extremely unpredictable. 

A recent contreoversial generator of earthquakes is fracking for unconcentional supplies of oil and gas which has led to numerous eathquakes in Oklahoma and north Lancashire.

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Global distribution of Volcanoes

`Basaltic lavas are formed by the melting of oceanic crust, whereas rhyolitic lavas with a high silica content are formed from the melting of continental crust. 

  • Constructive plate boundaries (rift volcanoes)  Most of the magma that reaches the Earth's surface is extruded along these boundaries. This mainly occurs at mid- ocean ridges  where melting of the upper mantle produces basaltic magma. The eruptions tend to be non violent and as most occur on the sea floor they do not represent a major hazard except when they are near islands. Fissure eruptios producing lava plataux also occur widely. Continental constructive boundaries also have active volcanoes with a wide range of magma types depending on the local geological conditions through which the magma passes before reaching the surface. 
  • Destructive plate boundaries (subduction volcanoes) As the oceanic plate is subducted into the mantle and melts under pressure, basic magma rises upwards and mixes with the continental crust to produce largely intermediate magma with a higher silica content than at other ocean ridges. These andesitic, in some cases nore acidi, rhyolitic magmas can cause violent volcani activity
  • Hotspots - See card 7
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Magnitude of earthquakes

Magnitude is the most important influence on the severity of impact of a tectonic hazard event. It is the size or physical force  of a hazard event.

Magnitude can be measured by the Richter scale. The Richter scale is based on the magnitude of lines made on a seismogram, using the largest wave amplitude recorded. It is recorded in a logarithmic scale.

The Moment Magnitude (MM) scale is based on a number of parameters of an earthquake event, including area of fault rupture and the amount of fault movement involved, which determines the amount of energy released. Results are similar to the Richter scale.

The Mercialli scale  is also used to measure earthquakes. It is a descriptive scale that measures the amount of damage caused by surface shaking of particular earthquakes.

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Magnitude of Volcanic eruptions

All volcanoes are formed from moleten material in the Earth's crust. There is no fully agreed scale for measuring the size of eruptions but Newhall and Self (1982) drew up semi-quantative volcanic explosivity index (VEI) which can be related to the type of magma tat influences the type of eruption. It combines:

  • The total volume of ejected producs
  • The height of the eruption cloud
  • The duration of the main eruptive phase
  • Several other items such as eruption rate

into a basic 0-8 scale of increasing hazard. 

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Frequency and Duration

Frequency is sometimes called the recurrence level. There is an inverse relationship between frequency and magnitude. The larger the magnitude of the event,the less frequent its occurence. The effect of frequency on severity of impact is difficult to gauge. Theoretically, areas that experience frequent tectonic events hae both adaption and mitigation measures in place, including extensive monitoring, education and community awareness about what to do, and various techniligical strategies for shockproofbuilding desgin or protection. 

Duration is the length of time for which the tectonic hazard exists.Often an initial earthquake event if followd by massive aftershocks or a series of eruptions occurs. While individual earthquakes often last for only around 30 seconds, the damage can be extensive

Secondary hazards often pro;ong the duration of impact and increase damage. Secondary hazards include things like lahars jokulhlaups which are very damaging due to their spatial unpredictability. 

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Spatial concentration, speed of onset and predicta

Spatial concentration  is the areal distribution of tectonic hazards over geographical space. It is controlled largely by type of plate boundary. Theoretically, permanent settlement is avoided in hazardous regions but often such locations present other opportunities like volcanic soils are vry fertile so agricultural settlements occur. Or spring water may be available. Active tectonis, especially volcanic landscapes encourage tourism.

Speed of onset can be a crucial factor. Earthquakes generally come with little arning. The speed of onset and the almost immediate shaking of the ground can lead to maximunm destruction. Volcanoes generally have a slower speed of onset so are easier to control the amount of destruction that happens. 

Predictability of occurence is the random temporal distribution of both earthquakes and volcanoes can add to their potential impact. While gap theory  can increase the possibility of predicting the 'Big One', in reality earthquakes are unpredictable. Volcanic eruptions can also be hard to predict precisely, even with close monitoring. 

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Types of volcanoes

Sheild volcanoes - formed when basaltic lava pours in huge quantities out of a central vent. Because of the effusive nature of the basic fluid lava, it can spread over a wide area before solidifying. The result is a huge volcanic cone with gently sloping sides. The lava has low viscosity because of its low silica content, and erupts at temperatures of about 1200°C.

Composite volcanoes - form from alternating layers of lava and ash resulting from eruptions at destructive plate margins. The lava itself is typically acidic with more tha 50% silica content. It has a temperature of about 800°C. This means it flows more slowly, creating cones with more steeply sloping sides. the ash is produced in highly explosive eruptive phases, often after the vent has been blocked.

Acid or dome volcanoes -  form when acid lava quickly solidifies on exposure to the air. These volcanoes often have parasitic cones fromed as the passage of the rising rhyolitic magma through the main vent is blocked. The cones are steep sided and convex in shape.

Ash and cinder cone volcano - formed when ash and ciners build up in a cylindrical cone of relatively small size. They are highly permeable as they are composed of loose volcanic cinders. A typical size is 800m in height with a bowl-shaped crater. 

Caldera volcanoes - occur when the build up of gases becomes extreme. Huge explosions may clear the magma chamber beneath the volcano and remove the simmit of the cone, or cauldron subsidence may occur. This causes the sides of the crater to collapse and subside, thus widening the opening to several kilometeres in diameter. 

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Pyroclastic flow and surges

Pyroclastic flows are clouds of hot volcanic gases, ash and volcanic bombs that can sweep down the volcano's sides and other steep hills at speeds over 100 miles per hour. When a volcano erupts violently its common for large volumes of rock to be pulverised in the explosion and reduced to tiny particles. These are mixed with high temperature gasses, ash and larger pieces of rock, forming a red hot cloud that is very dense. A pyroclastic has an added killer element; poisonous gasses at temperatures hot enough to burn your lungs away. They can be literally red hot, up to 1000°C.

They are responsible for most volcanic deaths to date. The greatest risks occur when the summit crater is blocked by viscous rhyolitic magma and blasts are directed laterally in Pelean type eruptions

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Lava flows

These pose more threat to property than human life. The lava flows biggest danger to human life come from fissure eruptions, nog central vents, as highly fluid basalt magma can move down a hillside at 50km per hour and can spread a long way from the source. 

Pahoehoe  lava is the most liquid of all lava and tends to form a ropey wrinkled surface. On steep slopes this low viscosity lava can move downhill at speeds approaching 15m/s

A'a lava tends to form blocks, and moves more slowly downhill, leaving a rough irregular surface. A'a is characterized by a rough, jagged, spinose, and generally clinkery surface. Aa lava flows tend to be relatively thick compared to pahoehoe flows.

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Airfall tephra (ash falls)

Ash is material below 4 millimetres in diameter whilst tehpra is anything above this. It is usually formed when magma is fragmented by explosions, and can stay in the atmosphere causing global variations in weather patterns. Coarser, heavier particles fall out of the sky close to the volcano vent. Ocasionally tephra is sufficiently hot to spontaneously combust and start fires. Ash clouds can be blown many miles away from the original eruption by strong winds.

Ash falls do not cause many deaths but can lead to a number of problems 

  • Hevay falls of cinders and ash can blanket landscape, contaminating farmland and poisoning livestock
  • Ash causes health issues such as skin abrasion and breathing problems
  • The weight of ash can damage roofs
  • Ash washes into lakes and rivers to become a larhar source.
  • Wet ash conducts electricity and can cause failure of electronic equiptment
  • Fine ash can clog air filters and famage vehicles and aero engines
  • Ash can lead to vehicle accidents, poor visibility, slippery roads
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Volcanic gases

Large amounts and a wide range of gases are released from explosive eruptions and from cooling lava. The complex gas mixture includes water vapour, hydrogen, carbon monoxide, carbon dioxide, hydrogen sulphate , sulphur dioxide. chlorine and hydrogen chloride in variable amounts.

CO causes deaths because of its toxic effects at very low concentrations but most fatalities have been associated with CO2 releases because CO2 is colourless and odorless. It can cause asphyxiation. 

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These are volcanic mudflows composed of largely silt-sized sediments. Lahars consist of ash and rock combined with torrential rain which often accompany eruptions. They create dense viscous flows that can travel even faster than clear-water streams. They occur widely on steep volcanic flanks, especially in tropical humid or monsoon climates. 

Lahars can be primary hazards if they occur directly during an eruption or secondary which are triggered by the high intensity rain which can reactivate old flows of ash etc.

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Vocanic landslides

Landslides and debris avalanches are a common feature of volcano-relate ground failure. They are particularly associated with eruptions of siliceous acidic dacitic magma of relatively high viscosity with a large content of dissolved gas.

Volcanic landslides are gravity-driven slides of masses of rock and loose volcanic material.They can occur during an eruption or be set off as a result of heavy rainfall or, more commonly, earthquakes.

Ground deformation of volcanic slopes by rising magma, which creates a bulge, can also trigger slope instability and landslides before an eruption

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In most subglacial eruptions, the water produced from melting ice becomes trapped in a lake between the volcano and the overlying glacier. Eventually this water is released as a violent and potentially dangerous flood. Events of this type are so common in Iceland they named it jökulhaups which means glacial outburst.  These rarely turn into disasters as they occur in remote unpopulated areas.

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Types of volcano eruption

Hawaiian - Lava slowly and easily escapes from vent. It is runny, basaltic. Gases escape easily & gentle sided volcanoes result.

Strombolian - Gas explosions occur more frequently, small but frequent eruptions. Cone shaped volcano.

Vulcanian  -Gas emissions involved, more violent but less frequent than above. Plugs of cooled lava may be ejected in blast.

Vesuvian - Extremely strong explosions, often after volcano has been dormant for a while. Gas and ash clouds, which fall over a large area.

Krakatoan - Exceptionally violent.

Plinian - Usually most violent. Massive amounts of lava, gas and pyroclastic material emitted. Part of the volcano may be removed.

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Environmental impacts of volcanic hazards

  • Increasesd precipitation due to H2O given off during eruption, local scale
  • Reduction of diurnal cycle due to blockage of short-wave and emission of long-wave radiation, local scale
  • Reduced tropical precipitation due to blockage of short-wave radiation, reduced evaporation, regional scale
  • Summer cooling of northen hemisphere tropics and sub-tropics due to blockage of short-wave radiation, regional scale 
  • stratopsheric warming due to absorption of short-wave and long-wave radiation, global scale
  • Winter warming of northen hemsphere continents due to blockage of short-wave radiation, regional scale
  • Global cooling due to blockage of short-wave radiation, global scale
  • Global cooling from multiple eruptions due to blockage of short-wave radiation, global scale
  • Ozone depletion, enhanced ultraviolet due to dilution,heterogenous chemistry and aerosols, global scale
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Characteristics of earthquakes

Most earthquakes result from movemeny along fractures or faults in rocks. These faults usually occur in groups called a fault zone. 

Movement occurs along fault planes of all sizes as a result of stresses created by crustal movement. The stresses are usually built up until they become so great that the rocks shift suddenly along the fault.

  • As the fault moves, the shockwaves produced are felt as an earthquake by a process known as elastic rebound
  • The point of break is called the focus, which can be anything from a few kilmeters to 700km deep
  • If the stresses are releases in small stages there may be a series of small earthquakes
  • Conversely, if the stresses build up without being released, there is the possibility of a major earthquake

During an earthquake, the extent of ground shaking is measured by motion seismometers activated by strong ground tremors, which record both horizontal and vertical ground accelerations caused by the shaking.

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Types of seismic waves

  • Primary (P) waves - P waves are vibrations caused by compression. They spread outfrom the earthwuake fault as a rate of about 8 km/s and travel through both solid rock and liquid. These waves are refracted when they pass through a medium (e.g. outer core) 
  • Secondary (S) waves - S waves move through the Earth's body at about half the speed of P waves. They vibrate at right angles to the direction on travel. S waves which cannot travel through liquids are responsible for a lot of earthquake damage. They can't pass through he outer core.. They are transverse.
  • Rayleigh (R) waves - R waves are urface waves in which particles follow an elliptical path in the direction of propagation and partly in a vertical plane- like water moving with an ocean wave
  • Love (L) waves - L waves are simlar to R waves but move faster and have vibration solely in the horizontal plain. They often generate the greatest damage, as unreinforced masonry buildings cannot cope with horizontal accelerations.
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Earthquake depth of focus

The recorded time interval between the arrival of the waves at different seismogram stations are used to locate the epicentre (the point of the Earth's surface directly above the focus of an earthquake)

There are three categories of earthquake focus, by depth

  • Deep focus (300-700 km) 
  • Intermediate focus (70-300km)
  • Shallow focus (0-70km) These are the most common (around 75%) and cause the most damage as they are nearer to the Earth. 
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Ground movement and ground shaking

Surface seismic waves represent the most severe hazard to humans and their activities, since buildings and other structures may collapse and kill of injure their occupants. Ground motion severs underground pipes and power lines, resulting in fires and explosions, especially from escaping gas. Ruptured water pipes mean that often it is difficult to extinguish these fires.

Near the epicentre. ground motion is both severe and complex, as there is an interlocking pattern of both P and S waves and, theoretically, most damage should occur at the epicentre. Different surface materials responf in different ways to the surfac waves, with unconsolidated sediments being most affected because they amplify the shaking. This leads to differential damage of buildings and infrastructure, based not only on distance from the epicentre but also on surface materials. Steep topography also amplivies waves.

The duration of shaking is also important, longer periods of shaking cause more damage for events of the same magnitude.

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Liquefaction is an important secondary hazard that is associated with loose sediments. This is the process by which water-saturated material can lose strengh and behave as a fluid when subjected to strong ground shaking which increases pore water pressures. Poorly compacted sands and silts situated at depths less that 10m below the surface are most afftected when saturated with water.

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Landslides, rock and snow avalanches

Sever ground shaking causes natural slopes to weaken and fail. The resulting lanslides, rock and snow avalanches can make a major contribution to earthquake disasters especially in the mountain areas such as the Himalayas. These landslides hamper relief efforts. It is estimated that landslides can double earthquake deaths, especially with high magnitude earthquakes because they can occur over a huge area.

Landslide risk post-earthquake varies with differences in topography, rainfall, soil and land use. Landslides can also make floods occur by doing things like damming lakes, subsequently making the water burst through.

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Tsunamis are the most destructive secondary earthquake related hazard. Most tsunamis are generated at subduction- convergent plate boundaries, with 90% of damaging tsunamis occurring in the Pacific Basin. 

Tsunamis occur if an earthquake rupture occurs under the ocean or in a coastal zone, if the focus is not deep within the Earth's crust, and if the magnitude of the earthquake is large enough to create significant vertical displacement. A tsunami is a series of ocean waves that 'spread out' from the earthquake focus, carrying large volumes of water, and debris too once they reach the land. 

Tsunamis intensity can be measured by descriptive, observational scale devised by Soloviev in 1978 which is based on run-up height.

A number of physical factors influence the degree of devastation, including wave energy, which is dependant on water depth, the process of shoaling, the shape of the coastline, the topography of the land and the presence or absence of natural defences such as coral reefs or mangroves. Human factors include the population profile, the degree of coastal development, the cohesiveness of the society and people's experience of the tsunami hazard, as well as the prescense or absence of warning systems and evacuation plans. 

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Demographic, economic and social impacts of eathqu

The primary effects of major earthquakes are the immediate consequences, such as damage to houses from shaking or fires, and instantaneous deaths of people hit by failing tiles and roofs. On the streets,cracks from across roads and bridges collapse; there is widespread destruction of gas mains and water pipes; and severe fractures or the concertina downwards of badly built concrete high-rise blocks. Within a few minutes people are trapped and injured; many die quickly.

The secondary  effects of an eathquake are those that manifest in the days,weeks and even months after an earthquake  event. Air pollution might result from burning fires and combustion from leaking gas mains. Contamination from sewage is another serious secondary danger, causing diseases such as typhoid or cholera as a result og a shortage of clean water.

In MEDC's , there are contingency plans for all states of the hazard management cycle underpinned by financial support mainly from within the country. LEDC's have fewer resources for resucue and recovery so rely on international aid.

Many factories and offices are so damaged that work cannot resume for a considerable time, costing money in wages, lost production, future orders and exports. The community might also be threatened by hunger and disease and possible social disorder from looting. 

In rural areas, farmland and crops will be seriously affected if draiage or irrigation systems are disrupted and fields covered in rubble. Where landslides have blocked roads, farmers are not able to get their products to market. On the other hand, in urban areas the effects can be ectremely severe because of the high density of buildings and the high value of infrastructure. If buildings are completely destroyed, leaving large areas of derelict land, uncollected refuse and decomposing organic material can result in infestation of rats and flies. 

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Risk is defined as 'the probability of a hazard occurring and creating loss of lives an livelihoods'. It might be assumed that risk of exposure to tectonic hazards is involuntary but in reality people conciously place themselves at risk for a variety of reasons including:

  • unpredicatability of hazards - area may never have experienced a hazard
  • the changing risk over time (e.g. a percieved extinct volcano)
  • Lack of alternative locations to live - especially poor
  • An assessment that economic benefits outweigh the costs (e,g, for areas of rich volcanic soils or of great tourism potential
  • Optimistic perveptions of hazard risk: 'it can all be solved by technofix' 'it won't happen to me'

The risk is altered by human conditions and actions, with two earthquakes of the same magnitude, one may have a much larger impact than the other because it is in a developing country where they are more vunerable.

Risk = frequency and/or magnitude of hazard x level of vunerability
                           capacity of population to cope


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Factors impacting vulnerability

  • Poverty levels - LEDC's lack the money to invest in eduation, social services, basic infrastructure and technology, all of which help communities overcome disasters
  • Technology plays a major role, especially in building design and prevention and protection and also in the design of monitoring equiptment
  • Density of population and population profile increases vulnerability as there is more people to evacuate and things like an ageing population can slow evacuation
  • Housing conditions and quality of buildings have a major impact, disadvantaged people are more likely to die, suffer injury and psychological trauma during the recovery and reconstruction phase because they live in poorer housing which is not earthquake proof.
  • The lack of strong central government produces a weak organisational structure. Lack of financial institutions inhibits disaster mitigation and both emergency and post-disaster recovery
  • Increasing urbanisation- vunerable to post earthquake fires
  • Destruction of rural environments can result in disasers among rural populations, loss of supplies and livelihoods
  • Relief of the land (difficult to get to recovery in mountain ranges)
  • Multi-hazard hotspots
  • Timing of first earthquake and aftershocks
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Prediction adn monitoring of earthquakes

  • Seismographs - Eathquakes predicted by foreshocks
  • Strain meter - monitors stress changes in rocks
  • Laser reflector - Lasers detect small amounts of movement along faults
  • Creep meter to monitor small movements along the fault
  • Magnetometer to measure slight changes in the Earth's magnetic field
  • Well levels to monitor groundwater movements
  • Observation of unusual animal behaviour
  • Tilt meter and gravity meter to detect changes in the local magnetic field and minor earth movements
  • Radon gas counter; the amount of radon gas dissolved in groundwater has been shown to increas before some earthquakes
  • Water table changes in the height of the water table have been recorded just before an earthquake
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Prediction and monitoring of volcanic eruptions

  • Earthquake activity - common near volcanoes so cna indicate there may be an eruption soon
  • Ground deformation - Tilt meters and other equiptment can measure change in slope and Electronic Distance Meters (EDM) can measure the distance between benchmarks placedon a volcano to pinpoint when magma is rising and displacing the ground surface
  • Global positioning sustems (GPS) rely on satellites that orbit the earth twice a day and constantly feedback information that can detect the build up of magma from GPS recievers in the volcano
  • Thermal changes occur as the magma rises to the surface and increases the surface temperature. Ground observations of hydrothermal phenomena can be supplemented and confirmed by thermal imaging from satellites
  • Geochemical changes can be detected in the composition of gases issuing from volcanic vents. Direct field smapling of gases escaping from surface vents is the usual method, but remote sensing has been used too. 
  • Lahars have been monitored for years by local people but more recently videocams allow automatic detection systems. Seismometers detect ground vibrations from an approaching lahar, so an emergency message can be transmitted downslope to population centres enabling short-term warning and emergency evacuation
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Prediction and warning of tsunamis

Global scale - Pacific Warning System for 24 Pacific Basin nations established in Honolulu, Havaii. Seismic stations detect all the earthquakes and the events are interpreted to check for tsunami risk. 

Regional scale - These have short warning times and pose a much greater threat. Japan has a system that aims to issue a warning within 20 minutes of the tsunamigenic earthquake.Tsunamis may destroy powere and communication lines so warnings cannot be sent, events may occur too quickly for warnings to be issued and the warnings need to be supported by land-based evacuation plans and community education.

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Modifying event, vulnerability and loss


  • Diverting lava flows - barriers of concrete
  • hazard - resistand building design 


  • Land us planning and layout - avoid at risk areas, mapping of high-risk zones
  • Community preparedness and education - learn how to evacuate effectively, warning signs etc.
  • Smart technology to prepare emergency services
  • Monitoring hazard events
  • International comparison 
  • Closure of airports and air space
  • Buldings with aseismic design, fire proof buildings


  • Give aid and insurance to everyone - easier for richer nations
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Modifying event, vulnerability and loss


  • Diverting lava flows - barriers of concrete
  • hazard - resistand building design 


  • Land us planning and layout - avoid at risk areas, mapping of high-risk zones
  • Community preparedness and education - learn how to evacuate effectively, warning signs etc.
  • Smart technology to prepare emergency services
  • Monitoring hazard events
  • International comparison 
  • Closure of airports and air space
  • Buldings with aseismic design, fire proof buildings


  • Give aid and insurance to everyone - easier for richer nations
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Short and long term responses to hazards

  • Immediate response - emergency services, government, military, community, charities like RedCross
  • Help with search and rescue, urgent medical supplies, research equiptment, clothing and food
  • Repairs and reconstuction of lifelines and buildings 
  • financial assistance from elsewhere 
  • efforts made to restore temporary communities - tent communities etc
  • improved strategies to reduce vulneribility - building of earthquake resistant buildings etc. 
  • LEDC's have funding from other countries 
  • restore economic stability and quality of life
  • return area to pre-disaster state or better
  • ensure jobs are available
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really helpful!!! thank you :D

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