tectonic processes and hazards

• inner core


  a solid ball containing iron and nickel
• outer core


  a semi-molten layer thought to contain iron and nickel
• lower mantle


  nearest the core and is quite rigid

  the rocks found here have a degree of plasticity, which means they can reshape under stress
• upper mantle


  asthenosphere

  semi-molten - has the ability to flow

  cooler than the lower mantle so the rocks tend to ben weaker and more likely to break apart under stress

  focus of earthquakes is found here
• Define natural hazard


  A naturally occurring process or event that has the potential to affect people
• California as a multiple hazard zone

  Droughts - high pressure area (anticyclones) la Nina cycles ( no evaporation from eastern pacific so no precipitation)

  Earthquake Sam Andreas fault 2 or 3 each year with mag over 5.5 (potential to damage structures) San Francisco 1906 7.8 Richter scale along with subsequent fires destroyed most of the city

  Earthquakes under Pacific Ocean cause tsunamis on California coastline - Alaska earthquake in 1964 triggered a tsunami killing 22 and destroying 1300 homes

  -landslides, steep slopes of the rockies, also coastal land (la conchita)

  -more than 70% live within 50km of fault line

  - building on unstable land (marina district)

  Large economy means great losses

  20% in LA live below poverty line
• Nepal case study

  7.8 mangnitude (Indian + Eurasian plate)

  Killed nearly 9000

  3mill homeless

  Vulnerable -

  One of the worlds poorest (2016 ranked 197th)

  Weak infrastructure

  Around 100 aftershocks

  In himalayas (landslides

  Lost 25% of GDP

  Tourism reduced.
• Inner core

  6000 degrees

  Solid iron
• Outer core

  4500-6000

  Semi molten

  Nickel and iron
• Mantle


  Upper part solid

  Lower part semi-molten forming the asthenosphere
• Oceanic crust

  Thin

  Dense

  6-10km
• Continental


  Older

  Thicker

  Less dense

  45-50km thick
• Lithosphere

  Crust and upper mantle, the solid layer in which tectonic plates are formed
• Paleomagnetism


  The study of the earths past changes in magnetic feild( determined from rocks, sediment or archeological records)
• Destructive ocean+ continental formations

  Deep ocean trenches

  Fold mountains

  Earthquakes (benioff zone)

  Volcanoes (explosive)

  Among the most seismically active areas of hazard
• Ocean/ocean destructive

  Denser or faster subducted first

  Ocean trenches

  Magma rises up from Benioff zone to form underwater volcanoes

  Island volcanoes (island arcs)

  Shallow earthquakes or deep

  Marianas trench (pacific faster moving subducted under Philippines plate)
• Ocean divergent boundary

  Mid ocean ridges with transform faults due to spreading at different rates

  Submarine volcanoes, can create island ie Iceland on the mid Atlantic ridge

  Shallow focus earthquakes (low risk no humans)
• Conservative


  Major break in crust (fault)

  Large scale = transform fault

  Powerful earthquakes
• On average how many yearly deaths by earthquake

  10,000
• What's the difference between the focus and the epicentre, and what can a focus also be called?

  A focus is where the point inside the crust where pressure is released (also called the hypocentre) and the epicentre is the point on the surface directly above the epicentre
• What type of waves are primary and secondary and why?

  Body waves - because They travel through the earths body
• What type of waves are love waves

  Surface waves because they travel along the earths surface
• P waves


  Push through crust mantle and core Fastest

  Travel Through solids and liquids

  Travel via compressions

  Only damaging in the most powerful earthquakes
• Secondary waves


  Shake through crust and mantle Slower

  Only through solids

  Move in a sideways motion at right angles to the direction of travel

  More damaging
• L waves


  Slowest

  Last to arrive

  Most damaging (shake the earth side to side)

  Focus all their energy on earths surface

  Larger
• Moment magnitude scale


  Measures magnitude

  Measures total energy released by earthquake at the moment it occurs (seismic moment)

  Measures : size of seismic waves

  Amount of slippage

  Area of fault broken

  Resistance of affected rocks

  Generally goes up to 10

  Logarithmic
• Modified mercalli intensity scale


  Measures intensity

  Observations of the effect on people structures and the environment

  I to XII
• secondary effects of earthquakes

  Liquefaction - Christchurch New Zealand

  Landslides and avalanches - Nepal

  Tsunami - 2004 Thailand tsunami
• 1989 Loma prieta earthquake


  6.9 near San Francisco

  Marina district build on man made landfill that was soft and Sandy and amplified the love waves increasing shaking increasing damage on infrastructure - liquefaction also happened

  Two level cyprus freeway collapsed (causing 42 of 67 deaths)

  The part of the freeway that collapsed was on soft mud, whereas parts built on the firmer ground remained standing.
• An example where aftershocks caused more damage than the initial earthquake

  Christchurch New Zealand 2011 6.3 aftershock caused more deaths (185) and damage than the initial 2010 earthquake mms 7.1 no deaths

  (This was because the focus was more shallow and the aftershock was centred closer to the city)
• What does research focus on about predicting earthquakes

  Finding precursors to earthquakes

  None are proving reliable
• Example of intraplate earthquakes and why scientists think they occur

  Three earthquakes of around 7.5 magnitude in central USA between 1811 And 1812

  
  

  They may occur due to old faults build up stresses causing them to become active again
• Pyroclastic flow example and what it is

  Mount St Helens

  Hot broken fragments of rock ejected with great velocity

  1980 eruption hundreds of square miles were reduced to wasteland 1bill damage
• Tephra example and what it is

  Monserrat

  Collective term for all airborne or ground flowing pyroclasts including solidified magma

  May spread over vast distances

  The ghost town of Plymouth became isolated when the 1997 eruptions Coated everything in ash

  4000 people left
• Lava flows example and what it is

  Mt nyiragongo

  Forms solidified surface

  May cause fires and burial of land objects

  Low risk to life

  Contained the worlds largest continually active lava lake - in 2021 lava leaked 400,000 forced to flee their homes 32 died
• Volcanic gases


  Ash laden gases HCl

  Co2 SO2

  Toxic and contribute to acid rain which can ruin crop yield and ruin ecosystems

  Lake nyos (1700 deaths due to carbon dioxide)

  1986
• Lahars

  Volcanic mudflows when rainwater loosens tephra ie mount pinatubo 1991

  Lahars washed through air base 840 deaths

  Every bridge within 30 km destroyed

  Several lowland towns flooded

  1991
• What is the violence of a volcanic eruption determined by?

  Amount of dissolved gases in the magma

  How easy is can escape
• Explain a volcanic hotspot

  An area in the mantle where heat rises as a thermal plume - high heat and low pressure causes the lithosphere to melt, magma rises up through cracks to the surface and erupts to form an active volcano.
• Alfred Wegener


  17th century people thought Africa and South America fit together

  1912 - he proposed continental drift

  Fossil evidence - the same reptile fossils (mesosaurus) found in South America and Africa (suggests they were once joined)

  Fossils of the same green plants found all over the world (could have been transported by sea or air however)

  
  

  Glacial evidence

  300mil years ago glaciers covered Southern Hemisphere

  The pattern they made as they moves across earths surface doesn't make sense unless continents were arranged as he proposed

  
  

  Mountains formed together