Tectonics

• What is the inner core made from?

  solid iron and nickel
• What is the outer core made of?


  Semi-molten iron and nickel
• What is the mantle made of?


  Silicate rock (silicon and oxygen)
• What is the asthenosphere?


  Semi molten upper layer of the earth's mantle. Rock is weaker meaning the focus of earthquakes are found here
• What is the lithosphere?

  the rigid outer part of the earth, consisting of the crust and upper mantle.
• Continental crust properties


  30-70km thick, mostly made of granite
• Oceanic crust properties


  6-10km thick, made of basalt
• What did scientists first believe to be the cause tonic plate movement ?

  Convection currents
• What is now considered the mean cause of plate movement?


  Slab pull
• What is slab pull?


  The oceanic crust above the rising limb of a convection current becomes hotter and less dense. The part of the crust furthest from the rising limb will be cooler and more dense, making it more likely to be forced underneath another plate. The sinking of the plate as one of its edges pulls the rest of the plate is called slab pull.
• What is subduction?


  When one section of denser crust is pulled down into the mantle
• What is the Benioff zone?


  The path of mantle taken by the subduction plate
• What is sea floor spreading?


  When magma rises the fill the gaps created by diverging plates, forming new crust. This process creates mid - ocean ridges
• What are rift valleys?

  places on Earth's surface where the crust diverges
• What is a destructive margin


  When two plates move towards each other (converging)
• oceanic-continental convergence


  - denser oceanic plate is subducted to form a deep sea trench

  - fold mountains also form when the plates meet from accumulated sediment

  - oceanic crust is heated by friction, causing upper mantle to melt into mantle

  - the magma rises up and can form a composite volcano

  - as one plate tries to move from under the other a locked fault it formed
• oceanic-oceanic convergence


  - the slightly denser plate is subducted forming a deep sea trench

  - earthquakes can occur here leading to tsunamis

  - volcanic eruptions under water can create island arcs
• Example of an island arc?

  Mariana Islands
• continental-continental collision margin


  - neither plate is subducted as they have the same density as each other

  - two sections of the crust fold up to form fold mountains e.g Himalayas
• What is a constructive margin?

  Where two plates are moving apart (diverging)
• What happens at a constructive margin?

  - mantle is under pressure from above plates

  - the release of this pressure as the plates move can cause the mantle to melt producing magma

  - the magma is less dense than the plate above causing it to rise through the gap (forming new crust or a volcano)
• How is a fault line formed?

  Two diverging plates don't move apart in uniform ways causing pressure to build up and the plates can eventually crack
• What is a Conservative margin


  Two plates trying to move past each other (also known as a transform boundary)
• What happens at a conservative margin?


  - the movement creates increased friction between the plates

  - this pressure can build up causing an earthquake

  - typically fault lines are formed by these boundaries
• What are earthquakes caused by?

  A build up and sudden release of tension at all four types of plate margin
• Where do the highest magnitude earthquakes occur?

  - at destructive margins where a subduction zone is created
• What plate margin has the most frequent earthquakes?

  Constructive
• What type of focus caused more damage?

  Shallow focus
• Why do deep focus earthquake create less damage?

  The shockwaves generated deeper in the earth must travel further to reach the surface, reducing their power
• Where do the strongest earthquakes tend to come from?

  The Wadati Beinioff zone
• What are the three type of seismic waves?

  Primary

  Secondary

  Love
• What is amplitude?

  The size of a wave disturbance compared to a straight line
• Characteristics of a primary wave?

  - fast moving

  - horizontal vibrations created in mantle

  - travel through solids liquids and gas

  - don't cause much damage
• Characteristics of secondary waves?

  - slow moving

  - vertical vibrations that pass through centre of crust

  - only travel through solids

  - more damaging than primary, less than love
• Characteristics of love waves?

  - move perpendicular to primary waves

  - surface waves that move out from epicentre on surface of crust

  - only travel through solids

  - cause the most damage
• What is soil liquefaction?

  Earthquake vibrations put groundwater under pressure causing the ground surface to loose its usual structure and become liquid

  This increased the likely hood of building subsidence
• How does a landslide occur.

  Shaking of ground dislodges rock and soil which can move quickly down a slope. The loosened ground material can increase the likelihood of water infiltrating
• Process if a Tsunami occurring

  - water column displaced by seafloor moving up or down after a submarine earthquake

  - waves start small but travel fast

  - waves lose energy as they approach land causing them to rise in height
• What causes more powerful tsunamis?

  - if the epicentre is close to the coastline

  - travelling through deep water
• What are mantle plumes?

  Vertical columns of hot magma caused by radioactive decay in the asthenosphere