Plate Tectonic Revision

  • Created by: MadzCook
  • Created on: 03-06-19 13:43

Plate Tectonics


Distributions of Earthquakes

70%of earthquakes are found around the ring of fire – the most powerful ones on convergent and conservative boundaries

 15% on the Mediterranean belt and 5% in interior plates

Distribution of Volcanoes

Mostly along divergent plate margins.

Many are on the Pacific ring of fire

Do not occur on conservative plate boundaries.

Similarities and Differences

Both occur on plate boundaries

Earthquakes found on – convergent, divergent and conservative plate boundaries however volcanoes are never found on conservative

Volcanoes that are found away from plate boundaries- hot spots- Earthquakes that are found away from boundaries – fault lines

Plate boundaries


Convection currents cause plates to move together

The oceanic plate is subducted in the asthenosphere below the continental plate (denser). This melts about 100km below the surface.

Melted surface is less dense (now) and so it rises through weaknesses in faults and plate boundaries

It may form a Composite Volcano-most hazardous and explosive

Earthquakes are also common at the Benioff zone where plates get locked due to the pressure and break away after release.

Eg. The Philippines and Pacific plate tectonic movement in the August 2012 earthquake and September Earthquake.




Divergent Boundary

Plates move away from each other due to the two convection currents diverging beneath the surface, which leads to magma from the mantle brought up to the surface.

Doming of the surface is due to pressure from the rising magma and forms a ridge. As the plates move apart, cracks and fissures, lines of weakness that allows magma to escape eg Indian & Eurasian plate

Small, frequent and low hazard earthquakes

Create rift valleys volcanoes- less explosive and effusive – mid Atlantic Ridge

Conservative Boundary

Mountains and volcanoes are not found as crust isn’t destroyed

2 plates slide past each other in opposite directions or in different speeds causing friction. The grind on one another and parts of the fault line “LOCK”. When the stress energy is released it causes earthquakes.

Eg San Andreas Fault in California, where Pacific Plate is moving NW faster than the North American Plate


Structure of the Earth


700km to 2890km deep and 870o

Less Dense to Medium à Phases of liquids and solid in layers

Body waves pass through at variable rates due to density changes

Mantle makes up 84% of the Earth’s volume

Upper layer- olivine and lower layer-magnesium and silicate

Outer Core

2890km to 5150km deep and 4400o-6100o

Dense à 12% sulphur and 88% iron

Liquid (generates magnetic field)

Only P waves can pass through an s wave shadow zone is created from about 105o from the focal point

Inner Core

 5150km deep to centre and 7000o (radioactive decay)

Very dense à 20% nickel and 80% iron

Solid (radiates heat) maybe two parts with huge crystal aligned in opposite directions

Only P waves pass through but their refraction and the core mantle boundary creates a ring shadow between 105o and 140


No comments have yet been made