geo topic 1.4

• Tectonic plate boundaries


  • Divergent
  • Convergent
  • Transform
• Divergent plate boundary


  Where two tectonic plates move apart
• Divergent plate boundaries


  • Oceanic-oceanic: North American Plate and Eurasian Plate
  • Continental-continental: Nubian Plate and Somalian Plate
• Convergent plate boundary


  Where two tectonic plates move towards each other
• Convergent plate boundaries


  • Oceanic-oceanic: Philippine Plate and Pacific Plate
  • Continental-continental: Eurasian Plate and Indo-Australian Plate
  • Oceanic-continental: Nazca Plate and South American Plate
• Transform plate boundary


  Where two tectonic plates slide past each other
• Transform plate boundary


  • San Andreas Fault where Pacific Plate and North American Plate slide past each other
• What happens at divergent plate boundaries


  1. Tectonic plates move apart, resulting in mid-ocean ridges, volcanoes, rift systems, and earthquakes

  2. Magma rises through weak areas in the crust to the Earth's surface and fills gaps caused by the spreading plates

  3. Lava cools and solidifies to form basaltic rocks, making up new oceanic crust

  4. An extensive underwater mountain chain, the mid-ocean ridge, forms
• What happens at continental-continental divergent plate boundaries


  1. Continental plates move apart

  2. Rocks fracture to form parallel faults

  3. Rocks between faults collapse to form deep rift valley

  4. Decrease in overlying pressure causes parts of the underlying mantle to melt, forming magma that rises through weak areas in the crust to the Earth's surface, forming volcanoes

  5. Earthquakes occur due to stress and tension released when plates move
• What happens at convergent plate boundaries


  Tectonic plates move towards each other, resulting in fold mountains, volcanoes, oceanic trenches, and earthquakes
• What happens at oceanic-oceanic convergent plate boundaries


  1. Two oceanic plates collide

  2. Denser plate subducts beneath the other plate, forming a deep depression known as an oceanic trench

  3. Subducting plate sinks into the mantle, high pressure forces water out of its oceanic crust, lowering the melting point of the overlying mantle and causing it to melt, forming magma

  4. Magma rises through weak areas in the crust to the Earth's surface, forming a chain of volcanoes known as a volcanic island

  5. Friction along the subducting plate causes earthquakes
• What happens at continental-continental convergent plate boundaries


  1. Two continental plates collide

  2. Subduction does not take place because continental plates are too buoyant

  3. Enormous pressure causes the rocks to be uplifted and buckled to form fold mountains

  4. Friction along the convergent plate boundary causes earthquakes
• What happens at oceanic-continental convergent plate boundaries


  1. Oceanic plate collides with continental plate

  2. Denser oceanic plate subducts beneath the continental plate, forming an oceanic trench

  3. Subducting plate sinks into the mantle, high pressure forces water out of its oceanic crust, lowering the melting point of the overlying mantle and causing it to melt, forming magma

  4. Magma rises through weak areas in the crust to the Earth's surface, forming volcanoes on the continental plate

  5. Friction along the subducting plate causes earthquakes

  6. Enormous pressure causes rocks on the continental plate to be uplifted and buckled, forming fold mountains
• What happens at transform plate boundaries

  1. Tectonic plates slide past each other

  2. No crust is created or destroyed

  3. Stress caused by the plate movement produces a fault, a zone of fractures

  4. Earthquakes occur as one plate suddenly slips past another

  5. Magma does not rise to the Earth's surface, hence no volcanoes
• Earthquake

  A vibration in the Earth's crust caused by the sudden release of stored energy in the Earth's lithosphere
• Earthquakes


  • Generally occur along plate boundaries, which contain systems of deep fractures called faults
• Cause of earthquakes


  1. Rock masses on either side of the fault are pushed by tectonic forces

  2. The rock masses get locked due to friction, causing stress to build up

  3. When the stress exceeds the strength of the fault (or rock), the rocks snap or suddenly move to a new position
• Aftershock


  After an earthquake event, the stress from the ground within the earth's crust may cause many smaller earthquakes to occur along the faultline
• Seismometer


  A device used to measure seismic waves and determine the magnitude or size of an earthquake
• Richter Scale (ML)


  Calculates earthquake magnitude using the height of the largest wave recorded on the seismometer
• Richter Scale (ML)


  • Numbered from 1 to 10, with 10 being the greatest strength or magnitude
  • Because the scale is logarithmic, an earthquake of magnitude 6.0 releases an estimated 32 times more energy than an earthquake of magnitude 5.0
  • Magnitude 7 and greater earthquakes are very powerful but are less frequent
• The Richter scale would rate an earthquake with a single drastic spike in wave energy as having a higher magnitude than a long earthquake with many large, intense waves, which underestimates the overall energy released
• Moment Magnitude Scale (mw)


  Rates an earthquake based on total energy released instead of the largest waves, making it more accurate in measuring earthquakes of magnitude 5 and above
• Locations of major earthquakes

  • Convergent plate boundaries
  • Divergent plate boundaries
  • Transform plate boundaries
  • Intraplate regions
• The Pacific Ring of Fire is a broad belt around the Pacific Ocean where most earthquakes and active volcanoes occur, making it the most seismically and volcanically active zone in the world
• Convergent plate boundary


  • Pacific plate moving towards the Philippines plate
• Divergent plate boundary


  • Pacific plate moving away from Cocos plate
• Transform plate boundary


  • Pacific plate sliding against North American Plate