Global Distribution of Tectonic Hazards (Edexcel A Level Geography)

Earthquake distribution

• The majority of earthquakes (about 95%) occur close to or at a plate boundary
• Many occur around the 'Ring of Fire' surrounding the Pacific Ocean
• The most powerful earthquakes are usually associated with convergent or conservative plate boundaries
• Intra-plate earthquakes are those which do not happen at plate boundaries - these are often linked to hot spots or old fault lines

Global earthquake distribution

Volcano distribution

• Like earthquakes, most active volcanoes occur at or near to plate boundaries
• Many (about 75%) occur around the 'Ring of Fire' surrounding the Pacific Ocean
• Volcanoes occur at convergent and divergent plate boundaries
• They can also be found at hot spots in the middle of plates like Hawaii in the central Pacific

Global distribution of active volcanoes

Tsunami distribution

• Over 70% of tsunamis occur around the Pacific Ocean
  • 15% Mediterranean Sea, 9% Caribbean Sea and Atlantic Ocean, and 6% Indian Ocean
• They are caused by tectonic activity 
• Most occur due to activity at convergent boundaries

Global tsunami distribution 1900-2020

• Plate boundaries are the locations where the tectonic plates meet
• Due to the movement of the plates, these are areas where a range of processes take place
• There are three main types of plate boundary:
  • Divergent - plates moving apart
  • Convergent - plates moving together
  • Transform - plates moving past each other or in the same direction at different speeds
• There are three categories of convergent boundaries:
  • Oceanic - continental
  • Oceanic - oceanic
  • Continental - continental (also known as a collision boundary)

Types of plate boundary

• Some earthquakes and volcanic eruptions occur away from the plate boundaries
• These are intra-plate earthquakes and hot spots

Intra-plate earthquakes

• These can occur anywhere
• The cause is not fully understood but is thought to be:
  • Tectonic stresses causing ancient fault lines to reactivate
  • The plates are moving over a spherical surface and this causes zones of weakness
• The New Madrid earthquake in 1812 and the 2011 Virginia earthquake are examples of intra-plate earthquakes

Hotspot volcanoes

• These occur over stationary magma plumes (columns of rising magma) in the asthenosphere
• The tectonic plate moves over the plume leading to the formation of a chain of volcanic islands (Hawaii)
• The oldest island is the one furthest away from the plume

Hot spot