Tectonics topic 2.3 (distribution of earthquakes, volcanoes and tectonic hazards)

distribution of earthquakes

Earthquakes occur along all types of plate boundaries and the largest concentration is at pacific ring of fire. 

• At plate boundaries, plates are pushed by tectonic forces, stress builds up and energy is eventually released 

• Example : 

  • Broad belt of earthquakes along convergent plate boundaries in the pacific ring of fire

  • Narrow belt of earthquakes along divergent plate boundary at mid atlantic ridge

  • Narrow belt of earthquakes along the transform platte boundary at the San Andreas fault. 

• Earthquakes occur more commonly along convergent plate boundaries at subduction zones as more stress is built up during subduction 

• Exceptions : some earthquakes may occur away from plate boundaries (eg within Eurasian plate)

pacific ring of fire

Pacific ring of fire → broad belt around the pacific ocean where most earthquakes and active volcanoes occur

Compromise all 3 types of plate boundaries

1. Convergent : pacific plate moving towards the philippine plate

2. Divergent : pacific plate moving away from the cocos plate

3. Transform : pacific plate sliding past the north american plate at the san andreas fault 

distribution of volcanoes

Volcanoes are generally located near convergent and divergent plate boundaries → at these plate boundaries, magma rises up to the surface, forming volcanoes

Belts of volcanoes may be observed along : 

• Convergent plate boundaries : a belt of volcanoes along subduction zones in the pacific ring of fire

• Divergent plate boundaries : a belt of volcanoes along divergent plate boundaries between the north american and eurasian plates

• Volcanoes are NOT found near transform plate boundaries and continental-continental convergent plate boundaries (magma do not rise to earth’s surface to form volcanoes at these boundaries) 

Exceptions : hot spot volcanoes (found away from plate boundaries)

• Example : The Piton de la Fournaise is a hot spot volcano located on the island of Reunion in the Indian Ocean, away from plate boundaries

earthquake hazards

1. ground shaking

2. soil liquefaction

3. landslides

4. tsunamis

volcanic eruption hazards

1. tephra

2. volcanic gases

3. lava flows

4. pyroclastic flows

5. lahars

6. volcanic landslides

distribution of tectonic hazards

earthquake hazards → generally located within the same geographic region as earthquake

volcanic hazards → generally found along convergent and divergent plate boundaries

Exception : not all tectonic activities localized

• Hazards such as tsunamis and volcanic ash may spread beyond geographic regions

• Tsunami waves and volcanic ash may trave thousand of kilometres from where they originated

• Example (tsunami) : The 2004 Indian Ocean tsunami travelled almost 5000km to Africa, with sufficient energy to cause deaths and death

• Example (volcanic ash) : during the eruption of Mount Pinatubo in 1991, ash spread across SEA.