1.1 Distribution of tectonic hazards

Question 1

Where are earthquakes distributed?

Answer 1

OFZ (Oceanic fracture zone) - a belt of activity through the oceans along the mid-ocean ridges
CFZ (Continental fracture zone) - a belt of activity following the mountain ranges e.g Himalayans, Alps
70% of all earthquakes are found on ‘ring of fire’ in Pacific ocean
Usually found clustered around plate boundaries
A few earthquakes occur along old fault lines in continental interiors and the hazard is associated with the reactivation of this weakness

Question 2

Where are volcanoes distributed?

Answer 2

Found clustered near plate boundaries
Strong presence around ‘ring of fire’ in pacific ocean
Rare intraplate volcanoes(hotspots) can happen in the middle of plates

Question 3

What is a divergent/constructive plate boundary?

Answer 3

Plates are moving away from each other
Mostly found at mid-ocean ridges
Usually shallow focuses and low magnitude earthquakes
Mostly found under the sea

Question 4

What is a convergent/destructive/subduction plate boundary?

Answer 4

Plates move towards each other
They actively create collision locations(oceanic and continental plates moving towards each other causing subduction)

Question 5

What is a conservative/transform plate boundary?

Answer 5

Plates slide past each other
Either both same direction or opposite direction
Shallow focus earthquakes of considerable magnitude

Question 6

What are earthquakes like at divergent/constructive plate boundaries?

Answer 6

At this boundary, new oceanic crust is created
Earthquakes are frequent, small and low hazard risk due to them being in the ocean
Usually do not trigger tsunamis

Question 7

What are earthquakes like at convergent/destructive/subduction plate boundaries?

Answer 7

Create some of largest, most damaging earthquakes
When a plate slides under the other, at the subduction zone, lots of strain builds up, and the friction is overcome, releasing energy
This energy produces both earthquakes and volcanoes
Subduction zone in pacific ocean is the reason why ‘ring of fire’ has many earthquakes and volcanoes
Continental collision takes place between two continental plates and creates many mountain ranges- no volcanoes here

Question 8

What are earthquakes like at conservative/transform plate boundaries?

Answer 8

Creates quite a lot of risk
When they slide past each other, a zone of friction is created = earthquakes

Question 9

What are volcanoes like at divergent/constructive plate boundaries?

Answer 9

Create rift volcanoes as plate move away from each other at mid-ocean ridges
Less explosive and more effusive(low viscosity)
e.g mid atlantic ridge

Question 10

What are volcanoes like at convergent/destructive/subduction plate boundaries?

Answer 10

Subduction zones created when denser oceanic plate is forced under floating continental plate
Surface volcanoes are volcanoes at ocean floor of earth’s surface
Most of world’s active volcanoes here
Creates most explosive volcanoes
Infrequent but most destructive

Question 11

What are hotspot volcanoes?

Answer 11

Found in the middle of tectonic plates
A volcanic hotspot is an area in the mantle(mantle plumes) from which heat rises as a hot thermal plume from deep in the earth
This high heat and lower pressure at lithosphere enables melting of the rock
This molten magma rises through cracks and erupts to form seamount which is below ocean, which turns into island volcano when it breaks through the water surface
e.g hawaiian volcanoes within pacific plate

Question 12

What are intraplate earthquakes?

Answer 12

caused by stresses WITHIN a plate
as plates move over the spherical earth, zones of weaknesses are creates and intraplate earthquakes happen here
may take place along ancient faults or rift zones