Tectonic Hazards- EQ1: Locations at Risk of Tectonic Hazards

Question 1

Natural Hazard

Answer 1

A naturally occurring process or event that has the potential to affect people and their livelihoods

Question 2

Global Distribution of Earthquakes

Answer 2

Commonly found in clusters along plate boundaries (90%) or intra-plate

Question 3

Global Distribution of Volcanoes

Answer 3

Commonly found at plate margins such as the Pacific Ring of Fire (60%) or hotspot regions

Question 4

Global Distribution of Tsunamis

Answer 4

Generated along subduction zones and 90% around the Pacific Basin

Question 5

Divergent (conservative) Plate Boundaries

Answer 5

Two plates are moving away from each other leading to new crust being created by magma being pushed up from the mantle

Question 6

Convergent (destructive) Plate Boundaries

Answer 6

Denser oceanic plate subducts under the lighter continental plate. Built up pressure from the plate melting due to friction can cause a volcano. The movement of plates can cause earthquakes

Question 7

Transform Plate Boundaries

Answer 7

Two plates are sliding past each other, often at different speeds which causes a build up of friction as they drag against eachother

Question 8

Volcanic Hotspot

Answer 8

A volcanic hotspot is an area in the mantle from which heat rises as a hot thermal plume from deep in the Earth

Question 9

How do volcanoes form at hotspots?

Answer 9

Heat melts through the lithosphere, rising through the cracks to form active volcanoes on the Earth’s surface. As the tectonic plate moves over the hotspot like a conveyer belt, a series chain of volcanoes forms called archipelagos (e.g. Hawaii)

Question 10

Oceanic Crust

Answer 10

Thinner, denser, mainly made of basalt

Question 11

Continental Crust

Answer 11

Thicker, less dense, mainly made of granite

Question 12

What drives plate movement?

Answer 12

Convection currents

Question 13

How does slab pull drive plate movement?

Answer 13

The force of an oceanic plate plunging into the mantle due to it’s own weight drives the movement of the plate

Question 14

How does ridge push drive plate movement?

Answer 14

Rigid lithosphere slides down the hot, raised asthenosphere below mid ocean ridges, pushing plates away from each other

Question 15

Sea Floor Spreading

Answer 15

Continuous input of magma forming a mid ocean ridge such as the Mid Atlantic Ridge

Question 16

Paleomagnetism

Answer 16

Record of the Earth’s magnetic field in rocks, sediment and archaeological materials

Question 17

How does paleomagnetism help the study of plate tectonics?

Answer 17

Rocks that contain minerals align with the magnetic field preserving the direction of the magnetic field at the time of their formation which allows geologists to age the rock and map the position of the field for that date.

Question 18

Locked Fault

Answer 18

A fault that is not slipping because the frictional resistance on the fault is greater than the shear stress across it.

Question 19

Why are locked faults a cause for concern?

Answer 19

Locked faults can hold for hundreds of years that is eventually released in a high magnitude earthquake

Question 20

Benioff Zone

Answer 20

Area of seismicity corresponding with the slab being thrust downwards in a subduction zone

Question 21

3 Types of Seismic Waves

Answer 21

P Waves
S Waves
L Waves

Question 22

P Waves

Answer 22

-Caused by compression
-Spread quickly from the fault

Question 22

S Waves

Answer 22

-Vibrate at right angles to the direction of travel
-Can’t travel through liquids
-More destructive than P Waves
-Slower than P Waves

Question 23

L Waves

Answer 23

-Surface waves
-Vibrations in the horizontal plane
-High amplitude

Question 23

Hypocentre

Answer 23

Point within the Earth where the earthquake ruptures

Question 23

Soil Liquefaction

Answer 23

Water-saturated material temporarily loses normal strength and behave like a liquid under the pressure of strong shaking

Question 23

Epicentre

Answer 23

Point on Earth’s surface directly above the hypocentre

Question 24

Landslides

Answer 24

Secondary earthquake hazard where slopes weaken and fall

Question 24

How are tsunamis generated?

Answer 24

-Series of waves caused by sea bed displacement
-Often caused by submarine earthquakes at subduction zones
-Leads to the displacement of a water column

Question 25

How is and earthquake generated?

Answer 25

-Gradual build up of tectonic strain
-When pressure exceeds strength of fault, the rock fractures
-Produces a sudden release of energy, creating seismic waves radiating from point of fracture
-Brittle crust then rebounds either side of fracture (ground shaking)

Question 25

Secondary Hazards of Earthquakes(2)

Answer 25

-Liquefaction
-Landslides

Question 25

Primary Hazards of Volcanic Eruptions (5)

Answer 25

-Pyroclastic flows
-Tephra
-Lava flows
-Volcanic gases
-Ash falls

Question 25

Primary Hazards of Earthquakes(2)

Answer 25

-Crustal fracturing
-Ground shaking

Question 26

Lahars

Answer 26

Volcanic mudflows generally composed of fine sand and silt material

Question 26

Secondary Hazards of Volcanoes(2)

Answer 26

-Lahars
-Jokulhaup

Question 26

Jokulhlaups

Answer 26

Glacial outburst flood which have a very quick onset and rapid discharge of large volumes of water, ice and debris from a glacial source that has been melted

Question 26

Volcanic Eruptions at Convergent (conservative) Boundaries

Answer 26

Larger magnitude due to subduction of old oceanic lithosphere producing andesitic lava

Question 26

Volcanic Eruptions at Divergent (destructive) Boundaries

Answer 26

Smaller magnitude due to rising magma being basic in nature