Tectonics EQ1

Question 1

Where do most earthquakes occur?

Answer 1

At plate boundaries

Question 2

What type of plate boundaries usually lead to the most powerful earthquakes?

Answer 2

Convergent & Conservative

Question 3

What percentage of earthquakes occur at plate boundaries?

Answer 3

95%

Question 4

Where are active volcanoes most usually found?

Answer 4

At or near plate boundaries, in particular the Ring of Fire (75%)

Question 5

What percentage of all earthquakes are found in the Ring of Fire?

Answer 5

70%

Question 6

Why can intra-plate earthquakes occur?

Answer 6

Usually due to hotspots or old fault lines

Question 7

What did Alfred Wegener propose?

Answer 7

The theory of continental drift where the continents were once joined together but have gradually moved over time

Question 8

What are some evidence of continental movement?

Answer 8

Basalt lava flows where continents tear apart
Coal in Antarctica
Fossils of Mesosaurus
Fossils of Glossopteris
Outlines of continents piece together

Question 9

What is the plate tectonic theory?

Answer 9

The Earth consists of plates which have a section of lithosphere, that move slowly over the lower mantle due to convection- this leads to crust being created, destroyed, torn or thrust up

Question 10

Is the oceanic crust or the continental crust thicker?

Answer 10

Continental. (70km), whilst oceanic is 6km thick

Question 11

Is the ocean crust or the continental crust more dense?

Answer 11

Oceanic. Continental crust has 60% silica content, making it less dense than oceanic which has basic composition (similar to basaltic lava)

Question 12

What is the Mohorovicic Discontinuoty?

Answer 12

The division between the upper mantle and lower mantle, due to differences in seismic wave speed

Question 13

What is the Benioff Zone?

Answer 13

An area of seismicity corresponding with the slab being thrust downwards in a subduction zone (area in which earthquakes occur)

Question 14

What is the hypocentre?

Answer 14

The ‘focus’ point within the ground where the strain energy of the earthquake stored in the rock is first releases

Question 15

Focal length

Answer 15

The distance between the hypocentre and epicentre

Question 16

Epicentre

Answer 16

The point of the ground directly above the hypocentre

Question 17

Seismic waves

Answer 17

Waves that transmit the energy released by an earthquake (either primary, secondary or love waves)

Question 18

Liquefaction

Answer 18

The process by which water-saturated material can temporarily lose normal strength and behave like a liquid under the pressure of strong shaking

Question 19

Convection currents

Answer 19

Heat produced by the decay of radioactive elements in the Earth’s core heats the lower mantle causing upwards movement, creating convection currents (which are thought to move in circles)

Question 20

Paleomagnetism

Answer 20

The alternating polarisation of our magnetic field (evidence of sea floor spreading)

Question 21

What is sea floor spreading?

Answer 21

Hot magma is forced up the asthenosphere, before hardening and forming new oceanic crust, which pushes the plates apart (forming mid-ocean ridges/underwater mountain ranges_

Question 22

What is subduction?

Answer 22

As two oceanic plates (or continental+oceanic) move towards each other, one slides under the other (due to differences in density) into the mantle before melting in the subduction zone

Question 23

What is slab pull?

Answer 23

The density of the plate and gravity causes a plate to be pulled down into the mantle

Question 24

What is ridge push?

Answer 24

Newly formed oceanic crust at mid ocean ridges becomes denser and thicker as it cools, causing the lithosphere to slope away from the ridge and gravity to pull it down

Question 25

What are the three ways volcanoes can be formed?

Answer 25

Convergent plate margins- composite cone volcanoes Divergent plate margins- rift volcanoes Hotspots

Question 26

What are hotspots?

Answer 26

Areas in the mantle that form where radioactive decay is concentrated, from which heat rises as a hot thermal plume from deep in Earth

Question 27

How are volcanic arc islands eg. Hawaii formed?

Answer 27

Hotspot volcanism, as magma plumes stay stationary, the lithosphere continues to move, creating a series of islands

Question 28

Characteristics of effusive volcanoes

Answer 28

-High temperature -Low viscosity -High dissolved gas content -Low silica, basic magma -More likely at divergent margins

Question 29

Characteristics of explosive volcanoes

Answer 29

-Low temperature -High viscosity -Low dissolved gas content -High silica, acidic magma -More likely at a subduction zone

Question 30

How do volcanoes vary? (5 ways)

Answer 30

1) Viscosity (determined by temp+ dissolved gases) 2) Plate margins 3) Explosiveness of eruption 4) Materials ejected (lava/ash/lahars?) 5) Proximity of population centres

Question 31

How do earthquakes occur?

Answer 31

1) Gradual build up of tectonic strain, storing elastic energy in the crust 2) When the pressure > strength of the fault, the rock fractures 3) Sudden release of energy (seismic waves) 4) Brittle brust rebounds on either side of the fracture (ground shaking)

Question 32

P-Waves

Answer 32

Primary waves -fastest and first to reach surface -travel through solids and liquids -compressional waves (backwards + forwards motion)

Question 33

S-Waves

Answer 33

Secondary waves -only travel through solids -move with sideways motion (right angles to travel direction) -more damaging than P waves but slower

Question 34

L-Waves

Answer 34

Surface Love Waves -causes the most damage through crustal fracturing -shakes ground from side to side -slowest

Question 35

What are impacts of liquefaction?

Answer 35

Causes the ground to sink and buildings to collapse

Question 36

What is the difference between an ocean wave and tsunami wave?

Answer 36

Ocean waves are caused by the wind on the surface of the sea, tsunamis are caused by a large volume of water being displaced eg. volcanoes/earthquakes

Question 37

How does a tsunami form?

Answer 37

1) An earthquake/volcano causes the displacement of the water column, causing waves to radiate in all directions 2) As the water becomes shallower, waves slow down and increase in height, which causes the wave energy to be concentrated in a smaller volume of water 3) The tsunami breaks onto the shore

Question 38

What physical factors affect a tsunami?

Answer 38

-Magnitude of eruption/earthquake -Topography of ocean -Relief of the land -Speed of onset -Duration -Coastal ecosystem buffer -Distance travelled

Question 39

What human factors affect a tsunami?

Answer 39

-Quality warning systems -Education of people (preparedness) -Population density -Degree of coastal development eg. coastal defences