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Geography - Tectonic Processes And Hazards❌ > Earthquakes > Flashcards

Earthquakes Flashcards

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1
Q

How far is it to the centre of the core?

A

6500km

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2
Q

How hot can it be?

A

6000c

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3
Q

How do scientists map the internal structure of the earth?

A

Can’t drill into it because of the heat so they use evidence from seismic waves

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4
Q

What are seismic waves?

A

Shock waves released by tectonic movements

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5
Q

What are the main layers of the earth?

A

Core - inner and outer
Mantle
Crust - oceanic and continental

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6
Q

What is the core?

A

At the centre

Inner - It is solid and mostly consists of iron (6000c).

Outer - semi-molten and mostly consists of liquid iron and nickel (4500-6000c).

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7
Q

What is the mantle?

A

Surrounds the core, and is the widest layer making up the earth.

The upper part is solid, but below it the rock is semi-molten - forming asthenosphere

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8
Q

What is the asthenosphere?

A

Top of the mantle.

Tectonic plates ‘float’

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9
Q

What is the crust?

A

Forms the outer shell of the earth.

Oceanic - a thin, dense layer (6-10km thick), which lines the ocean floor

Continental - an older, thicker, less dense layer (45-50km thick), which makes up the earths landmass.

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10
Q

What is the lithosphere?

A

The solid layer from which tectonic plates are formed.

The crust and the upper mantle.

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11
Q

What is the lithosphere broken into?

A

Into 7 major and several minor parts called tectonic plates, that more relative to each other over the asthenosphere.

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12
Q

What are tectonic plates?

A

Large, irregularly shaped slabs of solid rock that vary greatly in size and more slowly (about 2-15cm a year).

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13
Q

What drives the movement of tectonic plates?

A

Mantle convection
Slab pull
Subduction
Seafloor spreading

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14
Q

What is mantle convection?

A

Heat produced by the decay of radioactive elements in the earths core heats the lower mantle - creating convection currents.

These hot, liquid magma currents are thought to move in circles in the asthenosphere - causing the plates to move.

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15
Q

What is slab pull?

A

Newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it cools.
This causes it to sink into the mantle under its own weight - pulling the rest of the plate further down with it.

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16
Q

What is subduction?

A

As two oceanic plates (or an oceanic and continental plate) move towards each other, one (denser) slides under the other into the mantle - where it melts in an area known as the subduction zone.

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17
Q

What is seafloor spreading?

A

In the middle of many oceans are huge mid-ocean ridges, or underwater mountain ranges.
These are formed when hot magma (molten rock) is forced up from the atmosphere and hardens - forming new oceanic crust.

This new crust pushes the tectonic plates apart in a process called seafloor spreading.

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18
Q

What’s a plate boundary?

A

Where two tectonic plates meet

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19
Q

What happens at plate boundaries?

A

Most tectonic activities occur (mountain building, earthquakes, volcanoes).

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20
Q

What are plate margins?

A

The areas adjacent to plate boundaries.

And includes areas either side of the boundary that may be affected by movement.

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21
Q

What are the types of plate boundaries?

A

Convergent - destructive margins
Divergent - constructive margins
Conservative - transform margins

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22
Q

What is a destructive plate margin?

A

The plates move towards each other (converge)

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23
Q

What happens at destructive plate margins?

A

The plates are moving together. The denser crust sinks below the lights crust into the mantle where it melts in the subduction zone.

The energy released by this movement may create an earthquake and the molten magma may rise upwards causing a volcanic eruption.

Fold mountains and oceanic trenches may form.

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24
Q

What are the types of destructive plate margins?

A

When oceanic plate meets continental plate
When oceanic plate meets oceanic plate
When continental plate meets continental plate

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25
Q

What is the Benioff zone?

A

The area where friction is created between colliding tectonic plates, resulting in intermediate and deep earthquakes.

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26
Q

What happens when an oceanic plate meets a continental plate?

A

Oceanic plate is denser, so when the plates collide, the oceanic plate slides beneath the continental plate into the mantle and melts.

Deep ocean trenches mark the place where oceanic plate starts to sink beneath the continental plate.
The subduction also leads to the formation of fold mountains.

Volcanic eruption are also generated as magma created by the melting oceanic plate pushes up through faults in the continental crust to reach the surface - where it causes explosive volcanic eruptions.

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27
Q

What happens when an oceanic plate meets an oceanic plate?

A

The denser or faster oceanic plate is subducted beneath the other.

Deep ocean trenches form where this occurs, and the subducted plate then melts - creating magma, which rises up from the Benioff zone to form underwater volcanoes.

The subduction also produces shallow- to deep-focus earthquakes - e.g. the 2004 Indian Ocean tsunami

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28
Q

What happens when a continental plate meets a continental plate?

A

A collision margin occurs.

As both plates are about the same density, and are less dense than the asthenosphere beneath them, neither plate is actually subducted.
Instead they collide and sediments between them are crumpled and forced up to form high fold mountains, like the Himalayas.

However, there can be some subduction, caused when the compressed (therefore denser) sediments result in plate subduction beneath them.

There is no volcanic activity, but any earthquakes are likely to have a shallow focus - increasing their severity.

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29
Q

What are fold mountains?

A

As the two plates collide, the continental plate is folded and slowly pushed up, forming chains of fold mountains.

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30
Q

What happens to underwater volcanoes?

A

Over millions of years, these growing volcanoes rise above the sea level to form separate island volcanoes, which are usually found in curved lines called island arcs.

31
Q

What are constructive plate margins?

A

Two plates are moving apart

32
Q

What do constructive plate margins form?

A

In oceans = mid-ocean ridges

On continents = rift valleys

33
Q

What are mid-ocean ridges?

A 
Mid-ocean ridges of underwater mountains extend for over 60,000km across the world’s ocean floors. 
Regular breaks (called transformer faults) cut across these ridges as they spread at different rates.

Shallow-focus earthquakes (less than 70km depth) occur, but they pose little risk to humans because the shocks are minor and occur underwater.

Regular volcanic eruptions also create submarine volcanoes along these mid-ocean ridges, some of which grow above sea level to create new islands such as Iceland on the Mid-Atlantic ridge.

34
Q

What are rift valleys?

A

When plates move apart on contents, the crust stretches and breaks into sets of parallel cracks (faults).
The land between these faults then collapses, forming steep-sided valleys called rift valleys.

35
Q

What happens at conservative plate margins?

A

The plates are sliding past each other where they meet at a fault.

Sometimes the plates stick as they move past each other, causing stress and pressure to build until the two plates suddenly jerk past each other causing an earthquake and creating crumpled and ridged land.

The San Andreas fault in California is an example.

36
Q

What is formed at a conservative plate margin?

A

No crust is made or destroyed, and there is no volcanic activity.

However, this type is very tectonically active, and can be associated with powerful earthquakes.

37
Q

What are conservative plate margins?

A

Plates slide past each other

38
Q

Where does most tectonic activity occur?

A

95% of earthquakes occur along tectonic plate boundaries.

Many hazards occur around the ring of fire (around the Pacific Ocean)

39
Q

What is the focus?

A

The point inside the crust from which the pressure is released.

40
Q

What is the epicentre?

A

The point above the focus - this is where most shaking and damage occurs

41
Q

What is a fault and transform fault?

A

Break in the crust

On a larger scale, which affects a wider area

42
Q

What happens at constructive plate margins?

A

This type of boundary is mostly found under the ocean where plates are moving apart.
The gap created is filled by magma rising up from the mantle below, forming new crust and often forming volcanoes.

Some volcanoes have become large enough to create islands such as Iceland.

43
Q

What are seismic waves?

A

How an earthquakes energy is released

44
Q

How do seismic waves work?

A

These waves radiate out from the focus, like the ripples when a stone is thrown into a pond.

45
Q

What are the main types of waves?

A

Primary waves and secondary waves are called body waves, because they travel through the earths body

Love waves are surface waves, because they travel along the Earth’s surface.

46
Q

What do P waves stand for?

A

Primary or pressure waves

47
Q

What are P waves?

A

These are the fastest and first to reach the surface.

They travel through both solids and liquids (and shake in a backwards and forwards motion).

They are only damaging in the most powerful earthquakes

48
Q

What do S waves stand for?

A

Secondary or shear waves

49
Q

What are S waves?

A

These are slower (60% of the speed of P waves).

They only travel through solids (and move with a sideways motion, shaking at right angles to the direction of travels).

They do more damage than P waves.

50
Q

What do L waves stand for?

A

Love waves

51
Q

What do L waves do?

A

These are the slowest (last to arrive), but they cause the most damage (shaking the ground from side to side).

They are larger and focus all of their energy on the Earth’s surface.

52
Q

How do you measure seismic waves?

A

Seismometer - which detects and measures ground shaking

53
Q

What is used to measure earthquakes?

A

Magnitude and intensity

54
Q

What does magnitude measure?

A

The amount of energy released at the epicentre.

55
Q

What scale is used to measure magnitude?

A

Moment Magnitude Scale (MMS) - generally preferred, because it’s accurate and better at measuring large earthquakes.

56
Q

What does the MMS measure?

A

The total energy released by an earthquake at the moment it occurs using the:

  • size of the seismic waves
  • amount of slipping or rock movement
  • area of the fault surface broken by the earthquake
  • resistance of the affected rocks
57
Q

How does the MMS scale work?

A

Goes from 1 (smallest) to 10 (can be infinite).

It’s logarithmic - each number is ten times the magnitude of the number before.

58
Q

What is earthquake intensity?

A

An earthquakes effect on people, structure and the natural environment.

59
Q

What’s a scale used to measure intensity?

A

Modified Mercalli Intensity Scale - takes observations from people who experienced the earthquake and rates them on a scale from I (hardly noticed) to XII (catastrophic).

60
Q

What are the two types of earthquake effects?

A

Primary

Secondary

61
Q

What are primary effects?

A

Those that happen as a direct result of an earthquake

62
Q

What are types of primary effects?

A

Ground shaking - causes infrastructure to collapse - killing or injuring those nearby.
Crustal fracturing - when energy released during an earthquake causes the earths crust to crack - leaving gaps

63
Q

What are secondary effects?

A

The effects that occur directly as a result of this earthquake shaking and energy release.

64
Q

What are types of secondary effects?

A

Liquefaction
Landslides/avalanches
Tsunami

65
Q

What is liquefaction?

A

The violent shaking during an earthquake causes surface rocks to lose strength and become more liquid than solid.

The subsoil loses its ability to support building foundations, so buildings and roads tilt or sink.

It can make rescue efforts more difficult, and also disrupt underground power and gas lines (leading to fires).

66
Q

What are landslides/avalanches?

A

The ground shaking places stress on slopes, so that they fail (resulting in landslides, etc).

Many of these effects account for a large proportion of the damage and injuries caused by an earthquake.

67
Q

How are tsunami secondary effects?

A

Some underwater earthquakes generate tsunami that cause major problems for coastal areas.

68
Q

What are aftershocks?

A

For weeks, months or even years after an earthquake, other smaller earthquakes may follow

69
Q

Where do aftershocks occur?

A

In the general area of the original earthquake

70
Q

What results in aftershocks?

A

They’re the result of the earth ‘settling down’ or readjusting along the part of the fault that slipped at the time of the main earthquake.

In general, the larger the earthquake, the larger and more numerous the aftershocks.

71
Q

What are intra-plate earthquakes?

A

Earthquakes that occur in the middle of plates

72
Q

What is forecasting?

A

Provides a percentage chance of a hazard happening, but cannot say exactly when.

73
Q

What are precursors?

A

Research today focuses on identifying ‘warning signs’, that may suggest a major earthquake is about to happen.

74
Q

What’s an example of a precursor?

A

Foreshocks - small earthquakes that happen before a larger one.

None have proved to be a reliable sign that an earthquake is about to happen.

Geography - Tectonic Processes And Hazards❌ (10 decks)

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