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AS/A-Level Geography > HAZARDS: Seismic hazards > Flashcards

HAZARDS: Seismic hazards Flashcards

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1
Q

Love surface waves.

A

Seismic waves that travel along the surface of the earth, which shake the ground at right angles to direction of movement.

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2
Q

Describe the Richter scale:

A
  • Measures magnitude of earthquake.
  • No upper limit.
  • Logarithmic.
  • Major earthquakes are above 7.
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3
Q

Describe the randomness vs. regularity of earthquakes:

A
  • Don’t seem to follow any clear pattern or trend
  • Occurance is largely random
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4
Q

Often the first warning of tsunami.

Wave trough in front of the tsunami which results in a reduction in sea level.

A

Drawdown.

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5
Q

The nature of an earthquake and its magnitude are affected by what three factors?

A
  • Margin type
  • Rate of movement
  • Depth of focus
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6
Q

What are the three different scales that can be used to measure an earthquake?

A
  • Mercalli scale
  • Richter scale
  • Moment magnitude scale (MMS)
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7
Q

How does depth of focus affect the nature of an earthquake?

A
  • Deep focus quakes tend to be higher magnitude than shallow focus, but often do less damage.
  • This is because deeper shockwaves have to travel further to reach teh surface, which reduces their power.
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8
Q

The point which the pressure release occurs within the crust.

The shockwaves spread out from this.

A

Focus of an earthquake.

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9
Q

What can trigger a tsunami?

A
  • Underwater earthquakes
  • Volcanic eruptions
  • Landslides that slide into the sea
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10
Q

What are the two different types of body waves?

A

Primary or secondary.

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11
Q

What is the primary hazard associated with a seismic event?

A

An earthquake.

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12
Q

What are the primary hazards of an earthquake?

A
  • Ground shaking
  • Ground rupture - major risk for large engineered structures like dams, bridges and nuclear power stations.
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13
Q

Seismic waves that travel along earth’s surface.

A

Surface waves.

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14
Q

What causes an earthquake?

A
  • Tension builds up at all three types of plate margin.
  • When the plates jerk past each pther it sends out shockwaves/vibrations.
  • This is the earthquake.
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15
Q

Surface waves.

A

Seismic waves that travel along earth’s surface.

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16
Q

When a tsunami reaches land, what will its effects depend on?

A
  • Height of the waves and distance they have travelled.
  • Length of the event at the source
  • Extent to which warnings could be given
  • Coastal physical geography, both offshore and on the coastal area
  • Coastal land use and population density
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17
Q

In earthquake-prone areas buildings and other structures can be fitted with devices such as shock absorbers and cross-bracing to make them more earthquake proof.

A

Retrofitting

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18
Q

Body waves.

A

Seismic waves that travel through the earth.

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19
Q

What are the two types of seismic waves?

A

Body waves - travel through earth

Surface waves - travel along earth’s surface

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20
Q

What is a tsunami?

A

Giant sea waves caused by the displacement of large volumes of water.

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21
Q

Ground rupture.

A

Visible breaking and displacement of the earth’s surface, probably along the line of the fault.

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22
Q

Benioff zone.

A

Where earthquakes tend to happen as oceanic crust is being subducted underneath continental crust at destructive boundaries.

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23
Q

What broad category of earthquake tends to cause the greatest damage?

A

Shallow focus.

24
Q

How does rate of movement affect the nature of an earthquake?

A
  • Tectonic plates move in relation to each other at different rates.
  • There is no clear relationship between rate of movement and earthquake magnitude.
25
Q

Where pressure is released (after the slow build up of stress within the rocks due to the movement of the Earth), and parts of the surface experience, for a short period, an intense shaking motion.

The primary hazard caused by seismic activity.

A

What is an earthquake?

26
Q

Tsunami

A

Giant sea waves generated by shallow-focus underwater earthquakes, violent volcanic eruption, underwater debris slides and landslides into the sea.

27
Q

Drawdown.

A

Often the first warning of tsunami.

Wave trough in front of the tsunami which results in a reduction in sea level.

28
Q

Describe the occurance of earthquakes at plate boundaries and intraplate earthquakes:

A

Plate boundaries - 90%

Intraplate - 10%

29
Q

Where earthquakes tend to happen as oceanic crust is being subducted underneath continental crust at destructive boundaries.

A

Benioff zone.

30
Q

What are the similarities and differences between the Richter scale and the Mercalli scale?

Use a table.

A
31
Q

Why do tsunamis cause a high death toll?

A

The often come with very little warning, as they travel very fast in deep water.

It is not until they reach shallower water, that they gain height.

32
Q

Describe the magnitude and frequency of seismic hazards:

A
  • Hundreds of low magnitude quakes happen around the world every day.
  • Higher magnitude happen much less frequently.
  • Number of quakes varies from year to year.
33
Q

What is an earthquake?

A

Where pressure is released (after the slow build up of stress within the rocks due to the movement of the Earth), and parts of the surface experience, for a short period, an intense shaking motion.

The primary hazard caused by seismic activity.

34
Q

Describe the predictability of earthquakes:

A
  • Movement of plates can be monitored to predict at risk areas.
  • But it’s currently impossible to tell when an earthquake will strike a particular place, and what magnitude it is likely to be.
35
Q

Seismic waves that travel through the earth.

A

Body waves.

36
Q

Epicentre

A

The point of the Earth’s surface directly above the focus.

Where the quake is first felt.

37
Q

When will a tsunami be most powerful?

Why?

A

If it starts closer to the coast.

Becuase waves lose energy as they travel towards land, so the closer it starts to the coast, the less energy it will lose.

38
Q

How is a tsunami triggered by an underwater earthquake?

A
  • Earthquake causes seabed to move, displacing water.
  • Waves radiate out from the epicentre.
  • The greater the movement of the sea floow, the greater the volume of water displaced and the bigger the wave produced.
39
Q

How can earthquakes cause landslides and avalanches?

A
  • Shaking of the ground can dislodge rock, soil or snow, causing landslides or avalanches that move downslope quickly.
  • Shaking may also loosen ground material, making it easier for water to infiltrate - the weight of the extra water may trigger a landslide even after ground shaking has stopped.
40
Q

Seismic waves that travel along the surface of the earth, which have a rolling motion.

A

Rayleigh surface waves.

41
Q

Describe the moment magnitude scale (MMS):

A
  • Based on total amount of energy released by earthquake.
  • Logarithmic.
  • No upper limit.
  • More accurate than Richter scale so is more widely used.
42
Q

What are the three broad categories of earthquakes?

A
  • Shallow focus - 0 to 70 km
  • Intermediate focus - 70 to 300 km
  • Deep focus - 300 to 700 km
43
Q

Retrofitting

A

In earthquake-prone areas buildings and other structures can be fitted with devices such as shock absorbers and cross-bracing to make them more earthquake proof.

44
Q

What is soil liquefaction?

A

When soil is saturated with water. the vibrations of an earthquake can cause it to act like a liquid.

This makes the soil weaker and easier to deform, so its more likely to subside, especially where it has a heavy weight on top of it.

45
Q

Rayleigh surface waves.

A

Seismic waves that travel along the surface of the earth, which have a rolling motion.

46
Q

List some secondary effecs of earthquakes:

A
  • Soil liquefaction
  • Landlsides/avalanches
  • Tsunamis
  • Fires
  • Effects on people and the built environment
47
Q

How does margin type affect the nature of an earthquake?

A
  • Biggest occur at destructive margins, as subduction of a plate causes massive pressure to build up, causing a huge quake when released.
  • At constructive margins quakes tend to be lower magnitude than at destructive or conservative margins.
48
Q

Focus of an earthquake.

A

The point which the pressure release occurs within the crust.

The shockwaves spread out from this.

49
Q

At what plate boundary are the most powerful earthquakes associated with?

A

Destructive margins.

50
Q

Seismic waves that travel along the surface of the earth, which shake the ground at right angles to direction of movement.

A

Love surface waves.

51
Q

Visible breaking and displacement of the earth’s surface, probably along the line of the fault.

A

Ground rupture.

52
Q

What human activity might cause minor earthquakes?

Why?

A
  • Building large reservoirs - puts pressure on underlying rocks .
  • Fracking - hydraulic fracturing of rock in order to release gas.
53
Q

Describe the Mercalli scale:

A
  • Measures impacts of earthquake using observations of event, eg reports and photos.
  • Scale is between 1-12
    • 1 = earthquake only detected by instruments.
    • 12 = earthquake that cause total destruction.
54
Q

The point of the Earth’s surface directly above the focus.

Where the quake is first felt.

A

Epicentre

55
Q

Giant sea waves generated by shallow-focus underwater earthquakes, violent volcanic eruption, underwater debris slides and landslides into the sea.

A

Tsunami

56
Q

What are the two different types of surface waves?

A

Love and Rayleigh

AS/A-Level Geography (45 decks)

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