HAZARDS: Seismic hazards Flashcards Preview

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Flashcards in HAZARDS: Seismic hazards Deck (56)
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1

Love surface waves.

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

2

Describe the Richter scale:

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

3

Describe the randomness vs. regularity of earthquakes:

  • Don't seem to follow any clear pattern or trend
  • Occurance is largely random

4

Often the first warning of tsunami.

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

Drawdown.

5

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

  • Margin type
  • Rate of movement
  • Depth of focus

6

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

  • Mercalli scale
  • Richter scale
  • Moment magnitude scale (MMS)

7

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

  • 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.

8

The point which the pressure release occurs within the crust.

The shockwaves spread out from this.

Focus of an earthquake.

9

What can trigger a tsunami?

  • Underwater earthquakes 
  • Volcanic eruptions 
  • Landslides that slide into the sea

10

What are the two different types of body waves?

Primary or secondary.

11

What is the primary hazard associated with a seismic event?

An earthquake.

12

What are the primary hazards of an earthquake?

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

13

Seismic waves that travel along earth's surface.

Surface waves.

14

What causes an earthquake?

  • 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.

15

Surface waves.

Seismic waves that travel along earth's surface.

16

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

  • 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

17

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.

Retrofitting 

18

Body waves.

Seismic waves that travel through the earth.

19

What are the two types of seismic waves?

Body waves - travel through earth

Surface waves - travel along earth's surface

20

What is a tsunami?

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

21

Ground rupture.

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

22

Benioff  zone.

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

23

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

Shallow focus.

24

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

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

25

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.

What is an earthquake?

26

Tsunami 

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

27

Drawdown.

Often the first warning of tsunami.

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

28

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

Plate boundaries - 90%

Intraplate - 10%

29

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

Benioff  zone.

30

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

Use a table.