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A Level Physical Geography > Hazards: Seismic > Flashcards

Flashcards in Hazards: Seismic Deck (96)
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1

Where do the most violent earthquakes usually occur?
Give an example

Subduction zones

Eg Nepal, 2015
Eg Sendai -> tsunami

2

Give the physical causes of earthquakes

• Plate boundaries - collision, conservative, constructive, destructive.
• Quakes that occur away from boundaries are associated with the reactivation of minor fault lines.

3

Do earthquakes always occur along major fault lines?

No.
Quakes that occur away from boundaries are associated with the reactivation of minor fault lines.

4

Give the human causes of earthquakes

Human activity:
- building of large reservoirs.
- deep mining.
- fracking.

5

Define focus

The point at which pressure is released within the earth's crust

6

Define epicentre

The point on the earth's surface immediately above the focus, where the most intense ground shaking is felt.

7

Does a shallow or deep focus cause the greatest damage?

Shallow focus

8

Give the depths that defines a shallow focus, intermediate focus and deep focus

Shallow focus = 0-70km deep.
Intermediate focus = 70-300km deep.
Deep focus = 300-700km deep.

9

How many deaths occurred during the Haiti earthquake, 2010?

>300,000 deaths

10

When did the Haiti earthquake occur?

2010

11

Name the different types of shock waves

Primary / pressure waves (P waves)
Secondary / shear waves (S waves)
Surface love (L waves)
Rayleigh (R waves)

12

Where do shock waves originate from?

The focus or epicentre

13

Which type of shock wave is detected first? Why?

Primary waves - they travel fastest so are detected first by seismographs.

14

Which type of shock wave causes the least damage?

Primary waves

15

What type of wave are primary waves? Which direction does the ground move?

Longitudinal waves - ground pulled in same direction as waves.

16

Can primary waves travel through solids and liquids?

Yes

17

Which type of shock wave travels slowest?

Surface love (L waves)
- come after P and S waves

18

Are P waves or S waves more dangerous?

Secondary waves

19

What type of wave are secondary waves?

Transverse wave

20

Can secondary waves travel through solids and liquids?

Only solids

21

What direction do surface love (L) waves travel?

Move back and forth horizontally

22

Which type of shock wave causes the majority of building damage?

Surface love (L)

23

Where are surface love (L) waves created?

Close to epicentre

24

Which direction of shaking is caused by Rayleigh waves?

Vertical and horizontal shaking

25

Which type of shock wave is the most destructive?

Rayleigh

26

Name the scales used to measure earthquakes

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

27

What is the Richter scale? How does it work?

A logarithmic scale with 10 categories.
The magnitude is calculated based on the amplitude measured on seismographs.
Each number on the scale is 10X greater mag than the last.
Energy release is proportional to mag -> for each unit increase on the scale, energy release is 30X higher.

28

How many categories are on the Richter scale?

10

29

Has a Richter scale 10 earthquake ever been recorded?

No

30

What is the mercalli scale?

12 point scale.
Measures the intensity of an event and its impact.
1 = virtually imperceptible (equiv 2 Richter)
12 = total destruction (equiv 8.5 Richter)