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GEO1020 > Earthquakes > Flashcards

Earthquakes Flashcards

1
Q

Where are the effects of earthquakes greatest?

A

In built up areas

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2
Q

What are the two main causes of earthquake fatalities?

A

Soilifluction

Landslides

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3
Q

What type of earthquake is more frequent?

A

Small earthquakes are more frequent than big ones

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4
Q

What affects the severity of an earthquake?

A

The depth of the focus

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5
Q

What was the magnitude of the Tainan earthquake in Taiwan on 5th February 2016?

A

6.4

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6
Q

Where do the largest events occur?

A

Where there is subduction

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7
Q

What is the depth of the earthquake like if it is not caused by subduction?

A

If it isn’t a subduction earthquake then it is a shallow earthquake

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8
Q

Why are some poorer areas devastated by earthquakes?

A

Due to finance-
Concrete is expensive so cans are used as foundations
Money is made by selling the top (building) but foundations have to be financed themselves which leaves them poorly constructed

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9
Q

What is an issue with compression?

A

Compression causes more stress which leads to higher pressure, this means the effects are more destructive

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10
Q

What is the first thing heard when an earthquake occurs?

A

A noisy p wave

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11
Q

When do people start to notice earthquakes?

A

When they are magnitude 4 or above

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12
Q

When was the first study of earthquakes?

A

1906 after the San Francisco earthquake

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13
Q

Where do most earthquakes occur?

A

Near plate boundaries

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14
Q

Define hazard

A

The potential to cause harm

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15
Q

Define risk

A

The likelihood of harm in defined circumstances

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16
Q

Give two examples that prove that not all events are equal

A 
Kokoxili earthquake (Central Tibet) in 2001 had no fatalities  M 7.8- high seismic hazard, low seismic risk
Weichuan earthquake in China May 2008 had nearly 90,000 fatalities - high seismic hazard, high seismic risk
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17
Q

What are risks?

A

This is the probability that an event can occur in a given time by the damage that the occurrence would cause

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18
Q

What is the risk equation?

A

Hazard x (people + property0

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19
Q

Define earthquake

A

An abrupt movement in the earth caused by the sudden release of slowly accumulated strain

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20
Q

What is an earthquake?

A

A sudden slip on a fault resulting in ground shaking and radiated seismic energy caused by the slip from the hypocenter or focus

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21
Q

Define epicentre

A

The place on the surface of the earth under which an earthquake rupture originates

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22
Q

Define fault

A

A fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture

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23
Q

What are the 4 types of fault?

A

Normal fault
Right-lateral fault
Reverse fault
Left-lateral fault

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24
Q

Where do normal faults normally occur?

A

Where rifting occurs (at divergent plate boundaries) where two plates or blocks divert away from each other

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25
Q

What is the motion of normal faults?

A

Vertical motion

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26
Q

Give an example of an earthquake on a normal fault

A

Dixie Valley, Nevada 1954 M 7.3

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27
Q

What is the motion of a reverse fault?

A

Vertical motion

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28
Q

Give an example of an earthquake caused by a reverse fault

A

Chi-Chi Taiwan 1999 magnitude 7.6

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29
Q

Where do most reverse faults occur?

A

In a subduction setting (convergent plate boundary) where two plates or blocks converge towards each other

30
Q

What do reverse faults lead to?

A

Changes in the topography as one part moves up and one moves down

31
Q

Give an example of a strike slip fault earthquake

A

Izmit, Turkey 1999 M 7.6

32
Q

Where do most strike slip faults occur?

A

In a transform fault setting (conservative plate boundary) where two plates or blocks slide away from each other

33
Q

What are the two types of strike slip faults?

A

Right lateral and left lateral

34
Q

What is the motion of strike slip faults?

A

Lateral motion

35
Q

What seismic waves are released by earthquakes?

A

P and S body waves and surface waves

36
Q

What are the 5 factors that control the level of shaking?

A 
Magnitude
Distance
Geology
Building style- construction not height
Duration of shaking
37
Q

How can geology affect the intensity of the shaking?

A

Local soils amplify the shaking

38
Q

What is earthquake magnitude a function of?

A

Energy release

39
Q

What is the main scale for measuring earthquake magnitude?

A

Richter Magnitude Scale

40
Q

What sort of scale is the Richter scale?

A

Logarithmic

41
Q

What does it mean that the Richter scale is logarithmic?

A

The amplitude of the seismic waves recorded by a seismograph goes up 10 times for each point on the scale

42
Q

What happens to the energy of the earthquake if the amplitude on the seismograph increases by a factor of 10?

A

There is an increase in energy by a factor of 33

43
Q

What is more common, foreshocks or aftershocks?

A

Aftershocks are more common

44
Q

Where do aftershocks occur?

A

Along the surface rupture of the main event

45
Q

What are 4 indirect effects of earthquakes?

A 
Collapse of structures
Fire 
Liquifaction
Landslides
Tsunamis
46
Q

How many people died as a result of the 2003 Bam earthquake?

A

30,000

47
Q

How many people were injured as a result of the 2003 Bam earthquake?

A

30,000

48
Q

What percentage of buildings were damaged or destroyed as a result of the 2003 Bam earthquake?

A

85%

49
Q

What was the magnitude of the 2003 Bam earthquake?

A

M6.5

50
Q

What was the magnitude of the Boxing Day 2004 earthquake?

A

9.2

51
Q

what are the 3 forms of earthquake records?

A

Instrumental
Historical
Geological

52
Q

What is an issue with instrumental records?

A

They are not available everywhere and records are only since 1950

53
Q

What is an issue with historical records?

A

They are fragmentary anecdotal and not everywhere

54
Q

What do geological records show?

A

Recent fault activity, tectonic geomorphology

55
Q

What don’t undeformed beds experience?

A

Stress

56
Q

What does extension do?

A

It makes faults and regional thinning

57
Q

What does compression make?

A

Faults and folds

58
Q

What does shearing do?

A

It displaces layers horizontally and can result in strike-slip faulting

59
Q

What is elastic?

A

All solids including the Earth’s crust

60
Q

What are the 3 Fs of earthquakes?

A

Forces
Faults
Friction

61
Q

What do jerky motions on faults cause?

A

Earthquakes

62
Q

What is the periodic earthquake model?

A

Earthquakes occur when stress reaches a critical value
Stress is released back down to an ambient value
Therefore size and time are predictable

63
Q

What is the size predictable earthquake model?

A

Earthquakes occur at some point when stress is above a critical value
Stress is released back down to the ambient value
therefore size is predictable but time is not

64
Q

Explain the time predictable model

A

Earthquakes occur when stress reaches the critical value
Variable stress is released by the earthquake
Therefore time is predictable but size is not

65
Q

What are 6 ways to cope with seismic risks?

A 
Hazard maps
Frequency/magnitude of earthquakes in specific regions
Building planning
Building regulations
Emergency planning and insurance
Tsunami monitoring systems
66
Q

What does a hazard map do?

A

It takes into account active faults, landslide hazards and geology

67
Q

What is an issue with hazard maps?

A

They don’t take into account building density so the full risk isn’t shown

68
Q

What is one important method of coping with seismic risks?

A

Making sure buildings are resistant to shear

69
Q

How can resistance to shear be improved?

A

Supporting corners in buildings

70
Q

What sort of bedrock is safer to live on?

A

Solid bedrock

71
Q

What is the Richter scale based on?

A

Resistance

GEO1020 (16 decks)

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