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323: Geological Hazards > 1: Earthquake Location And Size > Flashcards

1: Earthquake Location And Size Flashcards

Questions based on the Lecture 1: Earthquake Location and Size, as well as surrounding reading.

1
Q

What percentage of earthquakes occur at plate boundaries?

A

95%

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2
Q

What are the three fault types?

A

Normal, reverse and strike-slip

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3
Q

Give an example and case study of mixed faulting

A

Oblique-slip, san-andreas 1906: 6m horizontal, a few vertical.

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4
Q

What are intraplate earthquakes?

A

Earthquakes which occur in the centre of a plate

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5
Q

Why do intraplate earthquakes occur (two potential reasons)?

A

Either former/failed plate boundaries, or unloading of crust – we don’t fully understand

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6
Q

What is the difference between the focus and the epicenter?

A

Focus – at depth, epicenter – at surface.

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7
Q

What is the deepest depth an earthquake can generally occur at?

A

690km

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8
Q

Besides at subduction zones, most earthquakes occur above what depth?

A

35km

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9
Q

What is a Watadi-Benioff zone?

A

The 3D zone upon which earthquakes occur in a subduction zone, the dipping plane.

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10
Q

Name the two types of body waves and explain how each works

A

P-waves: propel through rock in direct form (compressional-dilation), S-waves: traditional wave moving side to side as it propels forward (shearing motion).

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11
Q

Name the two types of surface waves and explain how each works

A

Love waves: side to side shearing, rayleigh waves: rolling motion

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12
Q

What is the typical velocity through a rock such as granite for each of these 4 waves?

A

P-waves (Vp): ~5 km s-1, S-waves (Vs): ~3 km s-1, Love waves: 0.9 of Vs, Rayleigh waves: slightly slower than Love waves.

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13
Q

Which type of waves are the most hazardous?

A

Love and Rayleigh waves as they cause the most destruction at the surface.

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14
Q

Which component of a three-component seismograph is best to measure P-wave velocity?

A

Vertical

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15
Q

What is needed to triangulate the position of an earthquake?

A

The difference between P-wave travel time and S-wave travel time for multiple locations

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16
Q

How many stations would be needed to triangulate the focus of an earthquake?

A

4

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17
Q

How many stations would be needed to triangulate the epicenter of an earthquake?

A

3

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18
Q

Give three examples of earthquake intensity scales

A

Modified Mercalli (MM), European Macro-scale (1998) (EMS-98) and the Japanese Meterological Agency (JMA).

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19
Q

Where is the MM primarily used, and how does it work?

A

USA official, has 12 levels of intensity

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20
Q

Where is the JMA primarily used, and how does it work?

A

Japan and Taiwan. There are 10 devisions, the scale is ranked 0-7, with ranks 5 and 6 divided into upper and lower

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21
Q

Where is the EMA-98 primarily used, and how does it work?

A

European countries with a number outside. 12 divisions similar to MM.

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22
Q

What is the biggest difference between EMA-98 and MM?

A

Slight differences on how the event is described: eg Destructive is at VIII on MM, while at IX on EMS.

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23
Q

How many values are given for each earthquake on a magnitude scale?

A

1

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24
Q

What does the symbol “μ” stand for in seismology?

A

Shear Modulus

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25
Q

What does the symbol “A” stand for in seismology?

A

Area of ruptured fault plane

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26
Q

What does the symbol “d” stand for in seismology?

A

Displacement along fault plane

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27
Q

What is the formula for Seismic Moment, M0?

A

μAd = M0

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28
Q

What are the units for M0?

A

Nm

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29
Q

Besides estimating μ, A and d, how else can we determine Seismic Moment?

A

Directly from spectral analysis of seismograms

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30
Q

What is the name for a fault that does not rupture at the surface?

A

A blind fault

31
Q

How is M0 related to Mw?

A

Mw = 2/3 ((logM0)-9.1)

32
Q

What are the units for Mw?

A

No units

33
Q

What is the range of Mw?

A

1-10

34
Q

Energy release increases by a factor of __ for each increase of 1 on the Mw scale.

A

32

35
Q

Name the 5 key factors that the intensity of an earthquake depends upon.

A

Magnitude, focus depth, distance from epicenter, rupture direction, type of rock or sediment

36
Q

What is the principle of the Gutenberg-Richter Law?

A

The frequency of earthquakes decreases with increasing magnitude.

37
Q

What event was closest in energy equivalent to Mw:7.8: San Fransisco (1906)?

A

Mt Saint Helens eruption

38
Q

Give an example and case study of mixed faulting

A

Oblique-slip, san-andreas 1906: 6m horizontal, a few vertical.

39
Q

What are intraplate earthquakes?

A

Earthquakes which occur in the centre of a plate

40
Q

Why do intraplate earthquakes occur (two potential reasons)?

A

Either former/failed plate boundaries, or unloading of crust – we don’t fully understand

41
Q

What is the difference between the focus and the epicenter?

A

Focus – at depth, epicenter – at surface.

42
Q

What is the deepest depth an earthquake can generally occur at?

A

690km

43
Q

Besides at subduction zones, most earthquakes occur above what depth?

A

35km

44
Q

What is a Watadi-Benioff zone?

A

The 3D zone upon which earthquakes occur in a subduction zone, the dipping plane.

45
Q

Name the two types of body waves and explain how each works

A

P-waves: propel through rock in direct form (compressional-dilation), S-waves: traditional wave moving side to side as it propels forward (shearing motion).

46
Q

Name the two types of surface waves and explain how each works

A

Love waves: side to side shearing, rayleigh waves: rolling motion

47
Q

What is the typical velocity through a rock such as granite for each of these 4 waves?

A

P-waves (Vp): ~5 km s-1, S-waves (Vs): ~3 km s-1, Love waves: 0.9 of Vs, Rayleigh waves: slightly slower than Love waves.

48
Q

Which type of waves are the most hazardous?

A

Love and Rayleigh waves as they cause the most destruction at the surface.

49
Q

Which component of a three-component seismograph is best to measure P-wave velocity?

A

Vertical

50
Q

What is needed to triangulate the position of an earthquake?

A

The difference between P-wave travel time and S-wave travel time for multiple locations

51
Q

How many stations would be needed to triangulate the focus of an earthquake?

A

4

52
Q

How many stations would be needed to triangulate the epicenter of an earthquake?

A

3

53
Q

Give three examples of earthquake intensity scales

A

Modified Mercalli (MM), European Macro-scale (1998) (EMS-98) and the Japanese Meterological Agency (JMA).

54
Q

Where is the MM primarily used, and how does it work?

A

USA official, has 12 levels of intensity

55
Q

Where is the JMA primarily used, and how does it work?

A

Japan and Taiwan. There are 10 devisions, the scale is ranked 0-7, with ranks 5 and 6 divided into upper and lower

56
Q

Where is the EMA-98 primarily used, and how does it work?

A

European countries with a number outside. 12 divisions similar to MM.

57
Q

What is the biggest difference between EMA-98 and MM?

A

Slight differences on how the event is described: eg Destructive is at VIII on MM, while at IX on EMS.

58
Q

How many values are given for each earthquake on a magnitude scale?

A

1

59
Q

What does the symbol “μ” stand for in seismology?

A

Shear Modulus

60
Q

What does the symbol “A” stand for in seismology?

A

Area of ruptured fault plane

61
Q

What does the symbol “d” stand for in seismology?

A

Displacement along fault plane

62
Q

What is the formula for Seismic Moment, M0?

A

μAd = M0

63
Q

What are the units for M0?

A

Nm

64
Q

Besides estimating μ, A and d, how else can we determine Seismic Moment?

A

Directly from spectral analysis of seismograms

65
Q

What is the name for a fault that does not rupture at the surface?

A

A blind fault

66
Q

How is M0 related to Mw?

A

Mw = 2/3 ((logM0)-9.1)

67
Q

What are the units for Mw?

A

No units

68
Q

What is the range of Mw?

A

1-10

69
Q

Energy release increases by a factor of __ for each increase of 1 on the Mw scale.

A

32

70
Q

Name the 5 key factors that the intensity of an earthquake depends upon.

A

Magnitude, focus depth, distance from epicenter, rupture direction, type of rock or sediment

71
Q

What is the principle of the Gutenberg-Richter Law?

A

The frequency of earthquakes decreases with increasing magnitude.

72
Q

What event was closest in energy equivalent to Mw:7.8: San Fransisco (1906)?

A

Mt Saint Helens eruption

73
Q

What is the name of the law which states as magnitude of earthquakes increases, frequency decreases?

A

Gutenberg-Richter law

323: Geological Hazards (7 decks)

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