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1st Semester > GHC Ch 3: Earthquake Geology and Seismology > Flashcards

GHC Ch 3: Earthquake Geology and Seismology Flashcards

1
Q

What are earthquakes most commonly caused by?

A

Caused most commonly by movement of the Earth across a fault.

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2
Q

Fault

A

Complex zones of breakage in the Earth across which the two sides move relative to each other. Has irregular surfaces, and is many miles wide and long.

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3
Q

How does an earthquake occur?

A

Stresses build up until they are enough to cause rocks to fracture and shift, sending off waves of seismic energy, felt as earthquake.

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4
Q

Understanding faults begins with understanding what rock relationships, formalized by Steno?

A

Law of original horizontality and Law of superposition

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5
Q

Law of original horizontality

A

sediments are originally deposited in horizontal layers

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6
Q

Law of superposition

A

in un-deformed sequence of sedimentary rock layers, each layer is younger than the layer beneath it and older than the layer above it

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7
Q

Law of original continuity

A

sediment layers are continuous

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8
Q

If a sedimentary layer ends abruptly, it may have been…?

A

eroded by water action or truncated by fault passing through layer

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9
Q

Identifying truncated sedimentary layers and recognizing their offset continuation allows determination of…?

A

fault length

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10
Q

Length of fault determines size of…?

A

earthquake possible on fault

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11
Q

Longer fault ruptures create bigger or smaller earthquakes?

A

bigger earthquakes

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12
Q

Where does ‘jointing’ occur?

A

where brittle lithospheric rocks fracture and crack

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13
Q

Large stress differential on either side of a fracture results in movement, and then…?

A

fracture becomes a fault

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14
Q

Movement, ranging from millimeters to hundreds of kilometers, results in what?

A

tilting and folding of layers

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15
Q

Use strike and dip to describe what?

A

describe location in 3D space of deformed rock layer

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16
Q

Dip

A

angle of inclination from horizontal of tilted layer

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17
Q

Strike

A

compass bearing of horizontal line in tilted layer

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18
Q

Dip-slip faults are dominated by what movement?

A

vertical

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19
Q

Miners refer to the block beneath them as the…?

A

footwall (block beneath the fault)

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20
Q

Miners refer to the block above them as…?

A

the hangingwall (block above the fault)

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21
Q

what are dip-slip faults caused by?

A

pushing or pulling force

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22
Q

Strike-slip faults are dominated by what movement?

A

horizontal

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23
Q

right-lateral strike-slip fault

A

When straddling a fault, if right-hand side moved towards you

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24
Q

left-lateral strike-slip fault

A

When straddling a fault, if the left-hand side has moved towards you

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25
Q

How does an earthquake occur at a fault?

A

Stress produces strain , which builds up until rupture occurs at weak point and propagates along fault surface

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26
Q

hypocenter or focus

A

Point where rupture first occurs

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27
Q

epicenter

A

Point directly above hypocenter on surface

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28
Q

Fault rupture

A

series of events over weeks to months to years, with largest event referred to as ‘the earthquake’

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29
Q

foreshock

A

Smaller events preceding ‘the earthquake’

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30
Q

Can you identify a foreshock before the earthquake has occurred?

A

no

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31
Q

aftershocks

A

Smaller events after ‘the earthquake’

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32
Q

Left step in right-lateral fault or right step in left-lateral fault

A

Compression, uplift, hills and mountains

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33
Q

Right step in right-lateral fault or left step in left-lateral fault

A

Extension, down-dropping, basins and valleys

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34
Q

transform faults

A

faults link spreading centers, or connect spreading center to subduction zone. transform fault motion is same as strike-slip fault

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35
Q

Seismology

A

study of earthquakes

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36
Q

seismometers

A

Instruments to detect earthquake waves

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37
Q

seismographs

A

Instruments to record earthquake wave

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38
Q

How does a seismograph work?

A

One part stays as stationary as possible while Earth vibrates: heavy mass fixed by inertia in frame that moves with the Earth, and differences between position of the frame and the mass are recorded digitally

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39
Q

Amplitude of a wave indicates

A

displacement

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40
Q

Wavelength indicates

A

distance between successive waves

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41
Q

Period

A

time between waves (= 1/frequency)

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42
Q

Frequency

A

number of waves in one second (hertz)

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43
Q

Seismic waves come in what two categories?

A

those that can pass through entire Earth (body waves) and those that move near surface only (surface waves)

44
Q

Are body waves faster or slower than surface waves?

A

faster

45
Q

Where are body waves most energetic?

A

near earthquake hypocenter

46
Q

Do body waves have short or long periods?

A

short

47
Q

What are the two types of body waves?

A

P and S

48
Q

Which is the fastest of all waves?

A

P waves

49
Q

Are the P or S waves the first to reach a recording station?

A

P waves

50
Q

How does a P wave move?

A

as push-pull – alternating pulses of compression and extension, like wave through Slinky toy

51
Q

Where can a P wave travel?

A

Through solid, liquid, and gas.

52
Q

What kind of motion does an S wave exhibit?

A

transverse motion – shearing or shaking particles at right angles to the wave’s path (like shaking one end of a rope)

53
Q

Where can an S wave travel?

A

Only through solids

54
Q

What is interesting about the recording of large earthquakes?

A

Waves from large earthquakes can pass through the entire Earth and be recorded all around the world

55
Q

Where do surface waves travel?

A

near the Earth’s surface

56
Q

What creates surface waves?

A

body waves disturbing the surface

57
Q

Do surface waves have longer or shorter periods than body waves? What does this mean?

A

Longer period than body waves. Means surface waves carry energy farther.

58
Q

What are love waves?

A

Similar motion to S waves, but side-to-side in horizontal plane

59
Q

Are love or Rayleigh waves faster?

A

Love

60
Q

Where do love waves not move?

A

through air or water

61
Q

How do rayleigh waves move?

A

Backward-rotating, elliptical motion produces horizontal and vertical shaking, which feels like rolling, boat at sea.

62
Q

When is more energy released as Rayleigh waves?

A

when earthquake hypocenter is close to the surface

63
Q

How far can a rayleigh wave travel?

A

Great distances

64
Q

You need the distance of an earthquake from how many stations to pinpoint location of earthquake?

A

three

65
Q

How does the Richter scale work?

A

Bigger earthquake means greater shaking, which produces greater amplitude of seismogram lines

66
Q

What does an increase by one mean on the Richter scale in regards to magnitude?

A

10 fold increase in recorded amplitude

67
Q

What does an increase by one mean on the Richter scale in regards to energy?

A

the energy release increases by about 45 times, but energy is also spread out over much larger area and over longer time

68
Q

Bigger earthquake means more people will experience shaking and for longer or shorter time?Does this increase or decrease damage to buildings?

A

longer. increase.

69
Q

What is one problem with the Richter scale?

A

Does not work well for distant or large earthquakes

70
Q

Are all magnitude scales equivalent? Why?

A

no. Larger earthquakes radiate more energy at longer periods which are not measured by Richter scale or body wave scale, so large or distant earthquake magnitudes are underestimated

71
Q

What does a Seismic moment (Mo) measure?

A

Measures amount of strain energy released by movement along whole rupture surface

72
Q

Is the Moment Magnitude Scale more accurate for large or small earthquakes?

A

large

73
Q

How is a Seismic moment (Mo) calculated?

A

Calculated using rocks’ shear strength times rupture area of fault times displacement (slip) on the fault

74
Q

What is the equation for a seismic moment?

A

Mw = 2/3 logsub10 (Mo) – 6

75
Q

Large earthquakes are not just single events but…?

A

part of series of earthquakes over years

76
Q

mainshock

A

Largest event in series of earthquakes.

77
Q

foreshocks

A

Smaller events preceding mainshock

78
Q

aftershocks

A

Smaller events following mainshock

79
Q

Fault-rupture length greatly influences what?

A

magnitude

80
Q

Fault-rupture length and duration influence

A

seismic wave frequency

81
Q

Short fault rupture and duration mean

A

high frequency seismic waves

82
Q

Long fault rupture and duration mean

A

low frequency seismic waves

83
Q

Seismic wave frequency influences

A

damage

84
Q

What do high frequency seismic waves do?

A

cause much damage at epicenter but die out quickly with distance from epicenter

85
Q

Where do low frequency seismic waves do the most damage?

A

farther away

86
Q

Where do low frequency seismic waves travel?

A

great distance from epicenter

87
Q

What direction of forces are buildings designed to handle? How does this affect building damage in an earthquake?

A

Vertical. Horizontal shaking during earthquakes can do massive damage to buildings.

88
Q

How is movement measured in an earthquake?

A

Measure in terms of acceleration due to gravity

89
Q

Weak buildings suffer damage from horizontal accelerations of more than

A

0.1g

90
Q

Periods of swaying are about how many seconds per story?

A

0.1

91
Q

What affects building periods?

A

building materials

92
Q

What induces longer periods of shaking?

A

Flexible materials (wood, steel)

93
Q

What induces shorter periods of shaking?

A

Stiff materials (brick, concrete)

94
Q

Velocity of seismic wave depends on what?

A

on material through which it is moving

95
Q

When waves pass from harder to softer rocks, they slow down and must therefore increase their what in order to carry same amount of energy?

A

amplitude

96
Q

resonance

A

If the period of the wave matches the period of the building, shaking is amplified and resonance results

97
Q

Mercalli scale

A

developed to quantify what people feel during an earthquake

98
Q

What should one do before an earthquake?

A

Inside and outside your home, visualize what might fall during strong shaking, and anchor those objects by nailing, bracing, tying, etc.
Inside and outside your home, locate safe spots with protection – under heavy table, strong desk, bed, etc.

99
Q

What should one do during an earthquake?

A

Duck, cover and hold
Stay calm
If inside, stay inside
If outside, stay outside

100
Q

What are the variables of the Mercalli scale?

A

Earthquake magnitude
Distance from hypocenter
Type of rock or sediment making up ground surface

101
Q

How can one eliminate resonance?

A

Change height of building
Move weight to lower floors
Change shape of building
Change building materials
Change attachment of building to foundation
Hard foundation (high-frequency vibrations)  build tall, flexible building
Soft foundation (low-frequency vibrations)  build short, stiff building

102
Q

Shear Walls

A

Designed to receive horizontal forces from floors, roofs and trusses and transmit to ground

103
Q

Braced Frames

A

Bracing with ductile materials offers resistance

104
Q

Base Isolation

A

Devices on ground or within structure to absorb part of earthquake energy

105
Q

What kind of houses houses perform well in earthquakes?

A

Modern 1-, 2-story wood-frame houses

106
Q

What are 5 ways a building can be made to withstand earthquakes?

A

(1) brace it (2) Infill it (3) frame it (4) buttress it (5) isolate it

1st Semester (27 decks)

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