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Geohazard > Earthquakes - SEISMIC WAVES AND PLATE TECTONICS > Flashcards

Earthquakes - SEISMIC WAVES AND PLATE TECTONICS Flashcards

1
Q

three basic types of stress that are acted upon on rocks for them to deform

A

compression; tension; shear

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2
Q

it is a type of stress that pushes on rocks from opposite directions which causes rocks to be shortened parallel to the stress applied

A

compressional stress

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3
Q

a type of stress that pulls rocks from opposite direction, resulting it to become stretched/lengthened

A

tensional stress

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4
Q

occurs when rocks are being pushed in an uneven manner, causing the rocks to be skewed

A

shear

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5
Q

in a shear stress, different sides of a rock body slide or move in ______ directions

A

opposite

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6
Q

rocks near the surface of the earth are ____

A

elastic

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7
Q

when a force (stress) acted on rock is removed, they will ____

A

return to their original shape

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8
Q

t or f: all elastic materials have elastic limit

A

T

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9
Q

the point in which materials no longer behave elastically and deformation becomes permanent

A

elastic limit

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10
Q

a fracture plane where rocks slide past one another

A

fault

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11
Q

t or f: all faults involve slippage while fractures do not

A

T

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12
Q

what type of fault is north bohol fault?

A

reverse fault with minor right and left lateral displacement

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13
Q

which direction of displacement is more dominant in NBF?

A

right lateral displacement

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14
Q

when was bohol earthquake and what magnitude

A

October 15, 2013, Mag 7.2

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15
Q

thrust faults are low angle reverse fault with what angle according to phivolcs?

A

<30 degrees

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16
Q

where is the surface manifestations of NBF be found?

A

Brgy. Anonang, Inabanga, Bohol

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17
Q

how high was the vertical displacement of the NBF? and what is it composed of?

A

1-2m high ; it was an uplifted marine platform

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18
Q

when was the Luzon 1990 earthquake and what magnitude was it?

A

July 16, 1990 ; Mag 7.8

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19
Q

how long was the surface rupture during the Luzon 1990 earthquake? in what location does it extend from and to?

A

125 km-long ; from Dingalan, Aurora to Kayapa, Nueva Viscaya

(Imugan, Nueva Viscaya yung may rice paddies na na displace)

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20
Q

what caused 1990 Luzon earthquake?

A

movement of the NW portion of the PFZ and it splay, the Digdig Fault

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21
Q

how long is the PFZ and what is its estimated age?

A

1,200 km-long ; less than 5 mya

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22
Q

slip rate of the PFZ

A

approx 2-2.5 cm/yr

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23
Q

t or f: the PFZ and Digdig fault are both sinistral type of strike-slip fault

A

T

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24
Q

t or f: the Luzon 1990 earthquake was linked to the succeeding 1991 Mt. Pinatubo Eruption

A

T

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25
Q

a scotting geologist who systematized the knowledge on the geometry and stress fields of various faults

A

Ernest Masson Anderson

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26
Q

the direction of maximum principal stress along normal fault is:

A

vertical downward

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27
Q

the direction of maximum principal stress along reverse fault is:

A

horizontal

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28
Q

the direction of maximum principal stress along strike-slip fault is:

A

horizontal, depending on the direction of the displacement

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29
Q

a weathered fault scarp is called a ____

A

fault line scarp

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30
Q

what is a transpressional fault

A

compression and strike-slip

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31
Q

what is a transtensional fault

A

tensional and strike-slip

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32
Q

seismic waves may be _____, _____, or _____ in origin

A

tectonic, magmatic, or artificial

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33
Q

refers to vibrational waves that travel through earth’s materials

A

seismic waves

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34
Q

two general types of seismic waves

A

body waves ; surface waves

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35
Q

two types of body waves:

A

primary waves ; secondary waves

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36
Q

this type of wave travel through the earth’s interior and radiates outward a hypocenter in all directions

A

Body wave

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37
Q

primary waves have _______ movement that is ____ to the direction that the wave is travelling

A

compressional ; parallel

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38
Q

transverse/perpendicular to the direction of wave propagation

A

secondary waves (s-waves)

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39
Q

travels on the earth’s surface away from the epicenter

A

surface waves

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40
Q

surface wave is ____ slower than secondary waves

A

10%

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41
Q

two types of surface waves

A

rayleigh and love waves

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42
Q

also known as ground roll, spread to the ground as ripples, similar to rolling waves in the ocean

A

rayleigh waves

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43
Q

rayleigh waves move both ___ and ____ in a ____ plane

A

vertically and horizontally ; vertical plane

44
Q

love waves move the ground from ____ in a _____ plane but at _____ to the direction of propagation

A

side to side ; horizontal plane ; right angles

45
Q

velocity of primary waves

A

4-7 km/sec

46
Q

velocity of secondary waves

A

2-5 km/sec

47
Q

it is a type of wave that can only travel through solids

A

secondary (s) waves

48
Q

a type of wave that is particularly damaging to the foundation of the structure

A

love waves

49
Q

the instrument used to detect seismic waves

A

seismometer

50
Q

a seismometer makes use of a _____ held as motionless as possible, suspended by ____ or hanging it as a ______

A

heavy suspended mass ; springs ; pendulum

51
Q

the ____ of the heavy mass in a seismometer keeps it from moving and act as a _____ in determining the amount of ________

A

inertia ; point of reference ; ground motion

52
Q

t or f: a seismometer determine the amount of ground motion as well as records it

A

F (does not record)

53
Q

a seismometer with a recording device that produces a permanent record of the earth motion

A

seismograph

54
Q

the paper record of the earth vibration

A

seismogram

55
Q

T or F: seismic waves arrive at seismic station in this order: P waves ; S waves ; Surface waves

A

T

56
Q

analysis of the seismograms can reveal the _____ and ____ of the earthquake

A

location ; strength

57
Q

t or f: the longer the time of arrival interval between p and s waves, the greater the distance the seismograph is from the epicenter

A

T

58
Q

P and S waves start out from the _____, as they travel they gradually ____ because of their ______

A

hypocenter ; separate ; different speeds

59
Q

t or f: a single seismograph can record only the distance but not the direction to an earthquake

A

T

60
Q

in triangulation method, seismograph stations are the _____ and the corresponding distances from the earthquake is the ______

A

centers ; radii

61
Q

classification of earthquake based on depth

A

shallow - 0 to 70km
intermediate - 70-350 km
deep - 350-670 km

62
Q

how were the major layers of the earth inferred?

A

through seismic waves and discontinuities of the earth

63
Q

it is the property of the mantle in which the seismic waves aren’t in uniform velocity because of the alignment of iron minerals

A

seismic anisotropy

64
Q

deformation corresponding to change in shape

A

distortion

65
Q

deformation corresponding to change in volume

A

dilation

66
Q

the maximum amount of strain a material can accumulate before fracturing or undergoing plastic deformation

A

elastic limit

67
Q

brittle materials deform by

A

fracturing

68
Q

ductile materials deform by

A

plastic deformation

69
Q

earthquake is defines as:

A

shaking or trembling of the ground caused by the sudden release of energy stored in rocks beneath the erath’s surface

70
Q

two types of earthquake

A

volcanic ; tectonic

71
Q

earthquakes caused by volcanic activities

A

volcanic earthquakes

72
Q

earthquakes caused by the movement of rocks past one another along faults

A

tectonic earthquakes

73
Q

refers to the theory that explains the occurrence of earthquakes

A

elastic rebound theory

74
Q

elastic rebound theory is based on the relationship between

A

stress and strain, and the deformation of rocks

75
Q

strain released when a material reaches elastic limit is transformed into

A

vibrational wave energy

76
Q

the release of energy begins at the point called the _____

A

focus / hypocenter

77
Q

the point of surface directly above the hypocenter

A

epicenter

78
Q

at what depth earthquakes can no longer occur

A

435 miles (700 km)

79
Q

redistribution of strain commonly produces a series of smaller earthquakes called

A

aftershocks

80
Q

t or f: aftershocks may continue for days or weeks

A

T

81
Q

the primary earthquake is sometimes called the

A

main shock

82
Q

t or f: fore shocks are only considered to be fore shocks right after the main shock happen

A

T

83
Q

cotabato fault system is a _____ type of fault

A

strike-slip

84
Q

cotabato series earthquakes

A

oct 16 - Mag 6.3
oct 29 - Mag 6.6 and 6.1
oct 31 - Mag 6.5

85
Q

rocks are much stronger under a ______ force compared to _____ force

A

compressional ; tensional

86
Q

t or f: at convergent boundaries, where compressive forces dominate, rocks accumulate less strain

A

F (rocks accumulate more strain)

87
Q

at divergent boundaries, tensional forces are dominant over ______

A

frictional forces

88
Q

the other key factor in the ability of a rock body to store strain is the _________

A

frictional resistance of the faults

89
Q

t or f: high frictional resistance of fault generate larger earthquakes

A

T

90
Q

a process where faults slip continuously because of low frictional resistance

A

fault creep

91
Q

t or f: when a rock body experiences fault creep, it can build up more strain therefore generating larger earthquake

A

FALSE (it cannot build up high amount of strain, therefore cannot generate large earthquakes)

92
Q

what kind of fault is the San Andreas fault

A

dextral transform fault

93
Q

it is a network of interlocking faults on either side of a main fault

A

fault zone

94
Q

small branches of larger fault

A

SPLAY

95
Q

strain relieved along one fault can disrupt the ________ within the fault zone, triggering additional earthquakes

A

delicate balance of relationships

96
Q

planar zone of seismicity corresponding with the down-going slab of a subduction zone

A

Wadati-Benioff zone

97
Q

in Northern California, where the San Andreas fault moves offshore the boundary of the _______, it changes from a ______ setting to ______

A

North American Plate ; transform (shear) ; convergence (compression)

98
Q

the ________ starts to override a series of relatively small oceanic plates along what geologist call the _______

A

North American Plate ; Cascadia Subduction Zone

99
Q

Cascadia subduction zone produces volcanic arcs known as the _______, it also generates _______

A

Cascade Mountain Range ; subduction zone earthquakes

100
Q

subduction zone earthquakes are formed when

A

an oceanic plate is overridden by another plate

101
Q

t or f: subduction zones generate extremely powerful and devastating earthquakes

A

T

102
Q

of the ten largest earthquake ever recorded, how many was subduction zone earthquakes? how many were more than a magnitude of 9?

A

9 subduction zone earthquakes ; 4 of those having a magnitude of greater than 9

103
Q

four factors why subduction zone earthquakes are stronger

A
  1. overriding plates buckle and becomes locked
  2. greater slippage or rupture surface area
  3. oceanic plates descend and cool down, making them brittle
  4. tsunami up to 100 feet (30m)
104
Q

when was the last major earthquake to occur in cascadia subduction zone?

A

1700

105
Q

earthquakes that occur far from a plate boundary or active mountain belts are generally called

A

intraplate earthquakes

106
Q

how are intraplate earthquakes formed?

A

tectonic forces travel through rigid bodies into the interior of the earth, in which strain are accumulated and eventually released along buried fault systems

107
Q

of considerable interest in the US are the _____ and _____ seismic zones because they have a history of producing powerful intraplate earthquake

A

Charleston and New Madrid

Geohazard (25 decks)

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