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Geohazard > Lesson 2: Earthquakes > Flashcards

Lesson 2: Earthquakes Flashcards

1
Q

For rocks to be deformed, they must be acted upon by stress which can be classified into three (3) basic types. what are they?

A

compression, tension, shear

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2
Q

stress that pushes on rocks from opposite directions which causes rocks to be shortened parallel to the stress applied

A

compression

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3
Q

stress that pulls rocks from opposite directions, resulting it to become stretched/lengthened

A

tension

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4
Q

stress that occurs when rocks are being pushed in an uneven manner, causing the rocks to be skewed such that different sides of a rock body slide or move in opposite directions

A

shear

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5
Q

Rocks near the surface of the earth are _______

A

elastic

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6
Q

when a force (stress) that is acting on them is removed, the rocks will return to their original shape

A

elastic

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7
Q

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

A

elastic limit

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8
Q

the specific fracture along a fracture plane where rocks slide past one another

A

fault

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9
Q

do all fractures involve slippage/movement? do all faults?

A

all faults do, not all fractures, some are just joints

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10
Q

What type of fault is the North Bohol Fault (NBF)?

A

Reverse Fault with minor right- and left lateral displacement

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11
Q

what type of fault is the PFZ

A

left lateral fault

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12
Q

thrust vs reverse fault

A

thrust -gentler slope (less than 30 degrees
reverse -steeper

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13
Q

fault scarp vs fault-line scarp

A

fault scarp is fresh, fault-line scarp if underwent significant weathering

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14
Q

location of north bohol fault

A

uh several towns, but famously a scarp is seen in Anonang Inabanga, Bohol

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15
Q

He is a Scottish geologist who authored the The Dynamics of Faulting and Dyke Formation with Application to Britain (Edinburgh, 1942, 1951)

A

Ernest Masson Anderson

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16
Q

He systemized our knowledge of the geometry and stress fields of various faults.

A

Ernest Masson Anderson

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17
Q

According to a specific famous Scottish geologist, the direction of the maximum principal stress along normal faults is ?

A

vertical

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18
Q

refer to vibrational waves that travel through solid earth materials

A

seismic waves

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19
Q

Types of origins of seismic waves

A

magmatic, tectonic, or artificial

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20
Q

2 classifications of seismic waves

A

body waves
surface waves

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21
Q

waves that - travel trough the earth’s interior, spreading outward from the hypocenter in all directions (like sound in air)

A

body waves

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22
Q

subdivisions of body waves

A

primary waves
secondary waves

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23
Q

compressional waves; parallel to direction the wave is travelling, causing rocks to alternately compress and decompress as successive waves pass through.

A

primary (P) waves

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24
Q

Body waves that travel transverse/perpendicular to direction of wave propagation

A

secondary (S) waves

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25
Q

travel on the earth’s surface away from the epicenter (like ripples on water); slowest wave (typically at a speed that is 10% slower than S-waves), can cause more property damage compared to body waves.

A

surface waves

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26
Q

2 basic types of surface waves

A

Rayleigh waves
Love waves

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27
Q

waves also known as ground roll, spread to the ground as ripples, similar to rolling waves on the ocean; move both vertically and horizontally in a vertical plane pointed in the direction in which the wave is travelling;

A

Rayleigh waves

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28
Q

Surface waves that move the ground from side to side in a horizontal plane but at right angles to the direction of propagation.

A

Love waves

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29
Q

speed of waves P and S?

A

P →4 to 7 km/s
S →2-5 km/s

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30
Q

describe the order of arrival of the 2 types of body waves

A

P is first to arrive, S arrives at a later time than P

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31
Q

describe the mediums of transport of the two types of body waves

A

P →can pass through solid and liquid
S →cannot pass through liquid, only solid

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32
Q

the instrument used to detect seismic waves.

A

seismometer

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33
Q

describe how a seismometer works

A

➮A heavy suspended mass is held as motionless as possible
➮suspended by springs or hanging it as a pendulum.
➮When the ground moves, the frame of the instrument moves with it.
➮The inertia of the heavy mass keeps it from moving and act as a point of reference in determining the amount of ground motion, but does not record the motion

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34
Q

a seismometer with a recording device that
produces a permanent record of earth motion, usually in the form of wiggly line drawn on a moving strip of paper.

A

seismograph

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35
Q

the paper record of earth vibration.

A

seismogram

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36
Q

explain how a seismogram works

A

➮The different waves travel at different rates, so they arrive at seismograph stations in a definite order: first P waves, then S waves, and finally, the surface waves.
➮Analysis of seismograms can reveal the location and strength of the earthquake.

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37
Q

describe how earthquakes can be located

A
  1. P and S waves start out from the hypocenter.
  2. As they travel, they gradually separate because of their different speeds.
  3. The interval of the time of arrival between P and S waves increases with increasing distance of the seismic stations from the focus and epicenter; the longer the time, the greater the distance is.

➮The interval of arrival between S and P waves is used to calculate the distance of the seismograph station from the earthquake source.
➮The increase in P-S interval increases with distance so a travel-time curve can be constructed from earthquake records.

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38
Q

describe how one station vs many can record an earthquake

A

➮A single station can record only the distance, not the direction to a quake.
➮The location of an earthquake is determined by drawing circles on a map (or globe) with the seismograph stations distributed in different parts of the globe as the centers and the corresponding
distances from the earthquake as the radii.
➮The intersection of the three circles pinpoints the location of the earthquake.

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39
Q

classification of earthquakes according to the depth of focus

A

1) Shallow – 0-70 km
2) Intermediate – 70-350 km
3) Deep – 350-670 km

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40
Q

How were the major layers of the earth inferred?

A

basically seismic surveys.

changes in seismic wave velocities/behavior that depend on the change of density/characteristic of earth layers

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41
Q

the layer in which almost all rocks that are exposed on the Earth’s surface are formed

A

lithosphere

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42
Q

defined as a trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath the earth’s surface.

A

earthquake

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43
Q

Prior to modern science, many people believed what about earthquakes?

A

many people believed earthquakes were random events; some even thought they were punishment by gods for evil or immoral behavior.

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44
Q

when rocks are subjected under a force, also called ________, they can become deformed and have a corresponding change in their shape (_______) or volume (________), a process known as __________;

A

stress;
distortion;
dilation;
strain

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45
Q

rocks are also considered to be _______, meaning that if the force is removed, they will ________.

A

elastic;
return to their original shape

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46
Q

maximum amount of strain they can accumulate before either fracturing or undergoing plastic deformation

A

elastic limit

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47
Q

When brittle materials reach their elastic limit they undergo __________deformation by________, whereas ductile materials deform by _________.

A

permanent;
fracturing;
flowing plastically

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48
Q

2 types of earthquakes

A

volcanic;
tectonic

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49
Q

describe volcanic earthquakes

A

earthquakes due to volcanic activity (eruption or rising magma under a volcano)

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50
Q

earthquakes due to movement of rocks past one another along faults.

A

tectonic earthquakes

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51
Q

tectonic earthquakes occur when a rock breaks, ________ are sent out or produced, known as ________, causing earthquakes

A

waves of energy;
seismic waves

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52
Q

Based on the relationship between stress and strain and the deformation of rocks, earth scientists have developed the _________ that explains the occurrence of earthquakes

A

elastic rebound theory

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53
Q

explain the elastic rebound theory

A

➮This theory holds that earthquakes originate when a force (stress) acts on a rock body,
➮causing it to deform and accumulate strain.
➮Eventually the rock reaches its elastic limit, at which point it ruptures or fails suddenly, releasing the strain it had accumulated.
➮This sudden release of strain, lasting anywhere from several seconds to a few minutes, is transformed into vibrational wave energy that radiates outward and causes the ground to shake

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54
Q

The release of energy generally begins at a point called ?

A

focus/hypoceneter

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55
Q

the point on the earth’s surface directly above the hypocenter is termed as ?

A

epicenter

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56
Q

When rocks become more ductile (less _____) they tend to _______, and instead undergo _________.

A

brittle;
accumulate less strain;
plastic deformation

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57
Q

why do earthquakes not occur deeper than a specific depth below the earth’s surface?

A

because of plastic deformation. below this depth, the higher temperatures cause the rocks to become so ductile that they deform only by plastic flow, hence do not rupture

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58
Q

depth past where earthquakes no longer occur

A

700 km

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59
Q

a series of smaller earthquakes which may continue to occur for days or weeks after the primary earthquake

A

aftershocks

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60
Q

how do aftershocks happen?

A

Rocks in tectonically active areas usually contain numerous faults and the sudden release of strain along one fault can alter the distribution of strain on the other faults. This redistribution of strain commonly produces the aftershocks

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61
Q

aka the primary earthquake

A

main shock

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62
Q

what type of force are earthquakes much stronger? implication?

A

under compressional force, thus convergent boundaries where compressive forces dominate, rocks are able to accumulate much more strain before rupturing than at divergent boundaries where tensional forces are dominant.

also under shear forces in transform fault boundaries

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63
Q

aside from the type of force, what other factor is key to the ability of a rock body to store strain? explain.

A

frictional resistance.
➮In areas where tensional forces dominate the friction along faults is naturally low, allowing them to slip in an almost continuous process.
➮When a rock body experiences this, it obviously cannot build up much strain, which helps explain why large magnitude earthquakes generally do not occur at divergent boundaries.

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64
Q

the process of an almost continuous slipping of faults in low friction areas

A

fault creep

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65
Q

type of fault: San Andreas Fault

A

transform fault, right-lateral (dextral) transform fault that separates the Pacific and North American Plates.

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66
Q

why is the San Andreas Fault often referred to as a fault zone?

A

due to the network of interlocking faults located on either side.

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67
Q

why can strain relieved along one fault disrupt the delicate balance of relationships within the fault zone, triggering additional earthquakes.

A

because of the interlocking nature of fault zones

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68
Q

In northern California where the San Andreas fault moves offshore, the boundary of the North American plate changes from _______ setting to one of ________.

A

from a transform (shear) setting to convergence (compression)

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69
Q

a series of relatively small oceanic plates overridden by the north American plate

A

Cascadia subduction zone

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70
Q

what is produced/generated by the Cascadia subduction zone

A
  1. Cascade Mountain Range
  2. subduction zone earthquakes
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71
Q

4 key factors as to why subduction zone earthquakes are capable of releasing unusually large amounts of energy

A

(1) the way the overriding plate buckles and becomes locked.
(2) the surface area over which the slippage or rupture occurs can be quite large compared to that in other plate settings.
(3) the descending oceanic plate is relatively cool, which makes the rocks more brittle and capable
of accumulating more strain before rupturing.

in addition to the intense ground shaking,

(4) some of this energy can be transferred to the ocean, creating tsunamis that reach heights of 100 feet (30 m) as they crash into coastal areas.

72
Q

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

A

Wadati-Benioff zone

73
Q

what is particularly worrisome about the Cascadia subduction zone and what is the implication?

A

worrisome: the last major earthquake to occur there was in 1700

implication: this means that over the past 300 years strain may have accumulated to dangerously high levels.

74
Q

fault in the PH that hasnt moved in a long time

A

Marikina Valley fault

75
Q

earthquakes that occur far from a plate
boundary or active mountain belt and are generally believed to be related to tectonic forces that are being transmitted through the rigid plates.

A

intraplate earthquakes

76
Q

explain how stress and strain works for intraplate earthquakes

A

➮tectonic forces cause crustal rocks to slowly accumulate strain,
➮which is then released along buried fault systems,
➮producing earthquakes in the interior of continents.

77
Q

areas in the US with considerable history of producing powerful intraplate earthquakes

A

➮New Madrid seismic zone;
➮Charleston seismic zone

78
Q

This strong intraplate earthquake (Mm 7.5) occurred in a heavily populated area, which was totally unprepared largely because the people had no memory of a large earthquake ever occurring in the
region.

The 250,000 to 650,000 people that perished provide a sober lesson for cities located in areas with large but infrequent earthquakes.

A

1976 Tangshan disaster in China

79
Q

what is the common saying among seismologists

A

“EARTHQUAKES DON’T KILL PEOPLE, BUILDINGS DO.”

80
Q

the leading cause of death and property damage in most earthquakes.

A

Structural failure

81
Q

the forces engineers need to take into account when designing structures, and which is the most important? and why?

A

➮gravity;
➮horizontal (lateral) forces: wind

➮gravity is the most important because all
structures have mass, at a bare minimum they must be strong enough to support their own weight against the force of gravity.

82
Q

in what direction are structures usually the strongest? and why?

A

➮vertical direction
➮because of gravity being the most important force that engineers have to take account of when designing structures

83
Q

is wind a minor consideration when designing buildings?

A

yes, compared to compared to the vertical load or weight.

84
Q

is the lack of structural strength in the lateral direction a concern?

A

➮in most places of the world, not really
➮but it becomes one of critical importance in areas where strong earthquakes occur, like the Philippines :”)

85
Q

the most destructive kinds of earthquake waves, and why?

A

➮surface waves
➮due to the fact they cause the ground to vibrate in a lateral direction and at the same time, roll up and down like an ocean wave.

86
Q

The most dangerous types of homes, and why

A

➮those constructed of unreinforced masonry
➮because they offer very little resistance to lateral shearing motion.

87
Q

describe homes constructed of unreinforced masonry

A

➮walls are usually constructed of brick
or stone bound together with mortar
➮as opposed to reinforced walls with internal supports of wood or steel

88
Q

describe the normal setting of building structures

A

➮for multistory buildings, many of
which are nonresidential, construction usually involves an interior skeleton made of steel or steel-reinforced concrete.
➮Under normal conditions the entire weight of the building is easily supported by its vertical columns

89
Q

describe the setting of building structures during an earthquake

A

➮the strong lateral forces will cause the structure to sway.
➮In some cases this swaying motion may become so great that some of the floors within the building become detached from the columns, leaving the floors to fall freely.

90
Q

a process when a floor of a building becomes free, it naturally falls onto the one below, which can cause additional floors to fail in a cascading manner that
engineers

A

pancaking

91
Q

example of structural failures during earthquakes

A
  1. pancaking
  2. rupture of steel reinforced concrete columns
92
Q

explain how rupture of steel reinforced concrete columns happen

A

➮columns are widely used for supporting highways, bridges, and buildings.
➮However, they can fail when the swaying motion of a structure becomes so great that the concrete columns, which are quite brittle, reach their elastic limit and literally explode.
➮Once the concrete shatters, the entire structure can collapse since the steel reinforcing rods alone are not capable of supporting the weight of the structure.

93
Q

3 factors that affect ground shaking

A
  1. Period, Natural Vibration Frequency, and Resonance
  2. Focal Depth and Wave Attenuation
  3. Ground Amplification
94
Q

the time (in seconds) it takes for a building to naturally vibrate back and forth

A

Period

95
Q

describe how the size of structures relate to the period of natural vibration

A

the smaller the structure, the shorter the time it takes to vibrate back and forth

96
Q

T or F: The ground, where structures are built, follows the building’s natural period during motion

A

The ground, where structures are built, also HAS ITS OWN natural period during motion

97
Q

Describe how the type of ocean wave can affect different sized ships

A

➮small frequent waves will shake small boats but wont affect large ships

➮large infrequent waves shake large ships but wont affect small boats

98
Q

describe the relationship on the lithology and period

A

➮harder lithologies like hard bedrocks have shorter periods
➮while softer sediments have longer periods

99
Q

refers to the vibration of a structure/building at a fixed frequency;

A

natural vibration frequency

100
Q

the number of times the motion is repeated in a set
amount of time.

A

frequency

101
Q

relationship between building height to the natural vibration frequency

A

as building height increases, the natural vibration frequency decreases

102
Q

what is then the danger of earthquakes and the natural vibration frequency of buildings?

A

➮The problem occurs during an earthquake when the natural vibration frequency of a given building matches that of the seismic waves
➮whereby the amplitudes of the individual waves combine

103
Q

phenomenon when the amplitudes of the individual waves combine causing a building to sway more violently

A

resonance

104
Q

how many stories of buildings are the most susceptible to resonance

A

Buildings around 10–20 stories high

105
Q

T or F: tall skyscrapers are unlikely to experience resonance as their vibration frequency is beyond the frequency range of most seismic waves

A

True

106
Q

energy of the resulting seismic waves steadily decreases as they travel away from the focus

A

wave attenuation

107
Q

explains why the most dangerous earthquakes tend to be those with a combination of large magnitude and shallow focal depth

A

wave attenuation

108
Q

T or F: it is quite possible for a relatively shallow, low-magnitude quake to generate greater ground motion than a deep, high-magnitude quake.

A

True

109
Q

explain how Seismic waves experience different amounts of wave attenuation, depending on the types of geologic materials the waves pass through

A

➮Loose materials and rocks of lower density will absorb more energy from passing seismic waves compared to rocks that are more rigid and dense
➮On areas of rigid rocks, seismic waves are able to retain more of their energy as they travel farther. Because the waves undergo less attenuation, they therefore have the potential to cause damage farther from the focus.

110
Q

When seismic waves travel through weaker materials, they slow down and lose energy at a faster rate. This, in turn, causes wave amplitude to increase, creating a phenomenon known as ?

A

ground amplification

111
Q

how does Ground amplification occur in sedimentary basins

A

➮when seismic waves enter a basin and begin to amplify since they are forced to slow down in the sedimentary material.
➮Such areas may have an extended duration of ground shaking and subsequent increase in the likelihood of structural failure as seismic waves can become trapped within a basin and undergo internal reflection creating a reverberating effect.
➮Also, the convex shape of a basin can cause waves to refract and merge, focusing their energy into localized areas which then experience more
intense shaking.

112
Q

secondary earthquake hazards

A

intense ground shaking often
produces secondary hazards such as:

  1. Liquefaction
  2. ground displacement
  3. ground fissures
  4. earthquake-induced mass wasting
  5. fires
  6. tsunamis
113
Q

process when compacted sand-rich layers of sediment that are normally in contact with one another behave as fluid

A

liquefaction

114
Q

explains how liquefaction happens

A

➮this happens as a result of the shearing motion of S-waves that increase the water pressure within the pore space of the sediment
➮thereby preventing the vibrating sand grains from making contact with one another.
➮As soon as the shaking stops, the sand-rich material will again behave as a solid as the individual sand grains are able to make contact with each other.

115
Q

structure evidence for historical earthquakes esp for trenching

A

sand blows

116
Q

rocks on either side of a fault move way from each other horizontally and/or vertically. Because of the potential for displacement, critical structures like dams, nuclear power plants, underground pipelines, hospitals, and schools should not be built across known faults

A

ground displacement

117
Q

are large open cracks that typically develop close to the surface in loose sediment where there is little resistance to the rolling and stretching motion associated with surface waves.

A

ground fissures

118
Q

When earthquakes provide one of the basic triggering mechanisms for the downslope movement of earth materials due to gravity such as landslide (debris slump), rock falls, and mudflows.

A

earthquake-induced mass wasting

119
Q

secondary hazard when underground gas lines are easily broken when surface waves roll through a city and are likely to be ignited by sparks from countless electrical shorts in damaged buildings and downed power lines.

A

fires

120
Q

a series of ocean waves that form when energy is suddenly transferred to the water by an earthquake, volcanic eruption, landslide, or asteroid impact.

A

tsunamis

121
Q

when do most of tsunamis form

A

The majority of tsunamis, however, form during subduction zone earthquakes when crustal plates abruptly move and displace large volumes of seawater.

122
Q

In 1902, an Italian seismologist developed a means of comparing both modern and historical earthquakes through the use of firsthand human observations during earthquakes. who was he?

A

Giuseppe Mercalli

123
Q

what was the scale created by the famous Italian seismologist

A

Mercalli intensity scale

124
Q

scale whereby earthquakes are ranked based on a set of observations most humans could report objectively, particularly the type of damage sustained by buildings.

A

Mercalli intensity scale

125
Q

is a seismic scale used and developed by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) to measure the intensity of an earthquake.

A

Philippine Earthquake Intensity Scale (PEIS)

126
Q

how was the PEIS developed?

A

It was developed as a response to the 1990 Luzon Earthquake (magnitude 7.7) and was adopted in the Philippines in 1996

127
Q

what did PEIS replace?

A

Rossi-Forel Intensity Scale

128
Q

who developed the RFIS?

A

Michele Stefano de Rossi
and
Francois-Alphonse Forel

129
Q

range of the PEIS

A

Intensity scale ranges from I to X, with X classified as completely devastating.

130
Q

these types of scales are useful because they quantify the amount of ground motion during an earthquake, and the energy that was released when the rocks ruptured.

A

magnitude scales

131
Q

scale that - rates earthquakes based on the size of their seismic waves, as measured by seismographs; governed by amplitude (wave height) and distance

A

Richter Magnitude Scale

132
Q

who developed the Richter Magnitude Scale

A

Charles F. Richter

133
Q

the problem with Richter Magnitude Scale

A

➮as the number of seismograph stations around the world steadily increased, scientists eventually realized that results obtained using the Richter magnitude scale were not always consistent with one another,
➮particularly for large-magnitude earthquakes.

134
Q

based on similar types of seismogram measurements as Richter’s, but is more accurate over a wide range of magnitudes and geologic conditions; based on the total amount of energy released and is determined by measuring the surface area of the ruptured fault and how far the land moved along the fault

A

Moment Magnitude Scale

135
Q

describe the magnitude of the values in the Richter magnitude scale

A

➮each increase represents a 10-fold increase in ground shaking

➮ this corresponds to about a 30-fold increase in energy released at the focus

136
Q

7 classes of earthquakes and their corresponding magnitudes

A

Microearthquake — 1.0-1.9
Minor — 2.0-3.9
Light — 4.0-4.9
Moderate — 5.0-5.9
Strong — 6.0-6.9
Major — 7.0-7.9
Great — 8.0-+

137
Q

Mw 8.1 earthquake that happened in Davao City 1979
>intensity V
>59 depth

A

Moro Gulf Earthquake

138
Q

3 methods of assessing earthquakes

A
  1. long-term forecasting
  2. short-term prediction
  3. other methods
139
Q

Forecasting based mainly on the knowledge of when and where earthquakes occurred in the past.

A

Long-term forecasting

140
Q

T or F: In seismically active areas, small earthquakes are more likely to occur as
the amount of time increases since the last major event.

A

False, LARGE earthquakes are more likely to occur as
the amount of time increases since the last major event

141
Q

two important aspects in long-term forecasting

A
  1. paleoseismology
  2. seismic gaps
142
Q

study of prehistoric earthquakes

A

paleoseismology

143
Q

what does paleoseismology involve

A

the study of offsets in sedimentary layers near fault zones to determine recurrence intervals of major earthquakes prior to historical records

144
Q

a zone along a tectonically active area where no earthquakes have occurred recently, but it is known that elastic strain is building in the rocks.

A

seismic gap

145
Q

what happens if a seismic gap can be identified?

A

then it might be an area expected to
have a large earthquake in the near future

146
Q

involves monitoring of processes that occur in the vicinity of earthquake
prone faults for activity that signify a coming earthquake.

A

short-term prediction

147
Q

Anomalous events or processes that may precede an earthquake are called ?

A

precursor events

148
Q

what do precursor earthquakes signal?

A

a coming earthquake

149
Q

why has short-term earthquake prediction been difficult to successfully obtain

A

the processes that cause earthquakes occur deep beneath the surface
and are difficult to monitor.
* earthquakes in different regions or along different faults all behave
differently, thus no consistent patterns have so far been recognized

150
Q

Delete

A

Delete

151
Q

what are the 6 earthquake precursors

A
  1. increase in foreshocks
  2. slight swelling/uplift or tilting of the ground surface
  3. decreased electrical resistance
  4. fluctuating water levels in wells
  5. increased concentration of radon gas in groundwater
  6. generation of radio signals
152
Q

Causes microcracks to form prior to complete rupture, or main shock.

A

increase in foreshocks

153
Q

microcracks
increasing the rock volume

A

Slight swelling/uplift or tilting of the ground surface

154
Q

water entering new void spaces that is more conductive than surrounding minerals.

A

Decreased electrical resistance

155
Q

water entering new cracks causes water
levels to lower; levels rise when voids close again.

A

Fluctuating water levels in wells

156
Q

new cracks allowing the gas, a radioactive decay product of uranium, to escape from rocks and enter wells.

A

Increased concentration of radon gas in groundwater

157
Q

caused by changes in rock strain or movement of saline groundwater.

A

Generation of radio signals

158
Q

3 examples of non-conventional/non-intrusive methods

A
  1. microtremor survey method
  2. refraction microtremor survey
  3. horizontal-to-vertical ratio method
159
Q

This method uses seven (7) portable seismometers that will record microtremors for a few minutes

A

microtremor survey method

160
Q

what are instruments for microtremor survey method equipped with?

A

GPS for time synchronization and
location coordinates

161
Q

full GPS

A

Global Positioning System

162
Q

describe how refraction microtremor method works

A
  1. A series of geophones planted on the ground connected to
    a seismograph
  2. A hammer striking a steel plate is used as the seismic
    source
  3. Propagating waves are measured and analyzed
163
Q

Uses the same instrument as
the ones used in microtremor
array method

A

horizontal-to-vertical spectral ratio method

164
Q

do you need to set up horizontal-to-vertical spectral ratio method

A

no, only single station

165
Q

describe the recording of horizontal-to-vertical spectral ratio method

A

Records fundamental ground period of an area

Only requires a recording time of 20 minutes at most

166
Q

4 ways to reduce earthquake risks

A
  1. seismic engineering
  2. early warning systems
  3. planning and education
  4. earthquake control?
167
Q

specific example of seismic engineering

A

Addition of cross-bracing and shear walls, base isolation, wrapping of columns with a steel jacket, and spiral wrapping technique on vertical reinforcing rods

168
Q

benefits of seismic engineering

A

➮provide greater structural strength with respect to the shear forces generated by lateral ground motion and a structure’s own inertia; and
➮reduce the actual amount of shear force that can develop on the structure.

169
Q

instead of demolishing old buildings with outdated designs or without any seismic controls, what can be done?

A

A somewhat expensive, but viable option is to retrofit existing buildings with seismic controls

170
Q

The basic idea behind this is to take advantage of this time lag and the fact that P-waves do very little damage. The first P-wave then is simply used as an alert that the highly destructive S-waves and surface waves will soon follow.

A

Early Warning Systems

171
Q

3 specific examples of early warning systems

A
  1. Only seconds are needed for preprogrammed systems to close valves on gas lines, thereby reducing the risk of uncontrolled fires.
  2. Trains can be programmed to automatically stop.
  3. Electric utilities can also shut down critical control systems on electrical grids and at power plants.
172
Q

the first step in planning and education as a way to reduce earthquake risks

A

➮The first step is to determine the level of severity of risk in a given area
➮by conducting hazard assessment
➮and subsequent construction of hazard maps.

173
Q

based on hazard assessments, what do government agencies do to mitigate earthquake hazards?

A

➮government agencies will develop
building codes
➮that require appropriate levels of seismic engineering in buildings and other structures

174
Q

in terms of education what can be done to reduce earthquake risk?

A

➮Raising of awareness on what to do before, during, and after an earthquake on all levels of society, from school-aged children up to emergency management
officials.
➮Regular earthquake drills

175
Q

examples of how humans can induce earthquakes

A
  1. fluids can change affect the energy distribution of rocks (dam construction, injecting toxic wastes into wells)
  2. nuclear testing (explosions causing earthquakes)

Geohazard (7 decks)

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