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EAS 205 > Earthquakes > Flashcards

Earthquakes Flashcards

1
Q

What are the 3 main types of earthquakes?

A
  1. dip-slip
  2. thrust fault
  3. strike-slip
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2
Q

Dip-slip earthquakes are due to what kind of stress?

A

tensile

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3
Q

Thrust fault earthquakes are due to what kind of stress?

A

compressive

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4
Q

Strike-slip earthquakes are due to what kind of stress?

A

shearing

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5
Q

Where is the focus of the earthquake?

A

point on a fault where the first movement/break occurs

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6
Q

Where is the epicenter of the earthquake?

A

point on Earth’s surface directly above the focus

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7
Q

What are seismic waves?

A

intense vibrations that travel outwards from the focus

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8
Q

What occurs during elastic rebound during an earthquake?

A

rocks snap back elastically to their previous position after the stress release

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9
Q

What is the displacement of rocks after the release of stress during an earthquake known as?

A

slip

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10
Q

What is the difference between P waves and S waves?

A

P wave: compression waves
S wave: shear waves

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11
Q

Which waves are faster? P waves or S waves?

A

P waves

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12
Q

Which wave pass only through solid rock (i.e. not magma)? S or P waves?

A

S waves

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13
Q

What are the 2 different types of seismic waves? What is the difference?

A

body waves - travel through interior of earth
surface wave - travel along surface of earth

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14
Q

What are the 2 different types of body waves?

A

P waves and S waves

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15
Q

Which type of seismic wave results in the most earthquake damage?

A

surface waves

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16
Q

Which type of seismic wave results in larger ground displacement?

A

surface waves

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17
Q

Do waves move faster through high density rocks or low density rocks?

A

faster through high density rocks

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18
Q

What does a seismograph detect and how does it work?

A

detects ground movement –> used to determine LOCATION OF EPICENTER
- record arrival of different seismic waves
- interval of time between first arrivals of P waves and S waves is a function of distance to the epicenter

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19
Q

What is the minimum number of seismographs required to locate an earthquake (epicenter)?

A

3

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20
Q

What is the difference between magnitude and intensity of an earthquake?

A

magnitude - amount of ground motion
intensity - effect on humans and their structures caused by energy released by an earthquake

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21
Q

What dimensions of an earthquake slip are related to the energy released during an earthquake?

A

length x depth (i.e. strength of rock and area of break)

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22
Q

What is the maximum Richter scale magnitude that can be recorded?

A

8.6

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23
Q

What are the 2 measurements of an earthquake?

A

magnitude and intensity

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24
Q

What is the difference between Richter magnitude and Moment magnitude?

A

Richter - measures amount of ground displacement or shaking at epicenter; logarithmic
Moment - measures what area, displacement, and strength of rock at the earthquake source (focus)

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25
Q

Which historical event used to be a common energy marker when analyzing earthquake energy?

A

hiroshima atomic bomb

26
Q

What does the Modified Mercalli Intensity Scale measure?

A

impact of earthquake events on humans and surface features

27
Q

What are intensities (mercalli) reported as? What is the range of this scale?

A

roman numerals (I, not felt –> XII, total damage)

28
Q

what kind of plate boundaries are associated with shallow earthquakes? Why are they shallow in origin?

A

divergent boundaries and transform faults; shallow b/c due to crustal movements

29
Q

What kind of plate boundaries are associated with deep earthquakes? Why are they deep in origin?

A

convergent boundaries (oceanic and continental crust) i.e. SUBDUCTION ZONES; deep b/c brittle lithosphere is forced deep into asthenosphere

30
Q

What are 2 ways that earthquakes can occur when they are not associated with plate margins?

A
  1. at old faults that were once part of ancient plate boundaries
  2. result of isostatic rebound
31
Q

Are wood frame houses safe for earthquakes?

A

No

32
Q

What are 3 examples of ground failure due to earthquakes?

A
  1. landslides
  2. liquefaction
  3. cracks
33
Q

How does liquefaction cause destruction even when buildings are strongly reinforced?

A

when ground shakes, soil loses cohesive strength, cavities form, water-saturated granular layer pushes up into sediment –> sand boils

34
Q

liquefaction is a big problem for which province in canada?

A

lower mainland of BC

35
Q

What are the 4 steps in creating a tsunami?

A
  1. initiation
  2. split
  3. amplification
  4. runup
36
Q

Describe what occurs during the first step of creating a tsunami.

A
  1. INITIATION (potential energy converted to kinetic energy)

ground shaking –> seafloor permanently uplifted and down-dropped –> entire water column pushed up and down –> potential energy from pushing water up is transferred to horizontal propagation of tsunami wave (kinetic energy)

37
Q

Describe what occurs during the second step of creating a tsunami.

A
  1. SPLIT

initial tsunami split –> one to deep ocean, one to coast

38
Q

How high are tsunami waves when they get split?

A

half the original size

39
Q

Do deep-ocean tsunamis travel faster or slower than tsunamis that are heading towards the shore? Why?

A

deep-ocean tsunamis are faster; speed = square root of water depth

40
Q

Describe what occurs during the third step of creating a tsunami.

A
  1. AMPLIFICATION

amplitude increases as tsunami travels over continental slope; wavelength decreases –> LEADING WAVE STEEPENS

41
Q

Describe what occurs during the fourth step of creating a tsunami.

A
  1. RUNUP

tides come in fast and strong –> tsunamis that break form “bores”

42
Q

What is runup?

A

measurement of the height of the water onshore observed above a reference sea level

43
Q

What is much of the damage inflicted by tsunamis caused by?

A

strong currents and floating debris (NOT usually giant waves)

44
Q

What is a “bore”?

A

vertical walls of turbulent water that form when a tsunami breaks

45
Q

What are edge waves? What is their significance in a tsunami?

A

waves that travel back and forth, parallel to the shore; result in many arrivals of the tsunami at a particular point on the coast (rather than a single wave)

46
Q

TRUE or FALSE: the first runup of a tsunami is the largest.

A

FALSE

47
Q

What kind of plate boundaries do most tsunamis originate from? Explain how the tsunami forms.

A

convergent boundary (subduction zone); the overriding plate is uplifted and then breaks…this causes a sudden uplift at the edge of the plate, which causes the tsunami

48
Q

What are the 4 categories of the tsunami warning system?

A
  1. information advisory
  2. watch
  3. advisory
  4. warning
49
Q

Are tsunami barriers actually effective?

A

not really

50
Q

What would twisted bars in a column indicate about the earthquake that caused it? (i.e. what kind of stress caused it? and what is the name of the earthquake type?) What should the replacement columns look like?

A
  • shearing stress –> strike-slip earthquake
  • replacement columns with more vertical and wrapping rebar (circles)
51
Q

What is the elastic theory of earthquakes?

A

decreasing strain on one fault may increase strain on another fault

52
Q

TRUE or FALSE: Correct predictions of earthquakes are common

A

FALSE: correct predictions are RARE

53
Q

Arrange the following in order of fastest to slowest.

P wave, S wave, radio wave

A

radio wave > P wave > S wave

54
Q

Short term warnings (less than 1 minute) for an earthquake are possible. How is this the case?

A

radio waves travel faster than P waves

55
Q

What is the name of the system in Japan that enable automatic braking of bullet trains in the case of large earthquakes?

A

Urgent Earthquake Detection and Alarm System (UrEDAS)

56
Q

What happens to the overriding plate between earthquakes?

A

overriding plate buckles upwards

57
Q

What happens to the overriding plate during earthquakes?

A

some areas on the overriding plate subside, and others rise (>5m)

58
Q

What is a megathrust zone? Why is it given this name?

A

thin boundary layer between a tectonic plate that sinks into the Earth’s mantle and an overriding plate; largest earthquakes and tsunamis occur here

59
Q

Are shallow-rupture earthquakes more damaging than deep ruptures?

A

yes, shallow is more damaging

60
Q

What is another name given to deep ruptures at megathrust zones?

A

pulse-dominant rupture

61
Q

What is another name given to shallow ruptures at megathrust zones?

A

crack-like rupture

62
Q

Which rupture produces higher frequency seismic waves?

a) pulse-dominant rupture
b) crack-like rupture

A

a) pulse-dominant rupture

EAS 205 (16 decks)

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