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EAS 205 > earthquakes > Flashcards

earthquakes Flashcards

1
Q

where do earthquakes occur?

A

along linear belts parallel with plate boundaries
(some are within plates)
follow certain bands and patterns

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2
Q

earthquake focal depths are?

A

deep
intermediate
shallow

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3
Q

what is an earthquake?

A

shaking or vibration of the ground due to the built up force from ruptured rocks

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4
Q

how are earthquakes started?

A

built up stress on a block of rock creates a fault (crack), energy rises and springs back since friction prevented easy sliding

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5
Q

what are the three main types of fault movements that can initiate an earthquake and the stresses that cause them??

A

dip-slip: tensile stress
thrust fault: compressive stress
strike-slip: shearing stress

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6
Q

what is a focus?

A

point on a fault at which the first movement or break occurs during an earthquake (crack in the earth)

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7
Q

what is a seismic wave?

A

intense vibrations travel outward from the focus (think waves ripple outward from spot a stone was dropped in a pond)

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8
Q

what is the epicenter?

A

project where rip started to surface; on the earth surface directly above the focus

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9
Q

what is an elastic rebound?

A

sudden displacement and release of stress leads rocks to snap back to their previous dimensions

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10
Q

what is a slip?

A

distance of displacement

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11
Q

what are body waves?

A

travel through earth interior
p and s waves

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12
Q

what are P waves?

A

compression waves; pushing and pulling
mimics a slinky

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13
Q

what is an S wave?

A

shear waves that pass only through solid rock (shaking)

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14
Q

what is a surface wave?

A

travels along surface
larger ground displacement than body waves
most earthquake damage

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15
Q

what factors may affect the energy that is released from an earthquake travels?

A

density of rock = travel time seismic waves
(fast = high density rock)
(slow = low density rock)

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16
Q

what is the order in terms of speed that each type of wave travels (fastest to slowest)?

A

p-wave; s-wave; surface wave

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17
Q

how can we locate where the epicenter is?

A

seismograph (detects ground movement)

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18
Q

how does a seismograph work?

A

separation between the arrival of first p-waves to the arrival of s-waves

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19
Q

how many seismographs are required to locate an earthquake?

A

3

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20
Q

what is an earthquakes magnitude?

A

amount of ground motion

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21
Q

what is an earthquakes intensity?

A

effect on humans and their structures, caused by energy released

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22
Q

energy released by an earthquake are related to what two factors?

A

strength of the rock and area of break (length X depth)

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23
Q

what is the richter scale?

A
  • measure first arrival of p-wave, and count time between receiving s-wave –> provides with distance / how far away it is
  • how high the needle went = how much the earth shook
24
Q

what is the max level the richter scale can record up to?

A

8.6

25
Q

what is moment magnitude?

A

measures what happened at the earthquake source point

26
Q

each step / level in the magnitude scale is __X bigger than the other number?

A

10

27
Q

the richter scale uses _________ to determine the magnitude level; while the mercalli scale uses ___________?

A

numbers (level 5 earthquake); roman numerals (level V earthquake)

28
Q

the mercalli intensity scale can be useful knowledge for earthquake prediction because it can measure?

A

ancient earthquakes based on old texts and folklore

29
Q

what was the biggest earthquake in canada?

A

vancouver island 1949

30
Q

where do shallow earthquakes occur?

A

divergent boundaries and transformation faults
on continents

31
Q

where do deep earthquakes occur?

A

subduction zones (brittle lithosphere forced deep into asthenosphere)

32
Q

earthquakes at convergent margins?

A
  • can be very large deep earthquakes, but not very catastrophic because its too deep
  • bend while subducted, can cause earthquakes where bend takes place
  • large earthquakes on the landside above subduction zone, but shallow and damaging
33
Q

what do earthquakes damage?

A
  1. ground motion
  2. ground failure
  3. fire
  4. tsunamis
34
Q

what is ground motion

A

ground shaking and fault movement

35
Q

in an earthquake, what determines the amount of shaking / damage

A

quality of bedrock

36
Q

what happens when plates are tilted during an earthquake?

A

tilt can cause some to be pushed under sea level, and others raised above sea level

37
Q

ground shaking can cause loose soil to undergo liquefaction, what is that?

A

process that generates a liquid from a solid or a gas

38
Q

how can a tsunami be created from an earthquake?

A

motion of fault block on seafloor causes water to be shifted up

39
Q

how do tsunamis carry out and create damage

A

spring action, hits ground that is carrying water, water proceeds to onshore, water gets shallower and shallower, creating bigger wave, higher runup, causes damage
(waves come in, go back, exposed seafloor)

40
Q

what are three ways to mitigate earthquake damage

A
  1. avoid it!
  2. engineering! better construction and design
  3. predicting / give warnings!
41
Q

how are we learning from past earthquakes?

A

examine damage that took place
way that things shake depend on local environment
safety standards improving all the time

42
Q

can animals have a sense of predicting earthquakes?

A

potentially

43
Q

what does a seismic gap indicate?

A

danger

44
Q

how did the san andreas fault relate to seismic gaps?

A

breaks into slivers, bunch of broken jigsaw puzzle pieces, and unless you know where all the pieces go, do not know the seismic gap

45
Q

what were the two largest earthquakes in Canada

A
  1. 1949: fort bernie, vancouver island
  2. 1929: newfoundland
46
Q

a magnitude earthquake is likely to occur every ___ years?

A

600

47
Q

how can we predict when another earthquake will occur

A

looking at shoreline (raised or sunk) and record

48
Q

deeper sediment allows us to have?

A

better earthquake knowledge

49
Q

what are the types of induced earthquakes?

A
  1. fluid injection and withdrawal
  2. hydraulic fracturing
  3. dams
  4. engineered?
50
Q

what is fluid injection earthquake?

A

pump poison into ground
injecting fluid into grounds causes earthquakes
water injection can cause earthquakes

51
Q

what magnitude of earthquake do you begin getting real damage?

A

5 or higher

52
Q

how does fluid injection cause an earthquake?

A

2/3 water, 1/3 oil, water injected deeper down into the ground

fault where injected, break in the rock is beneath the earth, pressure of the fluid hit the fault, went down, and generated an earthquake

53
Q

how does a fluid withdrawal cause an earthquake?

A

decrease pressure

54
Q

how do dams trigger an earthquake?

A

Large dams that impound deep water reservoirs will change water pressure deep within the ground greatly strained rock

55
Q

how does induced seismicity cause an earthquake?

A

change of stresses

56
Q

what is fracking?

A

drill hole in ground, bend to produce more oil, pump high pressure water in it, rock cracks, squeeze in sand grains to fill the cracks, allows oil and gas to flow back through pipe

57
Q

what was the traffic light system?

A

red = 4.0 (cease operation)
yellow = greater than 2.0 (inform, create respose plan)
green: less than 2.0 (no action)

EAS 205 (17 decks)

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