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Earthsci 2GG3 > Lecture 3 - Earthquakes and Volcanoes > Flashcards

Lecture 3 - Earthquakes and Volcanoes Flashcards

1
Q

What is the most common reason for an earthquake?

A

Movement of the plates

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2
Q

Epicentre?

A

The point where the seismic rupture begins (origin)

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3
Q

Seismograph?

A

Used to measure an earthquake

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4
Q

Earthquake magnitude?

A

Measured by moment magnitude, logarithmic, quantitative measurement (M1, M5, etc.)

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5
Q

Earthquake intensity?

A

Modified Mercalli intensity scale: qualitative, based on damage to structures/perceptions (I - XII)

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6
Q

Shake maps?

A

Use seismograph data to show areas of intesnes shaking

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7
Q

Dip slip fault?

A

Vertical movement, includes Normal, Reverse, and Blind

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8
Q

Hanging wall?

A

The top wall of a fault

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9
Q

Footwall block?

A

The bottom wall of a fault

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10
Q

Normal fault?

A

The hanging wall moves down

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11
Q

Reverse fault?

A

The hanging wall moves up

thrust fault: if a reverse fault is 45º or less

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12
Q

Blind fault?

A

Don’t extend to the surface

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13
Q

Strike slip fault?

A

Horizontal movement: the plates slide past eachother

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14
Q

Active fault:

A

movement during the past 11 600 years

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15
Q

Potntially active fault:

A

movement during the past 2.6 million years

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16
Q

Inactive fault:

A

no movement in the last 2.6 million years

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17
Q

Tectonic creep?

A

Movement along a fault is so gradual that earthquakes are not felt

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18
Q

P waves (primary/compressional)?

A

move fast with a push/pull slinky motion, good in all states of matter

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19
Q

S waves (secondary/shear?)

A

moves like a water wave, but only through solids

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20
Q

Surface waves?

A

rolling waves on the surface that move more slowly than body waves

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21
Q

Love waves

A

surface waves that cause horizontal shaking

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22
Q

Rayleigh waves

A

surface waves with rolling motion

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23
Q

How can distance to the epicentre be determine from S and P waves?

A

Compare travel times of the two wave types using triangulation

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24
Q

When does amplification occur?

A

When energy is transferred from P and S waves to surface waves

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25
Q

What are the steps of the earthquake cycle?

A
  • inactive period (stress builds)
  • foreshock (occur prior to major release)
  • main shock (majority of the stress is released)
  • aftershock (releases of stress after major earthquake)
26
Q

Intraplate Earthquakes?

A

Occur within plates, not at a boundary

- often smaller than plate boundary earthquakes

27
Q

Precursor?

A

An event that signals that an earthquake may be imminent

  • pattern/freq of earthquakes
  • land level change (uplift/subsidence)
  • seismic gaps (haven’t seen an earthquake in a while)
  • physical/chemical changes
28
Q

How much time does the current warning system give for an earthquake?

A

15s to one minute

29
Q

Where are 2/3 of all active land volcanoes found?

A

Pacific Ring of Fire

30
Q

Magma

A

molten rock

31
Q

Lava?

A

magma that reaches the earth’s surface

32
Q

Pyroclastic debris?

A

Leava and rock fragments ejected in a volcanic eruption

33
Q

Volcano?

A

hill or mountain produced by volcanism

34
Q

Vent?

A

opening through which eruption akes place

35
Q

Crater?

A

depression over the vent

36
Q

Caldera?

A

a depression over 1km wide

37
Q

Where does most magma come from?

A

Asthenosphere

38
Q

Decompression

A

Magma is formed - pressure on hot rock is reduced

39
Q

Addition of volatiles

A

Magma is formed - chemcial compounds lower the melting temp of the rock

40
Q

Addition of heat

A

Magma is formed - heat overlying rocks as magmas rise

41
Q

What are the two most abundant elements in magma

A

Silica and Oxygen - SiO2

42
Q

Silica-Rich (felsic) Lavas

A

Very viscous, flow slowly

  • violent explosive eruptions
  • rhyolite
43
Q

Silica-Poor (mafic) lavas

A

Low viscosity, flow easily, quiet eruptions/lava flows

- basalt

44
Q

Intermediate lavas

45
Q

Shield Volcanoes

A
  • largest volcanos in the world
  • arch/dome
  • low silica (mafic) lava
  • basalt
  • not too explosive
  • mauna loa (hawaii)
46
Q

Composite Volcanoes

A
  • Cone shaped
  • intermediate lava, high silica but low viscosity
  • andesite (dicitic)
  • lava flows and explosive activity
  • volcan osorno, chile
47
Q

Volcanic Domes

A
  • dome shaped
  • high silica (felsic) magma
  • very explosive
  • rhyolite
  • mono craters, california
48
Q

Cinder Cone Volcanoes

A
  • steep cone
  • low silica (mafic) magma
  • not very explosive
  • basalt
  • mount edziza, BC
49
Q

Maars?

A

The interaction of magma and groundwater: produces roughly circular craters filled with water

50
Q

Ice Contact Volcanoes

A

Erupt beneath or against glaciers

51
Q

Jokulhaups

A

Huge floods produced from subglacial volcanoes

52
Q

Hot springs

A

hot rocks heat grounwater that discharges at the surface

53
Q

Geysers

A

Groundwater boils an underground chamber, erupting steam at the surface

54
Q

Resurgent Calderas and super eruptions

A

very rare but very violent eruptions from supervolcanoes

55
Q

Highest mountain in canada?

56
Q

Volcano that poses the biggest threat to Canada?

A

Mt baker in washington

57
Q

What are some primary effects of a volcano?

A

Lava flows, ash fall, volcanic bombs, pyroclastic flows, pyroclastic surges, lateral blasts, poisonous gases

58
Q

Secondary effects of a volcanic eruption?

A

Lahars (mudflow), debris avalanches, landslides, groundwater/surface contamination, floods, fires, tsunamis

59
Q

Two types of balsaltic lava flows?

A

Pahoehoe (smooth ropy texture, faster)

Aa (more viscious, more damaging, slow)

60
Q

Sector Collapse

A

the flank of a volcano may collapse due to shaking

61
Q

Mt St Helens

A 
May 1, 1980, a large bulge began to grow
May 18, a M5.1 earthquake triggers a landslide/debris avalanche
Seconds later, a LATERAL BLAST
Cloud of ash
Mudflows (Lahars)
57 People Killed
62
Q

How can we manage volcanoes?

A
  • Bombing (block channels to cause lava flows to take a dif route)
  • Hydraulic Chilling (water)
  • Wall construction

Earthsci 2GG3 (12 decks)

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