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GEOL 106 > Earthquakes > Flashcards

Earthquakes Flashcards

1
Q

Earthquake

A

shaking (vibration)produced by the rapid release of energy

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2
Q

Generates seismic waves

About earthquakes

A

that travel through the Earth

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3
Q

Focus

A

point of energy release; radiates out in all directions (hypocentre) - when rupture of fault plan started

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4
Q

Epicentre

A

point on Earth’s surface directly above focus

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5
Q

Where do earthquakes occur?

A

Along faults with plate boundaries

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6
Q

Three levels of fault depth

A

Shallow, intermediate, deep

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7
Q

Shallow (which boundaries?)

A

divergent and transform boundaries

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7
Q

Shallow to deep

A

Convergent boundaries

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8
Q

Which depth causes most damage

A

Shallow

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9
Q

Increasing distance from focus results in

A

Diminished shaking strength

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10
Q

Intraplate earthquakes

Where and what depth?

A

Far from boundary, shallow

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11
Q

Earthquake Early Warning

A

Rapid detection, real-time estimation of shaking hazard

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12
Q

Last major quake, what depth

A

April 2015, Nepal

Shallow

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13
Q

Nepal earthquake triggered

A

Landslides and avalanches

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14
Q

interplate vs intraplate earthquakes

A

Occur at plate boundaries vs. occurrence in the interior of the plate boundaries

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15
Q

Earthquake magnitude

Measurement of what radiated by an earthquake?

A

Objective measurement of the energy radiated by an earthquake

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16
Q

Richter magnitude vs moment magnitude

A

Based on distance and amplitude vs. measurement of amount of energy released by earthquake

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17
Q

Moment magnitude (in depth)

Factors in measurement

A

size of area where movement occurs, distance moved, rock type, combines data from seismograms and seismic moment

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18
Q

Modified Mercalli Intensity Scale

A

Qualitative way to describe/compare earthquakes, 12 levels

Describes effects on a place, natural feature, buildings, or humans

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19
Q

Magnitude

q vs. q

A

Quantitative measure of amount of energy released at its source earthquake, one magnitude, not variable

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20
Q

Intensity

Magnitude vs. Intensity (q vs. q)

A

Qualitative, amount of shaking, variable - depends on location

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21
Q

Fault

Is a response to? That allows what?

A

Response to stresses in the rock

Allows blocks to move relative to each other

22
Q

Plate boundaries are

made up of

A

made up of a series of faults

23
Q

Stress

What does this force do to the rock?

A

Force acting on rock, changes shape and/or volume

24
Q

Rupture

starts at

A

starts at focus and propagates outwards; seismic source

25
Q

3 types of faults

A

Normal, reverse, strike-slip

26
Q

Reverse and thrust faulting

Which boundaries?

A

Convergent: Raise up relative to rocks across the fault, compression

27
Q

Normal faulting

A

Drop down relative to rocks across the fault, extension

28
Q

Strike-slip faulting

A

Slide laterally relative to rocks across the fault, right-lateral fault plane

29
Q

What plate boundary is associated with each fault?

A

Normal - divergent plate boundaries

Reverse - convergent

Strike-slip - transform

30
Q

Rayleigh waves - surface waves

A

Arrive after body waves, most damaging, rolling motion

31
Q

P-waves

A

Compressional waves, arrive first, travel through solid, liquid, and gas, compression and stretching

32
Q

S-waves

A

Shear waves, second to arrive, travel only through a solid, up and down

33
Q

Longest fault zone

A

San Andreas Fault System, 1200km long

34
Q

What frequencies do seismic waves have? Which buildings do they affect?

A

Low frequency - tall buildings vibrate

High frequency - low buildings vibrate

35
Q

Attenuation

About high-frequency waves
How does this occur?

A

Weakening or removal of high-frequency waves

Occurs with increased distance, low frequency waves travel farther

36
Q

Mexico City quake - why so much damage?

What frequency waves?

A

Low frequency waves, building heights 6 to 15 stories

37
Q

Material amplification

A

Subsurface materials respond differently to seismic waves

Shaking increases in unconsolidated sediment (mud high shaking, igneous rock low shaking)

38
Q

Seismic Gap

L P Gap

A

e.g. Loma Prieta gap

post-earthquake aftershocks fill the gap, meaning smaller earthquakes in the same general area days to years following a larger event

39
Q

Subduction zone earthquakes

A

Also known as megathrust earthquakes, convergent plate boundaries, largest earthquakes on Earth

40
Q

What type of faulting is involved in a subduction zone earthquake?

A

Reverse fault, thrust fault - shallower dip, meaning its stronger

41
Q

Land elevation changes

A

Uplift and shortening on overriding plate prior to the rupture, extension and subsidence afterwards

42
Q

Where is the Cascadia Subduction Zone

A

3 plates: Explorer, Juan de Fuca, Gorda

Considered “locked in zone”

West coast of America and Vancouver Island

43
Q

What 2 plates are involved in the CSZ

A

Oceanic plate and continental plate

44
Q

Evidence for past megathrust earthquakes in CSZ

A

Oral traditions of First Nations and physical evidence (e.g. coastal ghost forest in Pacific NW)

45
Q

When is the next ‘big one’?

A

Canada’s West Coast, also causing a tsunami

46
Q

What is a locked fault

A

A fault that does not slip due to high friction, causes uplift in overriding plate and stored strain, resulting in a high magnitude earthquake once strain is overcome

47
Q

Earthquake hazard?

A

Any physical phenomenon that may produce adverse effects on human activities

48
Q

Primary hazards

A

caused directly by fault movement=ground shaking

49
Q

Secondary hazards

A

caused as a consequence of ground shaking

50
Q

Primary hazard examples

A

Ground shaking (christchurch) and surface rupture (Kaikoura)

51
Q

Secondary hazard examples

A

Liquefaction , landslides, fires, tsunami, land elevation changes, disease and poverty

52
Q
A

GEOL 106 (4 decks)

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