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Geoscience > Test 3 > Flashcards

Test 3 Flashcards

1
Q

Explain what causes an earthquake.

A
  • Fault motion causes an earthquake
  • Time 1 - Friction causes most faults to “stick”
  • Time 2 - Build up of stress causes the rock to deform
  • Time 3 - After some time (can vary), stress overcomes friction and causes fault movement (slip). i.e. earthquake
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2
Q

Where do earthquakes occur?

A

Earthquakes occur on faults, which are commonplace along plate boundaries.

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3
Q

Are there lots of earthquakes worldwide, or only a few throughout the year?

A

Yes there are lots of earthquakes world wide, around about 55 per day.

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4
Q

Define Strike

A

Horizontal line on an inclined surface

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5
Q

Define Dip

A

Inclination or slope of surface (measured from horizontal)

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6
Q

Define hanging wall

A

Above fault

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7
Q

Define foot wall

A

Below fault

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8
Q

What is a strike slip?

A

One block slides horizontally past another (and therefore parallel to the strike line), so there is no relative vertical motion.

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9
Q

What is a dip slip?

A

Sliding occurs up or down the slope (dip) of the fault

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10
Q

Explain the fault movement for a normal fault

A

Hanging wall moves down (tension)

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11
Q

Explain the fault movement for a Reverse fault

A

Hanging wall moves up (compression)

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12
Q

What type of stress leads to a reverse fault?

A

Compression

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13
Q

What type of stress leads to a normal fault?

A

Tension

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14
Q

What type of stress leads to a Strike-Slip fault?

A

Shear (side by side motion)

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15
Q

What controls the magnitude of an earthquake?

A
  • The amount of slip along a fault

- the length of the fault that slips

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16
Q

Define epicenter

A

The point on the surface of the Earth directly above the focus of an earthquake.

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17
Q

Explain multiple reasons why earthquake prediction is so difficult.

A
  • No reliable precursor
  • No reliable way to measure stress or know how much stress a fault can handle
  • For most faults, there is no clearly definable periodic earthquake behavior.
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18
Q

What are the 3 types of seismic waves and their relative velocities?

A
  1. P waves - Travel fastest arrive 1st
  2. S waves - arrive 2nd
  3. Surface waves - are the slowest, arrive last
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19
Q

What are the two types of surface waves?

A

L-waves and R-waves

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20
Q

What waves travel along Earth’s surface?

A

All surface waves

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21
Q

What waves travel through Earth’s surface?

A

P and S-waves

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22
Q

How seismograms vary as a stations distance from an earthquake increase.

A

If it is further away from an earthquake P-waves would arriver later and the gap between the arrival of P and S waves would be larger.

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23
Q

What type of seismic wave typically causes the most damage and why?

A

Surface waves because these waves physically move the ground/surface.

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24
Q

Describe the process of determining earthquake location using seismographs.

A
  • Need at least 3 seismometer recordings of the event
  • Distance from each station determined by time gap between P and S waves.
  • Triangulation marks the epicenter.
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25
Q

Define magnitude and what scale is used to measure it.

A

A standard measure of the shaking and/or energy released (objective). Logarithmic scale

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26
Q

Define Intensity and what scale is used to measure it.

A

A measure of the effects on people and buildings (subjective) Measured by I-XII scale.

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27
Q

True or false: Earthquake magnitude and intensity are always correlated?

A

False

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28
Q

What plate boundaries can shallow earthquakes be found on?

A

-Convergent, Divergent, and Transform boundaries

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29
Q

What plate boundaries can deep earthquakes be found on?

A

Convergent boundaries

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30
Q

What is the common type of fault at a convergent boundary? What type of stress produces them?

A

Reverse faults which is caused by compression

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31
Q

What is the common type of fault at a divergent boundary? What type of stress produces them?

A

-Normal faults cased by tension

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32
Q

What is the common type of fault at a Transform boundary? What type of stress produces them?

A

Strike-slip faults caused by shear.

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33
Q

Where are shallow earthquakes like to occur

A

Divergent and transform boundaries

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34
Q

Where are deep earthquakes likely to occur?

A

Convergent Boundary

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35
Q

List common earthquake hazards

A
  • Ground Shaking
  • Aftershocks
  • Landslides
  • Elevation Changes
  • Liquefaction
  • Tsunami
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36
Q

Explain how liquefaction occurs.

A

Friction causes grain to settle together and water fills the pores between the sediment and shaking makes it weaker.

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37
Q

What kind of fault most commonly produces tsunamis?

A

Revers Fault

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38
Q

What is the principle of uniformitarianism?

A

What’s happening now happened in the past.

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39
Q

Explain the difference between relative and numerical age.

A

Relative age is the age of a rock layer (or the fossils it contains) compared to other layers around it. Numerical age is the numeric age of the layer of rocks or fossils which is determined by radiometric dating.

40
Q

Explain what an unconformity is and what it represents.

A

An erosion surface representing a gap in time between two rock layers.

41
Q

What are the three types of unconformities?

A
  1. Angular
  2. Disconformity
  3. Nonconformity
42
Q

How does an angular unconformity form? How is it identified?

A
  • Limestone formed (shallow marine conditions) → Uplift & erosion exposes limestone → Limestone folded and eroded during mountain building → New sediment deposited
  • Flat layers overlie tilted layers
43
Q

How does an Disconformity form? How is it identified?

A
  • Limestone formed (shallow marine conditions) → Uplift & erosion exposes limestone → sea level rises
  • Flat layers overlie flat layer
44
Q

How does a nonconformity form? How can you identify it?

A
  • (Igneous or metamorphic rocks are involved) Non layered rock forms below surface → Uplift & erosion exposes the igneous/metamorphic rock at Earth’s surface → Sediment is deposited on top of the igneous/metamorphic rock
  • You can identify it if it has a igneous or metamorphic rock
45
Q

Describe the principle of original horizontality

A

Sediments are deposited in flat layers

46
Q

Describe the principle of superposition

A

Youngest is on top oldest is on bottom

47
Q

Describe the principle of cross-cutting

A

The rock or magma that is cutting through is younger than the rock it is separating

48
Q

Describe the principle of inclusions

A

Inclusions found in other rocks or formations must be older than the rock that contains them.

49
Q

What is fossil succession and how does it helps in correlating rock sequences?

A
  • The sequence of assembly for fossil species preserved in the stratigraphic record.
  • It helps by serving as the fossil timeline
50
Q

What is an index fossil and why are they useful?

A

Fossil species that are widespread but survived for only a relatively short interval of geologic time. These are useful because they can be used to associate the strata with a specific time interval.

51
Q

What is the age of the Earth? What is this age based on?

A

4.54 billion years old based on how far back meteorites date back to.

52
Q

Describe the process of radioactive decay and how it can be used to date rocks.

A
  • Each element has a unique atomic number (ex. Potassium (K) = 19 (19 protons)
  • Potassium has three isotopes (same number of protons) identified by their mass numbers
  • Decay occurs when an isotope loses or gains protons and/or neutrons
53
Q

What is a ‘half-life’?

A

Time for half of the parent isotopes to be converted to daughter isotopes

54
Q

Explain why radioactive decay typically isn’t all that useful for dating the formation of sedimentary rocks.

A

Because decay has already begun for elements in minerals that form sedimentary rocks

55
Q

What is the formula to calculate the age of a rock?

A

Age of rock = number of half lives passed X length of one half life

56
Q

Describe the basis for the Geologic Time Scale.

A

Earth’s history divided up; mostly based on fossils (biological evolution)

57
Q

In chronological order, list the major divisions of the Geologic Time scale.

A
  • Precambrian: 2 Eon’s
    • Archean (1st in relative length)
    • Proterozoic (2nd in relative length)
  • Phanerozoic Eon (3 Era’s) Represents the last 12% of geologic time
  • Paleozoic (3rd in relative length)
  • Mesozoic (4th in relative length)
  • Cenozoic (5th in relative length)
58
Q

Were there continents on early earth?

A

Yes

59
Q

What was the general composition of the atmosphere during early earth?

A

Nitrogen and carbon dioxide

60
Q

Indicate what the first evidence of life on Earth is and when it occurred.

A

A stromatolite and it occurred during the Archean

61
Q

Describe how the oceans formed and how their chemical composition evolved over time.

A
  • Formed from volcanism and comets/asteroids

- There was a lot of iron that combined with oxygen to form iron-oxide deposits

62
Q

Explain when and how Earth got its oxygen-rich atmosphere.

A

The great oxygenation event happened in the Proterozoic eon because other environments could no longer absorb or dissolve the oxygen produced by organisms, so the oxygen began to accumulate as gas in air.

63
Q

Describe what a stromatolite is and why they are important to Earth’s evolution over time

A

A stromatolite are formed by cyanobacteria and are important because they are the earliest fossil evidence of life on earth.

64
Q

Describe what a banded iron formation is, and the process that their deposition represents (the great oxygenation event).

A

Colorful sedimentary beds consisting of layers of iron-oxide materials and jasper. Because of the increase in oxygen from the great oxygenation event iron began to settle out of the ocean to form BIFs.

65
Q

What is the snowball earth? How did it form? How did it end?

A

At the end of the Proterozoic Eon a radical climate shift occurred which covered the earth in ice and snow. It ended because of volcanic activity.

66
Q

What is the Cambrian Explosion? When did it happen?

A
  • Rapid Evolution of complex life (mostly in oceans)
  • Greenhouse Earth (tropical climate everywhere)
  • Cambrian period
67
Q

General time period for the formation of the Earth

A

Hadean Period

68
Q

General time period for the formation of the Moon

A

Hadean Period

69
Q

General time period for the first evidence of life

A

Archean Period

70
Q

General time period for the Oxygenation of the atmosphere

A

Proterozoic Period

71
Q

General time period for the Snowball Earth

A

Cambrian Period

72
Q

General time period for evolution of complex life

A

Cambrian Period

73
Q

General time period for life on land

A

Devonian Period or Paleozoic Era

74
Q

General time period for the age of the Dinosaurs

A

Mesozoic Era or Jurassic Period

75
Q

General time period for Dinosaur extinction

A

Paleogene period or Cenozoic Era

76
Q

General time period for the Age of Mammals

A

Early Cenozoic

77
Q

General time period for the evolution of modern humans

A

Late cenozoic

78
Q

What events mark the boundaries between the Paleozoic, Mesozoic, and Cenozoic periods?

A

Major Extinction events

79
Q

What happen at the end of the Mesozoic Period?

A

K/T (Cretaceous/Tertiary) extinction wiped out the dinosaurs

80
Q

Define the term ‘The Anthropocene ‘

A

An informal name for the most recent interval of geologic time.

81
Q

Where do rivers get their water from?

A
  • The sky/precipitation
  • The ground/erosion
  • From things that melt
82
Q

What is a drainage basin?

A

The entire area that provides water to a given river

83
Q

What is a drainage divide?

A

A highland or ridge that separates one watershed from another

84
Q

Differences between braided and meandering streams

A 
Braided:
-Steep gradients 
-Coarse sediment
-near mountains and or glaciers
-Generally no floodplain
Meandering:
-Low gradients 
-Fine sediments 
-Low elevations 
-Floodplain
85
Q

How does a river delta form?

A

From deposition of sediment carried by a river as the flow leaves its mouth and enters slower-moving or standing water.

86
Q

List several reasons why there are different types of rivers on Earth

A
  • Rock type
  • Tectonic setting
  • Climate
  • Base level
  • Human influence
87
Q

As a river flows downstream channel size…

A

Increases

88
Q

As a river flows downstream discharge…

A

Increases

89
Q

As a river flows downstream flow velocity…

A

Increases

90
Q

As a river flows downstream grain size…

A

Decreases

91
Q

As a river flows downstream sediment load…

A

Increases

92
Q

What is discharge?

A

Amount of water passing through some body of water at a certain point.

93
Q

What factors control the discharge of a river

A

-Precipitation, evaporation, and storage factors

94
Q

How is stream discharge calculated?

A

Discharge (m3 /s) = width (m) x depth (m) x velocity (m/s)

95
Q

Why does discharge matter?

A
  • Flood forecasts
  • Availability of drinking water
  • Water levels in freshwater ecosystems
  • Design of construction project
  • Recreational use of stream systems

Geoscience (4 decks)

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