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Tectonic Processes and Hazards EQ1 Flashcards

1
Q

What is the global distribution of earthquakes?

A

Most earthquake zones are found at or close to tectonic plate boundaries in clusters.
- 70% of all earthquakes are located in the ‘Pacific Ring of fire’ in the Pacific Ocean
- most powerful found ad convergent (destructive) and conservative boundary’s
- rare intro-plate earthquakes can occur

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2
Q

What patterns do the distribution of earthquakes follow?

A
  • The oceanic feature zone (OFZ)
  • The continental fracture zone (CFZ)
  • Scattered earthquakes in continental interiors (old fault lines e.g. Church Stratton Fault, Shropshire)
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3
Q

What is the OFZ?

A

The oceanic fracture zone is a belt of tectonic activity through the oceans along mid-ocean ridges. They come onshore in Africa, the Red Sea, the Dead Sea rift and California.

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4
Q

What is the CFZ?

A

The continental fracture zone is a belt of activity following the mountain ranges. From Spain, via the alps to the Middle East, the Himalayas to the East Indies and the finishing in the Pacific.

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5
Q

What is the cause of earthquakes?

A

Earthquakes are formed from the sudden releases of stored energy. As tow plates move past each other they inevitably get stuck. This results in the build up of strain and pressure putting the plates under increasing stress. The sudden releases of this ‘stress’ (‘stick and slip’) causes a pulse of energy to radiate out from the earthquake focus.

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6
Q

What is the definition of a intra-plate earthquake?

A

These occur in the middle or interior of tectonic plates and are much fares than boundary earthquakes.

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7
Q

What is the global distribution of volcanoes?

A

Volcanoes tend to occur at or close to tectonic plate boundary’s with exceptions for hotspots. There are 500 active volcanos with an average of 50 erupting each year.

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8
Q

What is the definition of a volcano?

A

A landform that develops around a weakness in the Earths crust from which molten magma, volcanic rock and gases are ejected or extruded.

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9
Q

What is the global distribution of Tsunamis?

A

Tsunamis are fairly predictable with then happening along plate margin activity.
- 90% of all event happen in Pacific basin
- most are generated at destructive boundary’s at subduction zones

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10
Q

What causes a Tsunami?

A

Tsunamis are generated what a sub-marine earthquake displace the sea bed vertically. As a result a large volume of water is displaced in the ocean water column which then moves outwards in all directions from the point of displacement.

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11
Q

What tectonic hazards can be found at constructive (all types) plate boundary’s)?

A
  • volcanoes
  • earthquakes
    Convections currents forces the two oceanic plates away from each other allowing magma to rise in a small basaltic eruptions creating new oceanic plate. Minor earthquake are also found.
    E.g. Mid-Atlantic ridges, Iceland
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12
Q

What tectonic hazards can be found at destructive (oceanic - oceanic) plate boundary’s)?

A
  • frequent earthquakes
  • volcanos
    One oceanic plate is subducted beneath another due to slap pull. This generates frequent earthquakes and a curving chain of volcanic islands, which erupt.
    E.g. The Aleutian Islands, Alaska
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13
Q

What tectonic hazards can be found at destructive (continental-continental) plate boundary’s)?

A
  • infrequent major earthquakes
  • rare volcanic eruptions
    The collision of two continental plate boundary’s create a mountain belt as they crumple together. Magma is generated at depth meaning it has time to cool and solidify making eruptions rare. Major earthquakes are created over a large area.
    E.g. the Himalayas with the Indo -Australian and Eurasian plates creating Nepal 2015)
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14
Q

What tectonic hazards can be found at destructive (oceanic - continental) plate boundary’s)?

A
  • earthquakes
  • volcanos
    1. Mantle convection move the two plates together.
    2. Denser oceanic plate is subducted beneath the lighter continental the density of the plate pulls in self into the mantle (slap pull).
    3. The oceanic plates begins to melt into the mantle generating a high pressures and causing it to erupt explosively (high gas and silica).
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15
Q

What tectonic hazards can be found at conservative plate boundary’s)?

A

Plates slide past each other causing
- frequent earthquakes (shallow focal depth)
E.g. San Andreas Fault

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16
Q

What are the three types of plate boundaries?

A
  • constructive (divergent)
  • destructive (convergent)
  • conservative
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17
Q

What is a constructive plate margin?

A

These are plate margins are moving away from each other driven by convection current. There are most clearly displayed at mid-ocean ridges. Create shallow and low magnitude earthquake event (majority sub marine).

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18
Q

What is a destructive plate margin?

A

This is where plates are moving together creating actively deforming collision. This causes frequent earthquakes and volcanic eruptions.

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19
Q

What is a conservative plate margin?

A

This is where one plate is sliding against another in sinistral (left) or dextral (right). Lithosphere is nether created nor subduncted resulting in extensive high magnitude earthquakes.

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20
Q

What does the type of plate margin depend on?

A
  • motion (are the plates moving apart, colliding or sliding last one another)
  • plate type (continental or oceanic)
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21
Q

What is a hotspot volcano?

A

Volcanic eruptions that can occur intra-plate meaning they are at a distance from plate margins.
E.g. Hawaii within the Pacific Plate

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22
Q

How does a hotspot volcano form?

A
  1. An isolated plume of convecting heat called a mantle plume rises towards the surface.
  2. This high heat and pressure causes the lithosphere to melt
  3. This allows molten magma to rise through the cracks and erupts as an active volcano (basaltic)
  4. The mantle plume stays stationary but the tectonic plates moves slowly over it creating a chain of volcanic islands.
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23
Q

What is an intra-plate earthquakes?

A

This is when earthquakes o cud in a mid plate setting, it usually happen on major fault lines being reactivated by tectonic stress.
E.g. New Madrid Seismic Zine generates high magnitude earthquake but is miles away form a plate boundary

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24
Q

What are the key characteristic of plate tectonics?

A
  • move at speeds of 2-5 cm annually
  • they are split into 7 very large plates (Pacific) and smaller minor plates (Nazca)
  • they fit together in a constantly moving jigsaw
  • made up of two types of crust
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25
Q

What are the two types of crust?

A

Oceanic crust - thin but very dense. It underlined the ocean basins and is composed primarily of basalt
Continental crust > thicker but much lighter. It underlines the continents and is composed of primarily granite.

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26
Q

What are the key discoveries about plate tectonics throughout the years?

A
  • 1912 Alfred Wegener’s came out with continental drift hypothesis and postulated that now sap rates continents had once been joined.
  • Arthur Homes in 1930 theory was the the earths internal radioactive heat was that driving the mantle movement (convection currents)
  • 1950, discovery of the rocks in the lower mantle being plastic and flow allowing the rigid lithosphere to move.
  • 1960s discovered paleomagnetic signals to prove the processes of sea floor spreading at mid ocean ridges
  • 1965, Tuzo Wilson recognised transform faults
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27
Q

What are the key elements/process of plate tectonics?

A
  • paleomagnetism
  • earths internal structure
  • mantle convection
  • sea floor spreading
  • subduction
  • Slap pull
28
Q

What is subduction?

A

This is the process when two plates are living together at a destructive plate boundary with the denser plate sinking beneath the lighter plate.

29
Q

What is slap pull?

A

When the cold denser oceanic plate in sub-ducted beneath the continental the high density if the oceanic plate pulls itself into the mantle with the help of gravity.

30
Q

What are mantle convections?

A

As the earths mantle has a temperature gradient (geothermal gradient). The highest temperatures is near the core causing the Madame to heat up and rise before cooling and sinking creating a convection cell.

31
Q

What is the earths structure?

A
  • crust (oceanic or continental)
  • upper mantle (cool and brittle rocks)
  • lower mantle (hot and plastic so they flow)
  • outer core (liquid due to high temperatures)
  • inner core (solid due to high pressure)
32
Q

What is palaemagnetism?

A

As the sea fall spreads at constructive plate boundary’s, magma rises forming mid-ocean ridges. Paleomagnetism is the zones of magma ‘locking in/cooling’ in the direction of the earths magnetic polarity.

33
Q

What does paleomagnetism show scientists?

A

Scientists can use this tool to determine historical periods of large scales tectonic activity using it to date the age of the new tectonic crust. Creating a geo-timeline.

34
Q

What is seafloor spreading?

A

This occurs at submarine constructive plate margins with convection currents pulling the two oceanic plates away from each other resulting in a continuous input of magma which forms new oceanic crust called mid-ocean ridges. On land Rift Valleys from.
E.g. Mid-Atlantic ridges

35
Q

What are transform zones?

A

Conservative plate boundaries consist of transform faults. These faults ‘join up’ sections of the plate as they transverse the earths surface in a zigzag motion.
E.g. San Andreas Fault, California

36
Q

How does constructive margins affect the magnitude and type of volcanic eruption?

A

At constructive margins eruptions are small and not violent. This is because the erupted material is basalt lava which have a low gas content and high viscosity.

37
Q

How does constructive margins affect the magnitude and focal depth of an earthquake?

A

At constructive margins earthquakes are shallow (<60m) and have low magnitudes.

38
Q

How does destructive plate margins affect the magnitude and type of volcanic eruption?

A

Volcanic eruption happen at oceanic - oceanic and oceanic - continental. Here their are high magnitude volcanic eruptions due to the magma generated having high gas and silica contents.

39
Q

How does destructive plate margins affect the magnitude and focal depth of a earthquake?

A
  • earthquake can occur on a range of focal depths (10km-400km) following the line of the subduction plate. (Benioff zone)
  • resulting in earthquakes with a range of magnitude. Shallow (high magnitude as energy not dispersed) and deeper ones (Weaker strength)
  • collision zone have shallow, high magnitude earthquakes generated a thrust faults
40
Q

How does conservative plate margins affect the magnitude and type of volcanic eruption?

A

Conservative plate margins have no volcanic activity.

41
Q

How does conservative margins affect the magnitude and focal?

A
  • often produce shallow focal depths and high magnitude earthquakes
  • quite frequent
42
Q

What is the Benioff Zone?

A

The ares of seismicity corresponding with the downwards movement of a sub-ducted plate. It is the line we’re the two plates are connecting. The different speeds of movement at this rock produced numerous (normally deep focus) earthquakes. It determines the positions of the hypocentre and focal depth.

43
Q

What is a locked fault?

A

A fault that is not ‘slipping’ because of the frictional resistance on the fault is greater than the shear stress across the fault. This results in high pressure building up over a long time which is eventually released in high magnitude earthquakes.
E.g. 2004 Tsunami resulted from the realest of a mega thrust locked fault from the subduction Indian plate.

44
Q

What is the hypocentre?

A

The focus point within the ground where the strain energy of the earthquake stored in the rock is first released.

45
Q

What is the focal length?

A

The distance between the hypocentre and epicentre.

46
Q

How do earthquake occur at fault lines?

A
  1. Movements cause a gradual build up of strain within the fault. This leads to the build up of elastic energy is crustal rocks.
  2. When the pressure exceeds the strength of the fault, the rock fractures
  3. This produces the sudden release of energy. This is given off as seismic waves away from the point of fracture.
  4. The brittle crust then rebounds either side of the fracture causes the shaking on the surface.
47
Q

What are the three types of earthquake waves?

A
  • P - waves (Primary waves)
  • S - waves (Secondary waves)
  • L - waves (Love waves)
48
Q

What are the main characteristics of P - waves?

A

These are vibrations caused by compressions, making the waves longitudinal
- they are the tasters (8 km/s)
- cause the least damage

49
Q

What are the main characteristics of S - waves?

A

These are secondary waves, with transverse waves which vibrate at a right angle to the direction of travel
- second fastest waves (4 km/s)
- shake the ground violently causes more damage
- cannot table through liquids

50
Q

What are the main characteristic of L - waves?

A

These are surface waves with vibrations occurring in the horizontal plane.
- slowest waves so arrive last
- large amplitudes
- cause the most and significant demand (fracturing the ground surface)

51
Q

How does the type of waves influence an earthquake?

A

The overall severity of an earthquake is linked to
- amplitude and frequency of the different wave type
- if the ground surface is displaced horizontally, vertically or obliquely is determined on the strength of the individual waves
- S and L waves are more destructive as they have a large amplitude and energy force

52
Q

What are the secondary hazards form an earthquake?

A
  • soil liquefaction
    -landslides
53
Q

What is soil liquefaction?

A

This happens in areas that have high amounts of unconsolidated material.
The intense earthquake shaking compacts the loose sediment together, this forces any water stored in the sediment out and upwards. This undermines foundation and cause the ground to behave like a liquid.

54
Q

What do the physical factors that increase earthquake risk?

A
  • earthquake hypocentre depth (shallow more destructive as energy doesn’t have time to dissipate’
  • physical nature of the ground (if the ground is formed form loose unconsolidated material more prone to liquefaction)
  • location (mountainous regions more prone to landslides)
55
Q

What are the main effect of liquefaction?

A
  • damage to roads and bridges
  • damage to telecommunication and other service (gas and electricity) that run just underground
  • hinders the delivery of aid
56
Q

What is a landslide?

A

Landslide are secondary hazards form earthquake, as the ground shakes the slopes weaken and fail causing massive mass movements. Occur especially in geological younger areas which are weaker and more unstable such as the Himalayas.
E.g. Landslides accounted for 30% of the deaths in 2008 Sichuan earthquake

57
Q

Why are the main primary hazards of a volcanic eruption?

A
  • lava flows
  • pyroclastic flows
  • Tephra (ash fall)
  • gas eruptions
58
Q

What are the main secondary hazards of a volcanic eruption?

A
  • Lahars
  • Jokulhaups
59
Q

What is a lava flow?

A

These are steams of molten lava that can flow up to 40 km/h. The higher the viscosity of the lava (higher silicon dioxide). It occurs at subduction zones (composite cone) and hotspot volcanos (shield)

60
Q

What is a pyroclastic flow?

A

This are very large, dense clouds of hot ash and gas that can reached temperatures of 600 degrees. They can flow down flanks of the volcanic devastating large areas and posing a big threat to human life.
They occur at composite cone volcanos at subduction zone

61
Q

What is tephra?

A

Ejected ash particles and large rock fragments into the air blanketing large areas. This can cause roof building to collapse as well as reduce air visibility.
It occurs at constructive plate margins (cider cone) and subduction zone (composite cone)

62
Q

What is volcanic gas eruption?

A

This is the eruption if carbon dioxide, carbon monoxide and sulphur dioxide into the air during a volcanic eruption. It is dangerous due to the colourless nature which can accumulate in valleys poisoning people and animals.
E.g. Lake Nyos, Cameroon the emissions of carbon dioxide in 1986 killed 1700 people.
Occurs at subduction volcanic (composite cone) and hotspot volcanos (shield)

63
Q

What is a lahar?

A

Lahars are secondary impacts of a volcanic eruption. They are volcanic mudflows, and takes place when rainfall mobilises volcanic ash. They travel Aston high speeds down rivers systems causing major destruction.

64
Q

What are Jökulhaups?

A

These are a type of glacial outburst flood. When a volcano erupts beneath glaciers and ice caps creating a huge volume of melt water. These occur very suddenly (fast speed of onset) with a rapid discharge of large volumes of water.

65
Q

What factors influence the impacts of tsunamis?

A
  • duration of the event
  • wave amplitude
  • physical geography of the coast (water depth)
  • degree of natural defences (mangrove and coral reefs)
  • timing of the event
  • degree of coastal development
    The most serious events are when human physical factors interact with each other to produce a disaster.

temp (29 decks)

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