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Geogrpahy - Tectonics > EQ1 > Flashcards

EQ1 Flashcards

1
Q

What is a tectonic hazard?

A

Primary hazards such as earthquakes and volcanoes or secondary hazards such as tsunamis. They can be classified as either seismic or volcanic

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2
Q

Where are most earthquakes distributed?

A
  • Most earthquakes happen in clusters at or around plate boundaries, most notably around the Pacific ring of fire
  • Earthquakes can also occur away from plate boundaries in land. These are known as ‘intra-plate’ earthquakes
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3
Q

What is the oceanic fracture zone (ofz) and the continental fracture zone (cfz)?

A

Ofz: A belt of activity throughout the oceans along the mid-ocean ridges, coming ashore in Africa, the Dead Sea rift and California

Cfz: A belt following the mountain ranges from Spain, via the Alps, to the Middle East, the Himalayas to the East Indies and then around the Pacific

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4
Q

Where are volcanoes distributed?

A
  • Found In clusters at or near plate boundaries, especially around the ring of fire
  • There are a handful of intra-plate volcanoes, but these are less common than Indra-plate earthquakes. There are many intra-plate volcanoes in Hawaii
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5
Q

How are hot spot volcanoes formed?

A
  1. Small mantle plumes of superheated rock exist within the mantle of the earth
  2. The mantle plume is a constant source of heat known as a ‘hot spot’, which rises from the hot spot through the mantle. As it reaches the upper mantle, the asthenosphere and base of the lithosphere melt
  3. Magma rises through the weakness in the crust and erupts onto the sea floor, forming a sea mount. Continued eruptions cause the sea mount to break through the surface of the water and form a volcano
  4. The basaltic lava at hotspots creates shield volcanoes. At the hotspots, the lava is viscous and has the potential to form eruptive explosions. As the plate moves, the island is carries beyond the hotspot, cutting it off from the magma, stopping volcanic activity
  5. This process continues, leaving island chains such as Hawaii. The plat plume remains in a fixed location
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6
Q

What seismic activities are found at divergent plate boundaries?

A

Continental/continental:

  • Rift valleys
  • Earthquakes
  • Volcanoes

Oceanic/Oceanic:

  • Earthquakes
  • Volcanoes
  • Ocean ridges
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7
Q

What seismic activities occur at Conservative plate boundaries?

A

-Earthquakes

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8
Q

What seismic activities occur at convergent plate boundaries?

A

Continental/continental:

  • Mountain ranges (fold mountains)
  • Earthquakes

Oceanic/oceanic:

  • Earthquakes
  • Volcanoes
  • Ocean trenches
  • Islands
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9
Q

What happens at collision (convergent) plate boundaries?

A
  • Two continental plates collide
  • Since they are of similar densities and less dense than the asthenosphere, they do not subduct, they simply buckle and become uplifted to form fold mountains and plateaus
  • Since subduction does not occur, there is no volcanic activity
  • Earthquakes tend to have shallow to intermediate focus and are moderate in magnitude (between 6-8)
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10
Q

What happens at transform (Conservative) plate boundaries?

A
  • Conservative boundaries are where two plates rub side by side of each other
  • Shallow focus Earthquakes occur, and they are usually of moderate magnitudes (6-8)
  • There is no volcanic activity at Conservative plate boundaries as no plate subduct pls and there is no gap in the plate to allow magma to rise
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11
Q

What happens at divergent plate boundaries?

A
  • They occur when two plates move away from each other, either oceanic or continental
  • Earthquakes are low in magnitude (5-6) and have a shallow focal depth and effusive eruptions (low vei scale, 1-3)
  • Plates form ocean ridges and central rift valleys, as well as volcanic islands
  • As the lithosphere moves apart, plates fall down to form central rift valleys
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12
Q

What happens at convergent plate boundaries (Oceanic and continental)?

A
  • The denser oceanic plate subducts when the two plates collide
  • Fold mountains form on the continental plate, and when the oceanic plate subducts it forms ocean trenches
  • High magnitude (8-9) earthquakes occur, with a range of focal depths from shallow to 700km
  • Explosive Volcanoes occur (moderate to high vei scale (5-6))
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13
Q

What happens at convergent plate boundaries (oceanic/oceanic)?

A

-The denser of the two plates subducts, or whichever is moving faster

  • Moderate to high magnitude Earthquakes occur (7-9)
  • There are a range of focal depths (shallow to 700km)

-Explosive volcanoes occur (moderate to high VEI scale (5-6))

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14
Q

What is the subduction zone?

A
  • At a convergent plate boundary where a plate moves down (subducts) beneath another
  • It is common for the leading edge to lock under high friction
  • The contact between plates is sometimes called a thrust or mega thrust fault
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15
Q

What is a locked fault?

A
  • A fault that is stuck
  • The frictional resistance on the fault is greater than the stress across the fault
  • When the frictional resistance is overcome, the stated strain is eventually released as a large magnitude earthquake
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16
Q

What is magnitude?

A
  • The amount of energy released by an earthquake
  • There is less friction at Conservative plate boundaries, so magnitude is usually lower
  • At subduction zones there are more likely to be locked plates and more frictional stress, resulting in a greater likelihood of high magnitude Earthquakes
  • At convergent plate boundaries there is a greater likelihood of a locked fault lasting hundreds of years building up enormous stress and friction
17
Q

Where do shallow do ours Earthquakes mostly occur?

A

They usually occur at divergent and Conservative plate boundaries as neither of the plates subduct

18
Q

Where do deep focus Earthquakes occur?

A

They occur at convergent plate boundaries as there is a plate that subducts. This is especially the case when an oceanic plate is involved

19
Q

What are the three types of seismic waves?

A
  • P waves (fast)
  • S waves (slower)
  • L waves (surface)
20
Q

What are some primary hazards of seismic waves!

A
  • Ground shaking

- Crustal fracturing

21
Q

What are some secondary hazards of seismic waves?

A
  • Liquefaction

- Landslides/avalanches

22
Q

What are primary waves?

A
  • Waves from the focus
  • They are caused by compression and push in a forwards backwards motion
  • They are the fastest type of wave at 8km/s
  • They travel through solids and liquids and are only damaging in very powerful earthquakes
23
Q

What are secondary waves?

A
  • Slower waves from the focus, travelling at 4km/s
  • They can only travel through solids
  • They move perpendicular to the direction of travel
  • They do more damage than P waves
24
Q

What are surface waves?

A
  • They shake the earth’s crust away from the epicentre
  • The surface may be displaced horizontally, vertically or obliquely depending on the strength of the waves
  • Surface waves are more destructive as they have a larger amplitude and energy force
25
Q

What is liquefaction?

A
  • Occurs When soft sediment becomes like quick sand during an earthquake
  • The earthquake destabilises the soil and brings water to the surface, causing buildings to topple over and sink into the ground
  • The Lame Prida earthquake near San Francisco in 1989 was worsened due to liquefaction as much of the area was built on landfill and reclaimed land
26
Q

What seismic activities are found at divergent plate boundaries?

A

Continental/continental:

  • Rift valleys
  • Earthquakes
  • Volcanoes

Oceanic/Oceanic:

  • Earthquakes
  • Volcanoes
  • Ocean ridges
27
Q

What seismic activities occur at Conservative plate boundaries?

A

-Earthquakes

28
Q

What seismic activities occur at convergent plate boundaries?

A

Continental/continental:

  • Mountain ranges (fold mountains)
  • Earthquakes

Oceanic/oceanic:

  • Earthquakes
  • Volcanoes
  • Ocean trenches
  • Islands
29
Q

What happens at collision (convergent) plate boundaries?

A
  • Two continental plates collide
  • Since they are of similar densities and less dense than the asthenosphere, they do not subduct, they simply buckle and become uplifted to form fold mountains and plateaus
  • Since subduction does not occur, there is no volcanic activity
  • Earthquakes tend to have shallow to intermediate focus and are moderate in magnitude (between 6-8)
30
Q

What happens at transform (Conservative) plate boundaries?

A
  • Conservative boundaries are where two plates rub side by side of each other
  • Shallow focus Earthquakes occur, and they are usually of moderate magnitudes (6-8)
  • There is no volcanic activity at Conservative plate boundaries as no plate subduct pls and there is no gap in the plate to allow magma to rise
31
Q

What happens at divergent plate boundaries?

A
  • They occur when two plates move away from each other, either oceanic or continental
  • Earthquakes are low in magnitude (5-6) and have a shallow focal depth and effusive eruptions (low vei scale, 1-3)
  • Plates form ocean ridges and central rift valleys, as well as volcanic islands
  • As the lithosphere moves apart, plates fall down to form central rift valleys
32
Q

What happens at convergent plate boundaries (Oceanic and continental)?

A
  • The denser oceanic plate subducts when the two plates collide
  • Fold mountains form on the continental plate, and when the oceanic plate subducts it forms ocean trenches
  • High magnitude (8-9) earthquakes occur, with a range of focal depths from shallow to 700km
  • Explosive Volcanoes occur (moderate to high vei scale (5-6))
33
Q

What happens at convergent plate boundaries (oceanic/oceanic)?

A

-The denser of the two plates subducts, or whichever is moving faster

  • Moderate to high magnitude Earthquakes occur (7-9)
  • There are a range of focal depths (shallow to 700km)

-Explosive volcanoes occur (moderate to high VEI scale (5-6))

34
Q

What is the subduction zone?

A
  • At a convergent plate boundary where a plate moves down (subducts) beneath another
  • It is common for the leading edge to lock under high friction
  • The contact between plates is sometimes called a thrust or mega thrust fault
35
Q

What is a locked fault?

A
  • A fault that is stuck
  • The frictional resistance on the fault is greater than the stress across the fault
  • When the frictional resistance is overcome, the stated strain is eventually released as a large magnitude earthquake
36
Q

What is magnitude?

A
  • The amount of energy released by an earthquake
  • There is less friction at Conservative plate boundaries, so magnitude is usually lower
  • At subduction zones there are more likely to be locked plates and more frictional stress, resulting in a greater likelihood of high magnitude Earthquakes
  • At convergent plate boundaries there is a greater likelihood of a locked fault lasting hundreds of years building up enormous stress and friction

Geogrpahy - Tectonics (2 decks)

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