Chapter 1.1

Question 1

What is subduction

Answer 1

The process involving the descent of an oceanic plate into the upper mantle beneath a continental plate

Question 2

What is a mantle plume: There are two huge mantle plumes (Pacific and African); these are hotter areas of the mantle that move upwards underneath the crust and push it up. They can cause weak points in the crust which can become hot spots. These mantle plumes are irregular in shape. Attempts are being made to create mathematical models of them.

Answer 2

There are two huge mantle plumes (Pacific and African); these are hotter areas of the mantle that move upwards underneath the crust and push it up. They can cause weak points in the crust which can become hot spots. These mantle plumes are irregular in shape. Attempts are being made to create mathematical models of them.

Question 3

What is a intra-plate

Answer 3

Tectonic activity that is found away from the plate boundaries and closer to the middle of a tectonic plate. Locations are less frequent and require separate explanations such as the influence of mantle plumes or ancient fault lines.

Question 4

What is convection?

Answer 4

The process whereby heat is transferred from one part of a liquid or gas to another, by movement of the fluid itself. Convection carries excess heat from the Earth’s surface and distributes it through the troposphere

Question 5

What is the troposphere?

Answer 5

A lower layer of the atmosphere, extending to 16km at the equator

Question 6

What is the seismic focus?

Answer 6

The seismic focus is the point of origin of the earthquake within the crust. The velocity of the seismic waves varies with the density of the material through which they travel.

Question 7

What is slab Pull?

Answer 7

At a subducted zone the descending part of the oceanic tectonic plate pulls the rest of the plate with it

Question 8

What the Moment of Magnitude scale

Answer 8

The Moment Magnitude scale used to measure the size of earthquakes by the amount of energy released by an earthquake.

Question 9

How does the moment magnitude scale measure the size of an earthquake?

Answer 9

The moment of magnitude scale measures the amplitude (height of wave from the middle of the wave) of an earthquakes seismic waves, amount of slippage or rock movement, area of the fault surface broken by the earthquake, resistance of the affected rock (the ability of the affected rock to not to break) The moment of magnitude scale is logarithmic, so that an increase of 1 on the scale indicates the earthquake is 10 times as powerful.

Question 10

What is bathymetry?

Answer 10

Measuring water depth, mainly of seas and oceans but sometimes of deep lakes.

Question 11

What is the benioff zone?

Answer 11

the area where friction is created between colliding tectonic plates, resulting in intermediate and deep earthquakes.

Question 12

Where does most activity?

Answer 12

Most activity occurs at Plate Boundaries and there are different types of boundary as the combinations of plate type and movement can affect what occurs where. For example, Converging Oceanic and Continental plates where destructive and subducting boundaries occur leads to earthquakes of magnitudes 9 Mw or higher (moment of magnitude scale)

Question 13

Can different combination of plate type and movement affect what tectonics hazard occurs where?

Answer 13

Yes, most activity occurs at Plate Boundaries and there are different types of boundary as the combinations of plate type and movement can affect what occurs where. For example, Converging Oceanic and Continental plates where destructive and subducting boundaries occur leads to earthquakes of magnitudes 9 Mw or higher

Question 14

What is a hot spots and Mantle Plumes

Answer 14

A volcanic “hotspot” is an area in the mantle from which heat rises as a thermal plume from deep in the Earth. High heat and lower pressure at the base of the lithosphere (tectonic plate) facilitates melting of the rock. This melted rock is called magma which rises through cracks and erupts to form volcanoes. As the tectonic plate moves over the stationary hot spot, the volcanoes are rafted away and new ones form in their place. This results in chains of volcanoes, such as the Hawaiian Islands.
Example: Hawaii – not that dangerous as it is basaltic lava.

Question 15

What is a intraplate earthquakes (these are usually smaller magnitude)

Answer 15

Intraplate earthquakes ( are usually smaller magnitude): The main cause of an intraplate earthquake is a fracture (crack) along an old fault (a crack that been there for sometime so is old and no movement has occurred along is for sometime . Many current plates are parts of many old plates “stitched” together (are pushed together, due to plate movement) and have faults that are no longer active. However, stress can still build along these faults, as they happen to be the “weak points” in the plate. The plate along this old fault can easily slip to accommodate regional tectonic strain, this creates tension within the fault. When the fault cannot hold the stress anymore, it buckles and folds, sending out the energy in the form of an earthquake. Intraplate earthquakes are relatively rare compared to the more familiar boundary-located earthquakes. Therefore, large intraplate earthquakes can inflict heavy damage with such areas’ structures lacking seismic retrofitting. Examples of damaging intraplate earthquakes are the devastating Gujarat earthquake in 2001.

Question 16

What is one main reason why intra-plate earthquakes can be very damaging?

Answer 16

These earthquakes can be very damaging because they happen in areas where people are least expecting them to happen, so they think they are less at risk, intra-plate earthquakes happen in the middle of the plate boundaries not at the plate boundaries where most tectonic activity occurs. Therefore the people are unprepared therefore they will not be able to protect them and buildings e.g. by putting in seismic retrofitting. Therefore the people are more vulnerable to the intra-plate earthquake. Therefore, large intraplate earthquakes can inflict heavy damage with such places. The area will also be less resilient as intra-late earths are more rare the area wouldn’t be used to having earthquakes and therefore coping with earthquakes as they wouldn’t have had ‘practice’. Therefore they will be less resilient to it. This means that they will not be able to respond quickly and efficiently and know quickly and instantly know what do do. This will therefore cause more deaths which increasing the likelihood of it becoming a disaster.

Question 17

What is an ancient fault line?

Answer 17

an ancient fault lines are fault lines that were once active but are now no longer active with no tectonics activity taking place on them like earthquakes, but can be reactivated again.

Question 18

What is collision?

Answer 18

Collision can cause plates to crumple and crack in areas of crust away from the boundary itself. This can cause intra-plate earthquakes overtime as collusion takes place slowly. Movement caused along faults and can cause tensionsto build up due to friction stopping the plates form moving as the plates will still be pushing against each other and not moving causes tension to build up and when the plates can n longer with stand the pressure the pressure is realised is causes a sudden jolt creating an earthquake.

Question 19

1.What is a convergent/destructive plate boundary of continental and oceanic plates (remember different combination of plate type and plate movement effect what different tectonic hazards occur where?)
2.Seismic activity Large range of focus depths (shallow – near to surface and up to 700km in Wadati-Benioff zone).
Earthquakes general high magnitude of 8-9
3.Volcanic Activity Explosive eruptions with moderate to high VEI scale 5-6 (Volcanic Explosively Index)
4. Topography/Bathymetry: Ocean Trenches Fold Mountains with Volcanic peaks
5.Other Interesting things: Trench gas low heat flow and negative gravity anomaly.
Ranges of ages of rocks.
6. Location e.g. South American and Nazca plate boundary.

Answer 19

1.Plate (crust and lithosphere) coverage due to convection currents in the mantle (asthenosphere) and slab pull. Oceanic plates, which are denser are subducted below the continental plates creating an ocean trench. Sedimentary rocks are folded upwards by being compressed forming fold mountains. Friction between the two plates in the Benioff zone lead to Earthquakes and crustal melting due to hydration melting leads to magma forcing its ways upwards leading to extrusive eruptions or intrusive batholiths.
2.Large range of focus depths (shallow – near to surface and up to 700km in Wadati-Benioff zone).
Earthquakes general high magnitude of 8-9
3.Volcanic Activity: Explosive eruptions with moderate to high VEI scale 5-6 (Volcanic Explosively Index)
4.Topography/Bathymetry: Ocean Trenches Fold Mountains with Volcanic peaks
5.Other Interesting things: Trench gas low heat flow and negative gravity anomaly.
Ranges of ages of rocks.
6. Location e.g. South American and Nazca plate boundary.

Question 20

Convergent/destructive boundaries of oceanic and oceanic plates

1. Formation/Movement:
2. Seismic activity:
3. Volcanic Activity:
4. Topography/Bathymetry (features):
5. Other Interesting things:
6. Location:

Answer 20

1. When two oceanic plates collide, one plate (the denser) is subducted beneath the other. Deep ocean trenches form where this occurs, and the subducted plate then melts, creating magma, which rises up from the Benioff Zone to form underwater volcanoes. Over millions of years, these growing volcanoes rise above sea level to form separate island volcanoes (island arcs). The subduction also produces shallow to deep focus earthquakes (some can be very powerful).
2. Range of focal depths from shallow to 700km along Wadati-Benioff Zone; moderate to high magnitude (7-9)
3. Explosive (moderate to high VEI scale 5-6)
4. Topography/Bathymetry: Island arc, oceanic trench; back orc; fore arc zones
5. Trench gas low heat flow and negative anomaly; range of rock age.
6. Indian plate sinking beneath the Burma plate (part of Eurasian plate). This caused 2004 Indian Ocean Earthquake.

Question 21

Convergent/ destructive boundaries and continental plates

1. Formation/Movement: When two continental plates meet, a collision margin occurs. As both plates have about the same density, and are less dense than the asthenosphere beneath them, neither plate is actually subducted. Instead, they collide and sediments between them are crumpled and forced up to form high fold mountains like the Himalayas. However, inevitably, there can be some subduction (caused Nepal Earthquake) caused when the compressed land therefore denser sediments) result in plate subduction beneath them. There is no volcanic activity, but any earthquakes are likely to have shallow focus – increase their severity.
2. Seismic activity:
3. Volcanic Activity:
4. Topography/Bathymetry (features)
5. Other Interesting things:
6. Location:

Answer 21

1. When two continental plates meet, a collision margin occurs. As both plates have about the same density, and are less dense than the asthenosphere beneath them, neither plate is actually subducted. Instead, they collide and sediments between them are crumpled and forced up to form high fold mountains like the Himalayas. However, inevitably, there can be some subduction (caused Nepal Earthquake) caused when the compressed land therefore denser sediments) result in plate subduction beneath them. There is no volcanic activity, but any earthquakes are likely to have shallow focus – increase their severity.
2. Shallow to intermediate focal depth; moderate magnitude (6-8)
3. Usually none
4. Fold mountains and plateaus

Question 22

Constructive boundaries

1. Formation/movement:
2. Sesmic activity
3. Volcanic activity:
4. Topography/bathymetry
5. Other interesting things
6. Location

Answer 22

1. Two plates moving apart, leads to the formation of new crust. This forms mid-ocean ridges, on continents: rift valley.
   - mid ocean ridges of underwater mountain, extend for over 60000km across the world’s ocean floors. Regular breaks (called transform faults) cut across these ridges as they spread at different speeds. Shallow focus earthquakes (less than 70km) pose little risk to humans because shocks are minor and occur underwater. Regular volcanic eruptions also create submarine volcanoes along these mid-ocean ridges, some of which grow above sea level to create new islands like Iceland on mid-Atlantic ridge.
   - rift valleys: when plates move apart on continents, the crust stretches and breaks into sets of parallel cracks (faults). The land between these faults then collapses, forming steep sided valleys called rift valleys.
2. Shallow focus, usually low magnitude (5-6)
3. Effusive eruptions (low VEI scale 1-3)
4. Clean ridge with central rift valley; faulting at right angles; volcanic islands
5. Heat flow; young basaltic rock
6. Pacific plate and Nazca plate

Question 23

Transform boundary:

1. Formation/Movement:
2. Seismic activity:
3. Volcanic Activity :
4. Topography/Bathymetryfeatures:
5. Other Interesting things:
6. Location:

Answer 23

1. Slide past each other. This results in a major break in the crust between them as they move. The break itself is called a fault, and where it occurs on a large scale is known as a transform faults, which affects a wider area. Although new crust is made or destroyed here (and there is no volcanic activity), this type of plate margin is tectonically very active – and can be associated with powerful earthquakes. The two plates sometimes stick as they move past each other, causing stress and pressure to build up, which is suddenly released as a strong shallow – focus earthquake. One of the most famous conservation plate margins is the San Andreas Fault in California, which has generated significant earthquakes.
2. usually moderate magnitude (6-8)
3. Usually none; occasional fissure eruptions
4. Rides and scars on surface
5. Average heat flow rock age depends on oceanic (young) or continental (old) location
6. Pacific plate and north American plate (San Andrea Fault)