tectonics Flashcards
where is there a constructive and collision plate boundary
between India and Australia
where is a transform plate boundary present
At New Zealand
what is the Benioff zone
A dipping flat zone where earthquakes are produced by the interaction of a down going oceanic crustal plate with a continental plate.
what is the subduction zone
the place where two lithospheric plates come together, one riding over the other. Most volcanoes on land occur parallel to and inland from the boundary between two plates
whats crustal fracturing
occurs when the Earths crust causes rock to break and fracture under stress and strain caused by seismic waves.
what are constructive/ divergent plate boundaries
where plates move apart from each other
what are destructive / convergent plate boundaries
where lithospheric plate boundaries move together
where are the majority of earthquakes and volcanoes found
on plate boundaries
where do we find Earthquakes with a magnitude of 9 or higher
where convergence of a oceanic plate and continental plate occurs (a destructive plate boundary with subduction)
what are earthquakes called in the middle of plates
intra-plate earthquakes
why do intra-plates earthquakes occur
They are associated with ancient faults (such as the Rhine Rift Valley) in which the solid crust can crack.
Large faults then may turn into new plate boundaries.
why do we find earthquakes at collision boundaries *
collisions of tectonic plates may also fracture the crust well away from the plate boundary which can yield large magnitude earthquakes.
what are hot spots?
volcanic activity near the centre of some plates.
This is either the result of the upwelling of hot molten material from the core/mantle boundary, such as the Hawaiian hotspots or may result from the top of a large mantle plume just under the crust such as seen in the Cape Verde Islands. It is also possible that large meteorite impacts create symmetrical hot spots on opposite sides of the planet when they collide with the Earth.
where are hotspots found
-Hawaii
-Cape Verde islands
what is convection
convection is created in the mantle by heat radiating outwards from the inner core
how is the internal structure of the Earth known
the internal structure of the earth is known based around how the different earthquake (seismic) waves travel through the solid and liquid layers of the Earth.
seismic waves revealed that there are complicated patterns of hot and cold areas
what is the mantle mostly made from
made mostly from peridotite which behaves like a viscous liquid under pressure.
consists of multiple layers with density and mineral differences
describe slab pull
slab pull is where denser oceanic plates are subducted at cold downwelling’s (there is also some suction force).
This subduction may cause the location of cooler mantle areas and the downward movement within the large scale convection pattern
why does the pacific plate move faster than the other plates
The Pacific plate has lots of subduction around its edge
how can plumes impact a countries location
they can push the crust up on a large scale.
The one currently under West Africa may have also caused the Atlantic Ocean and Iceland to form with the creation of mid Atlantic ridge, and split Scotland from North America and Africa from South America.
for the crust what is the:
-Structure
-Temperature
-Density
-Composition
-Physical state
-Seismic waves present
-Structure: oceanic= 7km thick, continental= 70 km thick
-Temperature: oceanic= 400 degrees C
-Density: oceanic= 3.3g/cm^3, continental= 2.7
-Composition: oceanic= basalt continental= granite
-Physical state: solid
-Seismic waves present: surface and body waves able to pass through
for the mantle what is the:
-Structure
-Temperature
-Density
-Composition
-Physical state
-Seismic waves present
-Structure: 700km to 2890km deep
-Temperature: 870 degrees c
-Density: 3.3-5.4 g/cm3
-Composition: peridotite, upper=olivine lower=magnesium silicate
-Physical state: phases of liquid and solid in layers
-Seismic waves present: body waves (both p and s) pass through at variable rates due to density changes.
for the outer core what is the:
-Structure
-Temperature
-Density
-Composition
-Physical state
-Seismic waves present
-Structure: 2890km to 5150 km deep
-Temperature: 4400 to 6100 degrees c
-Density: 9.9 to 12.3 g/cm3
-Composition: 12% sulphur, 88% iron
-Physical state: liquid (+ generates a magnetic field)
-Seismic waves present: only p waves able to pass through, an S wave ‘shadow zone’ is created from about 105 degrees from the focal point
for the inner core what is the:
-Structure
-Temperature
-Density
-Composition
-Physical state
-Seismic waves present
-Structure: 5150 km deep to centre
-Temperature: 7000 degrees c (radioactive decay)
-Density: 13.5 g/cm^3 (v dense)
-Composition: 20% nickel 80% iron
-Physical state: solid (+radiates heat)
-Seismic waves present: only P waves, their refraction at the core mantle boundary creates a ring ‘shadow zone between 105 and 140 degrees from the focal point
what is a constructive/ divergent plate boundary
where two oceanic plates move apart.
sea floor spreading
convection in mantle occurs
for the plate boundary type of constructive (divergent), what is the:
-seismic activity
-volcanic activity
-topography or bathymetry
-seismic activity: shallow focus; usually low magnitude (5-6)
-volcanic activity: effusive (not very explosive) eruptions, low VEI scale (1-3)
-topography or bathymetry: ocean ridge with central rift valley: faulting at right angles; volcanic isalnds
for the plate boundary type of destructive (convergent) ocean and continent, what is the:
-seismic activity
-volcanic activity
-topography or bathymetry
-seismic activity: range of focal depths from 700km along the wadati-benioff zone: often high magnitude (8-9)
-volcanic activity: explosive (moderate to high VEI scale 5-6)
-topography or bathymetry: Island arc; oceanic trench; back arc and fore arc zones
for the plate boundary type of destructive (convergent) ocean and ocean, what is the:
-seismic activity
-volcanic activity
-topography or bathymetry
-seismic activity: range of focal depths from shallow to 700km along Wadati Benioff zone: moderate to high magnitude
-volcanic activity: explosive (moderate to high VEI scale 5-6)
-topography or bathymetry: island arc; oceanic trench; back arc and forearc zones
for the plate boundary type of Collison (convergent) continent and continent, what is the:
-seismic activity
-volcanic activity
-topography or bathymetry
-seismic activity: shallow to intermediate focal depth, moderate magnitude (6-8)
-volcanic activity: usually none
-topography or bathymetry: fold mountains and plateaus
for the plate boundary type of transform (conservative), what is the:
-seismic activity
-volcanic activity
-topography or bathymetry
-seismic activity: shallow focus, usually moderate magnitude (6-8)
-volcanic activity: usually none, occasional fissure eruptions
-topography or bathymetry: ridges or scars on surface
how do fossils confirm that tectonic plates move
places such Africa and South America have matching rock types. Fossils such as Cynognathus match across africa and south America
how did evidence supporting the study of seismic waves and the location of focal points in the 1950s confirm that tectonic plates move
in 1950s the ocean floor was surveyed showing the presence of mid ocean ridges where new crusts were formed.
how did evidence from The discovery in the 1960s of magnetic strips in the oceanic crust confirm that tectonic plates move
these palaemagnetic signals from past reversals of the Earth’s magnetic field and prove that new ocean crust is created by the process of sea-floor spreading at mid-ocean ridges. (seafloor spreading and palaeomagnetism occur at constructive margins, where new crust is being made)
how does coal confirm that tectonic plates move
coal forms in tropical conditions however coal is found in the north sea
where do we find the greatest friction and what is an example
at the wadati benioff zone within destructive plate boundaries.
due to this friction, there was a 9.5Mw earthquake in Chile, being the largest
give an example of a transform (conservative) boundary where the highest level of stress is found
the San Andreas fault line created the largest earthquake at 7.6Mw for a conservative plate boundary
what is the focus of an earthquake
the focus of an earthquake is where the stress is released, this sends earthquake (seismic ) waves in all directions, being strongest at the point above the focus which is the epicentre.
where are lower magnitudes found
at constructive plate boundaries magnitude is lower as less friction is present.
E.g. the largest recent earthquake in Iceland was 6.5Mw in 2000, but they are normally lower
what are body waves
both P and S waves
-primary waves-
how fast are they:
what does it move through:
how destructive is the wave:
how fast are they: fastest type of wave, they arrive first
what does it move through: moves through solid rock and fluids. P waves are only able to move through the inner and outer core (not body waves)
how destructive is the wave: they are only damaging in the most powerful earthquakes
-secondary waves-
how fast are they:
what does it move through:
how destructive is the wave:
how fast are they: slower than a P wave (travel 60% slower than a P wave)
what does it move through: they only travel through solids. Body waves are seen at both the mantle and the crust
how destructive is the wave: They do more damage than P waves
-rayleigh waves-
how fast are they:
what does it move through:
how destructive is the wave:
how fast are they: 7800 miles per hour
what does it move through: only travels through the surface or crust
how destructive is the wave: responsible for most of the shaking felt by people
-love waves-
how fast are they:
what does it move through:
how destructive is the wave:
how fast are they: slowest (last to arrive)
what does it move through: only travels through the surface of the crust
how destructive is the wave: cause the most damage
In what way do primary waves move
primary waves push and pull in the direction of travel
In what way do secondary waves move
secondary waves consist of an up and down movement
what does magnitude measure
magnitude measures the amount of energy released at the epicentre
how is earthquake magnitude measured
earthquake magnitude is measured using the moment magnitude scale (MMS)
MMS measures the energy released during an earthquake, it uses a logarithmic scale
what does an earthquakes intensity measure
an earthquakes intensity is the effect on people, structures and the natural environment
how is earthquake intensity meaured
by using the modified marcalli intensity scale which takes observations from people who experienced the earthquake
what are the primary effects (direct results) of an earthquake
ground shaking- causes buildings, bridges, roads and infrastructure to collapse, killing or injuring those nearby
crustal fracturing- when energy is released during an earthquake causes the Earths crust to crack -leaving gaps
what are the secondary effects of an earthquake
liquefaction- the violent shaking during an earthquake causes surface rocks to lose strength and become more liquid than solid. The subsoil loses its ability to support buildings. It can make rescue efforts more difficult and also disrupt underground power and gas lines.
landslides and avalanches- The ground shaking places stress on slopes, so they may fail (landslides, rockslides, mudslides and avalanches). This can lead to damage and injuries
tsunami- some underwater earthquakes generate tsunami that cause major problems for costal areas.
what are landslides
landslides are where material loses cohesive strength and moves downwards under the influence of gravity- they occur when seismic waves loose shock
give examples of where landslides have caused devastation
El Salvador, Central America
