Plate Tectonics - exam Flashcards
Amplification
The maximum height of a wave crest or depth of a trough.
Attenuation
The reduction in amplitude of a wave with time or distance travelled.
Benioff Zone
A narrow zone, defined by earthquake foci, that is tens of kilometres thick dipping from the surface under the Earth’s crust to depths of up to 700 kilometres.
Body waves (p and s waves)
A seismic wave that can travel through the interior of the earth. P-waves and S-waves are body waves.
deep-focus
The term “deep-focus earthquakes” is applied to earthquakes deeper than 70 km. All earthquakes deeper than 70 km are localised within great slabs of lithosphere that are sinking into the Earth’s mantle.
Deformation
The change in the Earth’s surface due to the tectonic forces operating below, and the earthquakes caused by them.
Epicentre
Precious- The point of the surface of the Earth that is directly above the focus.
Focus
Precious- Origin of earthquake underground aka hypocentre. Where seismic waves originate and spread in all directions out from it.
A deeper focus usually has less energy by the time it reaches the surface, as it loses more energy before reaching the surface. A shallower focus usually has more energy in a more concentrated area on the surface.
Friction
Ali - The collision and rubbing together of tectonic plates, causing heat and kinetic energy.
Liquefaction
Emma - when solid ground begins flowing as a liquid due to an increase in pore pressure and a reduction in stress.
Love wave
AKA Q wave, when wave moves horizontally, like a snake
s wave
Emma - surface seismic waves that travel in a circular, transverse motion.
Mercalli scale
The scale used to measure the amount of damage caused. Levels 1-12, 1 being the least damage, 12 being the most.
P wave
Longitudinal waves where the particles travel along the direction of the wave at 8 miles/second. They are primary waves, so arrive first. They change direction & speed when they go through a different material.
Primary effects
Blaise - primary effects are effects which are more immediate and predictable. These are also very often physical impacts to a place caused by a hazard. For an earthquake, primary effects may include ground shaking, fissures and in some cases tsunamis.
Rayleigh wave
Emma - a form of surface seismic wave that travels in a backwards vertical ellipse motion.
Richter scale
The scale used to measure the magnitude of an earthquake. Logarithmic and has scales 1-9 (now use Moment Magnitude Scale).
S wave
George - Waves that carry energy through the earth in transverse waves, slower than P waves but usually have bigger earthquakes. Cannot travel through the outer core as these waves cannot exist in fluids, water or molten rock.
Secondary effects
Effects caused by the impacts of the earthquake such as gas pipes bursting and causing building fires, sicknesses spreading and homelessness etc.
Seismic wave
Vibrations that generate from sudden movements of rock. After the earthquake the waves propagate from focus to the surface of the earth.
Shadow zone
George - The area on the Earth’s surface protected from seismic wave arrivals.
Shallow focus
The worst impacts occur when a focus is shallow as seismic waves have more energy when they hit the surface of the earth.
Stick-Slip
Phrase used to summarise the cause of an earthquake. Rocks of the plate stick which causes a build up in pressure which is then released when the plates slip causing the release of a large amount of energy (earthquake).
Surface waves (Rayleigh and Love
Blaise - Both of these are surface waves which means that they travel along the crust. Rayleigh waves travel in a backwards vertical ellipse motion whereas Love waves travel transverse and horizontal. For both, particle motion decreases with depth from the surface.
5 evidences for tectonic movement
Continental geology
Paleomagnetism
Age of crust created during sea floor spreading
Fossils
Fit of the continents
Continental geology as evidence for plate tectonics
Continents which share similar geology can be seen as evidence to support the idea of Pangea from 200-300 million years ago
For example, South America and Africa.
Both similar rock types and layers.
In addition, some mountain chains also can be seen to match in geological lithology and structure, e.g. NE Canada and N Scotland
Age of the crust by examining sea floor spreading as evidence for plate tectonics
As sea floor spreading involves constructive plate margins creating new plate in the ocean floor, by examining the age of the rock from further away from the mid-ocean ridge it can be identified as older than the rock closer to the mid-ocean ridge, which can be done using carbon dating.
Sea floor spreading occurs on average 2.5 km under the ocean
Example of a mid-ocean ridge is the Juan De Fuca located in the Pacific Northwest, spreading approx. 350miles in width.
Very reliable source due to modern sonar mapping
Convection currents
Currents operating within the asthenosphere, which mean that solid lithosphere and crust are moved around the Earth’s surface.
Fossils as evidence for plate tectonics
Similar fossils found on different continents, such as the mesosaurus, a freshwater, reptile like crocodile, found in both South America and South Africa. Mesosaurus went extinct after the the breakup of Pangea that began 250 million years ago. The fact that the fossils are the same in both places is powerful evidence for Pangea’s existence.
Additionally, fossils of the Glosopteris fern plant is found on all southern continents and therefore suggests that they were once linked.
Paleomagnatism as evidence for plate tectonics
Paleomagnetism is the observation that the rocks surrounding the mid-ocean ridge contain the mineral magnetite, which can align with the direction of the dominant polarity when the rock is molten enough to allow movements of the mineral.
As the dominant polarity changes from North to South every 300,000 - 600,000 years (on average, the direction of the alignment of magnetite can indicate a divergent plate boundary causing sea floor spreading.
Fit of the continents
By observing the fit of the continents, scientists can see that they were once in the same place due to the fact that they “fit together” like puzzle pieces.
On its own, this piece of evidence is very weak, as it relies on assumptions made on qualitative data, and not quantitative; Also, many of the continental coastlines do not ‘fit’ in a way that suggests that they were once together.
Best used in conjunction with other data.
Early cartographers realised this in late 16th century, now, we have satellites.
