Tectonics- Earthquakes Flashcards
What are plate tectonics?
Simple definition: The tectonic plates definition is large sections of the Earth’s crust that move independently. They float on top of a constantly moving, semi-liquid layer called the mantle
Long definition:
The Earth’s crust is made up of a number of large plates that are
moving in constant, slow motion.
• Convection currents in the mantle move the plates. The source of heat
driving the convection currents is radioactive decay which is happening
deep in the Earth.
• The ocean floors are continually moving, spreading from the centre
and sinking at the edges.
• At the edges of these plates (plate boundaries) earthquakes and
volcanoes occur.
What was Wegners theory and evidence?
In 1912, a Geologist called Alfred Wegener proposed that countries were once joined
together and had then moved apart. In fact he believed that all the continents were once
joined together as one big land mass called Pangaea and this was intact until about 200
million years ago. The idea that continents are slowly shifting their positions is called
Continental Drift.
Evidence to support tectonic plates? Jigsaw fit
Evidence 1: Jigsaw fit - Some continents fit together like a geological jigsaw
puzzle. All the rocks were formed when the land was a single continent – Pangea.
Evidence to support tectonic plates- convection currents
Evidence 3 – In the Mantle, Convection Currents were found to be slow yet extremely powerful
movements of volcanic rock in the mantle. The magma is heated to 50000C in the
mantle and rises to the crust where they cool and sink only to be heated again. The
process continues. This was powerful enough to move the earth’s plates
Evidence to support tectonic plates- study of fossils
Evidence 2 - Study of fossils
Similar fossils are found on different continents. This is evidence that these regions
were once very close or joined together. Such species could not have crossed
oceans, so they must have lived on the same land mass at some time in the past.
Evidence to support tectonic plates? Palaeomagnatism
A discovery of a ridge of mountains running along the middle of the Atlantic Ocean
known as the Mid Atlantic Ridge was made - these were formed by underwater
volcanoes and lava cooling. As lava cools the magnetic iron points to the north pole.
It was known at the time that the earth’s polarity switches approximately every
100mill years and when this reversed from north to south, the iron particles in the
erupting magma aligned themselves with the Earth’s new polarity at that time – this
creates evidence of seafloor spreading.
Name 5 major plate boundries/plates?
Pacific plate
African plate
Nazca plate
North american plate
Eurasian plate
Why volcanoes and earthquakes are found at plate boundries? Divergent
Plates rip apart at a divergent plate boundary, causing volcanic activity and shallow earthquakes
What is a convection current and why is it important?
Heat from the core makes magma in the mantle rise towards the crust. As the hot current nears the crust, it begins to cool and sink back towards the core. As the magma sinks, it drags the plates across the surface of the Earth.
Two ways to measure Earthquakes?
Moment magnitude scale (Richter) and Mercalli scale
What does the Richter scale measure?
It measures the magnitude of the Earthquake (how much the ground shakes)
What does the Mercalli scale measure?
It measures the intensity of the Earthquake (based on observations of the resulting damage)
What can be used to measure the magnitude (power) of a tremor in the Richter scale?
Seismometer
What is the other name for a richter scale?
Moment magnitude scale
Moment magnitude give 3 key details.
-Measures the magnitude of the earth ( how much the ground shakes )
-The scale is from 0-9.9 and over
-measured using siesmograph
-Good features- shows how much energy is released
Mercalli scale 3 key details
-measures the intensity of the Earthquake (based on observations of the resulting damage)
-scale from 1 to 12
- measured by observations of the earthquake damage
-good features- a more meaningful measure of severity
Which scale is most likely to use a seismometer?
Richter
