Week 9: Earth Structure and Geophysics Of Plate Tectonics Flashcards
(26 cards)
How thick is the oceanic crust compared to continental crust?
Oceanic crust - 7km
Continental crust - 35km
Which is more dense, oceanic crust or continental crust?
Oceanic crust is more dense.
Oceanic crust: 3.0 g/cm³ dense
Continental crust: 2.7 g/cm³ dense
How deep is the mantle?
2900 km deep
What is the mantle mostly composed of?
Peridotite in the upper mantle
What are the different layers of the mantle?
Lithosphere (rigid), Asthenosphere (weak, partially molten), Transition zone (bottom part)
How is a magnetic field generated in the outer core?
Movement of metallic iron in liquid iron-nickel
What are the phases of the core (inner/outer core)?
Outer core: liquid Fe-Ni
Inner core: solid Fe-Ni
What causes earthquakes?
Sudden and rapid movements along faults
What are faults?
Fractures on the Earth’s crust
Epicentre vs hypocentre
Epi → where on earth’s crust an earthquake is felt
Hypo → where earthquake actually occurs
What are seismic waves?
Packets of energy that travel through the Earth
What causes an elastic rebound?
Deformation of rocks caused by connection + differential stress
Causes rocks to bend and store elastic energy
Slippage occurs when frictional resistance is exceeded
Snapping back of rocks
What are P waves and their properties?
Compress / stretch
Creates sound
Solid/liquid
Fastest
What are S waves and their properties?
S waves shake particles at right angles to the direction of travel, pass through solids, and are slower than P waves.
What are love waves and their properties?
Love waves move side to side and are faster than Rayleigh waves.
What are Rayleigh waves?
Rayleigh waves roll and cause particles to move in ellipses.
What does a greater distance between P and S waves intervals indicate?
The greater the distance between the epicenter and the hypocenter.
How are earthquakes located?
By using the arrival time of P and S waves to determine the distance from the epicenter and triangulating from three seismic stations.
How is the size of an earthquake measured?
By intensity using the Mercalli scale and magnitude, which measures the energy released (Richter scale is logarithmic).
What was the largest earthquake in modern history?
The 1960 Valdivia earthquake in Chile.
What is continental drift?
Large scale movements of continents
What is seafloor spreading?
Convection in Earth’s mantle that could push and pull continents apart.
Evidence: Young basalt, not granite, mid Atlantic Ridge.
What is paleomagnetism?
Rocks that contain a record of the direction of the magnetic poles at the time of formation.
Earth’s magnetic field reverses polarity periodically.
What can faulting (focal) mechanisms tell us?
They tell us about the nature of a fault.
