Earth's deformation

Question 1

Elastic behaviour

Answer 1

Cold, surface rocks can deform elastically other millions of years.
Elastic rebound causes earthquakes
If the strain rate is high enough, hot rocks can also deform elastically. This allows for seismic waves to pass through the Earth, even through the mantle which is 3000 degrees celsius at its base

Question 2

Cataclastic flow

Answer 2

Repeated fracturing until grain size is small enough for fragments to slide over each other.
Common in fault zones

Question 3

Power Law creep

Answer 3

Dominates when 0.6 <= Homologous temperature <= 0.85 and high stress
Movement of dislocations
Some grain boundary sliding
Some recrystallisation
Strength proportional to (strain rate)^(1/n) where n is not equal to 1

Question 4

Homologous temperature

Answer 4

Temperature / Melting temperature

Question 5

Diffusion creep

Answer 5

Dominates when 0.85 <= Homologous temperature and low stress
Strength proportional to strain-rate. Constant of proportionality is viscosity
Very sensitive to grain size

Question 6

0.85 = Homologous temperature

Answer 6

Diffusion creep dominates
Virtually all rocks’ strength is lost
c. 125km
Weak region of the mantle called the asthenosphere

Question 7

Lithosphere

Answer 7

Top 125km of Earth. Rigid layer above asthemosphere.
Upper part is brittle and strongest
lower part, with 0.6 <= Homologous temperature <= 0.85, creeps significantly.

Question 8

How we know the viscosity of the asthenosphere

Answer 8

Rebound of scandinavia after the ice cap which covered it 10,000 year ago melted.
Rock in the baltic visited by Celsius and Lyell uplifted by about 100mm/year.
Asthenosphere’s viscosity is c. 10^(20-21) Pas

Question 9

Viscosity of Basaltic lava

Answer 9

30Pas

Question 10

Viscosity of water at room temp

Answer 10

10^-3 Pas