Lecture 4 - Volcanic Imagination Flashcards
A Quake struck the region of Yerevan and Tbilisi on what date, and what was magnitude and how many killed, injured?
23 October 2011
7.2M
600 dead, 4000 injured
What are the tectonic plates by the region of Yerevan and Tbilisi?
Arabian and Eurasian plates
What does an earthquake release energy in the form of?
Wave
How may a wave be reflected, deflected or retracted?
If the strength or density of the Earths interior changes
What can be used to probe and understand the Earths interior?
Earthquake waves
What happens to seismic waves when density of rock changes?
They bend and change speed
What are p waves?
Primary waves
Name 3 components of p waves?
- They travel through solids, liquids or gaseous materials
- They are the fastest of the 3 seismic waves
- Also called, push-pull waves
What are S waves also called?
Secondary waves
Name 3 components of S waves?
- Travel at half the velocity of P waves
- They have shear waves, and push material at right angles to their direction of travel
- Shear waves are only present in solids
Name 2 components of surface waves?
Travel around NOT through the Earths surface
Velocity slightly less than S Waves
What does the push pull, P Wave (compressional wave) do to material travelling in same direction?
Compresses and expands the material
What do S Waves shake?
The ground up and down, back and forth at right angles to the direction of travel
Surface waves (Rayleigh and Love waves) are like what?
Waves in the ocean
What increases with P and S waves?
Intervals, the further you get from te epicentre
Describe compressional waves, by Larry Braile, Purdue Universities animation (2010)
Particle motion has changing compression and dilation. Particle motion is parallel to direction of propagation. Material returns to original shape
Describe Shear Waves (S Waves) using animation by Larry Braile, Purdue Universities animation (2010)
Particle motion consists of alternating transverse motion. Particle motion perpendicular to direction of travel. Material returns to original shape
Describe Rayleigh waves (R-Waves) using animation by Larry Braile, Purdue Universities animation (2010)
Particle motion has elliptical motions in vertical plane and is parallel to direction of propagation. Amplitude decreases with depth. Material returns to original shape
Describe love waves (L-Waves) using animation by Larry Braile, Purdue Universities animation (2010)
Particle motion consists of alternating transverse motions. Particle motion horizontal and perpendicular to direction of propagation. Amplitude decreases with depth. Material returns to original shape
What is 2 components is the crust made of?
Oceanic Basalt
Continental Andesite
What can be found in the upper mantle? Think about the ‘Big Hole’ at Kimberly, South Africa.
Diamonds, they are formed in the upper mantle, bought to surface by volcanic rock called Kimberlite
What is Peridotite?
Special for of basalt that occurs in the Earths mantle
What can be found in the Lower mantle, name 2 things?
- Perivskite - magnesium silicate mineral
- Iron-Nickel meteorites
What did Anderson Celsius notice in Southern Sweden in the 18thC?
It was rising by 3cm a year
What happens with the weight of ice during glacial periods?
It pushes down the earths surface and lithosphere
What happens during a glacial period when the ice sheet melts?
The displaced mantle flows back and the depression rises
When the displaced mantle flows back and depression rises after a glacial period, what does the mantle appear to do?
Bulge and ‘flow’
What is the temperature gradient at Gold Reef City Mine - Jo’Burg?
12.5degrees km-1
Why is the temperature gradient not constant?
Rocks of mantle are mixed by convection currents, so heat is distributed more evenly
Can the mantle convect?
Depends on it’s Rayleigh number
What is runniness or viscosity measure in? Also give 3 examples?
Poise - the higher a value = the more sticky
E.g - Water - 0.0114
- Maple Syrup - 320000
- Mantle 10000000000000000000000 (22noughts)
What happens if rock is heated and put under enough pressure?
It will flow
Conclusion: the movement of Earthquake waves (refraction and reflection) through the earths interior suggests what?
The earths interior is like a scotch egg.
Crust, mantle, outer core, inner core
Conclusion: how can composition of layers of rock be deduced?
By examining terrestrial and extra terrestrial rocks
Conclusion: the 3-D structure of heat flow in Earths mantle suggest presence of convection currents, what does this mean?
It is the most probable force for plate movement
