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Lecture

Lecture 3


Department
Environmental Science
Course Code
EESA06H3
Professor
Nick Eyles

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Jan 23rd 2009
EESA06
What do earthquakes tell us about the planet's interior, and plate tectonics?
- how do we collect information about the earth's interior
o deep drilling
o russian hold record of 12Km deep
o at 12Km rocks are getting soft and will fill up the hole
earthquakes: what can we learn of the earth's interior?
- rocks are brittle, they will snap
- energy produced from the snap produces an earthquake
- epicenter: directly above the focus
- fault plane: line of breakage; smooth surface where rocks have slipped
- propagates the rocks as seismic waves
- fault trace: part of the fault showing on the surface; often buried (blind faults)
- fault plane: part of the fault showing underneath
New Zealand
- in between pacific plate and indo-australian plate
- a lot of fault scarps
Waves
- surface waves does most damage to buildings (e.g. love wave and rayleigh wave)
- primary waves(compressional waves): 5-7km/sec; arrive first, faster
- secondary waves: 2-4 km/sec; last type of wave to arrive, smaller
- there will be a gap in time between the arrivals of the primary and secondary waves
o separation of the arrival times can be used to find the epicentre
o if on the epicenter, both waves will arrive simultaneously
p-waves
- compressional waves
- p-waves that pass through the core are refracted
- area that does not receive direct p-waves is call the p-wave shadow zone
- p-waves spread directly around the epicenter for 103degrees latitude
s-waves
- core doesn't transmit s-waves; cannot travel through liquids
- spreads directly to 103degrees latitude around epicenter
- s-wave shadow zone very large
Seismic tomography
- image of the earth's interior in slices
- there are major physical properties (temperature, pressure) changes that affect the waves
- MOR spreading centers are underlaying by very hot rocks (plumes)
o plumes feed the MORs (convection)
o core->mantle->lithospheric plates(lithosphere: hard crust of the earth)
o some subducting plates cannot penetrate the boundary between lithosphere and
mantle
o if the plate bursts through the mantle, its descends into the mantle (downgoing slab)
and return to the top as plume (mantle overturning)
o this is a model for the earth's cooling system
A computer model of the earth's interior
- the core is hard
- the liquid on the outside is in the shape of plumes
www.notesolution.com
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